How am I doing?
calum_wilde
| Posted in General Questions on
I just finished the first two weeks of monitoring my water heater. It looks like we’re averaging ~5.5kWh/day. There’s two adults showering twice a day, and two elementary school aged kids showering every few days. The dishwasher runs about 8-9 times per week. My rough estimates puts us at around an average of 20 gallons of hot water per day.
Can anyone chime in with their usage and family makeup so I can get an idea of home we’re doing?
Thanks
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Replies
Calum,
Your family uses about half as much hot water per day as the average North American family. The best research puts the average daily usage at about 44 gallons per household.
As I wrote in Solar Thermal Is Really, Really Dead:
"According to a Canadian study, the average Canadian family uses 44 gallons of hot water per day. The Canadian researchers’ findings mirror those of several U.S. researchers; there is growing evidence from monitoring studies that the assumption used in the DOE’s Energy Factor test for water heaters — namely, that an American family uses 64 gallons of hot water per day — is unjustifiably high."
If you're using an electric resistance water heater, I'd say you're doing extremely well with your conservation efforts. My family of 5, including mother-in-law (3 adults, 2 elementary-school kids), averages a little over 3kWh/day with our heat pump water heater (1st-gen GE)....more in the winter with our much colder incoming water temperature from the mains, less in the summer.
With a newer HPWH, we could be down close to about 2.0-2.5 kWh/day.
Thanks Martin. It's really encouraging to see that we're doing so well compared to the average family.
John, thanks for reporting in. While it's good to know how we're doing compared to average, I'm much more concerned with how we're doing compared to more energy conscience people. Yes, that is a resistance water heater. I've looked a little at HPWHs but I'm not satisfied with their performance and setup for my climate here in Nova Scotia. I think a mini split style system would be vastly better when looking at the house as a system so for now I've been focusing my funds on conservation. I still have a drain water heat recovery unit to install this summer. I'm hoping I can get the consumption down a little further still with that.
> an idea of how we're doing?
Using what metric? atmospheric carbon, kWh, gallons/day, $?
kWh and gallons/day.
Atmospheric carbon would depend too heavily on things outside of my control, such as where the powre company buys their power.
Not trying to be difficult, but people who have put PV on their roof and wired it to their electric water heater have shown that atmospheric carbon (due to ongoing water heating) is very much under their control.
I don't find "it's hard to measure/control" a very good excuse for "let's not account for it".
JON R
I've read several of your comments calling for net zero carbon over net zero energy, but not once have I read a comment that is helpful in showing users/homeowners how to even measure or calculate that, net alone achieve it. The closest I can remember was a comment calling for carbon emissions to be included in modeling software. I'm just a home owner with a limited budget trying to make my mark on this world smaller than what it would have been if I hadn't done anything. If I can reduce that mark to zero, that would be truly awesome. But neither of us is going to benefit from you calling me out for not doing something I had never heard of until a couple of weeks ago and still have no means of achieving. Honestly, I'm not sure what the definition of net zero carbon is.
You say you're not trying to be difficult, but most comments I've read from you seem very inflammatory. If you want to help, then please, help. Just telling me to put PV on my roof and wire it to my water heater is only a small step ahead of useless, though. Are you going to mail me a roof with south facing exposure? How about the $6000ish that I'd need to put 2MWh of solar on my roof? How about even a link or some instruction on how to set that up? Personally, I'd rather save that money until I can benefit from economy of scale and put ~15MWh of solar on my future garage (that I intend to design to have as much roof area as possible facing due south) that I'm hoping will power both my house and two future electric cars. I have some bills I need to pay for first though, namely my mortgage, and I think there's a little more efficiency I can eek out of my house before that.
Calum,
in a more recent thread Jon seems to suggest that the solution is to find a clean energy supplier and not to worry about how efficient your house is. That strikes me a bit like the companies that do as they want and compensate by contracting with landowners in Brazil not to cut down trees in the rain forest.
Malcolm,
Agreed.
The other issue is that I only have one option for a provider, NS Power.
I'm honestly not sure if net zero carbon includes the manufacturing of the various materials in my home as well as energy consumption. Wouldn't net zero energy usage mean net zero carbon? Or is he trying to say that net zero energy with a grid tied system and a coal burning provider shouldn't be the goal?
In the case of someone stuck with a coal burning provider, wouldn't net zero energy be more even more important?
I don't know. I'd love to know what he's so passionate about, it seems, like the kind of bandwagon I might job on too. But I feel like I'll have to fight to get even half an answer out of him. He reminds me of a high pressure sales tactic, which makes me want to run for the hills.
Somewhat confusing as I have the same initials as Jon R.
