Solar Electric + Solar Water = Opportunity? (CoolPV)

[J.P.M.]

Keep PV and thermal separate. Combining them sounds like a marriage made in heaven, but in reality, the attempt will result in neither working well for more reasons than can be described here, and no good end will come from it.

I got interested in solar 40+ years ago, left a lucrative career as a peddler, got an additional degree in M.E., etc., and spent a lot of an engineering career doing the thermal and mechanical design of industrial heat transfer and process equipment, all the while treating solar as more than a hobby but less than a job. I may be somewhat unusually qualified to speak to the issue of combing solar thermal and PV.

Among the things and traits I learned about the solar business as someone with a foot in both worlds - solar and real world process engineering - was that an uncomfortably large number of folks selling solar, initially solar thermal back in the day, and later and currently PV, don't know fertilizer from shoe polish about solar and even less about energy matters. I also discovered that an inordinate number of those folks were/are involved in peddling schemes such as those that claim to utilize energy otherwise rejected as efficiency decreasing waste heat in solar PV processes. It's a form of heat recovery sometimes called scavenging, or heat recovery, or other names, and has been around for years, just like something called economizers on boiler systems. The first large commercial solar boiler in the early 20th century had an economizer section.

The idea as relates to PV continues to attract people because it seems to kill 2 birds with one stone. The devil is in the details. The way most heat scavenging works with respect to PV/thermal, the only things that get killed are workability and ease of operation.

If such things did work, you'd think that there would be solar thermal/PV combinations all over the place, particularly in climates with a lot of swimming pools. Look around. You see many ??

There are a few DIY systems. Most of them derelict, and not much else. Those uninformed and/or ignorant of the engineering involved reinvent the scheme every few years, sell a few systems to those more ignorant than the marketers and the cycle repeats.

Do what you want, but like most everything else, the less informed you are about something, the more likely you are to get screwed, financially and operationally.

Look : I think solar is great. It changed my life. I really want it to help humanity. I could probably design a workable PV/solar pool heater, but making it work safely, efficiently and in a fit for purpose and serviceable way for many years is not possible at this time if cost effectiveness is also a design requirement.

Systems of the type we're talking here do little more than give the solar naysayers more ammunition. In my opinion as a (retired) P.E. mechanical engineer, for whatever that may be worth, the combined systems I've seen are not fit for purpose.

[Sunking]

Theoretically, running cool water under the panels will increase output. Whether it make long-term financial sense, who knows.

That is a loser's game, and something they do not teach anymore in school. Unity gain and thermal dynamics. That means the energy it takes to pump and cool the water will be less than 100% efficient. That means throwing money and resources away.

It also poses some building code issues like water and electrical cannot occupy the same space. We see a lot of scammers come here with misting systems for solar panels.

Kronic, have you looked into this deeper and found any details out?

My situation. I've only got one really usable side of my roof for Solar - The West facing side is streetfront and chunked up anyway. The South side current has a 10x20' solar pool installation. I don't want to loose my Solar Pool installation (previous owner had installed) but I want to go Solar PV.

I don't really care if I don't get the 20% extra electric generation from the lowered temp, and if the thermal energy is only 1/2 as efficient, but I'm covering 2x the area (20 panel system should be 2x the area) then it would have the same effective pool heating. I'd be willing to pay a bit of a premium on it (like the cost of a Solar Pool heater installation more...)

Curious as to what pricing you may have found out. Especially if you've found anyone to who've had it installed and their thoughts after the fact?

[tyab]

kron - now that my PV system is done the better half keeps bugging me about getting our pool warmer beyond what our cover already does. Been reading all the stuff on the forums here under that subject. Can't miss it - scroll down the forums list and you will see the "Solar Pool Heating" section. Read all the past questions. Tons of info there - I'm looking to do mine early summer 2018 and it will be combination of using existing retaining wall and adding some covered shade space for those collectors.

[J.P.M.]

There are probably no thermally effective and simultaneously cost effective ways to combine water heating and PV in one assembly that is both practical and serviceable.

There are few people who have both a good working knowledge of PV and a thorough design knowledge of heat transfer engineering and technology necessary to discuss the possibilities.

Take this as brag or as you please, but take it FWIW: After an engineering career that was started by solar energy interest (and which has remained more than a hobby but less than a job), spent as a P.E. in the design and engineering of boilers, pressure vessels and process equipment and systems, I may be one of those people.

With enough money to throw at such an application as PV/thermal, anything is possible. I could design such a system, but it would be neither practical or cheap. Many have tried it. I know a few of them and did a bit of consulting for/with them along those lines after retirement.

The dearth of viable systems combining PV and thermal, except the few technically na

[sensij]

I should be clear that I was planning on doing this for a pool. A pool system by itself costs $5K or so. I have not yet priced out what these are... However, these panels have a MAx output of 275 watts. I imagine that even with cooling you aren't actually increasing the output beyond the max. Would reduced heat help efficiency earlier/later in the day?

No matter what time of day, if the panels are cooler, they produce more. The STC rating is not a "maximum", it is just the panel's output under specific test conditions.

[kronic24601]

I should be clear that I was planning on doing this for a pool. A pool system by itself costs $5K or so. I have not yet priced out what these are... However, these panels have a MAx output of 275 watts. I imagine that even with cooling you aren't actually increasing the output beyond the max. Would reduced heat help efficiency earlier/later in the day?

[kb58]

Theoretically, running cool water under the panels will increase output. Whether it make long-term financial sense, who knows.

[jflorey2]

There were at least two outfits at Solar Power International this year with combined PV+thermal panels. They claimed significantly increased power output from the cooling effect but I am skeptical; might work for pool heating (where the temp is always 80F or so) but not for DHW systems where water can be 140F.

I'll see if I can find the info.

[kronic24601]

I could find literally no documentation on this. Basically I'm that rare customer considering Solar Electric AND Solar water heating. Problem is roof space. So someone pointed me to http://coolpvsolar.com/ ... I'm not a huge fan of the specific panel they use, but I was curious about the hybrid approach. I've read a few posts on water cooling, but none abou tthis particular panel combo. Curious if anyone has ever used or heard of CoolPV (fafco + SolarWorld)