Has Anyone Combined An Electric Combi Boiler with Solar PV Panels and Batteries?
In the off grid world, a lot of people naturally turn to Solar for their lights, electronics and refrigeration, possibly for their cooking (induction) and maybe heating (mini-split heat pumps). But what to do about hot water for bathing, laundry, etc?
There seems to be a lot of interest in solar electric combi boilers in the UK but not a lot of interest in North America.
https://boilerandwaterheater.com/combi-boiler-with-solar-panels/#:~:text=Combi%20boilers%20are%20an%20excellent,and%20ground%20source%20heat%20pumps.
https://iheat.co.uk/boiler-help/boilers-powered-by-solar-power
https://www.boilerguide.co.uk/articles/running-electric-combi-boiler-solar-pv
https://www.easyboilers.com/boiler-advice/best-electric-boilers/
Has anyone installed a solar electric combi boiler here in the USA?
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Replies
Batteries are a lousy way of storing large quantities of energy.
Other than that, I've heard of systems where the solar cells are just wired directly to a resistance element in the tank, no inverter, no grid tie. With the way PV cells keep dropping in price it's cost competitive with the alternative, which is thermal solar. Plus you don't have to worry about overheating or freezing.
When you go off-grid all the payback calculations get thrown out, because you can't easily compare to grid electricity. Not that payback calculations are simple in the first place.
Rockies,
Q. "In the off grid world... what to do about hot water for bathing, laundry, etc?"
A. The answer (for those who live in an off-grid house) is generally "combustion" -- usually propane or wood.
The sun doesn't shine when you are most in need of hot water. For more information, see these two articles:
"How to Design an Off-Grid House"
"Off-Grid Homeowners Contemplate Our All-Electric Future"
Martin is spot on. I had an off grid summer cottage for almost 30 years with solar for power. We used a propane hot water heater and a propane gas stove. We even had a propane fridge for 10-15 years but finally got rid of it because it was too small.
The problem with going all-solar off-grid is that the solar isn't always there when you need it and there's no effective way to store it, batteries won't cut it. Really the only effective ways we've found to store energy are liquids -- propane, gasoline, diesel -- or solids -- wood or coal.
Well, I had 8 deep cycle batteries that did the job when the sun was down, or it was cloudy, for a few days at best. After that, you're right; gas generator.
The big problem with batteries is they offer very poor energy density, so you just can't store very much power in even a fairly large battery bank. If the concern is for heating water, it would be much better to just use the water itself as the "battery", heating the water whenever solar power was available, and then using that hot water directly as needed. Storing energy in batteries to use to heat the water later adds additional conversion steps, more losses, and doesn't gain you anything useful.
It's better to have a propane system as backup, since that works in extended periods of low solar output too. It's entirely possible to combine the two systems if you want, just use an electric resistance water heater for the solar heating and a propane fired water heater as backup.
Bill
The other big problem is that if you have a longer than expected outage you can't just run out and get more fuel.
Hello, thanks for everyone's reply.
The questions I have around a totally electric home off grid seem to start with the non-typical "add-ons" for electricity use - cooking, space heating and DHW. If you're miles out in the country then hauling large quantities of propane out there every month becomes cumbersome and I don't want a wood stove or a wood cookstove inside the house because of fine smoke particles trapped indoors all day (there will always be some no matter how air-tight the stove or whether you have an exterior combustion air intake).
Therefore, can a small induction cooktop be run off of solar (and use a propane stove outdoors in the summer). For space heating, would a small Mitsubishi air source mini-split work with solar (or a Mr. Cool)? As for DHW, what about those Sandon CO2 air source heat pump water heaters? Then there's fresh indoor air and dehumidification - how small a unit can you get that will still do a good job?
There seems to be a big push towards getting the world to go all electric but not much information on the smallest, most efficient products or systems needed to meet that goal. It's further complicated when you're not on-grid.
Yes, you can run an induction cooktop off of an off-grid solar setup. You’d need a beefy inverter, and you’d have to be careful with runtime. The issue is not if you CAN run it, the issue is HOW LONG can you run it on an off-grid system. Heating devices suck a lot of power. Induction is probably the most efficient option here for cooking, but it’s still a load of several kilowatts or more, which is BIG for an off-grid system. For a rough idea, a typical car battery sized battery can run a 2kw induction cooktop element for about 15 minutes before the battery goes from fully charged to completely discharged.
Hauling propane is easy! You get it delivered. They come fill up your tank at your home, which is often 500 or 1,000 gallons if you’re using it to heat your home. You don’t have to haul loads of BBQ tanks if that’s what you were thinking :-)
The issue people run into with off-grid planning is that they are very surprised how much energy even a pretty efficient home consumes. A typical home averages around 1-2kw over a day, which is about 24-48kWh per day. Even the low end of that range means you need the equivalent of about 32 fully charged car batteries every day. Your solar panels have to provide ALL of your power for the day, but they only have around 6-8 hours of time to do that, so they need to produce about four times your home's total daily electric use in that 6-8 hour time period. That’s to run your home and charge the batteries to store energy for the portion of the day when the solar panels aren’t producing. You have some system losses in there too, probably around 15-20 percent, which you also have to overcome. For a system to be reliable over a longer period of time, you need to have enough battery capacity and excess solar production (to keep the extra battery capacity charged) to be able to run through at least 2-3 days of poor solar output, such as a few rainy or overcast days. Most people use a generator to supplement their off-grid solar system for occasional periods of heavy load, and to deal with extended periods of poor solar output. Propane is a good fuel for the generator, because it doesn’t degrade over time which makes it easy to store. Diesel fuel is the other option.
Bill
Everything Bill said is correct. But some areas of the country -- including where I live in Vermont -- you can't expect 6 to 8 hours of sunshine daily for many months of the year (Nov. 1 to Feb. 10 are the roughest months). And waiting 2 to 3 days won't help. In late November, after three days of cloudy weather, do you think you're going to be blessed by 6 to 8 hours of perfect sunshine on the fourth day? No such luck. You'd be lucky to get a partly cloudy day with an hour of good sun.
In this climate, almost all of your electricity will come from a fossil-fuel powered generator for those 3 or 3 1/2 months.
I'd certainly go with Martin's expierience here -- there is no substitute for the experience gained from years of living with an off-grid power system.
Martin, have you every measured how much output you get on a typical cloudy day in the winter? I assume we in SE Michigan have similar winter weather to you, with many consecutive cloudy/overcast, generally "gray sky" days. You're likely to still get some level of solar output, but probably not a whole lot, so I'm curious if you have a "I generally see 12% or so of capacity compared to a sunny day" typo of info, anything like that.
Bill
Cloudy day solar gain is a myth, unless you're talking about thin clouds in the tropics. Here in Vermont, the winter sun is very low in the sky, and winter clouds are thick. Useful solar energy on a cloudy day in winter in Vermont = zero.
Yeah, on a typical July day I get around five hours worth of solar production. That's taking the production for the day in kWh and dividing by the rated capacity of the array in kW. On a February day I get around 1.5 hours. Looking at my logs, on July 10 it rained all day and I got 50 minutes worth. On a winter day that could be very close to zero.
My goal is to be net-zero, although I haven't been in the house long enough to be sure if I am or not. But I'm close. What makes it possible is net metering from the power company, I can bank the capacity from a sunny day in July and use it on the rainy day in February.
The tight EPA controls and similar regulations elsewhere have woodburning stoves that are very clean burning with very low emission rates.
Why don't you add up the total power needs for the system you suggested and calculate average daily load in kWh. It is illuminating. Then compare to the *best* output you can expect from the solar array. Then realize the size of the array you need to meet all these needs on the day that is 50% sun.
Then figure out the battery bank size to meet your average daily load on non-sunny days for your locale.
I have literally done that. It is illuminating. BTW, for water there are water pipes under the solar panels - might be of interest.https://natural-resources.canada.ca/energy-efficiency/products/water-heaters/solar/14562 - they require a storage tank (huge one) but intriguing.