But my understanding is that practically everyone sells their solar credits off to finance their solar panels. But once they've done that, they are technically not consuming the solar energy their roof is producing (even if the electrons technically don't leave their house) because they have sold the 'solar energy' production to the utility or other large industrial user which is now claimed as the percent renewable energy credits the industrial company is using and reporting in their annual report on how green they are in their consumption (or your neighbor without any solar panels, but checked the box from the utility that they only want to use renewable power). Which leaves the power going to heat the lowly basement water heater as the power coming from some 80 year old brown-coal powered plant which is now operating much more inefficiently than designed because it is now a peaker instead of operating at a consistent optimal level
Calum,
As to your original question - you sound like you are doing just fine. I wonder if there is enough fat left in your usage to worry about, or whether you can find more savings elsewhere?
Jonathan,
Does that mean all I have to do to go net zero carbon is check a box with my power company asking them to only send me power from renewable sources? That option doesn't exist to my knowledge, for me, but that doesn't seem right either.
Malcolm,
Thanks for the encouragement! My only remaining hot water energy saver left is a drain water heat recovery unit. There are dishwashers that use less water but I'll keep this one until it dies. I'm still waiting for cold water detergents for dishwashers, but I think that's a long way off, possibly never. Of course I could install a heat pump water heater, but I don't think I have the right setup/location for it, so I'm waiting for a mini split system that's reasonably priced.
Calum,
You do what you can. Other do what they can, and we see what happens. At least that's how I see where we are right now.
Jonathan: "...my understanding is that practically everyone sells their solar credits off to finance their solar panels...".
That may be true in locations like New England where production credits get traded in a regional pool/market, but that type of subsidy is not universal. Whether it's true in Calum's case only he can answer.
Calum: In many states residential ratepayers can buy 100% renewables from third party brokers rather than the utility, whose only part in the transaction is providing the billing & metering for the energy, along with their delivery charges, etc.
Dana, I'm in Halifax, Nova Scotia, Canada.
Here our solar is sold to NSPower at the same rate we pay for power, up to the point that we break even. We can't make money, but we can offset our entire bill minus a small meter fee.
I've never heard of a third party broker here. I've searched but I didn't find anything.
Calum: I assume that means in Halifax NS you are NOT being paid any sort production credit subsidy (which is what Jonathan was referring to), and are simply net-metered at retail, with no remuneration for excess annual exports to the grid?
Third party power sales are something that only happens where the utilities are primarily the distribution grid operator, and separate from power generators. Utilities are heavily regulated pretty much everywhere, but the regulations and business models vary. A century ago almost all electric utilities in the US were vertically integrated, and owned both the generators and the poles & wires, and were local monopolies. When large government entities developed large generators and transmission line infrastructure the models and regulations shifted a bit, but most local utilities still had generation assets as well as distribution grid assets. In the 1980s in the US there was a push for a more competitive electricity marketplace, and in many areas generation companies were allowed to compete with the utility head to head on the generation piece, with some restrictions on the utility to limit their ability to abuse their monopoly power. It has evolved quite a bit since then. But there are still locations in the US where the electric utility is effectively vertically integrated monopoly company covering a large regional area, with effectively no competition. (Georgia Power is a prime example.)
Dana,
Yes, that's correct.
And yes, our utility has a monopoly on the whole province. In most provinces the electrical utility is government owned, but here it's a private company that has a monopoly. They are heavily regulated, but it's also illegal to go off grid in a primary residence here.
Here in Maine, we have the same PV deal as Calum does. Full net metering, no payment for excess production annually. Central Maine Power delivers electricity, isn't permitted to produce it. A huge benefit is that ratepayers aren't on the hook if some lunatic company like Southern Company/ Georgia Power decides a new nuke would be nice as long as ratepayers pay for it.
Stephen: Don't EVEN get me started on the Vogtle albatross! It's clearly a shipwreck in progress, and it's not even over yet, even though the SCANA project has been put out of it's misery, though there's still some legal work to be done on ratepayer claw-backs. In SC the legislature is still hard at work trying to limit the ultimate damage to the ratepayers. At it's peak SCANA project financing was fully 18% of the bill(!) for ratepayers of the stakeholder companies. It's substantial in GA too.
Maine is allowed to trade in Massachusetts SREC programs via the NEPPOOL, and there are small scale residential rooftop PV owners in Maine collecting on that subsidy:
https://www.knollwoodenergy.com/srec-markets/me-srec-program/
Are you counting down the days before LePage is history yet, or does it still seem endless? Even when diverse PV & utility stakeholders reach agreement on how the future of PV will work, LePage can be counted on to to throw it all out with a stroke of the veto pen! (Maybe next year...)
