Water cooled solar panels for significant output boost

[J.P.M.]

I let you all intO this secret. Where I work many engineers before me had tried to make water cooling cost effective.. They got close because 10 yrs ago panels were expensive.. I thought they just didnt try enough variations. So Ispent weeks trying to come up with something thEy had not tried or thought of.. Sadly for me ended up giving up.. now when Isee someone else trying I know they wont do better.. thats life..

It's common sense to try to get as much out of a process as possible. Folks been doing it with machines and heat engines/pumps for as long as there has been a need for them, and that's even before Carnot and Clausius. To folks who work and make money finding new applications for such an old and common sense concept, the idea of combining solar thermal and solar PV is pretty much a no brainer.

Sometimes it makes engineering sense, but as Sunny Solar implies, the economics probably aren't there for flat plate solar for most small scale applications. Practical difficulties most likely also get in the way at the smaller level. Some things just don't scale well.

To my experience, the smart money doesn't put the cart before the horse and try to prove what may be an unsound concept before, and without, seeing what's already been done, and testing the idea against known scientific and engineering principles.

Lots of fun maybe for its own sake and so needing no further, if any justification. But to expect to be taken seriously and not embarrassing yourself in the process seems to me like an exercise in futility, as was, IMO, most of this thread.

Most of the time, the lower the entropy increase for a process before any energy scavenging is attempted, the harder the economics are to justify for grabbing extra energy that would otherwise go to waste. The scale of any such scheme often also plays a big part. A power plant operating on a thermodynamic cycle through a high temp. diff. will have more ways and opportunities, and have those ways easier to cost justify than most solar processes usually operating closer to the limits imposed by entropy.

For example, a municipal power plant that provides district heating using once through condenser cooling water has an entirely different set of practical considerations and opportunities for energy scavenging than what is mostly a once through spray condenser/film cooler on a small solar array that:

- Wastes most of the cooling water used
- May well be bad for the equipment and the roof
- May inhibit or decrease long term performance of the original array
- May well take half as much energy to run as it saves -

That's for starter's, but no way to tell any of the above because of the ignorance of what's involved or the possible/likely consequences. That's the sad part.

[russ]

On the other hand, Parabolic solar PV concentrators do work and provide both warm water plus electricity. They still require a special circumstance to make them economical.

[pleppik]

All I'm trying to say is this idea is not new. Universities, scientist, and engineers have tried 9 times to Sunday for the last 20 years to make it work. That group are my superiors and peers, and when they tell me it cannot work economically or establish a positive EROI, I believe them.

I agree with all this. The only thing I objected to was the claim that boosting total output by cooling the panels would violate the 2nd law of thermodynamics.

In my book there's a huge and important difference between "isn't economical" and "violates the laws of physics."

[pleppik]

So then you know the difference between the Carnot efficiency limit based on temp. and the Thermodynamic efficiency limit for various solar cell technologies having something to do with band gap energies, right ?

Yes, exactly right. Which is why it's not a violation of thermodynamics to boost the efficiency of PV panels by cooling them. Which was my entire point.

The 2nd law limits how much useful work you can extract from a temperature difference, regardless of whether the mechanism for extracting the energy is a heat engine, thermoelectric generator, or photovoltaic cell. But the efficiency of a PV cell is so far below the thermodynamic limit that there's a lot of room for improvement before you start running into the laws of physics.

[Ian S]

I agree with all this. The only thing I objected to was the claim that boosting total output by cooling the panels would violate the 2nd law of thermodynamics.

In my book there's a huge and important difference between "isn't economical" and "violates the laws of physics."

You're exactly right and that's the whole problem with this thread. Some "expert" proclaims that evaporative cooling violates the laws of physics and others leap to his defense by changing the subject to one of economics. Such antics are par for the course around here and are good for a chuckle if nothing else.

[J.P.M.]

I agree with all this. The only thing I objected to was the claim that boosting total output by cooling the panels would violate the 2nd law of thermodynamics.

In my book there's a huge and important difference between "isn't economical" and "violates the laws of physics."