This is where the shared grid is more efficient because both the production and storage can all be shared shared. Even if you and I build two houses next to each other - it is more efficient because chances are I take showers and cook at slightly different times, resulting in our peak combined demand being lower than the sum of our combined peak demands and lower combined storage needs than the two of us individually require. And with every "slightly different" user the system efficiency goes up.
I also do not think technology is quite there yet - off the grid communities looking for a low power draw dishwashers/fridges have virtually nothing to choose from.
(Having looked at Air to water heatpumps - they need 15/20 amps, and even Sandon. That is a lot for solar. And again, you probably want hot water not just on sunny days?)
There are plenty of people who live off the grid in rural areas Canada year round. They have large propane tanks installed behind screens/trees and have a truck come buy to fill it one a year.
They also use wood-fired equipment. See here for the low-emission options (central heaters).
https://cfpub.epa.gov/oarweb/woodstove/index.cfm?fuseaction=app.about
I have been to homes that have a stone hearth and rely on the stove slowly releasing heat (large inert mass). The problem with wood-fired (or pellet stoves) is that at some point people become too old to manage them. So propane is easier.
I understand they have had mixed success in switching to geothermal for heating, but that may be one possibility to explore if you are dead set on it (I have only cursory knowledge as I briefly considered geothermal for a new build).
If you do not have to be 4-seasons, but let's say 6 months of the year (and go to Florida in the winter) - that is also something to consider. Solar can work except for the depth of the winter in 6B.
Well, if you already have propane for a generator then you can also use it for cooking and DHW so that removes two big draws on solar.
Martin, I read on a propane website that they calculate the amount of propane used in a typical kitchen (just cooking) to be about 40-60 gallons per year. Does that sound about right?
https://propane.com/propane-products/ranges-ovens-stoves/
(under the FAQ section - How much propane is needed to operate a propane range or oven?)
The last big electrical draw is still space heating and the problems a mini-split has with the invertor and line losses. What if you take the invertor out of the equation with something like a DC Solar Mini-split?
https://www.hotspotenergy.com/solar-air-conditioner/
It's unfortunate that there just doesn't seem to be any off grid products available today that will run efficiently on electricity - it always comes back to propane. So what's left to consider for electrical loads? An ERV, a dehumidifier, a fridge, a freezer, a washing machine, electronics and lighting. Oh, and the well pump, the water filtration system....anything else I'm forgetting?
I don't want to pick nits, but you're looking at it the wrong way when you say "It's unfortunate that there just doesn't seem to be any off grid products available today that will run efficiently on electricity." It's not a question of efficiency. For the most part electrical devices are more efficient than propane devices when you compare what you get out to what you put in. The problem is that space heating and water heating take large amounts of energy; the sun tends to be least available when you need the most energy; and there is no practical technology today for storing the energy from the sun.
>"It's unfortunate that there just doesn't seem to be any off grid products available today that will run efficiently on electricity"
Efficiency is defined as the amount of useful work you get out of a device in relation to the amount of energy put into the machine to do that work. An example would be an 80% efficient gas furnace, which puts 80% of the BTU (heat) content of the input fuel into the air in the home, and the other 20% of the fuel's energy is lost as waste heat out the exhaust of the furnace. The best you can ever hope to achieve with anything is 100% efficiency, and that's not really possible EXCEPT in the rather unique case of electric resistance heating, where the losses are also heat, the same as the useful output, so such a device is usually considered to be 100% efficient. Heat pumps sometimes appear to be more than 100% efficient because they aren't MAKING heat, they are MOVING heat from outside to inside (when operating in the heating mode). They thus provide more heating BTUs than you'd get from the input electricity if used in an electric resistance heater, because some of the output BTUs originated outside, and were "moved", not "made".
You appear to be thinking of "efficiency" as a measure of how much energy it takes to do what you want to do, but that's just wishful thinking here. I like to jokingly say that "there is one true law of the universe, and that is that physics is a b*****." Physics is what it is, and we have to work with it. You'll never be able to get more heating BTUs out of any form of input energy than it contains, regardless of what kind of input energy you start from.
In the case of an off-grid system, "line losses" would be resistive losses in the wiring. Those losses will be pretty small in most systems, maybe a few percent or so. Physics has two pesky rules here: one is that you always lose some energy when you move energy from place to place, the other, and this is the big one, you always lose some energy when you convert it from one form to another. Silicon solar cells, as one example, are usually around 20-25ish percent efficient or so for commerically available panels. That means you only get somewhere around 20-25% of the energy of the light hitting the panels out as useful electricity. The rest of the sun's energy is lost reflecting off the panel, or heating up the panel, neither of which makes any useful power for you. Inverters these days are pretty efficient, usually up in the high 90s in terms of percentage. Losses usually go into heating up the inverter.
What you're trying to do, heat your home, requires some fixed number of BTUs based on a combination of your target indoor temperature (the thermostat setpoint), the insulation of the home, and the outdoor ambient temperature, along with a few other things of lesser concern. If you need 10,000 BTU/Hr to maintain your home's indoor temperature, you need about 3kwh PER HOUR, which is a continuous 3kw load, to do that, since 1kwh of electricity contains about 3,412 BTUs -- assuming a 100% efficient electric resistance heater. You can do better with a heat pump, lets say twice as good. That means you now need about 1.5kwh per hour to heat your home. You can increase the insulation on your home to help lower that a bit more, but that can be more complex to calculate, so let's just summarize that to say "insulation slows the rate of heat loss, so more insulation means less energy loss, so less energy required to maintain the indoor temperature".
Now you have a number. You need 1.5kWh per hour that you have to input those 10,000 BTUs to keep your home comfy. For a day like that, you need 36kWh. That's around 43 fully charged car batteries. That's a 6kW solar array, running for 6 hours with full sun. If we extrapolate that out for a utility cost for grid power at 20 cents per kWh, that's $216 for 30 days of heat.
If you heat with an 80% efficient propane fired furnace, you need 20% more input energy per hour, to deal with the losses. That means 12,000 BTU per hour. Propane contains 91,500 BTUs per gallon, so you need about 0.13 gallons of propane per hour. That's a little over 3 gallons per day, or about 94.4 gallons of propane for 30 days of heat.
No matter what you do, that's how the math works out. It doesn't matter if you heat your home with grid power, solar power, or propane, you ALWAYS need the SAME amount of total BTUs to keep the temperature stable, regardless of the input energy source you use. Efficiency just relates to how much of that input energy goes into actually heating your home compared to how much is lost in exhaust or anything else.
ANY electric appliance will work just as well on off-grid supplied power as it will on grid supplied power, as long as you can provide enough power. That means an inverter needs to be big enough to power your loads, and your solar/battery system needs to be able to produce, and store, enough energy to supply those loads for whatever period of time you require. The issue you have here isn't that no one makes efficient electrical devices, the issue is that you're underestimating how much energy it will take to achieve what you want to do.
Bill
Bill: Wow! Thank you for all that valuable information. I always think it is important to thank someone who takes the time to thoughtfully respond to a question - there is nothing ruder that to not respond after someone has taken a lot of time and done a lot of research to answer a question so thank you. Batteries are going to definitely be involved - do you have any recommendations for a solar PV system?
I would really love to move all fuel using appliances out of the house, and therefore I am extremely reluctant to use a propane cook stove or range (Wood stoves are absolutely out!)
I can run DMW off of propane because the water system is outside in an attached utility shed (I also want propane for a direct vent wall heather in emergencies) so for electriciity it's basically an induction range (with the oven not used very much), a washing machine, fridge/freezer, ERV, dehumidifier, lights and electronics.
As to the well and pumping water, I did find a solar well kit from RPS Solar Pumps that looks promising.
https://www.rpssolarpumps.com/
The house itself is going to be as near to passive as possible without going nuts. A simple box, well insulated with triple pane windows (most of them fixed). They always say on those Pasive House websites that "you can heat this house with a hair dryer" so to go off grid it all comes down to the choices for the appliances and the mechanical equipment.
