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Efficient low-cost thermal water/space heating

jinmtvt | Posted in Green Products and Materials on

I am working on a project with an engineer friend,
we are trying to develop an efficient low cost solution to thermal solar energy for northern climates.

I believe that what deters most owners from using the possible free/green solar heating
for their residences is the payback and up front cost of thermal systems and PV systems
( at least here in canada )

I’ve seen quotes in the 5000$/kw installed PV which just doesn’t make any sense
( when we can all purchase 25 years mitsubishi panels for ~ 1$/w )
And water thermals are in the same ballpark with paybacks ranging from 20 to 50 years locally.

If we could come up with an aesthetically pleasing solution
( i have plans to integrate the panels into a aluminum panels finish system i am working on as an example)

And come up with a water based battery system, very simple, as less parts as possible,
that could then be used by a few different methods for space heating during nights
( forced air through furnace type radiator , in slab radiant heating using pex setups, old style solid water radiators for examples .. )

We are working with some absorber coating manufacturers to understand the limitations and the implied costs , i believe that the absorber sheet performance is the key to efficient low cost design on flat plate collectors .

Then, hot water going to electrical water heater tank could be circulated in the water battery before getting to the tanks …matches the profile easily, setup is almost inexistent ( simple reroute )
it can also be used during summer time if required ( for water heating purposes and later if some units come available …ab/adsortption cooling )
Peak water battery temperatures comes in late day, right before most use shower hot water during the evening.

From what i could gather, seems fairly easy to get 30% solar efficiency, and with a low cost panel setup, more area could be turned to energy.

What do you think ?

I am certain we can lower panel cost as we’ve already come up with a few ideas for manufacturing
that cust involved labor by 5fold, and it could be all done here in Canada instead of china
as most other solar thermal panels manufacturer do right now ๐Ÿ™

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  1. GBA Editor
    Martin Holladay | | #1

    Welcome to the 1970s. Everything you describe is possible. Everything you describe has been done. And everything you describe costs more in hardware, repair bills, and hassle than the value of the gathered energy.

  2. jinmtvt | | #2

    Martin : could you please elaborate or link me

    I have yet to see a commercial system that is affordable and is simple as a good DIY system.
    all i have seen up to now are much too complex to be addordable.

  3. GBA Editor
    Martin Holladay | | #3

    You're right. If you can develop hardware that is simple and affordable, that would be news.

  4. jinmtvt | | #4

    Well Sifu Martin , i will . ( try )

    please tell me what you think of our basic reasonning.

    Simple insulated tank , probably made out of assembled steel frame with EPDM liner or of similar type of structure .
    Open loop with gravity drainage ( tanks need to be in basement or lower than panels of course )
    Probably around 1000liter tank could be sufficient, will need to work on temperature delta of solar thermal panles, but a 1000 liter tank is not too big to place in regular basement or mech rooms.

    Exchange loop ( let's say a large ratiator or a spiraled copper/pex loop ) in which water tank inlet goes through before the tanks.
    This should be simple and cheap, it is also not labor intensive to reroute water line .

    We are investigating use of aluminum ( probably 3003 series ) as panel piping and use of mechanical fit instead of welding/laser/glued to lower labore and equipment cost,
    and will try out using a single line pattern instead of manifold/runs , so only 2 welds ( port in and port out ) and much less chances of leaks. Piping would be bent to make the run.

    Lastly we are investigating use of plastic films in addition of glass glazing to help with frontal insulation for cold weather application.. may end up using double pane also ..

    It is solely a question of the framing alum extrusion , and i have access to extrusions at a very good pricing ( custom die and design ) .

    At the end the final pricing also reflects installer/distributor profits, which we would try to cut
    and try to work with government agency in canada to help normal folks get our of their energy misery. :p

  5. GBA Editor
    Martin Holladay | | #5

    It's all been done before. Do some Googling. There are good reasons why solar thermal collectors aren't made of aluminum and plastic. And plenty of people have built 1,000-gallon basement tanks lined with EPDM. Most leak.

