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PV+solar thermal panels ?

  • 1.  PV+solar thermal panels ?

    Posted 11-30-2021 11:50 AM

    Are there PV+solar thermal panels on the market yet?

    I saw a concept a couple years ago for an IR transparent PV panel that then has a solar heating panel below it to capture the IR.

    Sincerely,

    --  Allen Wilkinson


  • 2.  RE: PV+solar thermal panels ?

    Silver
    Contributor
    Posted 11-30-2021 05:10 PM
    There have been different configurations over the years for combining them (Heat + Elect). I personally think going regular solar thermal for SDHW and or space heating than add regular PV for the elect. is a better solution. A typical install would be 2 evac tube collectors (60 tubes) with an 80 gallon pre-heat tank (SDHW) then what ever amount of PV you can fit/afford. Solar thermal yields you much higher efficiency per sqft. and SDHW when properly sized. The specific configuration depends our you specific site, location and loads, etc.. When done right, there will be little wasted energy.

    ------------------------------
    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 3.  RE: PV+solar thermal panels ?

    ASES Life Member
    Posted 12-01-2021 01:00 PM
    William Fitch has a good idea about keeping PV and solar thermal separate.  Combining the two is not likely to have good results since PV works best at the lowest possible temperature (air flow between the roof and the underside of the PV modules helps with cooling), while solar hot water works best at the highest possible temperature.

    ------------------------------
    Stu Besnoff
    owner
    Alpine Solar Heat and Hot Water, LLC
    stu@alpineSolarheat.com
    ------------------------------



  • 4.  RE: PV+solar thermal panels ?

    Posted 12-01-2021 01:32 PM
    The HPWH will be in a basement area, outside the conditioned thermal envelope, but inside the building.  The heat will come from the basement floor and it'll help dehumidify the area.  Even in Maine the earth below the frost line stays around 45-55-degree range, and has a good buffer from the weather by a couple of months.  My cold climate heat pump that I use during the heating season is an air source split dx unit, and does fine with its outside unit, but that's a different beast than the HPWH unit that sits atop its hot water storage tank.







  • 5.  RE: PV+solar thermal panels ?

    Posted 12-01-2021 04:42 PM
    Heat transfer is greatest when heat sink (the solar thermal panel) is coolest. What if solar thermal is a preheat stage so that its liquid heat transfer fluid stays cooler than the PV array itself? That fluid could be the heat source for a heat pump that takes your DHW to the desired temperature.

    PV only uses the small visible spectrum of solar radiation energy. A much larger energy content is in the thermal IR spectrum where solar thermal is best. Why can't the PV panel let the thermal IR pass through it to a solar thermal panel?

    ------------------------------
    Allen Wilkinson
    research scientist
    NASA Glenn Research Center, retired
    aw@chaff.biz
    ------------------------------



  • 6.  RE: PV+solar thermal panels ?

    ASES Life Member
    Posted 12-02-2021 10:33 AM
    Hi Allen,

    I am working on a hybrid low concentrating PV-Thermal module.  Last month I received some promising test data showing a significant increase in electrical output while capturing about twice as much thermal energy.  I'm hoping to present the results at the New Mexico ASES conference in the summer....still need to submit my abstract.

    As someone mentioned because the PV wants to be cool--the module tends to produce a bunch of "lukewarm" water on the thermal side, to get the biggest boost from the electrical side.  If you are simply pre-heating water that is fine--energy is energy--and most people value a watt of electrical more than a watt of thermal.

    There are a few companies that produce PVT modules, but honestly I don't think anyone has cracked open the market yet.

    Daniel Simon






  • 7.  RE: PV+solar thermal panels ?

    Silver
    Contributor
    Posted 12-02-2021 11:45 AM
    I think you will find the problem is that when you try to join thermal with PV, it becomes a "practical" problem rather than a heat transfer problem. Pulling thermal energy using liquid transfer drags in all the liquid infrastructure with it. Think freezing climates, anti-freeze 50/50, heat exchanger on the pre heat storage side, pump(s), controls, etc., etc.. You are taking on complexities that make tracking for PV alone look simple, which would yield min 1/3 more energy with the same base PV KW. It is one of those ideas that sounds great in theory, but doesn't "compute" in the real world engineering. KISS is a valuable design guideline. Non tracking PV is at the top of this list. PV + thermal is hedging the bottom.