You can use a regular well pump. No need for anything fancy. A regular well pump that draws 2,000 watts while running but runs for 15 minutes a day is using the same amount of energy as a fancy "super efficient" well pump that draws 500 watts by runs for an hour a day. The only difference between the two is that the bigger pump pumps water faster, so it runs less. Since total energy involves both the rate used AND the amount of time you maintain that rate of use, you can use a larger pump if it runs for less time and end up in the same place as far as energy consumption goes.
A "hair dryer" is usually around 1,500 watts, which is about the same as a typical plug-in electric space heater. That hair dryer or space heater is using the equivalent of about 2 fully charged car batteries EVERY HOUR. For an off grid home, that is a BIG load, since it's a decent amount of power, but it can also be expected to run for fairly long periods of time.
I really think you need to think about a propane (or diesel) fueled generator here. If you're expecting a lot of cold weather, a propane generator will have some advantages for you in terms of less maintenance and fewer potential issues.
BTW, I think it's worth spending time to try to educate people. I spend a fair amount of time doing educational outreach for STEM students, and it's fun too! We get better results when everyone knows more stuff.
Bill
"You can use a regular well pump. No need for anything fancy. A regular well pump that draws 2,000 watts while running but runs for 15 minutes a day is using the same amount of energy as a fancy "super efficient" well pump that draws 500 watts by runs for an hour a day."
For centrifugal pumps, it's not a linear relationship. Output volume is directly proportional to the pump speed, but pump power is directly proportional to the *cube* of the pump speed. Doubling the run time to pump a given volume of water reduces the total energy required to 1/4. I replaced the fixed speed well pump that feeds my cistern with a variable speed Grundfos SQE pump so I could do exactly this (run it at 50% speed) and significantly reduce the electrical costs to irrigate my property.
I feel like we're just not getting through to you.
You are proposing an off-grid house where the power is supplied by solar electric backed up with a battery bank. That will power heating the house, an induction range, a washing machine, refrigerator, ERV, dehumidifier, lights and miscellaneous electrical loads. That's a huge load for off-grid.
Let's use Bill's estimate of 50kWh per day, which may even be low. I don't know where you're located, but in here in DC in February I get the equivalent of about 1.5 hours a day of solar production. So to average 50kWh/day in those winter months, you're going to need a 33,000 Watt array. I've been paying about $3 an installed so that's about a $100K system.
But that solar doesn't come at you continuously, you need some way of storing electricity for when you use it. How much storage you need is a big question, it's impossible to predict, but let's be conservative and say you need three days worth of storage. So 150,000 Watt hours. Let's look at the Tesla PowerWall, not because it's particularly good, but it's price and capacity are easy to find. It has a capacity of 13,500 Watt hours and costs $14,200. So you'd need eleven of them, cost $156,200.
So you're looking at a quarter of a million dollars just for the pieces. I won't say it's impossible, but it's daunting. And keep in mind that most of the cost of those PowerWalls is the batteries, and they only last for a few years. You probably need to budget something like $40-50K a year for battery replacement. And this is for a system where if you get four rainy days in a row, or a snowstorm that covers your solar panels, you end up cold, dark and hungry.
Going off-grid without fossil fuels isn't hard, it's just very expensive.
Let me add that I get about 1,000 hours worth of sunshine a year. Let's say that house that needs 50 kWh on high-demand days averages 33 kWh over the course of the year, that's 12,000 kWh per year. With net metering and 1,000 hours of sunshine a year, you can go net-zero with a 12kW array, which would cost about $36,000 installed.
So the cost of being all-solar off-grid is roughly seven times the cost of being net-zero with net metering. That doesn't include the cost of regularly replacing batteries.
Ok, it will be expensive. As fuel prices rise and homeowners are being encouraged to move to an all electric household eventually plentiful fuels like propane will become harder and harder to source and purchase.
As to building envelopes, products and methods that were considered difficult to detail and expensive to install 20 years ago are being built into average homes today because they are now acknowledged to be "sound building science" and easily sourced.
Products and methods and details have all evolved considerably in the last 20 years, so why is it so difficult to find simple solutions for an all electric house? Yes, it can be easily done on-grid but if you're 30 miles from the nearest electrical pole that's not possible.
If I keep coming back to the same questions, it's not because "You're not getting through to me". It's because every time I ask this question I get another reply with another piece of the puzzle. I don't want a standard, typical city house with every single electrical load out in the country - I just want to know what are the products and systems that use the least amount of electricity that I can use off grid. That's it.
And again, thanks to everyone that replies.
I honestly believe that the long-term trend will be it is more difficult, not easier, to live off-grid.
DC,
That's what I wrote about in my article, "Off-Grid Homeowners Contemplate Our All-Electric Future."
That's a good article. What it doesn't even touch on though is that right now all of the incentives to electrify the economy involve carrots but at a certain point the government is going to have to switch to sticks. I fully expect that once electrification achieves critical mass conventional fuels will start getting scarce and expensive. I can easily see a future where burning hydrocarbons on an individual level becomes extremely rare.
Upon reflection, I think Bill's estimate of 50kWh/day is low. Think of a house that on a winter day has a 24-hour average heating load of 20,000 BTU/hour, which isn't that much. Stipulate that at winter temperatures the heat pump that powers it has a COP of 2.0, that means it consumes the equivalent of 10,000 BTU/hr in electricity, which is just about 3,000 Watts. That's 72,000 Watt hours per day. Just for heat.
So really you need a system a minimum of 50% bigger than what I laid out in post #16, or something that would cost along the order of magnitude of $375,000, just for the pieces, just the initial cost. Upkeep for the batteries would probably be another $60-70K per year.
The utility industry generally uses 1 kw to 1.5 kw as an average load per connected home, which is where my numbers are coming from. An all-electric home is likely a higher average electric load, since for such a home, electricity is the sole source of input energy. I wouldn't be surprised if my numbers are bit low for an all-electric home, but since there are so many variables, at some point you just have to pick a number for the example and stick with it :-)
Bill
The biggest issue you have is that the entire purpose of the "power grid" is to allow for efficiencies of scale, which keeps power costs down (and also improves system reliability throught redundancy). When you have an off-grid home, you have NO economies of scale, because there is only you! You also have no redundancy, so lower overall reliability. You can help with reliability with a generator, since that generator can power you if the solar system isn't producing (or if somet part of it breaks), and the solar system can power you when you're doing maintenance on the generator.
If you want the least energy using gizmos, that means a heat pump for heating and cooling, and LED lights. If you want to good with electricity, an induction cooktop is your best option. Computers and the like are all about the same, with beefier (more powerful systems) drawing more power. Laptops are your best option here. After that, the energy use has nothing really to do with efficiency, and all about your use patterns. That means you need more energy to leave the lights on all night compared to going to bed when the sun goes down, for example. You want to use the most efficient light, and LED, regardless, but that efficient light will still use lots more power if you run it for longer periods of time.
"All electric" and "off grid" are not necassarily the same thing. Usually, an "all electric" home means a home with no fuel-burning appliances, so you have some type of electric cooktop, electric heat (usually a heat pump), a heat pump or electric resistance water heater, etc. No gas, propane or otherwise. Most homes are some kind of hybrid, using a fuel for some high demand loads, usually space heating, hot water, and sometimes also cooking.
If you have an "off grid" home, everything is the same (for the most part) as an "all-electric" on-grid home, but you have no grid connection, and produce all your own electricity. For most, this means solar power and batteries for night time. Some people have wind generation. A lucky few, where their land allows for it, get to use microhydro (my favorite!), but you need a flowing stream for that sort of thing to be possible. Of those three energy sources, only hydro power offers the ability to run continuously without a way to store power (i.e. no batteries are required), assuming the stream runs all year round. Solar and wind are both intermittent power sources, so you need energy storage to fill in the gaps when they're not producting.
All a power grid is is a network of wiring connecting many, many different generators together over a large geographic area. The only difference for a home, between "all-electric" and "off-grid", is the SOURCE of the electricity. Off-grid may or may not use propane, natural gas, etc, just like an on-grid home. I think you may be mixing up those two terms. You can use all the same "all-electric" type appliances in an off-grid home, you just have the issue of TIME that comes into play when off-grid, because you have only limited energy production and storage, which limits how long, and how often, you may be able to use the things in your "all-electric" off-grid home. BTW, in the engineering world we call the power grid an "infinite bus", which means it can provide essentially limitless power, indefinetely. That's what the grid can do that your off-grid system cannot, and it has nothing to do with the electric devices you're running inside your home.
