Solar thermal systems for heating water
wjrobinson
| Posted in Mechanicals on
Jin this is for you and Richard
Let’s run the costs and the systems through the paces
so far I hear $16,000 for a Caleffi system and maybe that for labor? $32,000
saves $500 a year
CO2 production unknown to manufacture
Very little CO2 to run the ECM circulators
There are much less costly systems
NYSERDA here in NY is unveiling a new program this January
Will post more about it when they tell us more
Jin, Richard, others… what say you all
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
AJ: don't ask me, i am no pro ..only a very interested being! :p
What i have come to think about solar thermal is that it is much less suited for cold climate as one might think.
The manufacturer state very high performance numbers, which are solely possible under 3 conditions :
1- high insolation
2- warm outside temp
3- high delta T of incoming water ( cie: lower than ~30c is best because of max possible of collector temp )
As always, most of mid/up usa and canada, where space heating is a large part of the bill,
receive pretty low irradiance during begining of winter + exterior cold temperatures.
As you might have seen on the viridiansolar website
to get enough panels to really make a diff during heating season, you have to install enough to run water heating for the hole district during summer time.
Richard :
yesterday you pointed to a study on the veridian website:
http://viridiansolar.co.uk/Assets/Files/006_Solar_Case_Study_Northpoint_Solar_for_Flats.pdf
if you look at the map, the location receives ~ 1000KWh/m2 /year
75m2 of the study panels
for a total of 30k kwh /year = 400kw/h per square meter
less than 50% total insolation and this includes high summer time
Again iam not saying that solar thermal does not work, it does...
IT is very advantageous as a simple water heating system in most of the south parts,
as it can be used year long to heat water tank, and can be kept to a small size.
But, in the south, one can also use heat pump water heater which provides with dehumidification and cooling while heating water and thus has a favorable COP .
It can also be supplied by PV which incidentally, has a higher yield in sunny parts.
Maths need to be done location wise,
but for my part of the world, "solar thermal is dead " to use Martin's words,
unless someone can prove with maths/testing data that it can be used during cold winter time effectively.
i am sorry if i quote a manuf website, i usually don't like to do that
so please all consider that the graphs and datas are not from an org
but rather from a manuf can could be "manipulated"
they do represent in general form what i have seen almost everywhere else
and are presented in a simple fashion
this page shows a bit of the problem with summer time on heating panels
http://viridiansolar.co.uk/Solar_Energy_Guide_4_1.htm
AJ: 16 000$ buys you around 45 250W+micro inverter right now .. that's 11KW+ of PV .
We'd have to work out the maths, but the more i think about it, PV during summer time + a heat pump water heater might be just nearly as efficient as solar thermal , even during summer time.
The newer panels are @ 20%.
The newer heat pump water heaters from Japan ( co2 ) and the european models with split compressors @ the exterior are in the ~ 4-5 COP range when temperature is higher than 15c.
4x20% = 80% eff, and when it is idling you still get to use some of the energy
A good thing with solar thermal also if if you are a "tinkerer" and can diy panels.
Compensate lower efficiency by area,simple drainback to cheap or 2 250l plastic tank.
Very low investment, usually low maintenance if done correctly,
but impossible to implement if you are a builder..that is DIY territory.
I'd like very much to be proven wrong,
as solar thermal is pretty green stuff when done correctly.
Most panels use recyclable materials such as copper, alum and glass,
and now have good life cycles.
Active solar energy systems designed to supply space heating to a house have almost never made economic sense. Even with the 70% tax credits of the late 1970s.
Solar domestic hot water heating systems made sense until the recent drop in PV system cost.
In my opinion, there was never a large enough R & D effort to simplify and value engineer active solar for North America (in non-freezing areas of China, systems cost less than $1000 installed). Also, since every home is slightly different, each home has its own peculiar opportunity to receive a unique installation error. So the retrofit market for space heat was never viable.
Remember, that Caleffi system is overkill for 6 months a year and lots of the available solar heat is wasted. That fact is not true for a grid tied PV system. The summer excess is put to good use.
Finally, the chance that an active solar system will survive 20 years without a costly repair is almost nil. A $3000 tank replacement means the system will probably be torn off the house.
I've been studying the topic intensely since 1977, and hadn't given up hope until this decade.
What is it that kills the tanks? And how about stainless steel tanks?
Let's talk about systems that are the best today even if they can be beat by non thermal systems.
We know the bad and the ugly.
One example is... for a summer use is to heat a pool. That way summer heat is used well possibly.
GBA had a blog as to how the Maine boys or someone up that way was able to make reliable relatively lower expense thermal systems. I have to search and attach that.
Anyway, this let's post what is working a bit, even though other strategies may might much better sense.
