Solar Electric + Solar Water = Opportunity? (CoolPV)

[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)

[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.

[kb58]

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

[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?

[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.

[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

[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.

[Guest]

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?

[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.

[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.

[jflorey2]

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 now at least two commercially available lines of panels out there that combine water heating and PV in one assembly - SolLink and HarvestHP. Whether or not they will be commercially viable, of course, remains to be seen.

[J.P.M.]

There are now at least two commercially available lines of panels out there that combine water heating and PV in one assembly - SolLink and HarvestHP. Whether or not they will be commercially viable, of course, remains to be seen.

In my professional opinion, they will not be viable much less practical, or cost effective anytime soon. Nor are they likely to be fit for purpose. Water and electricity don't go well together. Air as a working fluid has very poor film coefficients requiring large surfaces and pumping costs. It'll cost more energy to pump the air around than the differential increase in panel efficiency even when combined with reuse of the recovered heat. So, that leaves water as a working fluid, probably, as you suggest for pool heating.

A couple of off the top of my head reasons why such systems - using water - are not viable at this time: The most common scheme of separation between the thermal circuit and a PV (or other surface as in double wall heat exchanger) is a barrier, or more than one barrier between them. That barrier is often air, either completely intentional, or occurring as unintentional and unwanted but also unavoidable gaps left by incomplete joining of the surfaces. That by itself reduced heat transfer efficiency, increases thermal resistance just like electrical resistance from poor bonding/joining, and increases other problems and price. Then, there's the added material cost. Forget copper due to cost. That leaves aluminum, not itself cheap, particularly in the quantities needed, but only if material compatibility with pool H2O can be addressed - a bit of a challeng. Other materials will have lower thermal conductivity below usable or practical levels. Regardless of material, cyclic thermal expansion is going to be a problem, and as the thermal and PV surfaces undergo that cycling due to (hopefully, but not likely small dimensional differentials due to poor bonding) temp. differences between the thermal and PV sides. the bonding/contact will break down, the surfaces will separate more, guaranteeing that, even in the very unlikely event that thermal contact is good, it won't stay that way for long, with no or very unlikely possibilities for inspection and none for remediation.

That's just a start and a surface scratch.

After speaking with more than a few folks that seem knowledgeable about solar and PV design, my observation is that while they might know a lot about PV and solar PV design, they seem to know next to nothing about heat transfer or thermal design, much less mechanical design. Equally, on the other side, the heat exchanger folks not only don't know, but don't much care about PV.

Note: I'm not saying PV-T systems are impossible. Just not possible/viable at this time. In my experience, based on a pretty good knowledge of solar energy and a much larger body of professional experience in mechanical and thermal engineering design, helps me form the opinion that such systems, up to now, by and large have been poorly designed junk that the solar ignorant latch onto.

BTW, I checked those two sites you referenced. I wasn't impressed by either. Long on pretty pictures, short on information. More shyster cons IMO. Seen it all before. They come and they go.

[Sunking]

There are now at least two commercially available lines of panels out there that combine water heating and PV in one assembly - SolLink and HarvestHP. Whether or not they will be commercially viable, of course, remains to be seen.

There are two companies that make solar roof shingles. Completely useless.

[Sunking]

BTW, I checked those two sites you referenced. I wasn't impressed by either. Long on pretty pictures, short on information. More shyster cons IMO. Seen it all before. They come and they go.

I looked too. Not surprised, looks like another Musk con job like solar roof shingles. Fools and their money will soon part ways.

[J.P.M.]

I looked too. Not surprised, looks like another Musk con job like solar roof shingles. Fools and their money will soon part ways.

Not Musk, but seems to me Musk and these folks learned their craft at con school, same as every shyster in every business endeavor. Musk is one of the biggest, but far from the only con man out there.

Such cons are a part, but far from all of what killed solar thermal in the '70's - that and tax credits that allowed the cons to flourish. Today's tax credits have produced similar effects on product quality and peddler honesty.