    ------------------------------
    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 8.  RE: PV+solar thermal panels ?

    ASES Life Member
    Posted 12-02-2021 01:21 PM
    William,

    You may be right about complexity vs. K.I.S.S.  Don't make things any more complicated than necessary is a good operating principle.  

    I only chimed in because Allen was asking if anyone was making combined PVT.  My PVT solution won't be right for everyone, but I see the thermal energy captured as "free energy"--or even better than free since it improves the performance of the PV significantly.  For someone that needs both heat and electrical energy this might be a great solution.  

    If ASES lets me present in New Mexico--I'll be happy to discuss further.  

    Daniel Simon






  • 9.  RE: PV+solar thermal panels ?

    Chapter Leader
    Posted 12-03-2021 10:17 AM
    google sundrum

    i have used this product on several installations for radiant floor and dhw

    works great

    especially useful for area constrained sites

    no more costly than separate systems

    ------------------------------
    Drew Gillett
    p.e.
    Solar Engineers
    deaneg@hotmail.com
    ------------------------------



  • 10.  RE: PV+solar thermal panels ?

    Posted 12-01-2021 10:28 AM
    I built a couple concentrating hybrid SHW & SE panels with parabolic reflectors that were slightly tilted up (or down) every few days that produced promising results.  Dr. Komp also developed a hybrid SHW& SE troffer module, and provided hands-on classes back in the day.  When the cost of solar modules dramatically dropped, I swapped my hybrids for additional PVs.  I do have 15 year old Heliodyne flat plate collectors for my domestic hot water system.  When I replace my old SHW system, I plan to just add additional PVs and a heat pump water heater.  PVs don't leak nor need replacement pumps and valves and they require extremely limited annual maintenance. 
    I do love solar hot air systems, but they need a small fan and ductwork.  When it's warm outside I open my doors & windows to flush out the bedrooms that have these heating units.  The IAQ in my house is excellent!

    ------------------------------
    Michael Mayhew
    President, Sr. Energy Engineer
    Heliotropic Technologies
    coolsolarguy@yahoo.com
    ------------------------------



  • 11.  RE: PV+solar thermal panels ?

    Posted 12-01-2021 12:03 PM
    Michael, when you do the switch from SHW to heat pump DHW, where will the heat pump draw its air from? (From what you've said, I'm guessing you're planning on an air-source heat pump hot water heater, not geothermal/ground source/water source). Obviously, if you are drawing air from inside the house, you need to somehow replace the heat the heat pump pulls out of the air and puts into the hot water.
    I realize that even at zero degrees F, R-134 refrigerant heat pumps can attain a CoP of around 2.0, so even then twice as efficient as traditional resistance electric water heaters. (Resistance heating's Coefficient of Performance is basically 1.0).
    But you're in Maine, right? Do you plan to source your domestic water's heat from outside air even in wintertime?
    Of course, one can enjoy the incidental a/c and dehumidification a heat pump water heater exhausts in summer, if sourcing the water heater's supply air from inside the house, unless even your summers are too cool for a/c.

    ------------------------------
    Hugh Willis
    Old Engrs Never Really Retire
    GREENSBORO, NC
    ------------------------------



  • 12.  RE: PV+solar thermal panels ?

    Silver
    Contributor
    Posted 12-01-2021 04:27 PM
    I played around with concentrators back in the day as well. However from a practical perspective, concentrating sunlight is only realistic where 80+% of the total energy comes in direct form (Clear sky country). And you need active tracking as well. 
    The path you plan to take, I.E. throw PV at the load because it is simple and cheap, is pretty much the standard play these days. I choose to remain diversified because non-integration and diversity yields the greatest resiliency in failure situations, which I feel is important even though liquid solar thermal is a bit of a PITA. Hot air not so much... leaks are not really a big deal...

    ------------------------------
    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 13.  RE: PV+solar thermal panels ?

    Posted 12-02-2021 10:53 AM
    yes they do make PV+solar thermal panels,  about $225 + substantial shipping






  • 14.  RE: PV+solar thermal panels ?