  6. Expert Member
    Dana Dorsett | | #6

    If you're really dedicated to low cost DIY solar thermal, check out Gary Reysa's cheap solar hot water details:

  7. jinmtvt | | #7

    Martin: well anyhow, the important part now is the collector.
    Solar collector will all be Al in the near future, you might have missed some late years of European products sifu .. look for Hylife aluminium tubbing and a quick dozen of swiss, polish and deutsch manufacturers already switched to all aluminum systems.
    Some tests have been completed recently by many different groups and most have found that with proper precautions, systems show no to almost no corrosion after 20 years equivalent cycles.

    I will have to look into the tank later , if some plastic tank is required than so be it.
    I have a few plastic 1000liters laying around, will test using this for now.

    Dana: thanks , but i've already gone through that site many times ... :)

    If one is to use this only for water heating, then payback gets out of range.
    We need to focus on space heating for zone 6-7-8, and water "preheating" or "warming" becomes a by-product of the same setup.

    Heating inlet tank water by only a few 10c would already be a large improvement.

    In a very efficient passivhaus type of construction, a very basic solar thermal system might be
    all that is required to complete daytime solar heat gain for the night time.

    here is one of the commercial all aluminum collector, that use a semi-harp layout.

    Do you guys believe that using double glass ( glazing but not adhered..probably simply fitting in epdm seals with maybe some kind of pressure relief valve ? ) could pause any problem with the temperature difeerences ?

  8. jinmtvt | | #8

    Been crunching some numbers ..
    got some info back from manufacturers ..

    i don't believe we would be able to get a material cost under ~80$/m2
    ( that is with top notch Bleuetec absorber plate, low iron glass front, roxul insolation ( 3.5" thick back and sides ) custom alum extrusions for framing, epdm seals and alum tubings.

    although i believe we can cut alot on labor using a few ideas we''ve come up with,
    it would be stupid to assume less than 40$ worth of laber per panel let's assume 20$/m2 of labor cost.

    So already hit the 100$/m2 cost .

    Then using NRCAN maps and numbers, graphs i've found online, comparing with similar FP ST collectors efficiency, low temp efficiency factors etc ...

    ( )

    I ain't sure anymore ..
    worked on calculating PV payback and current costs also, got some good info,
    but again it proved PV is still not possible here at our "clean" hydro electricity price.
    I've used 1.5-2$ / W for PV equipement ( not factoring in installation )
    Takes more than 15 years for payback ...
    Could be interesting if the price of the electricity goes up a bit here though ..payback of 10-12 years
    would bring it in more.. let's wait a couple more years...

    I tried also to factor in the average of COP 3.0 for heating with current mini splits,
    since the thermal panels would be mainly used for it.
    Can't do it for water heater though, and also would be nice to use the thermal solar
    on intake HRV air to pre-heat.

    i get something like the following :

    PV = ~ 50kwh/m2 during the 6 months of heating season ( october to mars inclusively )
    PV= ~ 80kwh/m2 during remaining 6 months

    NRCAN gives us an average ( including cloud obstructions etc. ) of ~ 1000kw/h / years per installed KW of PV for my area

    6KW grid-tie system cost = ~ 8000/9000$
    6kw X7 = ~ 42 m2
    8000 / 42 = ~200$/m2 cost
    130kwh X 42m2 = 5500kwh, close to their 6000kw/h using their data ( just confirming here )

    solar thermal panel :

    average efficiency of similar flat plate from test data =
    ~ 60% in cold climate
    let's use 50% efficiency here

    from NRCAN data :
    ~ 250kwh/m2 for 6 months of heating again

    - summer performance is dependent on hot water usage , let's use the average of 70gal per day ( 260 liters )( 2600000g X 50degree delta X 1cal =13000000cal ) = ~14kwh X 182days ~ 2500kwh
    and let's use a ST to HWater efficiency of ~75% so 1875kwh maximum savings