Regarding fuels and fuel costs, I doubt very much fuel will become unavailable for decades or more, and will probably remain relatively affordable over that same period. The big reason that a wholesale conversion of everything to "all electric" is that it's simply not possible to do at the present time, and won't be for quite a while. The grid, while we like to use that "infinite bus" term, is actually finite -- there is only so much generation available, and we use most of it during times of heavy load right now. There is not enough excess capacity, for either generation or transmission (the lines that move the power around) to completely replace other energy sources right now. We would need approximately double the current grid capacity just to replace all gasoline use for transporation, for example (I calculated that out a while ago from EIA stats, and some power industry info I have access to). When we start talking large scale, for EVERYONE to convert to all-electric, the grid starts to have issues not unlike those the off-grid people have to deal with, just at a MASSIVELY larger scale.
At the end of the day, we're working with physics here. No matter how much any of us may want physics to be different, the laws of the universe just laugh at us -- we have to work within those physical limits and the realities of the various systems at work.
Bill
I have actual numbers from an all electric apartment in zone 5, heat is air source heat pump.
Jan usage 764kWh. Peak daily usage was 38.6kWh. Each day around that peak was also above 30kWh, so you need at least 100kWh of storage to make it through a cold spell.
Since my day job is dealing with solar and storage, I can tell you, you will NOT make it through Jan/Feb off grid with a reasonable battery and PV array without using fossil fuels.
I guess you can install a 200kWh battery and 75kW array (you need this big PV to have some production on those 0.5 to 1 sun hour days), you have a decent chance but even that might have issues during a polar vortex.
To put some numbers on that system, 100kWh of storage, using my earlier example, would be about 119 car batteries. Using some recent numbers for better batteries I just sold to a customer for a solar project, you'd need 44 of them. My wholesale cost on these was $425/each, so you'd have $18,700 just in the batteries for that 100kWh of storage. You'd have maybe another $5-10k for battery racks and cabling to connect those batteries. Those batteries have a 5 year rated life, and might make it out to 7-8 years if you treat them really well.
Bill
Bill, you said in comment #27 that the utility industry generally uses 1 kw to 1.5 kw as an average load per connected house. Is that a typical 1950's - 2000's house with incandescent bulbs, an electric coil top range, old fridge/freezer, etc?
While appliances like induction cooktops and LED bulbs are becoming more familiar to people who want to save energy costs (on or off grid) that still doesn't address all the "newer" mechanical equipment people are encouraged (Or required) to install in their dramatically tighter homes - things like HRV's, ERV's, and dehumidifiers.
Also, are there significant advantages to moving certain appliances and HVAC equipment directly onto solar power and bypassing the invertor altogether (Things like the Hotspot DC mini-split I mentioned previously)?
The average load number is for current homes, averaged over millions of homes. Even with today's modern gizmos, the number is still reasonably close in most cases, because someone who went from an electric resistance range to an induction range might use a little less electricity, but someone else probably just replaced their gas range with an induction cooktop, and they are now using a lot MORE electricity than before. It averages out. HRVs are small loads. The biggest thing you can do to up your averal electrical use is to replace your space conditioning system with a heat pump, which, for most people, means they are now using electricity for heating instead of gas/propane/fuel oil. Lighting with LEDs will use less power than incandescent, but remember that in the winter, you'll also be using a little more heat from your heating system because your lights now produce less heat.
I would say NO, there aren't usualy advantages to trying to run stuff directly off of the solar system. There are several reasons for this. The first is that 120v/240v AC is the standard power interface in North America, so using the inverter means you have access to many more options for all your power using gizmos. Another reason is that the output from solar panels varies when the intensity of the sunlight on the panels changes, such as when a cloud passes overhead. The inverter can compensate for this, keeping your gizmos happy with a steady power source. Without the inverter, the gizmos would "see" the lower output as a sort of brownout condition, which they'd either have to be able to deal with themselves (more $$ for the gizmo), or they'd not operate correctly.
Modern inverters are up in the high 90% range (usually 95+%) efficient, so they don't really contribute significant amounts of losses to the overall system. You DO gain some advantage running lights on DC directly (assuming you use a standard DC voltage on your battery system in an off-grid home), since that way the inverter doesn't have to run for very light loads, which is the worst case scenario in terms of system losses.
There are ways to optimize the energy efficiency of an off-grid home if you want to dig into things and fiddle with the system throughout the time you live in the home, but most people want their off-grid home to behave the same way as it would if it was grid connected. The tradeoff for the convenience of easy operation is increased energy usage in that case.
Most of the DC operated appliances I've seen are huge compromises, typically with much reduced performance. Reduced performance IS NOT "increased efficiency" -- it just means it will take you longer to do things (the water pump example), or you'll be unable to do things (a too-small heat pump).
In the easy to describe case of a well pump, imagine a DC only well pump that only draws 200w but also only pumps 0.15 gallons per minute. Compare that to a well pump that draws 2,500w but pumps 2.5 gallons per minute (and keep in mind that I'm just making up numbers here for the purposes of the example). That bigger pump draws 12.5 times more electricity than the little one while it's running! That's not better efficiency though. Let's say you are going to make some chicken stock, and you need to fill your big 24qt stock pot. You need to put some chicken and veggies in there, and you don't like when it boils over, so you won't completely fill it with water, let's say you only put in 20 quarts of water -- 5 gallons. With the little pump, it takes you 33.3 minutes to fill that pot (or replenish the water in the pressure tank that you used to fill the pot). The big pump fills the same pot in only 2 minutes.
Now here is the interesting part that is actually fairly common, but often overlooked. That little pump used a lot more power than the little one while it was running, but it didn't run for very long. It used 2.5kw for 2 minutes, which is 0.084 kWh. If you pay 20 cents per kWh on grid, that pump used about 1.7 cents worth of electricity. Now the interesting part: that little pump only used 200w while it was running, but it had to run a lot longer to do the job -- 33.3 minutes! In that time, the little pump used about 0.11 kWh of electricity, which would cost you about 2.2 cents.
The little pump, that uses less power while it's running, is actually less efficient than the big pump! The reason is that efficiency is defined as the unit useful output per unit of input energy. The big pump used LESS TOTAL ENERGY to pump THE SAME AMOUNT OF WATER as the small pump. That means the bigger pump, while it uses more power while running, is actually more efficient than the small pump because the big pump uses the electricity more efficiently, delivering more water per unit of energy consumed. It's very important to consider things like that when you're trying to optimize a complex system for the lowest OVERALL energy use, which is what you want to do for an off-grid home.
Bill
Bill, it's not only amazing that you know all these things but also that you obviously type really fast :) I mean, it was only half an hour from my question to your reply :)
So here's my totally, self-serving question: you have a little house, under 500 sq', with R30 walls, R-60 attic, triple pane windows and very air-tight. What brands or models of equipment and appliances would you put in it to give you great performance while using the least amount of electricity?
I used to be a UNIX system administrator, hard to do that if you type slowly. I also write about a bazillion quotes and contracts for work, plus several orders of magnitute more than a bazillion worth of emails :-D Practice makes perfect and all that, although I still make plenty of typos. It's actually interesting to see the typos, since I write stream of conciousness usually, so the typos give an insight into the psychology of written language, in a way.
Anyway, for a small house, space efficiency is very important. I'm assuming (based on past discussion here), you want to go all-electric. I would do something as follows, and keep in mind this is a very rough "kinda sorta" list, since a proper design needs lots more detail.
I'd use an induction cooktop, no question. I'd go with a 30" one, which is a little more compact, but not so restrictive in use as one of the very compact 2 burner models. I've used both 24" and 30" ovens, and 30" gives more flexibility, so that's what I'd use. The oven is a problem off-grid though, so you might need to do things differently depending on what you ultimately want in your place. I'd go with a narrow fridge, either a french door or "freezer on top", so that I could get narrower. Side by sides don't work as well when you have limited space. You want a compact dishwasher too.