Here's something Martin blogged recently, there have been earlier ones too I can't find yet.
https://www.greenbuildingadvisor.com/blogs/dept/musings/solar-hot-water
Well what do you wish to know AJ ?
you already answered your own question
Solar thermal is super efficient for pool heating, that's a fact.
Look at the A-B adnC rows in the SRCC report i linked on the other thread :
https://secure.solar-rating.org/Certification/Ratings/RatingsReport.aspx?device=5807&units=METRICS
Pretty efficient during high radiation months.
Do you wish to discuss about how water heating for residential ?
Or swimming pool whater heating ? :p
I don't want to derail AJ's post, but i have to interject this point. As i see it pulled into the PV vs Thermal fray far too often.
From post #3: Jin "The newer panels are @ 20%...The newer heat pump water heaters...are in the ~ 4-5 COP range....4x20% = 80% eff..." The 20% eff Jin references are solar PV module efficiencies.
That math makes sense when trying to determine which system can get you more energy from a given roof space. It has no real bearing the the efficiency that really matters most of the time, the cost efficiency. The "collection efficiency" quoted above only has a bearing if you are in a space constrained situation, if space is not a factor, then the solar PV efficiency vs Thermal efficiency isn't relevant IMO. In the end it boils down to what do you get for your $ spent. So cost efficiency would be the metric to use in my mind, and should be given in $/kwh produced (or $/BTU if you prefer that unit of energy).
As AJ said, we know the bad and the ugly for solar thermal. AJ, can you re-phrase your question given the responses so far? Then we can try again :) The company i work for has all but dropped Thermal for a few years now, but I'm the thermal designer so I'll try to answer what i can.
Daniel,
Thanks for your comments. I agree with you completely. What matters is the cost of the equipment; the number of square feet available is rarely the most important issue.
Daniel/Martin :
space is not an issue, unless you wish to use solar thermal for heating a small house in a cold climate and quickly run out of roof space because of their lower efficiency during winter time.
I do agree that cost vs payback is what matters though.
So what is the cost of thermal panels ?
It is easy to find PV panel costs ..but what about thermal panels and systems ?
I feel bad about thermal panels ..
when i started lookin at those, i really wanted it to work for my cold climate
until Martin pointed some of the maths i believe in a Q&A ..
I would like to be proven wrong...
But i am not sure the economics + maintenance VS performance make any sense in any heating dominated climate, anymore.
BTW ,the reason why i worked on eff. numbers was to continue from the discussion
with Richard McGrath from the other Q&A ...
Comparing PV vs Solar thermal is as valid as it gets though ..
aren't we looking for the best solution ?
Lastly, KWh$ produced is not what we are looking for with solar thermal in heating climate,
usable Kwh$ is what is important.
You can overproduce as much as you'd like during summertime,
will serve no purpose.
ah yes, a though i had yesterday while taking my shower...
In a water heater solar thermal setup, the water is kept hot by the solar during daytime,
and then,all 4 members of the family use the shower during the evening.
What happens then ?
Kick back electric heats the water back up which is probably 10 times more energy than solely for the standby losses?? :(
If my assumption is correct, it means that using solar thermal for how water needs another type of system to accumulate more than required for standby and use it after the showers to help with the consumed hot water ??
Storage is the word you're looking for Jin . As in the 535 gallon tank I mentioned for the large house . Which , by the way can accept energy from a number of other sources also . Partnered in a combi panel application one could run cold incoming water through the tank pre heating it before it reaches WHATEVER water heater is used therefore requiring less energy , no matter where it comes from to heat for your shower . You can capture waste water energy also in these tanks , so the water you already heated can give you a bit more before you throw away your paid for energy . the possibilities are endless , you don't ned any utility anymore . Their grasp is just about as weak as it can get . Why do you think the prices of many things are starting to look more attractive , ?
Might I add that you akll may possibly want to take the panels off the roof and put them on the ground . This also will lower installed and maintenance costs . This is of course considering the site will allow that placement .
Jin , Cold has nothing to do with effectiveness of any solar panel . Stand next to or touch a block wall when it is 10* outside and the sun is out and you'll see what I mean . Most times that wall will feel warm . Ever been on the beach when the outdoor temp is 90* , even when the sun is not bright or it is overcast the sand is hotter , or the road if that applies .
"Cold has nothing to do with effectiveness of any solar panel "
Don't be silly! Cold (or rather delta-T) very MUCH makes the difference in solar thermal effectiveness (which is why you try to keep the operating temps as low as possible).
Colder temps are a modest advantage to silicon PV, but the effect is quite small compared to the effect of the delta-T between the solar thermal panel and the ambient environment.
Thermal storage in tanks at moderate temperatures is cheap but lossy. Thermal storage in buried tanks at subsoil temps is cheap but not so lossy), but suffers the same thermodynamic efficiency issues of any other heat pump system bringing it up to the temperature at which that energy is used in a home.