Jon, have those people who "proved" net zero atmospheric carbon is within their control factored in the carbon that went into creating the solar panels? I would bet a large sum of money they did not.
Trevor,
I'm not sure what your point is. But according to many sources, including this one, the carbon payback period for a PV module is about one year or less: "The carbon footprint of a solar photovoltaic (PV) panel (the average level of greenhouse gas emissions it is responsible for over its lifetime) is about 72 grams of carbon dioxide-equivalent per kilowatt-hour of electricity generated ... representing a return time energy (Energy Payback Time) for the manufacture of ... less than one year (assuming a product life of 30 years)."
Dana: I'm definitely counting the days until we're rid of LePage. But I'm afraid we'll just end up with a more articulate version after this year's election.
Martin,
I thought it was a good question. But I think that because I don't know what is supposed to be included in trying to become carbon neutral, or net zero carbon.
Thanks for the information and the link. I don't know how you always manage to dig them up, but I always appreciate when you do.
Martin,
I thought my point was pretty obvious, that the carbon zero claim probably did not account for the total carbon cost of the panels. I am open to being proven wrong, but I am unconvinced by the link you provided. Far from being an independent study, that appears to be the advertising literature for a company that sells solar panels. The panels aside, I think it's also pretty obvious that one cannot meet all their hot water needs simply with PV panels. You either need battery storage and a charging/inverter system, or a supplemental power source, or some combination of both. Hot water demands do not always coincide with solar irradiance. So if there is proof of net zero carbon water heating, I don't think it's been plainly shown here.
Trevor, a good start would be to accurately reflect what I wrote.
Trevor,
Academic papers put the carbon payback period for PV modules at somewhere between 224 days and 4 years -- the longer estimates are out-of-date, based on older manufacturing processes. More references:
https://www.researchgate.net/publication/287242118_Energy_pay_back_period_and_carbon_pay_back_period_for_solar_photovoltaic_power_plant
https://www.sciencedirect.com/science/article/pii/S0927024813004455
https://www.nrel.gov/docs/fy04osti/35489.pdf
https://onlinelibrary.wiley.com/doi/epdf/10.1002/pip.706
I agree with you that in most climates, it's impossible to meet all of a family's domestic hot water needs with solar power alone.
That said, we shouldn't let the perfect be the enemy of the good. Just because a rooftop PV array can't meet 100% of a family's energy needs, doesn't mean that installing rooftop PV is a bad idea. We should all do what we can to reduce carbon emissions, even if each step we take doesn't get us all the way to our final destination.
Martin- those are ENERGY payback periods, which is not the same as carbon payback. Energy is not a good proxy for carbon or conversely, since energy sources can vary from EXTREMELY carbon intensive, or NOT AT ALL carbon intensive, at either the mining & manufacturing facilities, or the local grid environment where the PV panels are installed.
The local grid carbon intensity is a moving target, guaranteed to change over the lifecycle of the panels, usually toward the lower-carb direction which increases the carbon payback period. The mining & manufacturing carbon is fixed at the points where the materials are mined and processed, and the panels manufactured & transported, and will vary widely from manufacturer to manufacturer, or even within a manufacturer's stream, as well as year to year.
But at the extremes:
PV panels installed on a local grid driven by effectively 100% renewables + nuclear (say, Seattle City Light's service area) will essentially NEVER "pay back" any carbon emissions that came from from the materials mining & processing and manufacturing & transport of the panels.
PV panels manufactured in a facility with 50% carbon intensive energy sources but installed in the most carbon intensive grids (say, most of West Virginia) almost any panel would have a carbon payback in under 2 years, maybe under 1, depending on the particulars of the mining and manufacturing history of those panels.
There is no simple accounting scheme that works everywhere and for all time. It's possible to make crude estimates, given enough data on the particulars. It's also possible to estimate where the 2-sigma worst & best case lines lie. But should we care?
With any sort of water heating and energy sources there is likely a carbon footprint to the materials used for the water heater, the plumbing, the wiring, etc. but it's not clear what the point of that exercise would be. Even trying to get a firm grip on the carbon footprint of the panels is a bit silly- it's really not very big at all on a net carbon per lifecycle kwh basis. It's perhaps bigger than utility scale wind, until/unless you factor in the carbon footprint of the grid infrastructure required to deliver power over the transmission & distribution grid, at which point "it just depends", on the particulars.
Dana,
I think we can agree that the math is complicated, and the carbon payback period depends on the energy inputs during manufacturing as well as the source of the energy that the PV module displaces.
