Water cooled solar panels.

[Chris31415]

Originally Posted by RaymondR

Why use water?

Heat pipes use a volatile fluid to absorb heat at the heat sink end by way of a state change . The vapor produced rapidly flows to the heat reject end where it rejects the heat and changes back to a liquid which then flows back to the absorb end.

… Alcohol would probably work well since it would only require ambient pressures.

What could possibly go wrong?

[GordMay]

Originally Posted by StuM

Poor use of quotation marks is likely to lead to confusion here. It looks as though you are saying that Pmax is the abbreviation for temperture coefficient.

]Pmax is is the "Maximum Power Point" i.e. the the maximum power that the panel will generate at STC (Vmpp x Impp). It is expressed in Watts. not as multiplier per degree Celsius.

There are actually three Temperature Coefficients commonly found:

Temperature Coefficient of Pmax
Temperature Coefficient of Voc
Temperature Coefficient of Isc.

The first ("of PMax") is the combination of the other two.

Thanks, to StuM & HeywoodJ.

[sailorboy1]

The cooling of the panels of course would increase output.

I have NEVER seen my 640W of solar put out more than about 500W. If a 64W (around 5A pump at 13V) water system really could increase output it would more need to increase output by over 10% just to power itself. Near as I can tell it isn't going to happen.

I don't know what temp the surface of my panels get to, but experience says the peak daily power they put out doesn't change much if it is 75 F out, the STC according to my panel datasheet, or 100 F out. Actually I normally get more total daily power in the 100 F conditions as that is summer and the panels get more sun during the day.

But in real boat life use the question isn't IF the cooling of panels can offset the extra power use and still have power left over for use. The question is whether you can catch and store the extra power plus meeting your battery charging goals.

For me my 640W of panels already have more capacity than I can fully collect into my batteries as the batteries become acceptance limited in the afternoon anyway. I am not interested in providing the max power from my panels, I am interested in meeting my power needs of use plus battery charging requirement for lifecycle reasons.

So to me it is meaningless to think about whether cooling the panels gets me more power.

[valhalla360]

Originally Posted by sailorboy1

The cooling of the panels of course would increase output.

I have NEVER seen my 640W of solar put out more than about 500W. If a 64W (around 5A pump at 13V) water system really could increase output it would more need to increase output by over 10% just to power itself. Near as I can tell it isn't going to happen.

I don't know what temp the surface of my panels get to, but experience says the peak daily power they put out doesn't change much if it is 75 F out, the STC according to my panel datasheet, or 100 F out. Actually I normally get more total daily power in the 100 F conditions as that is summer and the panels get more sun during the day.

But in real boat life use the question isn't IF the cooling of panels can offset the extra power use and still have power left over for use. The question is whether you can catch and store the extra power plus meeting your battery charging goals.

For me my 640W of panels already have more capacity than I can fully collect into my batteries as the batteries become acceptance limited in the afternoon anyway. I am not interested in providing the max power from my panels, I am interested in meeting my power needs of use plus battery charging requirement for lifecycle reasons.

Good point about acceptance. On a land based system backfeeding the grid, you can dump that late afternoon power and get net metering credit for it. On a boat, with an appropriately sized array, you don't need a lot more power out of the array after 2-3pm on a typical day.

I think the combination of solar water heater where the cooling effect is largely incidental would be an area where it might make sense. If the water is picking up say 200w of heating and the increased solar output is negating the pump consumption...it's essentially free water heating (after install costs of course).

[Pete7]

By chance in an unusual heat wave last week in the UK (50'N) I measured the panel temperatures using one of those heat guns. Top of the panel was 28c and the underside was 38c. There may have been some error from the glass reflecting the beam. Panel is mounted on an arch on the stern.

Given the air temperature was 30c, it was mid day and clear sky, this didn't seem particularly hot. Tested by hand as well seemed to indicate the temperatures were about right, certainly not boiling hot. The back of my panels is black were as many are white. Perhaps this helps to cool the panel down.

Be interesting to hear what temperatures others are seeing.