System costs of PV are falling dramatically, to the point where it's breaking the standard utility model that has prevailed for the past century or so. "you don't ned any utility anymore . Their grasp is just about as weak as it can get ." will be pretty much the case everywhere in less than 20 years (it's today, in high-electricity price, higher insolation markets like Hawaii and Australia.) The cost curve on this stuff is breathtaking, but there are no comparable curves for solar thermal equipment.
The lifecycle cost per kwh (or MMBTU) delivered is really what's needed for comparison when looking at heat-pump leveraged PV vs. solar thermal. But whereas PV inherently delivers a premium energy product (electricity), solar thermal is of more limited use- low grade heat. You can't run your laptop, or light your house with solar thermal.
Some of us have different objectives and parameters:
I am looking to offset my energy costs with a retrofit but I can't afford a solution where the ROI takes decades.
Why can't I supplement my propane fired combi system's DHW all year around and even my hydronic heating in season, using a flat plate solar thermal collector (south side of Lake Ontario, mixed zone 5 A and 6).
Can't I pump into my buffer tank from a ground seated solar thermal panel. At best it might give me water at operating temps and at worst it will be pre-heating the DHW. Given retirement and age, a 20 year life cycle is not my concern, its short term low operating and maintenance costs for a system that lowers my overall energy bill.
I really would like to consider PV's but capital costs are hefty while solar thermal seems more reasonable to the pocket book. And I don't have to get into bed with anyone else.
I am seeing price lists of $4000 - $5000 for complete systems and stand alone 4 X 8' panels and line sets for ¼ that price.
Storage with the right stuff does not need to be so lossy . Coccoon tanks . Underground storage is even less lossy with the right stuff also . I agree you can't run your laptop or light your house with thermal but then again your laptop and lights are not anywhere near the percentage of energy use as space and domestic hot water heating .
Why not combine the 2 , are you guys just blind or just unwilling to participate in a discussion ?
http://sundrumsolar.com/
http://haloenergyllc.com/
It seems like you just quit halfway through the 3rd quarter instead of finishing the game . Remarkable . Check out the COPs on water to waters with a 70* EWT and get back to me .
Flitch : could you please repeat that ...
4K$-5K% is for 1 4X8 collector and lwhat? what is includedin a system you quoted?
1000$ / 3m = 333$/m2
unfortunately, thermal needs more than just a panel to operate
4000$/3m = 1333$/m2 ...ouch
for 330$ you get 1 recent PV + micro inverter
which is ~ 1.3m2 and will get you around 300kw/h yearly
let's assume 20years on both
PV= 330$/20y/300 = 0.055$/kw/hr
i'll use Toronto for your location for insolation
from http://pv.nrcan.gc.ca/index.php?n=1752&m=u&lang=e
@ 50%total eff = 4000$system cost = ~3m2 = 2200kwh /yearly
so thermal cost ( theor 100% usage ) = 4000$/20y/2200 = 0.09$/kwh
i'll have to give a +1 to Dana's plan again :p
Please someone correct me if i got the math wrong somwhere
( i like to do this, the way i learn the most !! )
Richard: "Cold has nothing to do with effectiveness of any solar panel " really ???
The last time I ran the hard numbers on Sundrum ( a company VERY local to me- I pass within 1/2 mile from their headquarters on my daily commute) it made financial sense only for space constrained & high fuel cost situations. PV & solar thermal was cheaper done separately, but the solar thermal part didn't cut it except in high fuel cost situations. That was back when just the panel cost on simple grid tied PV was north of $4/watt, with an installed cost nearly 2x that. (Currently you can get first-tier company 20% efficiency grid tied PV for $4/watt or less, all-in pre-subsidy cost.) That was also before propane hit $4/gallon.
Show me the installed cost, maintenance, and longevity numbers on water-to-water heat pump systems and then maybe we can have the real conversation about the lifecycle cost of low-temp solar thermal + water-to-water heat pumps vs. PV leveraged by ductless air source heat pump technology.
Or maybe I'm just blind... B-)
Flitch Plate: As with grid tied PV, it's not always useful to look at pre-packaged web-store pricing on the hardware alone. The installation, maintenance, and longevity all matter. Subsidies also skew the markets on this stuff, which is about the only way ground source heat pump folks stay in business in my neighborhood, which is also true for PV. But PV has hit the price point where in high-electricity cost markets it's financially rationale even without subsidy if the financing costs are reasonable. In three years the unsubsidized cost will be less than the subsidized cost is right now, but GSHP technology will be at the same price point, with only marginal if any improvement in lifecycle cost. The lifecycle cost of solar thermal depends a lot on maintenance & repair costs, which can be significant. Caveat emptor.