I'd put in a Mitsubishi minisplit. I've specced loads of those, and I've always had good luck with them. Try to locate it central-ish, and situate it so that it can have good airflow across as much of the floorplan as possible. There is just no beating one of these minisplit heat pump units for energy efficiency.
I'd use a small tank-type electric water heater. Tankless water heaters are a no-go for off-grid, due to the huuuuge amount of electricity they require while operating. Get one of the short and squat style tank type heaters, hide it under the kitchen counter if possible, or near your well's pressure tank, if you have somewhere you can access where the well stuff will be. I'd use a normal well pump (regular AC power), and I'd use a submersible pump unless I had a really shallow driven well, in which case you need a pump on the surface, which typically means a jet pump.
I'd go all LED lighting (obviously, it's so easy to do these days!), and I'd be very careful to placement. If on-grid, I'd light in the usual way. If off-grid, I'd pay particular attention to task lightning. Task lightning means small lights right where you need them, which uses less energy than trying to light an entire room. Think "a reading light by my favorite chair" instead of "can lights in the living room". This is especially important in the kitchen, where you want higher light levels in the workspace. Task lights in the kitchen can be a few strategically placed recessed lights over the sink, cutting board, maybe a small counter used for prep stuff. Get a vent hood for the cooktop that has LED lights in it to light that area. I'm a big fan of under cabinet lights for counters, and you can get nice ones these days that are very adjustable, so you can keep a low level of ambient lightning (less energy use) that way that's in an area where it's most needed (the counter work area), not wasted all over the floor. Almost all kitchen lightning guides are wrong too -- NEVER put the lights BEHIND you as you're working on the counter. Lights go over the WORK AREA, not over THE FLOOR! Be smart about light placement and you can get more useful light, which means better efficiency, remembering that "efficiency" means putting light where you need it, not wasting it lighting your baseboard or the hinges on your door.
If you are going off-grid, but you're OK with propane, I'd use propane for the water heater, and I'd use propane fueled generator for backup power. You need something that can run a long time too, and not break. That means not the usual residential standby stuff (you don't want Generac, etc.). Kohler makes a few generators that are popular with the off-grid guys, but if you really want something reliable, get an 1,800 RPM unit with a liquid cooling system, not an air-cooled 3,600 RPM unit.
When you go with your electric panel, get one with copper busbars, which usually costs little, if any, more. Siemens prices them almost the same wholesale, so I only get the copper versions. I don't put in off grid systems enough to really have much insight into good inverter options.
BTW, I'd try to get a lot of your R30 walls in the form of exterior continuous insulation, probably polyiso. A wall built that way will perform better than a wall with R30 cavity fill.
Bill
A low flow shower head is a must too. If you can use a long vertical or horizontal drain water heat recovery unit, even better. They have no moving parts and use no energy.
Thanks Bill for your help! I'm always reluctant to specifically ask for help on a real project because I don't want people to think I'm trying to get a free design out of them.
I agree with all of your advice: I definitely want to go induction, not just from the stand-point of not using fossil fuels but more to do with the indoor pollutants produced by burning the gas.
The oven will still be a problem though - maybe a separate induction cooktop and one of those smart countertop ovens might work (they seem to be recommended on America's test Kitchen on Youtube).
https://www.youtube.com/watch?v=LnjvzB0OZsc
As to fridges, the way solar DC fridges are marketed you'd think that they were far superior to regular AC fridges that you could go down to Home depot and buy but some of the Energy Star AC fridges seem to be pretty comparable.
I hadn't considered a dishwasher - I assumed it would take too much electricity but I've seen that TV commercial where they show that running the faucet for two minutes uses the same amount of water as a dishwasher's cleaning cycle so maybe it's a good idea.
I like Mitsubishi mini-split but considered a Mr. Cool since I wouldn't have to charge the linesets. Apparently there's a new mini-split from EG4 that comes with pre-charged linesets now.
What do you think of the Sandon CO2 air source water heater?
I'm thinking of the Grundfos soft start well pump.
For lighting placement, you will like the information on David Warfel's webiste and blog Light Can Help You.
https://lightcanhelpyou.com/
https://lightcanhelpyou.com/blog/
As to the electrical panel, what do you think of that new Span panel as discussed on Matt Risinger's Youtube channel?
https://www.youtube.com/watch?v=cPWR4-OlmqY&t=21s
All the exterior insulation is 3" of Roxul Comfortboard.
The way I would approach would be to create an energy budget. On one side of the ledger is all of the devices you want to have, for each calculate what their average and peak daily consumption would be. A good way to do that would be to start logging usage in your existing house to get a feel for what various levels of usage feel like. From the device numbers you can estimate what an average day and a peak day look like.
On the other side of the ledger is energy production. First step is to gather as much information as you can about sunshine levels -- "insolation" in the biz -- at your site. With that you can start to estimate how much electricity you can produce with a certain size array, and how big an array and how much storage you'll need to meet your consumption needs.
Then figure out how much all that stuff costs. If it's within your construction budget, congratulations, you're done. But if it's not then the horse-trading begins. There are two types of compromises you can make. One is switching out pieces of equipment, trying to find more efficient and/or cost-effective choices. The other is to make lifestyle choices. Maybe you'll decide that a dishwasher is a luxury you can live without. Or maybe you're OK with the inside temperature dipping down to 60F in the winter. Or maybe you're OK with a 3-minute shower on days the sun doesn't come out. Or maybe you decide that being all-electric off-grid is two big of a leap and you consider supplementing with liquid or solid fuel.
I heartily recommend analyzing your existing energy usage and getting a feel for what the big energy users are.
Choosing electric appliances for cooking, space heating, and water heating is all fine and good, but these choices only make sense for a grid-connected house. If you are off-grid, you're not going to want to use electricity for these purposes during the winter -- or you will end up powering the appliances with a fossil-fuel powered generator, which is expensive and inefficient.
That's why off-grid homeowners usually use a propane cookstove, a propane water heater, and a wood stove.
Martin, I know from your comments that you have lived off grid for almost 50 years, which means you built your off grid home around 1975. I'm sure that you more than anyone realize that construction materials, building details and forensic building science have advanced so much in the last 50 years that you would never build today what you built 50 years ago.
And yet, whenever the subject of off grid mechanicals pops up on this forum (usually started by me) you revert back to the principles of design from 1975 - use a wood stove, cook on propane, open a window if you want ventilation (you've said all these things to me before in other posts).
The world is moving away from fossil fuels. It's not just a question of cost, it's also a question of the amount of fossil fuels that's still existing for humanity to utilize. I mean, even Governments and major car manufacturers (probably the two organizations most entrenched in developing fossil fuels) are either encouraging people to switch to electric options or plan on stopping production of fossil fuel using products altogether.
So why the opinion that choosing electric appliances for cooking, space heating and water heating only make sense for a grid connected house? Eventually there won't be any fossil fuels, at least for the common man, and it won't matter if you're in the middle of a city or 50 miles out in the wilderness.
I want to build a really good, well insulated small house that is super air tight. I don't want wood burning inside the house because of the super fine particles that will inevitably be circulating through the air. I will have to have an ERV and I'm sure a dehumidifier. I will probably have to heat hot water with an air source heat pump. All these devices will use electricity. I just want to know what are the best options for 2023, not 1975?
What hasn't changed in fifty years is the physics.
The issue is that it just isn't realistic to run everything with the amount of electricity you can generate with a solar system at home throughout the year. The same issue exists with the grid too, which is just barely starting to become apparent to people. Right now, reliably running things requires burning something. The only other realistic option for the grid is nuclear power, there really isn't enough solar and wind production available to replace current "burning something" generation AND to replace all the other "burning something" appliances like natural gas furnaces.
Bill
You can absolutely have an all electric off grid house for the right price. Most people stop before that price.
I’d research / ask your question differently- ask for the most efficient electric methods for whatever you want to achieve.
What would be helpful is if you told us what climate zone you're in, and gave a rough idea of your construction budget. Did the numbers I tossed around in post #16 make you stop in your tracks, or was your reaction more like, "Hmm, that might work"?