    Posted 12-01-2021 06:09 PM
    Let's set aside the obvious, that as a generality, water and electricity don't mix well.
    I suppose we all know that there are some pv panels that do very well when floated on water.
    And we know that panel output drops by about 0.5% per degree C (about 0.3% per degree F) for every degree above STC (cell temperature 25 degrees C) reached by the panel in its normal operating condition.
    ... So it "makes sense" that cooling the pv panel by removing excess heat could improve its output.
    But realistically, how much heat can be removed, and what is the quality of this heat (i.e., temperature, aka "enthalpy" of the cooling fluid)?
    With ambient air at 25C, s typical air-cooled pv panel's NOCT (Normal Cell Operating Temperature) might be in the 50C (122F) ballpark.
    Because conductive heat transfer only flows from "hotter" to "cooler", any flowing coolant will never get even that hot.
    (Solar thermal panels, like solar ovens, are designed to capture radiant heat from the sun, and can reach temperatures far higher than this).
    Yes, the fluid used to cool the PV panel can be used as a heat source. But to get water, for example, up to a usable "hot" temperature for domestic use, it likely will be necessary to use a water-to-water heat pump to get the desired temperature.
    You could accomplish half of the intended result by collecting your conventional (air-to water) DHW heat pump's intake air from just above the top of the pv panels, using the panels' waste heat that transfers into the surrounding air and rises by convection up to the top of the panels.
    This would not improve the pv panel's efficiency, (unless you actively pulled air across the panel and thus cooled the panel somewhat).

    I think what we are dealing with here is the difference between what theoretically makes perfect sense, versus what is simple and practical.
    In a residential setting, how hard do you want to work to fractionally increase the panel's output? And what is the value of the heat you would capture, which otherwise would be "wasted" by heating the surrounding air?

    Now, in a fixed array commercial solar farm, there might be a way to make use of the large amount of relatively low-quality heat coming off all the pv panels, if it could be efficiently collected. But in a home situation (where what might be collected is much smaller), perhaps not so much.

    A "tracking" array? The complexity boggles my mind.

    Bottom line - PV energy is cheap, and getting cheaper each year. Trying to squeeze a bit more out of each panel, by not "wasting" the discarded heat, once all the costs are tallied, may not be the economical way to go.

    Just my 2 cents' worth.

    ------------------------------
    Hugh Willis
    Old Engrs Never Really Retire
    GREENSBORO, NC
    ------------------------------



  • 15.  RE: PV+solar thermal panels ?

    Posted 12-02-2021 05:46 AM
      |   view attached
    My experimental solar hot water system was a hybrid concentrating PV system with a cooling heat transfer water loop siliconed to the back of the PVs.  The PVs needed to be cooled to not lose their efficiency as they recieved about 3.5 Xs the their normal solar input.  This raised the water temp which was pumped into a 1000 gallon thermal reservoir in my attached greenhouse, that had a coil of pex tubing in it.  This required the parabolic trof reflectorized PVs to be raised (or lowered) a few degrees, a couple of times a week, to work optimally. The water circ pump was DC and ran off some of the PV's power.  It was successful, but the cost of creating the robust reflector and adding the heat exchanger to the back of the PV became more expensive than just filling up the area with a larger standard PV array, when the cost of PVs dropped.  I do miss the additional heat that was dumped into the greenhouse pool, but not too much.  My 3,000 sg ft house is naturally passively heated, but I temper it with a 19,000Btu air source heat pump, a solar hot air collector and about a cord of mixed wood and Dura Briques (a hardwood sawdust manufacturing biproduct).  My house is net zero electric and has a radiant hot water heated lower floor that is tied into my solar system. I designed, built and lived in this house, with 4 children and my wife for over 40 years on the coast of Maine, and it's been very comfortable and should cost little to live here in retirement.






  • 16.  RE: PV+solar thermal panels ?

    Posted 12-02-2021 06:43 AM
    Here is the house without the concentrating hybrid solar collector which was replaced with this PV canopy. The house now has fewer occupants, had to let the children escape, so the SHW system is oversized; so during the summer I pull up a shade reducing the area of the flat plate HW collectors.


    ------------------------------
    Michael Mayhew
    President, Sr. Energy Engineer
    Heliotropic Technologies
    coolsolarguy@yahoo.com
    ------------------------------