For the same $4000-5000 you can also get a 1.3-1.7kw of grid tied PV (after the 30% tax credit). Run the numbers on what kind of short term & intermediate term financial return you'd actually get with a $4-5K solar thermal system (probably $8-10K, if professionally installed) vs. the 1.3-1.7kw of grid tied PV. (which won't fully cover your power bill unless you live in the dark), net metered. Even offsetting propane fired heating & hot water my gut tells me you'll get less return out of the solar thermal system than net metered PV.
With propane heated DHW, even with only two people showering daily a drain water heat recovery heat exchanger makes short to medium term financial sense, if you have a section of vertical drain downstream of the shower. It can even be DIY-able for many situations. The cheapest place I've found to get 'em in the US is from EFI, which will give you the wholesale price if you open an account with them: http://test.efi.org/sites/default/files/power_pipe.pdf A 3" x 60" or a 4" x 40" delivers more than 50% energy return at 2.5gpm shower flows (higher at lower flows.)
Jin,
you are aware of SHG , correct . Maybe you should explore learning a bit more about how air and water accept energy . Riddle me this , the sun can heat a room in a home passively to 70+* but that same sun would be incapable of heating water which accepts energy more readily ? I don't quite think you are getting where i am coming from and probably never will but I'll give it one last shot .
On this Earth and in this industry there are panels that while producing Electricity also collect energy from the back of the Pv panel which in turn lowers the temp of the Pv panel and allows to perform maximally . If one is smart enough to store ALL the solar thermal energy in a tank and mix it down in the winter months with any number of different technologies as the source that stored energy can go a long . long way . At that point you can increase the efficiency of whatever you are using because it did not have to do as much work . Now , instead of putting 7.5 KW rack on the roof maybe you can just use 5.75 array . WTF is wrong with you ? Just pissing away any energy is not acceptable . You ar either gonna make the investment or you are not . Smart money gets every KW or BTU available .
Maybe this makes more sense , the COP of a particular WTW heat pump jumps from 4.88 to 6.4 when you increase the EWT from 50* to 70 * . How's that , multiply that over a 2500 hour heating season and tell me the MATHS ! Now that's a Negawatt ! Looks like 3,800.00 year in imaginary money . Now what's the payback ? I can almost guarantee without doubt that the sun will shine enough throughout the winter to make that possible throughout the heating season , even more in ALASKA where it's really cold but the day is 300 hours long ( exaggeration of course for the very literal ) .
Dana ,
It took 30+ years for Pv to become accepted and only when it was accepted did the prices start to come down . The same would be true of Thermal , these guys are just keeping their doors open which is why the price is higher . That is just economics . For those contemplating GSHP , solar with storage makes all the sense , add Pv and it's a homerun .
Richard,
Q. "WTF is wrong with you?"
A. Nothing is wrong with me. I've reviewed several types of solar systems that integrate solar thermal collection with PV arrays. In all cases, the value of the low-temperature heat energy collected by the thermal solar components was far too low to justify the high cost of the equipment.
Richard: WTW COP
where do you get the COP energy from ?
Please stay polite in your posts.
Martin ,
Maybe I buy the equipment differently than others , maybe I am just more dilligent with my designs and math than the corporate capitalist that gets his education from salesmen and reps who really have no idea about what they are doing either . I offer value for my compensation The comment also was directed at another . I also advise my customers on what is in their best interest and what makes financial sense for their house , way of life and the dwelling in which they live , I just don't wantonly offer recommendations because this is cheaper than that . It has become apparent that there is no constructive discussion to be had here that does not jive with what is being pushed here .
Dana ,
Maintenance and repair costs should not become a real factor for quite some time . If the system was designed right and the fluid is of good quality these things become less of an issue . you also do not have to use expensive collectors either as Jin pointed out , one can build his own that will perform as well if not better than manufactured . There are also other options for collectors which I will not get into here as I have wasted enough of my time on this fruitless discussion .
You gentlemen should explore some other sites to get a better grasp on what thermal storage has to offer .
See you in another discussion
Richard: are you abandoning so soon ?
Still have never seen your maths ...
DIY panels will NEVERoutperform manufactured ones.. believe me
i dwelved into that much much deep
but, it can be done at much lower cost, thus and increase of area to investment ratio
may be favorable on the DIY side.
Please read again this and tell me if i am wrong :
on 20 years lifespace ( no maintenance,no additional systems )
so thermal cost ( theor 100% usage ) = 4000$/20y/2200 = 0.09$/kwh
PV= 330$/20y/300 = 0.055$/kw/hr
You tell me how you plan to use the solar thermal stored energy better than the electricity from the PV ??? As far as i know, one could use resistance heating and still get more "hot water" ,
than from the thermal storage.
You have $$$$ for systems you wish to share yet?
btw, i've used 2200KWh production for solar thermal panel,
but if you look at the srcc link of earlier
https://secure.solar-rating.org/Certification/Ratings/RatingsReport.aspx?device=5807&units=METRICS
and follow line D ( water heating in cool climate ) and medium irradiation
this large collector actually produce an average of 4.2KWH /day
which would account to only 1533kw/h /year ...