I have provided five links to articles on this issue. Four of the five links include carbon payback estimates (not just energy payback estimates).
None of them made realistic carbon payback estimates, which are (to be sure) MUCH more difficult to assess than energy payback. The carbon accounting on most of them only included carbon footprints and energy payback, but did not attempt to calculate a carbon payback (and rightly so.)
The Science Direct paper calculates a lifecycle carbon footprint per lifecycle kwh for different PV technologies (between 21.4 and 38.1 g CO2-eq/kWh ), but not a carbon payback, only an energy payback.
The Wiley InterScience piece does the same thing- defines a carbon footprint and an energy payback, but not a carbon payback.
The NREL paper did NOT estimate a carbon footprint, but did discuss avoided carbon per year at a US average (and apparently static over time) grid carbon intensity over the lifecycle of the PV), along with an energy payback. Without the carbon footprint there's no way to infer the carbon payback.
The International Journal of Chemical Sciences piece (the researchgate.net link) is the only one that attempts to calculate a carbon payback period, but seriously flawed when applied to other conditions. That paper presumes that the future grid in Tamil Nadu will be just as carbon intensive as the grid when/where the PV was manufactured (also in Tamil Nadu), despite the rapid and accelerating roll out of renewables in that state. Over the lifecycle of the PV the amount of carbon it will be displacing will be falling monotonically year on year, which increases the carbon reduction ROI. At the calculated 224 days for simple payback the total lifecycle multiplier matters, assuming it's installed in Tamil Nadu. But take the same panel manufactured using Tamil Nadu's energy sources and install it in Seattle City Light's service area it's carbon payback would be over 224 years (= never) , not 224 days. A panel manufactured and installed in Tamil Nadu ten years from now will have a lower carbon footprint due to improvements in the energy efficiency in manufacturing and the then-greener grid, but will probably have much longer carbon payback period than 224 days due to the same greener grid. There's a lot of wind going up in Tamil Nadu too, currently India's wind leader with more than 8 GW of nameplate capacity, operating at a ~30% capacity factor, with offshore wind currently in the planning stages. ( People in India are getting fed-up with air pollution- the burning of coal for most purposes, including power is eventually going away. http://www.bbc.com/news/world-asia-india-43972155 )
This is why it's pretty pointless to spend any time trying to estimate the "carbon payback" that Trevor & Jon R seems intent upon estimating. At the end of the day the carbon footprint of PV is "in the noise" of daily life of modern industrial societies, and not a climate change driver. The energy return on energy investment and the energy payback period are both easier to estimate, and far more relevant than carbon payback.
That said, at average US coal fired heat rates coal fired power emits about 940 g CO2/kwh. That is ~25 times more emissions than the worst-case 38.1 g CO2-eq/kwh from the Science Direct paper, which is why the payback in currently coal-heavy Tamil Nadu is so short. The takeaway (which was already obvious) is that installing PV in the most carbon intense grid regions first will be putting it where it does the most good.
In Calum Wilde's NS the power system average was about 700 g/kwh as of 2016 (source: https://www.nspower.ca/en/home/about-us/environmental-commitment/air-emissions-reporting/total-system-emissions-all-plants.aspx See the SYSTEM TOTALS - EMISSION INTENSITIES section at the bottom.). That's better than a purely coal fired grid, but still pretty hefty. Given the level of carbon intensity relative to PV I'd say he's doing pretty good, WAY better carbon payback than if he lived in heavy-hydro B.C., and guaranteed to actually "pay back" the initial carbon footprint of the PV long before the NS grid average g/kwh reaches parity with PV. It doesn't really matter how long the simple payback period actually is in years or days- it's a no-brainer type of investment from purely a carbon emissions ROI point of view. THANK YOU Calum!
For the rest of us the 21-38 g/kwh doesn't really much matter. Even if the carbon payback happens to be "never" in your local grid environment the energy return on energy invested for PV is pretty good, the g/kwh is pretty small, and it only looks lousy in comparison to wind & hydro.
Dana,
I'm not there yet. Finger crossed I'll have my mortgage paid in four years, five on the outside. After that everything shifts to saving for the garage/solar setup.
I have reduce my all electric homes energy consumption by 56% so far, though, which I'm exceedingly proud of. Even just looking at that in dollars that's $180/month in perpetuity. Even better is the 9.41 metric tons/year of CO2 that we're saving the environment from. So yeah, sorry Jon R, but I'm gonna take this as a win. It's not perfect and I'm not done fighting this war. But I'll take a win for this battle.