    We know that during summer, any rightly sized ST system would suffice the hot water demand
    ( 75% of it ) so any size system could save a theoritical ~180$ maximum of the remaining 6 months

    let's keep our 15kwh for hot water, add another 5kw for preheat of intake HRV = 20KWH

    the ST system needs to be hit by a /3 on heating factor ( to be on par with mini spit COP for heating )
    so 250kwh -20 /3 drops to roughly ~75kwh /m2 .
    75 + 20 = 95kwh /m2 of possible gains VS 50kwh /m2 for the PV for the same period

  9. jinmtvt | | #9

    So if using the 6KW system as example :

    6KW PV setup for the heating 6 months should give (340X6 ) = 2040KWh

    to match that we would need ~ 21.5 m2 of ST FP

    the PV would be producing approx 6K KWh /year = 600$ worth of energy
    the ST ( 21.5 X 95 ) ~2050KW + 1875kwh ( other 6 months hot water ) = 3925kwh = ~400$/year

    Let's put the ST @ 150$/m2 of sale price , + 200$ piping +300 pumps + 1000$ battery = 4725$
    ( without installation to compare with same attributes )
    10 years payback

    the 6KW PV has a 14 years payback

    So did i get something wrong here ??

    If it is all correct ( for the purpose of approximate evaluation )
    I would need to get the price of the panels ( per m2) much lower than this for the ST project
    to be worth it.

    Will have to wait on final price quotes, and discuss on how much more we can work on estimations of costs, labor, components etc..

    How do the older costly systems ever payback ???

    In my example, its too close to choose the ST ..i'd take the PV system on that one .
    Problem here is no incentives, no tax credits ..nothing
    they don't even buy back the electricity, they just credit you KWh ..better than nothing but
    doesn't help anyone with the payback.

    ok enough ... sleep time now :)

  10. GBA Editor
    Martin Holladay | | #10

    There are several problems with your equations.

    The first is the apples-to-oranges problem. Grid-connected PV has a 24-hour "battery" with no losses; solar thermal energy, if not used within a few hours, is wasted and gone forever. PV systems don't have pipes that leak or antifreeze that needs to be checked or pumps that need to be maintained.

    The second problem is that no one cares about energy output per square meter. Area is not the limiting factor, in most cases; the limiting factor is equipment and maintenance costs.

    Different versions of these equations can be found in my blog on the topic: Solar Thermal is Dead.

  11. jinmtvt | | #11

    MArtin: i fully understand the difference of maintenance and complexity of PV vs ST .that is why i am trying verify the numbers before embarking ... needs to make for a good investment difference
    between PV and ST for the later to be worth at the current mini spit COP .

    I've read your blog a few times already ..

    power per area was used here to be able to compare prices and performance,
    it is very easy to obtain data on PV output, much less on solar thermal because of the many variations in different systems and setup.

    Then, in your blog ... 8000$ for 2 32sqft panels installed ..that is the problem why you believe ST is dead. The tag price of the installed system kills it.
    That is what i am working on now ..lowering this .

    are my maths off ??
    forgot something ??

    quoting you """""""""""""
    If you can get a two-collector solar thermal system installed for $5,000 or less โ€” an attainable price in areas of the country where people don't have to worry about freeze protection โ€” it may make sense to install one.
    I believe it can done for this cost, maybe even 1-2 additional panels ...even in cold climate.
    And that is what i am working to confirm on the other side ..

    And if you add in figures for commercial heating,
    with often very large unused area of walls, if we would to come up with a relitively cheap system that connects a very large array of collectors together...

  12. jinmtvt | | #12

    Martin: please explain why you said many times that the time buffer is not advantagous for ST

    Buffering thermal to a water type battery for reuse during evening/night
    which also happen to be when most folks use hot water to shower ...i don't see how it is a problem ?

    For personal understanding, PV is timeless if grid-tie right ?
    if not, batteries are required and it throws off green product/payback further..??