OK, so here is a REAL example for everyone to contemplate. (Assumes average system sizes for my region)
5kW PV system: Commercially installed to the current (2014) codes using commercially available products. Includes tier 1 solar modules, online monitoring, permits, structural engineering, 25yr warranty on major components (modules/ inverters), turn key.
- $20,700 ($4.11/watt)
- $14,490 after the 30% tax credit
- The cost of energy at the end of 25yrs is $0.10/kWh. (assumes little/no maintenance since main components are covered under warranty)
2x (4'x8') collector solar thermal system Closed loop glycol with 80gal buffer tank: Installed to code with licensed plumbers, permits, structural, online monitoring, etc (close to apples/apples as i can get with the two technologies) Major components only offer 10yr warranty
- $16,250
- $11,375 after 30% tax credit
- The cost of energy at the end of 10yrs is $0.33/kWh. (assumes little/no maintenance since main components are covered under warranty)
- The cost of energy at the end of 20yrs is $0.18/kWh. (assumes glycol flush and pump replacement have been performed)
- The cost of energy at the end of 25yrs is $0.16/kWh. (assumes another glycol flush has been performed)
- [It should be noted here that i assumed that the solar thermal system is assumed to be sized to barely cover the summer load, meaning a very high % of it's BTU output is captured, a larger system would have economies of scale, but a lower % of usable energy produced, i simply didn't have time today to go through all the scenarios] Also, as my company has drifted from thermal, so my estimating skills are not as sharp for thermal at the moment, but that just means i might have a 10% range on the thermal, where i'd have a <5% range on PV.
I'd love to do this for a dual PV+thermal hybrid collector, but i don't have good pricing info for those right now. Depending on the price of those collectors, i could the the $/kwh for 25yrs get right down there with PV, but still it would have more service work to be done, which adds more potential for increased cost down the road that are hard to anticipate.
This is one example, where the variables can swing either system a significant amount higher or lower. But what we've found to be true is that you have to have ideal circumstances for thermal, and pretty bad circumstances for PV on the same house for the thermal to come close to competing. Add that to the inconvenience of service/maintenance (hard to put a $ value there, i know) and i am pretty strongly on the PV side of the line.
In a perfect world, if thermal or hybrid PV/Thermal were established and had economies of scale that allowed the pricing grid-tie PV has today, i bet the numbers would be different, but the market has chosen it's technology of choice for now, and it's PV. (If we went purely on the theoretical efficiencies and potential of a technology, we'd be burning peanut oil in the 90+% diesel passenger car fleet right now ;) The absolute best product does not always make it to the finish line, because the greater human population does not always make the rational choice.
Anyway, above are real #'s from a real company to spark some real debate :)
FYI:
- The PV system would produce about 6,200 kWh/yr and take up 332 ft^2: (18 kWh/ft^2/yr)
- The thermal system would produce about 3,400 kWh/yr and take up 64 ft^2: (54 kWh/ft^2/yr)
Just to help reality check the #'s that's basically 11.8% total collection efficiency for PV (DC to AC, with soiling, connection losses, inverter eff, etc...), 35.4% for Thermal.
Daniel, your posts are super, and the kind of info I was hoping to see along with what systems are best today and prices and more. Thank you sir.
aj
Wow nice info Daniel !! :)
Missing only 1 basic info though ..what is YOUR region ?? :)
Expensive stuff ...
Would you mind sharing solar thermal formulas?? :)
always interested in formulas !
Sorry my region is Ohio.
Expensive stuff? Which tech strikes you as expensive?
- Remember the prices were for fully designed, professionally installed systems, there is going to be cheaper available by other installers. You can buy a brand new track home for $85/ft^2, and chances are you will have big problems long before you should, or you can get a well designed home for maybe 20% more that is far more likely to perform as expected. (It's not a direct analogy i know, but "you get what you pay for" still applies in it's own way, the details just differ)
What formulas are you referencing? We use a simulation software for energy outputs, the pricing is done the old fashion way, by hand (on a spread sheet). Sorry, but i can't share the spreadsheets, a lot of company "special sauce" went into them, as well as pricing that is protected with non-disclosure agreements and the like.
Daniel: The formulas were for collected energy etc..
but if done by the use of a software, fully understand the non-disclosure!
As for the price, turn-key is always more expensive.
5KW = ~ 20panels
Let's assume retail pricing of 350$/panel ( 1.4$/w )
and to each its Enphase micro inverter @ 150$
500$X 20 = 10 000$ retail prices for first tier panles and connected inveters
Then warranty, electrician, transport , engineering,labor, racking. ..
Goes up fast ...which almost justifies the 20K$ your company is charging .
Do we have some way to go before we can meet ~ Deutsch prices !
again thanks for the good example and info !