"So why the opinion that choosing electric appliances for cooking, space heating and water heating only make sense for a grid connected house?"
I feel like we've explained this many times, but since you boiled down the question to a single sentence I'm going to try and respond similarly briefly:
It is very, very expensive to provide high-availability electricity off-grid in any quantity without using fossil fuels. It doesn't make sense because it is expensive.
Well, you can start by estimating how many panels you can fit on the roof of this small and efficient house. Probably 7.5 kWh worth? If lucky - 14?
Look at what you can expect to generate per day on a "good" day and on a bad day.
Compare to the demand (how many BTU of heat do you need? chances are you need 40kwH on heating along - without the hot water or anything - on cold days. When your solar output is going to be 0.).
My point is - it may be possible (e.g. you live in a very temperate location where you need neither heating nor air conditioning much of the year). But you know that. You can estimate your heating needs and cooling needs and energy use (e.g. no hair dryers! yes power tools for a woodworking hobby! Electric vehicle charging stations! whatever it is.).
So I would do the math on the power supply (do you have a lot of land with good exposure to mount all these panels? Or are you surrounded by forest? Or highrises?)
Then do the math on the appliances. Then see if you can come even close or what is the biggest problem is (e.g. unduction stove is 30Amps at a minimum even for a 30 inch one. Unless you get a hotplate only) and then solve *that* problem. May be you like cold showers and a small water heater is fine?
Note that the amount of power used by electric cooktops varies with the number of burners active, and also the power level the active burners are set to. The “30A” rating is an absolute max, with average power levels likely to be quite a bit less. Admittedly, how much “less” does depend on your cooking demands.
Bill
This is basically what I proposed in #36, creating an energy budget.
Q. "So why the opinion that choosing electric appliances for cooking, space heating and water heating only make sense for a grid connected house? Eventually there won't be any fossil fuels, at least for the common man, and it won't matter if you're in the middle of a city or 50 miles out in the wilderness."
A. It's tough to admit, but living off-grid won't make sense in a world that struggles to avoid burning fossil fuels. For a deeper look at the problem, see "Off-Grid Homeowners Contemplate Our All-Electric Future."
My prediction is we're not going to stop burning fossil fuels, if we're successful at decarbonization we're going to stop burning them at small scale. Instead we'll burn them in facilities that have enough scale to make carbon capture practical. Because right now there's nothing on the horizon to produce the energy we need to maintain our current standard of living.
Another promising technology is capturing carbon from the atmosphere and combining it with hydrogen produced with off-peak electrical capacity to make synthetic hydrocarbons. This fuel would be net-zero carbon and would be useful for applications like air travel where nothing electrical can provide the energy density that is needed. I could see off-gridders moving to synthetic hydrocarbons, even if they're expensive it's the best alternative.
Oops, I should have included the climate zone: 6B.
The solar panels will be on a ground rack for easier snow removal so they can be as many as needed.
If it comes right down to it, I could install an outdoor wood fired boiler for DHW and radiator space heating. There will be some pumps involved but I'm sure they won't be too demanding to run. That leaves cooking as the last big hurdle. I definitely don't want propane for cooking indoors so it will have to be induction. At least my choices are narrowing down :)
Martin: Is there any way of releasing that article to the members who don't have a Prime Membership? I would think after a while (maybe 3 months) Green Building Advisor might consider doing that with all their Prime articles.
Lets get some real world numbers.
I have a 10kW ground mounted array up north, zone 6, plenty of snow. Set at 45deg and facing south for maximum winter production. In Dec, the array produced 350kWh, Jan dropped to 184kWh, Feb 191kWh.
Those are for the whole month, during a snow storm, I would not be surprised if the output was between nothing to a couple hundred watt hours in the whole day for a week.
You area dreaming if you think you can run a fully electric house off that.
A decent hydronic system uses between 75W to 300W 24/7. Lets say you have done your homework, so you are near the bottom, say at 100W which also makes the math easy. That is 72kWh for a month, so about 1/2 the production in Jan/Feb of that 10kW array above. It will simply not happen.
That 75kW array I guessed at above is not too far off for what you need.
At least he's come around to not having electric heat and DHW. Baby steps.
I don’t think a wood boiler would use nearly that much. The smallest Eko boiler uses 50 w for the fan when it’s on. If the OP load is 5kbtu, a 12 hour burn would use 500wh and provide about 120 hours of heat. Combined with a low energy distribution system (should be easy with the size of a house!) and you might end up using less than a kWh per day at max heat loss. It wouldn’t be cheap, but it would work.
I think he was thinking of the circulation pump or pumps, which would likely be at least 50-100w or so, depending on how beefy the pumps are and how many of them are needed (for zoning).
Bill
No way should a 500 sqft house with a low heat loss need 50-100w of circulation pump. That should be single digit watts if designed right, you only need .5gpm at a 20 degree delta T.
Bill, a variable speed Taco 015e maxes out at 44W. You’d only need a small fraction of that for distribution in this small system.
The problem you run into with very small systems like this is that you end up with having to oversize some components because you can’t get anything small enough. The common circulator pumps are 1/25 HP, around 70ish watts. There are a few a little bit smaller than that, and many larger. You end up picking the smallest standard pump in this case, which is still more than you need, but you’re stuck because they don’t make anything small enough.
The other potential issue is that you might want your boiler a distance from the house, and you then have to overcome the head of the pipe between the boiler and the house, requiring a beefier pump than you’d need with the boiler next to the house.
Basically the theory says you only need x worth of pump, but you’re stuck with y because that’s all you can get. It’s like the old saying: “theory is like mist on glasses, obscures facts” :-)
Bill
"There will be some pumps involved but I'm sure they won't be too demanding to run. "
Statements like that are why we're losing patience here. Don't be sure. Do the math. I feel like we keep saying that over and over in different ways.
The issue I think some people have is that they get confused with units of energy, especially the time component. I see, as one example, kW and kWh mixed up all the time, and they’re very different units.
Large loads that run only briefly seem “big” to many people, but they often use less total energy over time than small loads run continuously. I tried to make that clear with my example using well pumps. The bigger gizmo can even be more efficient than the little one, making the little gizmo false economy.
It’s all OK though, the purpose of these forums is to help people to learn this stuff so that they can build better and be more efficient overall, and the OP is getting lots of good info. I hope he is able to work towards a better and more practical final design due to the discussion here.
Bill
A friend who used to live in Sutton, Vermont lived in an off-grid house. The PV system worked OK until they installed an outdoor wood-burning boiler. The circulating pump drained their batteries -- they had to run their gasoline-powered generator so much the noise drove them crazy and they spent a fortune in gasoline. They eventually sold the house and moved.
It is so incredibly common for off-grid and passive solar houses to fail, and post-mortem to realize that had the barest amount of engineering been done it would have been obvious before construction that they were going to fail. But instead the owner-builder went ahead with the confidence of "this should work." And then it didn't.
I know I'm like a broken record but there's no substitute for doing the math.
Ok, even a 500 sq feet home needs some cooking and cleaning.
1 element on an induction stove (medium-sized) run for 1 hour per day is about 2kWh. If you run 3 elements in parallel (bacon and eggs, potatoes, kettle for pour over cofee or tea) your peak demand is higher - more like 6.5 kWh but may be for 30 minutes. Still, we are at 2-3kWh per modest cooking. Forget slow cooked stews and pot roasts and canning your own jam or account for it.
An oven - a small countertop Breville (which may be sufficient for all your needs) still needs 1.8kWh per 1 hour of cooking. Let's make it 30 minutes every day - that is 4kWh average just on cooking and baking.
Dishwasher - 1kWh per cycle for a small compact does not heat its own water. Washing machine - small euro sized one (shortest cycle 30 minutes), cold water wash - 1kWh for an hour of use. Dryer (small, compact, Euro sized one) -3 kWh for an hour of use. (in summer use clothesline, but in 6B you pain point is going to be winter, so need that dryer). Lets say 2 adults - that is about 1 load a day total in winter each washer and dryer. But on the day you use them - that is 4Kwh, or average 2 kWh. Staggering ("run dishwasher at night") requires battery capacity just for this (to smooth out the load, regardless of the sun hours).