  13. GBA Editor
    Martin Holladay | | #13

    Solar thermal systems collect heat during sunny weather. Much more energy is available during the summer than during the winter. Many solar thermal systems waste a high proportion of the heat collected during the summer, when it isn't needed.

    The same problem doesn't occur with a grid-connected PV system.

  14. jinmtvt | | #14

    MArtin: that is why i took account of the "water heating only" purpose of the ST during summers in my calculations.

    As for energy, what is the difference with PV ?? looks like very similar ratio of winter VS summer to me.

    At the end it all comes down to cost, maintenance/reliability and used/produced energy.

    I would tend to think that in view of the calcualtions, the difference of cost vs performance/payback of both systems are closer than i thought ... if my calcs are good ( please quick verify if i did a major error )

    What is the price range that would make ST ( space heating and water heating..not just WT ) interesting again ?? I will need now to focus on getting price of components and basic design to be able to determine if it is worth the effort !!

    Unfortunately, we don't benefit of much gov. incentives here, and Hydro QC only credits per KW, so no advantage on feedrates also ..

  15. GBA Editor
    Martin Holladay | | #15

    I have never heard of a solar thermal system that was able to perfectly balance energy production and load during the summer. Almost everyone goes away for a weekend or two, for example. Even if the family stays home every day during the summer, there will be wasted heat. It's impossible to use every drop of hot water that enters your storage tank before it cools.

    In contrast, all of the production of a grid-connected PV system is credited to the owner.

  16. jinmtvt | | #16

    Ok i understand what you mean now.

    That is still why i only used a % of hot water for the ST during 6 months of the year.
    Still comes ahead somehwat using /3 to compensate for mini splits COP.

  17. jinmtvt | | #17

    Ok i crunched some numbers again ..and went through ( for maybe the 4th time now ) the complete article ( ST is dead ) and it's related posts ...

    What i never took account for at first, was the grid-tie credit or buyback ( depending on local utilities )

    I was comparing the PV production during the 6 months of heating season and not using the whole year production using the credits ... with a COP of 3 for heating from mini split ..PV gets up to cost with ST and makes more sense

    Then again, the complete lack of incentives from our local governments makes both commercially not very attractive because of a ridiculous payback term that ends long after the warranties.

    I will still look into fabrication costs of the ST just to end up with some numbers and see how it would really compare if we use the 3000KWh equivalent pricing method per installed KW of PV.

    Est-ce que j'ai bien compris Martin ???

  18. GBA Editor
    Martin Holladay | | #18

    Q. "Est-ce que j'ai bien compris, Martin?"

    A. Si nous sommes maintenant d'accord, Jin -- vous avez bien compris.

  19. jinmtvt | | #19

    ok just to clarify with price cost ( without installation )

    PV credits + mini split = X3 on all KW produced

    let's assume 1KW isntalled @ 1$/w
    would require 12m2 of panels to match the energy ( at 50% total system efficiency )
    ..i don't believe i would be able to make panels and sell them for less than 100$/m2 ..
    so 1200$ ..already ST is more expensive than panels of similar power PV

    Then PV will require a ~1000$ inverter ... ST will require a ~ 1500$ tank+ pumps + controller


    if we use 6KW of PV
    18KW total output of heat using cop 3.0
    would require 72m2 of panels ..X 100$each ..

    6KW PV = 2000 - 3000$ inverter
    18KW ST = same 2000$ ..let's add 500$ for larger tank of system

    Still PV wins on cost

    and ST would need to be at least 25% to cover maintenance and complexity ( but i would like better if it would be off by 50% to make real sense )

    SO i am sorry i started this thread without getting into the real calculations...
    wait i am not sorry at all ... this thread pushed me to stimulate my brain, understand a few things
    and realize that without a good incentive, ST is dead .

    Without a good incentive, PV is not really attractive here unless DIY and energy concious mind !

    Sifu Martin, je m'excuse d'avoit doute de votre enseignement ! ahha Je continue mon parcours d'apprentissage humblement! ( au moin j'ai fini par comprendre!! cest bon signe non ? )
    Au plaisir :)

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