Jin, the paperwork is the last big cost along with workers comp and liability and marketing costs and a need to profit, pay health care and retirement expenses.
I know from my times dealing with NYSERDA and talking to my sales friend at a PV company the paperwork is a monster and a time delay item too.
Do you mean the paperwork to get the inventives/rebates?
It usually his very labor intensive here in Canada also.
Where Solar thermal system always priced similarly Daniel ?
Or did the price up with the regular inflation ?
I ask because solar thermal wouldn't make any sense at all at this price, with energy prices of 10+ years ago.
That $20,700 price assumes a middle of the road installation too. We could talk ideal case (all the solar modules in one nice clean rectangular block, on a single story building, 4/12 pitch, with a clear and short route to the buildings breaker box, etc) and then you could take over 1k off that #. Likewise, we could have a crazy install (3 different irregularly shaped sub arrays dodging roof vents, 2-3 stories, 10/12 pitch roof, with the homeowner requiring we run out and around the exterior of the house to a beaker box on the other side of the house) and add more than 1K to the price. Lots of variables, too many to cover them all here.
The order of costs right now goes: generally
- Solar modules
- Labor
- Inverter
- Racking
- Engineering/ Permit
- Balance of systems
If we were in Deutsch land, then we could drop another grand since we would almost eliminated the permit/engineering. Probably more if you consider the lack of red tape that AJ references.
The industry has made strides towards more affordable systems (And i think a $0.10/kwh cost for PV is pretty good actually) and there is room to go down further (may be longer than Dana thinks to get to $5.50watt, since we still have $1k in permits/engineering even for a 1kw job)
I think its communism to subsidize the PV industry like this. False economy for companies making a fortune though corporate welfare. There is no need for PV, solar thermal, geothermal or wind to be so expensive. And these systems should be plug and play, not installer dependent.
"Green" in my view would be to have low tech low cost solutions that are effective; not high technology, high capital cost dependent.
The one thing about solar thermal is that I can put a lot of it together myself and offset my propane costs by preheating the water. Even if I just made a silly preheating tank with a HX to run my cold water supply through before hitting the DHW tank and boiler.
http://www.builditsolar.com/Experimental/PEXCollector/Construction.htm
Can I do low priced, small scale supplementary PV, wind or geothemal? I don't see how? Do you?
https://www.youtube.com/watch?v=XwUT0ytPfLA
Good for you Flitch .
Why wouldn't you be able to do a small-scale DIY PV water pre-heater? You'd have panels that feed the elements on an electric resistance storage tank with a heat exchanger in it. Same design as the solar thermal pre-heater, but without any fluid or pumps.
Nathaniel . Show us the math on what that would cost . An electric resistance water heater cannot be considered passive while an ECM circulator does meet those requirements . Do you want your PV using all that energy heating water or let the sun do it and use a tiny bit of power to run a circ to move fluid from the panel to the tank ? Be careful .
Flitch, I agree and the day may come. I would love to install my own system and do so for the cost of parts AND get the money handed to me that the installed systems are handed. My cost would be half and my fun would be double. 5cent/KWH nice...
Richard don't start it up again ..we've been down there a few moments ago.
I told you; DIY solar thermal always end up being large to compensate for inefficiencies ( unless you have access to the right stuff ...which usually need to be purchased in very large quantities AKA full coated roll of alum sheets etc.. )
That said, there are better examples than the one you linked Flitch, on BIS site and elsewhere.If you have basic plumbing knowledge and can braze copper tubes, it is fairly easy to build a low cost, large unit , using known hardware store products and recycled materials.
Don't expect it to work good in cold winter unless you insulate the box and use an IGU as front glass
( that again could be sourced from recycled stuff ) ,and it still only collects during daytime.
On the other hand, building a solar thermal collector panel is a super fun adventure and you can't loose more than you invest, which should not be too bad if you take time to source parts and design properly.
If solar thermal system is as expensive as Daniel pointed out, it may soon be displaced to a DIY-only solution in all heating dominated climates .
Dana,
That is an interesting DWHR page . You are aware of the cost of copper DWV pipe I presume ? It just is not done anymore for economic reasons and for one to invest in it to harvest energy from drain water would be far more foolish than anything mentioned thus far . PVC , ABS and cast iron give up that heat much less than copper .
A better solution would be to run the drain water through a tank , with a coil for the incoming cold water located at the top of said tank , this would maximize collection . There are marketed DWHR units readily available on the market , I believe they were recently featured here actually . Only problem with them is they would likely be inaccessible within the building presenting a problem when drains need to be cleaned . The coils in there would take quite a beating when confronted with modern drain cleaning equipment . The tank makes much more sense and collects more energy .