So we are around 6-8 kWh with cooking and cleaning. No vacuuming, no other appliances, no mechanicals (air circulation?), no clothes irons, no hair dryers, no lights, no electronics. No snow blowers (lawn mowers), power tools. Let's add 4 kWh for that? (that is way too modest, btw).
So you need at least 10kWh per day in winter for a very energy-modest way of living (notice I assumed you need no power for heating or hot water).
In Chicago (which is 5-6) - using random news article - 14 days of no sunshine is common in the winter. No sunshine at all. And 20 days of no sunshine can happen too.
https://wgntv.com/weather/weather-blog/a-mild-work-week-without-sunshine-and-the-potential-for-measurable-snow/
Let's be not too conservative, and use 14 days no sunshine. On November 15 you have had 2 weeks of no sunshine and you drained your batteries, but the sun is out. Now you have the sun for daily needs, but you need to replenish your 14 day storage because you might hit another spell of 14 days no sun starting tomorrow. So now you need to generate 14x10 kWh in one day. In November. Which in zone 6b has an average generation capacity of something like 15-18 kWh per day on a 10kW sized solar panel array.
And you got an "average" day, so to generate 140 kWh on that day you need an array of the size 140/18 = 7 arrays of 10Kw size each.That is 70kW solar array just for backup. You still need another 10 kW array for your daily use that sunny day. That is an 80 kW size solar array? That is a basketball court size of panels with no obstruction and ideal orientation.
What would you do with this in the summer when that array generates a ridiculous amount of power you cannot feed to the grid?
What if you want to be prepared for 21 days with no sun?
I would take your locale - and calculate production possibility.
https://pvwatts.nrel.gov/pvwatts.php
Then figure out your consecutive days of no sun in winter months (for 6B that is likely the weak point). Then look at your needs (do you have teenagers who want hair dryers and hair irons which all hog up power? Do you have a woodworking hobby with power tools? Does your wife like quilting and needs an iron and a sewing machine every day?)
We do not know any of this - but you do. The calculators abound. Specific appliances have their power draw listed.
https://www.bchydro.com/powersmart/residential/tools-and-calculators/cost-calculator.html
(I am deeply sympathetic - I keep on hoping on progress in solar to have an off the grid four-season cabin in zone 6, but for now winter demand is not practical on solar only with no other backup (at the very least like a gasoline powered vehicle to get out of there to some place on the grid when the sun does not shine).
"What would you do with this in the summer when that array generates a ridiculous amount of power you cannot feed to the grid?"
This was the basic problem with all solar power until net metering came along. Almost everywhere in the US solar production is highest when you need it most and lowest when you need it least. At least with PV panels you can just turn them off, with thermal solar you had to figure out a way to vent the heat or you could ruin the system.
Akos: since you have an of grid home in climate zone 6B, what systems, equipment and appliances do you have? What would you change about your systems today?
DC: with all the extra power in the summer, couldn't you use it to heat water and store it in an extra holding tank - a dump load?
Orange Cat: no dryer, torn on a small dishwasher (electricity use vs water use - a dishwasher uses a lot less water than hand washing). No wife, no teenagers, no wood working shop, no vacuum, no hair so no hair dryers.
For a small outdoor wood fired boiler I found this one but I just started looking so maybe there's something better.
https://outdoorwoodfurnaceboiler.com/smallest-mini-boiler.htm
You could use your excess solar power to heat water, but you won’t be able to store enough heat that way long enough to help you in any meaningful way during the winter if that’s what you’re thinking. The usual rule for wood boilers is that 1,000 gallons of storage can get you a day or so worth of heat. With a really small place, and a well insulated tank, you could maybe get two days worth of heat stored. I doubt you could get much more than that though, since you’d end up lowering the temperature enough with the combination of heating load and losses that the water would cool off enough to no longer allow for efficient heating of your home.
My GUESS is that it will cost you less in the way of energy use to pump extra water from a well than it will to run a dishwasher, due to the need for the dishwasher to run heating and circulation motors for the duration of the cleaning cycle.
Bill
In a nutshell, storing energy in hot water is even less practical than storing it in batteries.
Assuming a load of 5kbtu and an 80 degree delta T, 1000 gallons would get you 5 days of storage. That’s workable I’d say.
Rockies63, I’d avoid the outdoor wood boilers (they’re technically furnaces) and look at the wood gasification boilers. Much cleaner and less work.
Paul,
Using the analogy to oil-fired and gas-fired residential heating equipment -- a furnace distributes heat by ductwork, whereas a boiler distributes heat by water-filled tubing -- then the outdoor wood-fired boiler is technically a boiler, not technically a furnace. Some people mistakenly call these appliances "wood-fired furnaces," but technically they are boilers.
Ha well by that definition a boiler feeding an air handler is a furnace. I think the difference was because the outdoor wood furnace heats water that’s only atmospheric pressure? It doesn’t matter.
A thousand gallon tank with an eighty degree delta holds 80,000 BTU. Setting aside for the moment the practical difficulty of getting the heat out of the tank, that's less heat than one gallon of propane. Which currently costs less than four dollars, delivered.
No, it doesn’t. You forgot to multiply by 8.34 lbs/ gallon.
You're right. So it's less than 7.5 gallons of propane. Still less than $30. What's the payback period on that thousand gallon tank and associated plumbing?
Rockies, I'm not adventurous enough to be off grid, that array and the cottage is grid connected.
As for wood boiler power consumption, that one you linked to uses 100W, so I was pretty close. You still would have some more for pumps depending on how it is plumbed plus for the indirect.
I would get a small drawer dishwasher - enough for one person, takes less than 1kwh energy per cycle, and would make life a little more enjoyable. You will have enough hardship feeding that wood fired equipment (and pumping water and heating it requires energy too).
Do you have a terrain where you can use gravity fed water supply? (Like down hill from a mountain river)? I have seen a fun setup as a kid - a cottage next to a fast flowing mountain river, which gravity fed water supply (and solar-heated tank on the roof for summer use). That is from before solar batteries. Again, your exact location and circumstances might help you find a pre-solar solution for some of your energy needs.
I mean next to a river one can generate one's own hydro. There are micro generators. I met a farmer who does that.
I had an off the grid summer cottage in Ontario, Canada. We supplied electricity with a small PV array with 8 deep cycle battery backup. Even then we would have to run a generator to charge the batteries when the weather ran lousy for a while.
Meanwhile, a propane DHW, stove and even a refrigerator took up the BTU part of the equation for the good part of 15 years. Then we got rid of the fridge and plugged a new small one in. Those things eat the juice, let me tell you.
When I did the analysis, we used in one day in our full time home in NY the same amount of KW we used in the cottage IN A MONTH. Still, propane provided the hard part. We used a wood stove for the colder days.
I think you need to reconsider propane. It solves a lot of your problems and you can solve the rest with a good sized PV array. Put the DHW on a timer or get a tankless. Hauling some refillable tanks form time to time isn't that hard.
Reply to #76: does payback matter here? People build homes for all sorts of reasons. If the goal is to build the cheapest house, then 99.99% of American homes fail that test. It’s a question of values, clearly this case is less concerned about lowest cost than others.
If Rockies63 wants to build an off grid house that uses no/few direct fossil fuels, let’s discuss how to get there, instead of dumping on them based on our own personal values. That might mean it’s expensive, complicated and has high imbedded carbon, but that’s okay!
This discussion started with the premise of going off grid without burning anything.
The general feedback was that simply won't happen, or would be cost prohibitive. People have been living off grid for a long time, usually the energy source either wood or a fossil fuel.
Of course there are many shades of green between the two, to know where you land one must do a very accurate energy model which rockies63 hasn't done yet.
It is easy to have grand ideas and plans a throw random ideas at the wall but until you do the math, you won't know it will actually work.
What I find is that the people who have been living off grid successfully have been doing it for years, if not decades, and that the systems they use are either the ones they initially installed or have added onto themselves in an "ad hoc" fashion.