I must have missed the part where anyone was claiming a violation of the 2d Law of Thermodynamics. Where was that ?

[pleppik]

I must have missed the part where anyone was claiming a violation of the 2d Law of Thermodynamics. Where was that ?

It was here:

You are fighting the Law of Physics and cannot change those Laws no matter what. It is the same reason you cannot use a trampoline to get into orbit, or pull a train with a motor cycle. You will never recover the energy you put into cooling. You are wasting energy, not making it.

It's true that he didn't actually use the word "thermodynamics," but there's not really any other law of physics which could apply.

But I think we've truly beaten this dead horse to death (or something). I apologize for yanking this thread so far off the original topic.

[J.P.M.]

It was here:



It's true that he didn't actually use the word "thermodynamics," but there's not really any other law of physics which could apply.

But I think we've truly beaten this dead horse to death (or something). I apologize for yanking this thread so far off the original topic.

The original topic was mostly a waste of time anyway. Might as well waste a bit more to clarify a few things.

To the extent that some parts of Thermodynamics share the world of Physics, how about the 1st law of Themodynamics being applicable as it relates to an energy balance on the system, which when applied to this situation with a control volume slapped around the heat recovery system would mean an examination and analysis to determine if more energy is required to cross the boundary surface into the control volume to make the heat recovery system work than is recovered and crosses the boundary surface in the other direction.

It may or may not be true that more energy is used than recovered in the subject system. But either way, contrary to your statement about no other laws of Physics being applicable I'd suggest the 1st law as being very applicable.

And while I'm not speaking (writing) for Derrick, my interpretation of what he had in mind was more with respect to the bottom line cost of the energy necessary to produce the resulting increase in system efficiency and account for all the parasitic extra costs associated with such heat recovery systems - that cost being greater than the value of any recovered heat.

That is, even if you can save more energy on an absolute basis than you input, the difference in the quality of the energy input and the cost of its low entropy (as in the high cost of electricity) compared to the relatively higher entropy (and lower value) of the recovered waste heat, plus the costs of the makeup water, plus the added cost(s) of maintaining and repairing the equipment required to keep it functional in what may well be way off design conditions, are perhaps and probably higher than the value of not recovering the waste heat and supplying it by some other method(s).

I'm of the opinion that, all things considered, it seems fairly certain that the heat recovery system as described would have the effect of a larger increase in the entropy of the surroundings than the entropy of the heat recovery system, resulting in a net increase in the entropy of the universe. That fits some of what I learned about the 2d Law. It would also cost more than what would be saved, both short and long term.

So, not only did Derrick's tirade about system inefficiency not say it was a violation of the 2d Law, but in a very real way, with a little thought, may have served as yet another consequent example and possible verification of it.

In either case, I concur with your latest statement that he indeed never mentioned the 2d law of Thermodynamics, contrary to your prior statement.

[Philippeberard]

Good discuss thanks i will take new idea.

[Sunking]

Get lost SPAMMER

[inetdog]

Get lost SPAMMER

Not yet a proven spammer, just a guy who has made ten posts and not actually said anything of interest. We are watching him though. Let us know if he does anything directly outrageous.
We are particularly sensitive to people who drop inane posts and go back and edit spam links into them later.

[Sunking]

Not yet a proven spammer, just a guy who has made ten posts and not actually said anything of interest. We are watching him though. Let us know if he does anything directly outrageous.
We are particularly sensitive to people who drop inane posts and go back and edit spam links into them later.

My guess he already has already gathered your member list for a SPAM attack via PM. If we see any of this on MH Forum we nuke them immediately, or shoot first and kill, then ask questions later.

[inetdog]

My guess he already has already gathered your member list for a SPAM attack via PM. If we see any of this on MH Forum we nuke them immediately, or shoot first and kill, then ask questions later.

Thanks for the tip. That explains why he went up to ten and stopped!

[Sunking]

Thanks for the tip. That explains why he went up to ten and stopped!

Nuke him, you got nothing to loose.

[inetdog]

Nuke him, you got nothing to loose.

Already did....