Flitch: My examples were for professionally installed systems. If we were talking DIY (either PV or Thermal can be DIY, just like you can DIY a whole hose if you know enough and save a ton of $) then the economics can be different. I plan to help my dad install a solar energy system on his home (basically DIY as i will just source materials from my company and install with him) i will be installing solar PV, because i can STILL DIY that for less than i can a solar thermal system. And i could still do better with PV even if i was buying some no-name pv modules/inverters at retail prices online. I would not do a full DIY solar thermal system because i value my time and my fathers time too much to waste it on that, but that's my own personal choice.
That might not be the case for everyone, so do your own research and put up what system you think serves you better for your dollars. If you know enough to install one of these systems, and not the other, that makes your decision easier.
I agree that solar PV should be more plug and play, but unfortunately it's not yet, and the closest technology that has promise to deliver that (micro inverters, eventually assembled into the PV module in the factory) still does not meet the reliability I'd like to see. I'll be happy when residential solar gets to that point, it's just not there yet.
Nathaniel:
That could be a good DIY solution. It would be almost impossible to get it past a code inspector, it could never comply with the 2014 NEC if it were installed on a building.
They make 24Vdc water heater elements, typically used as wind/hydro dump loads. You could essentially hard wire a few solar modules to one of these and they would produce heat when the sun is out (not as efficient in the end as a pv system tied to a grid-tie inverter, but cheap enough it should not matter). If one were to do that, they better know what they're doing (sizing wire correctly, putting in the correct fusing/circuit protection, etc...). Certainly an "at your own risk" venture.
Solar thermal seems a less daunting (for me) as a DIY effort than PV’s; due to the technology and risks/knowledge associated with electricity.
I do not understand how you can make PV for less $ than the thermal. If you watch the YouTube links I posted above and some others you will find there, there are claims to equal-to-copper performance using CPVC are possible. And thermo-syphoning is an amazing thing.
My late best friend (the one who passed from mesothelioma) and I wrapped copper tubing around a block of firewood and installed the homemade coil inside a Jotul stove flue many years ago, running it up to a 300 gal holding tank and thermosyphoned his showers and baths for a family for 4 for 20 years. The bath house was separate from the main house; we used the stove room for saunas; pumped water into the tank from Lake Huron; dove in afterwards and rolled in the snow on the lake in the winter. Now a days I would use an external HX on the stove.
Just sayin’, that I can safely and cheaply preheat my water with my woodstove and a DIY thermal panel, and I bet I can make it airtight and winter proof by using the woodstove to deliver some heat to the panel Nov through April.
But I see this too on YouTube; code approved:
https://www.youtube.com/watch?v=w67lsF7DRMg
DIY 3Kw Home Solar - Grid Tie - Final Installation Overview
That's pretty cool Flitch, on the DIY thermal stuff. Like i said, if you have the knowledge to do a DIY thermal, and not DIY PV. Then that's a simple choice. Are the above solutions code compliant? I have my doubts, but if you're confident in your work and your knowledge of the system, it's at your own risk and my work perfectly for decades. Awesome for those capable of accomplishing the task. Plus there's the satisfaction of doing it yourself which has value that i would not want to deny someone who's passionate about it.
The PV link you posted though.....It may have passed an inspection by and AHJ, but it's NOT code compliant. I'll list the obvious stuff (a lot of minor stuff, and a few MAJOR safety risks):
- They ran THWN-2 building wire on the roof to connect the far end of the solar array to the conduit run. BIG mistake, that wire will degrade in the heat, ozone, ambient conditions on a roof in a relatively short time. That mixed with the wires not being managed and allowed to touch the shingles themselves... that's a recipe for a ground fault, which at least will turn the system off, and at worst will start a fire or electrocute someone. Simple fix if the DIY'er knew not to do this.
- They did not install flashings correctly for the anchors to the roof. The guys said it was OK because he sealed the holes with black jack, and it doesn't violate any codes to install flashings above the shingles. That's entirely incorrect, both the International building code and international residential codes require flashings for all penetrations and that you follow the roofing manuf instructions when installing said flashings. If this were not in san diego, the guy would 90% likely have multiple leaks before 10yrs are up. Also, if his shingles were too brittle to lift up to install the flashings correctly (the reason he gave for putting them on top) then the roof was too old for an array to be installed on top of it. It really should have gotten a new roof first... That's not code, but just a good idea.
- He ran is pvc conduit directly on the roof. I honestly don't know if this is allowed or not by code, as i never researched this, but....really? does that not strike you as a problem? Lets take this plastic conduit that does not do well long term when exposed to heat and UV, then strap it directly on an asphalt rooftop.
- He terminated 3 strings into an inverter without fusing. The solar modules he's using have a fuse rating of 7A, which means that if you parallel more than 2 string together, you must fuse them to prevent a fault from burning up the modules.