Hi Calum: Danny Parker and a colleague at Florida Solar Energy Center (plus two NREL scientists) have compiled and tested the energy use of 13 different hot water heating setups, albeit at the Hot Water Systems Laboratory in east coastal Florida rather than in Halifax, Nova Scotia; check out their summary at: http://eedal2017.uci.edu/wp-content/uploads/Thursday-16-Parker-smaller.pdf Their latest effort, a PV assisted Heat Pump HW heater with some associated controls, recorded an average usage of 1.2 KWHr per day, using an older model GE Geospring HPWH with Energy Factor 2.5. The latest models (such as the Rheem Performance Platinum, which I recently installed in my house) feature an Energy Factor of 3.5, which should facilitate even better efficiency. Models such as the Rheem Performance Platinum also automatically switch to electric resistance element heating if the ambient temperatures drop too low, providing hot water during winter, but of course assuming you are able to find enough room to fit a HPWH including sufficient CF of air volume for its heat pump.
Dana,
It looks like we are in agreement -- in spite of the deficiencies in the papers I cited.
From a carbon emissions point of view, as well as an energy payback point of view, PV investments make sense. The implication that PV manufacturing involves high levels of carbon emissions -- levels of carbon emissions that can't be justified by the clean electricity produced by the PV module over 20 or 30 years of live -- are baseless.
Jan, That's awesome!
But... I love in Nova Scotia, it's going to be 4°C tonight. Even now I'm still heating the area of the house where the water heater is. I'm not putting in a HPWH that's going to pull heat out of conditioned air. We need minisplit water heaters, that don't require 100W/foot heat tape throwing heat to the outdoors all winter.
Either their figures are wrong, or their ground water temperature is drastically higher than I expected. They're using almost three times the hot water we are and only using ~30% more power to heat it.
They don't seem to be considering the heat loss for the room (and rightly so for Florida) but I highly doubt I would see anywhere near as drastic a change in overall cost.
I can't even find a HPWH at a local supplier for less than $2kCAD. An Rpi is about $70CAD. I'd guess the total setup for that in my area would be about $4kCAD. I'd rather try to find some reclaimed insulation for my basement slab at this point. The savings potention is likely about the same, but the insulation will prevent issues in the home such as mold, not create cold spots and noise issues.
I can only imagine my wife's reaction when I'm deployed (I'm in the Navy) and she's trying to muck about with a Rpi so she can bath the kids... What's the carbon footprint for flying half way around the world to reload a corrupt SD card or replace a current transformer?
That said, you show me a split system water heater, that has refrigerant going outside, and costs a reasonable price, and I'll buy it tomorrow.
Given the already fairly low hot water consumption the planned drain water heat exchanger is going to have a fairly long "payback" period (but is still NPV+ on a lifecycle basis), and is almost certainly going to have a measurable effect on the kwh/day numbers and probably more net energy cost savings than a conventional heat pump water heater would, which would still be adding to the space heating energy use 8 months out of the year in NS.
Insulating the space with the water heater may also have an easily measurable affect on the daily kwh numbers, by lowering the standby losses 365 days per year, and reducing/eliminating the need for running the heat tape during colder weather. It would reduced the space heating load too.
Even the worst-case PV carbon footprint per kwh is still going to be more than a full order of magnitude lower than the 2016 NS grid average numbers. From strictly a carbon reduction point of view it's huge, even if it's more $/kg than the carbon reductions from efficiency measures taken thus far. Even though nearby regions in the US are in the planning stages for offshore wind, I don't expect offshore wind to displace fossil burners in NS in a big way any time soon. The 1GW Beothuk Energy proposal from late last year seems all about exporting power to to the US, not powering NS.
Hi Calum: if/when you later decide to install a PV system, you might consider either a rooftop mount system on your new garage roof, or a ground mount depending on your particular circumstances. Gary Reysa provides very detailed info of his DIY ground mount system at: http://builditsolar.com/Projects/PV/EnphasePV/Mounts.htm
Dana,
My rough estimates on the energy savings of the DWHR vs HPWH were similar to yours, I was estimating about even reduction. The deciding factors were life cycle, noise & vibration, and cost. The DWHR just sits there and works. It should last the life of the house. Installation will be a little more involved, but still not too bad.
I wasn't very clear in my previous post, the heat tape would be required on the water lines running outside to the compressor/condenser, if I were to purchase the Sanden minisplit water heater. I love the idea, but I hate that execution of running the water outside. The space my water heater is in is conditioned living space, and the water heater is insulated with an additional R10 blanket around it, R5 on top of the water heater, and ~R25 between the water heater and the concrete floor.
Jan,
Thanks, I'll take a look. I don't THINK my site would be suited to ground mounts, but it's certainly worth a look.