Pete

[mcarthur]

We've looked into this for our flexible panels as a DIY: use 10 or 12mm poly (like on cheaper greenhouse roofs), and run a water line through the 10mm gap or just run water directly. At Stu points out, there's ample evidence for excellent panel benefits from the cooling*, though I haven't seen a cost-benefit since pumping details would be quite difference depending on your scale, height, continuous vs regular, etc. Obviously is only needed when the temperature climbs and the panels are inuse.
A little more difficult for solid panels.

*sorry, would have to look for the research I did before posting

[Dockhead]

Originally Posted by Paul Elliott

We pump salt water through metal tubes all the time -- engine heat-exchangers for example. You could glue the metal tubing to the back of the panels and get significant thermal transfer. This would work to cool the panel and increase the power output.



The question isn't the reliability, it's "will the power gained exceed the power needed to run the pump?" Which is what the OP was wondering. It's a good question. I don't know the answer, but I assume it depends on many factors, including water and air temperature, amount of sunshine, pump efficiency, etc.

Energy to pump could be very little even if the panels are mounted high if the return flow is led right back to sea level to siphon it through.

I would think that properly designed this could be good. Efficiency of the panels falls right off with temp. They get really hot baking in the sun.

[Q Xopa]

I dont know them but Custom Marine Products, their 'Solar water heating system for boats', seem to be doing what is being discussed here. Listed for $649.

Although they are marketing it as a Water heater, they do mention ad a benefit "The circulating water actually cools the panel this increasing its power generation efficiency".

It makes you think if there was enough gain picked from cooling the panels than spent running the circulating pump, then it might be worth having another heat dump for after the water was heated.

I dont know them or how well it works.

[Idaho]

Originally Posted by jeanathon

You could use a chimney to create a draw instead of a fan. The taller the chimney and the hotter the panels the more circulation you would get. Problem would be shading from the chimney.

A black chimney would work best due to sun and thermal effect.

Would a clear chimney work? That would reduce shading of the panels.

[Idaho]

If the warmed water from the panels is for domestic hot water, it can't be recirculated back to the panels. The energy efficiency increases best with cool water.

Slightly preheating the input to the hot water tank may be only a marginal gain. TBD.

[jeanathon]

Originally Posted by Idaho

A black chimney would work best due to sun and thermal effect.

Would a clear chimney work? That would reduce shading of the panels.

A clear chimney would work. The largest effect on draw would be from chimney height.

[jeanathon]

Another consideration would be a "solar pump". A pipe with two check valves when heated and cooled will push then draw water each time it is heated and cooled. On a cloudless day this happens only once but can be many times a day when cloudy.
Isn't physics fun?!

[Rumrace]

Well there are solar panels with fluid tubes but it’s oils oil. Oil to heat them. They proved a bad idea for space but heck was 30years ago. Cooling a panel would increase power a bit. They do expire and might extend life span also. The new Ultraviolet are interesting producing a trickle at night and screaming during circadian light when other panels produce nothing
Brave new world but I think mechanical cooling better

[valhalla360]

Originally Posted by jeanathon

Another consideration would be a "solar pump". A pipe with two check valves when heated and cooled will push then draw water each time it is heated and cooled. On a cloudless day this happens only once but can be many times a day when cloudy.
Isn't physics fun?!

Better would be some sort of wave action based pump but either would tend to be very fiddly.

[valhalla360]

Originally Posted by Idaho

If the warmed water from the panels is for domestic hot water, it can't be recirculated back to the panels. The energy efficiency increases best with cool water.

Slightly preheating the input to the hot water tank may be only a marginal gain. TBD.

Even if the recirculated water is at 100-110F, it may still provide a significant benefit. Looking online, I found indications of temps as high as 150-200F. Even at the lower end, that's a 40degree difference and water absorbs head 25 times faster than air, so it still may provide significant cooling.

And as mentioned up thread, late afternoon (when the hot water would be at it's upper limit), acceptance of the battery bank would likely be way down anyway.

Of course, I still think, the main advantage would be heating water which is energy intensive and you might get a small gain in electrical output.