- The wire colors in the sub-panel are blatant code violations, the PV breaker is correct, (black and red), but the other two are just silly. one has a black wire in each pole, the other has a black wire in one pole, then a white wire in another. White wires are supposed to be grounded. So if any electrician were to go into an junction box with this circuit in it and do some work, the wire that is normally supposed to be grounded (0V) is now hot with 120V, that's safe...yeah.
Those are the obvious ones at least. All easily avoided if you know what you're doing. (It's sad that this kind of stuff get's by inspector all the time. It is there job to know better, PV has been around long enough now. Especially in San Diego!)
Flitch, that was not to denigrate you or your response in any way. It's just to point out how a DIY can be done incorrectly (DIY can be done fully code compliant with ease, if seen a few myself that were very well done). You just happened to pick a bad example is all.
Flitch watching that person poke the live DC feeds...That video needs to be redone with his hands out of the panels, had me cringing waiting for him to get a little nip or a big thump.
One point Richard makes I like. which is for us to use sun energy and other of nature's energy.
I think thermal solar has it's place even though PV is right now coming on strong. PV ten years ago was no bargain.
Glad the Richard's and back yard experimenters and the big engineering companies keep this ball rolling forward.
AJ : all of the energy you are going to ever use in your life comes from the sun neway
the impact it has on the environment is of greater issue
You tell me what is the diff between PV and solar thermal ??
What are the points in favor or solar thermal ??
Richard- not only am I aware of what copper drainwater heat recovery units cost, I posted a link to a catalog page with prices, but here it is again: http://test.efi.org/sites/default/files/power_pipe.pdf
That's $500-600 for a unit that returns better than half the energy at 2.5gpm, higher returns at lower flow, and it's an easy DIY retrofit (or new construction) onto cheap PVC / ABS / iron drain pipe. Professionally installed by a licensed plumber it's maybe a grand as a retrofit, substantially less than that in new construction.
The return is pretty good when the cost of fuel is high (like $5/gallon propane, like some folks I know paid last year), not so much for buck-a-therm natural gas. In some instances it can partially pay for itself in reduced boiler or indirect tank sizing, etc.
To compare the financial performance to a plastic thermal buffer tank solutions for greywater heat recovery it would be useful to post at least budgetary pricing for that alternative solution, then provide a reasonable model of the amount of heat recovered. The advantage of a buffer tank solution would be that the heat of large batch dumps such as bathtubs could be recovered. The disadvantage is that they have to be periodic cleaned of the accumulated sludge, whereas gravity film type drain water heat exchangers are self-cleaning (more or less, mostly more), and do not accumulate enough grunge to affect performance for decades.
Before I comment with experience and facts . Would you be so kind as to tell us where the better than 50% number comes from ? There really is not alot of energy left in that segment of pipe after running through , in most cases , cold PVC , ABS or Cast iron pipe .
This is a very good thing should the shower , kitchen sink and washing machine be within 5 feet of this exchanger but even then it leaves alot to be desired . Just a quick observation about this particular unit is that if the cold water entered at the top of it (counter flow) it would increase the Delta and collect alot more . Maybe counter flow is not desirable when exchanging waste heat to incoming water , possibly one of mother nature's little tricks but I don't believe so .
I don't remember saying anything about a plastic tank either .
Why solar thermal appears to be a better investment than PV’s
“Heating and cooling costs are typically the largest energy expense for most U.S. homes.” EPA
For DIY, solar thermal seems easier and cheaper to make than PV (Daniel: assume upgrading the YouTube CPVC design to code). Solar thermal also seems the best ROI.
Dana: You know our neighborhood is propane dependent so my greatest concentration of energy costs is the space heating and tank-in-tank DHW. Drain water heat recovery will not work in my case as the DHW supply is through a ceiling chase; too far from the DWV’s while the shower drain is too close (24” riser) to the horizontal main and cellar exit to the septic tank.
In the kitchen where there is most DHW wasted in most houses (other than showers/baths), we reduce it with a foot valve; and cold water is used in the clothes washer. Shower waste is somewhat reduced with a low flow head. This is savings by reducing use, as opposed to recycling.
http://www2.buildinggreen.com/blogs/foot-control-faucet-convenience-and-savings
I see Daniel how you frame the ROI based on price of the house’s inputs (i.e the comparative cost per Kw or BTU of the PV vs. flat plates, over time), Dana made similar calculations on a previous thread and repeatedly recommends the PV over solar thermal.
But don’t we have to look at the relative net savings to the house budget (i.e. real operating costs)? Taking a chunk out of my highest input cost (propane), gives us a relatively better ROI than taking it from the lower input cost (electricity).
Isn't space heating/ DHW fuel the most pervasive consumption expense, eclipsing the high load and the 24/7 appliances: frig, boiler and pumps, stand-by loads, ductless AC, exhaust fans, washer/dryer.
So why isn't thermal solar clearly a better investment?
Here is a link to my latest article on this topic: Solar Thermal Is Really, Really Dead.