Now that construction is being heavily influenced by modern building science we're getting much tighter homes and every time you make a change to the building envelope it affects every other system - such as ventilation and humidity control. You pretty much have to install a mechanical unit today in order to handle these things (some areas of North America mandate in their building codes that you have to install an HRV or ERV in a new home) so despite appliances and light bulbs becoming more and more energy efficient the truth is that with all the extra equipment the electrical load for a modern home just keeps going up. I wish someone would write about their 2023 off grid system - exactly what products and appliances they bought and why.
There will be some propane but only for a direct vent emergency heater and a duel fuel generator but not for cooking.. I'll also have to add in a kitchen range hood and probably a make-up air system for that. The ERV could handle the bathfans but then there's the water purification equipment and the radiator circulating pumps. Anything else?
Paul: I did mean a gasification boiler.
Thanks everyone!
Since pretty much by definition off-grid building means construction that's not inspected this does actually raise an interesting question: are there things that you could do differently in an off-grid house to reduce total energy consumption, or even just electrical consumption? Of course this would be while achieving the same goals.
I can't think of much. One obvious thing would be to use passive ventilation if you have a generous source of non-electric heat.
"despite appliances and light bulbs becoming more and more energy efficient the truth is that with all the extra equipment the electrical load for a modern home just keeps going up. "
I disagree with that statement. Houses being built today use a lot less energy than even a few years ago.
>”I disagree with that statement. Houses being built today use a lot less energy than even a few years ago.
”
Overall, that’s true, but the type of energy used has been changing. If you put in a heat pump instead of natural gas, for example, you’re house now uses less (or even zero) natural gas, but you’re using a whole lot more electricity than before. The average electrical load placed on the grid by a house has been increasing over the past several decades. That trend is likely to continue as more people install combinations of electric appliances (instead of “burns something” appliances), and also more gizmos.
Bill
This is a very interesting discussion. I find it difficult to understand the home battery situation..........I am more familar with EVs. I have a 5500 lb electric car with a 77 kw battery (Ioniq 6) that can propel the car at 60 mph for 400 miles and is warrantied for 100,000 miles...which will involve hundreds of recharging cycles.... I don't understand why we haven't figured out how to use these vehicles with their high quality, mass produced batteries to also store energy to run home appliances.
In any event, I noticed that when off grid living is discussed it often involves someone living in a very cold climate who still wants access to most of the conveniences common for folks living in the developed world. That may be a tough goal to meet. It may be much easier when we focus on more temperate climates and lifestyles common in the developing world. For instance, my group works in the highlands of central Africa. Though near the equator, it is high elevation so nights are surprisingly chilly year round, but never frigid. There is no electric grid or propane and whatever electricty is generated by small PV systems powers a few lights and phone/computer charging. There is little or no refrigeration. People stay warm at night by body heat (families sleep in one room) and blankets. The only fossil fuel use is wood for cooking; although many foods are consumed raw (vegetables and fruit) or in dried form.
That would be a "77 kWh" battery, not a "77 kW" battery. A 77 kW battery could provide 77 kW, but there is no indication of how long it could do that before it went dead -- maybe only one second! There is no indication of how much energy the battery holds in this case, there is only an indication of the maximum rate of discharge that can be supported for any amount of time at all. This is like saying a pump can provide 77 gallons per minute, while neglecting to mention the size of the water tank the pump empties while it's running.
A 77 kWh battery is telling you how much energy it can store, but not the maximum rate at which it can be discharged. This is like saying you have a 77 gallon water tank, but you don't say how big the pipe coming out is. For batteries, what you care about most is the amount of energy they can store, so that little "h" is very important!
There are several issues with the "use the car battery!" idea. The big one is that if you use your battery for load leveling (which means it charges when the grid has excess power available, then discharges when loads are high and power is in short supply), you would typically charge every night and discharge every day. You'd probably not be stressed as much on weekends, but that's still 261 charge/discharge cycles per year. You're going to eat into your battery's life doing that, and who pays? The utility? It's certainly possible to come up with some kind of cost structure for that, but no one has. The other issue is that if you drive the car during the day, it's not available for supporting grid loads. That means, from the grid operator's perspective, there is storage available that is not predictable, which is a Bad Thing when your job is to ensure system reliability. It's like depending on the generator in your neighbor's RV, but never knowing if the RV will be at your neighbor's house on any given day.
Another issue with batteries is that 77 kWh isn't a huge amount of power. For a typical house, that's maybe a day and a half or so, less if in the depths of winter running heat as we've been talking about here. I have customers at work that would drain that entire battery just over 2 minutes. The problem is that batteries are really not very practical for very large scale energy storage, things like pumped hydroelectric storage works better at very large scales.
Bill
We lived off the grid for 47 years. (We hooked up to the grid a couple of years ago). Never had a ventilation system. Never had a dishwasher. (Still don't.) Never had a toaster. Cooked on a wood-fired range for years, until I got tired of that, and switched to cooking with propane. Heated the house with a wood stove.
We couldn't have done it without propane for cooking, wood for heating, and gasoline for the Honda generator. In general, keeping your loads as low as possible is always the first step.
Like most off-grid systems, our PV system produced more electricity in the summer than we could use, so the production was wasted, and never produced significant amounts of electricity in the depth of winter, when we needed it most.
Bill: One system that does seem to be worthwhile, despite the added load to your PV system, is the cold climate mini-split. Now that they can work effectively in low temperatures they have opened up a world of possibilities for heating a small space without the expense of natural gas or propane and the drudgery of chopping wood for a wood stove.
Air to water heat pumps also hold a lot of promise as they adapt to cold climates - something like the Sandon CO2 brand.
If you go back to post #16 I sketched out what it would cost to have a reliable off-grid solar system capable of providing 50kWh per day, I came up with around $250,000 for the initial outlay and something like $40-50K a year on average for battery replacement. To keep the math easy let's just say that the fully-capitalized cost of operating the system is $50K a year.
If you use 50 kWh/day, that's 18,250 kWh per day. Your cost per kWh works out to around $2.75. Now, the reality is that you probably won't use the full capacity every day, you'd probably size for peak loads, so your average cost per kWh is probably quite a bit higher, but let's use $2.75. That's about ten times what you'd pay for grid-produced electricity in most of the country, give or take.
The thing about liquid fuels -- propane, gasoline, diesel, heating oil -- or solid fuels -- coal, wood -- is that is that so long as you live someplace a truck can get to, they're not going to be much more expensive off-grid than on. (Obviously that wouldn't be the case if you live someplace that is only reachable by dog sled or float plane. ) In most of the US, the cost of heating with electricity is roughly comparable to the cost of burning fossil fuels -- you have to do the math to figure out which one is cheaper. But if your electricity is costing ten times as much you don't even have to do the math, it's not even close.
Yes there have been efficiency increases in recent years, but they are incremental. They're often enough to tip the balance to electrical in grid-tied systems. But they're not going to reduce your usage by a factor of ten.
The point has been made several times in this thread that money isn't anything. That's true. But if you're trying to gauge efficiency it's a very useful measure. And it's also useful if you're trying to gauge environmental impact. Everything we consume was at one point dug up, cut down, grown or caught. All of those activities impact the environment. The cost of something is a decent first-order proxy for its environmental impact.
To everyone that has installed solar panels, do you have them on micro-invertors? I watched a video where a solar consultant said that he sees a large number of regular, single invertors fail within a couple of years of installation, and when they do the entire system goes down but id a micro-invertor fails just that panel needs to be replaced.
Also, with grid-tied systems, if the grid goes down your solar system won't work either. How many of you have at least a couple of batteries as back-ups just to run critical equipment or appliances?
One micro-invertor that's been highly recommended is the Enphase IQ8 but are there benefits to staying with a standard big box, single invertor over micro-invertors?
https://enphase.com/homeowners/home-solar-systems
I've had solar on three different houses since 2014. They've all used the Enphase micro-inverters. The only failure I've had is when a squirrel chewed through the wiring on one of the micro-inverters. That caused that panel to go dark but the rest of the array continued to produce. Replacing the micro-inverter solved the problem.