Water cooled solar panels.

[Happ]

Originally Posted by Idaho

Boats are surrounded by water.

Why not pump up some water to cool the back of your solar panels?

Would the power to the pump use up all the efficiency gain?

Why would you want to add another complicated system powered by electricity to a boat when there already is an organic non powered system. Solar panels by design are suppose to allow air to flow under them. Kato Davits has already designed some very inexpensive solar panel brackets to raise them above the top of their davits.

[pbmaise]

Originally Posted by Atcowboy

I really like to see that even though this thread got off to a rough childish start, it came back around to OP's question!

I started skimming, love the thought about hot water... Has anyone discussed the potential longevity gains? Even if there were a net loss of power, for some applications a gain in panel life might be worth it.

- AT

I was utilizing German technology and branded panels made in China. I noticed the panels began with nice white colors around the edges and by the first season this had turned to a brownish white.

I noted no performance decrease, however, wasn't taking accurate measurements nor had a controlled laboratory situation.

"A study conducted by The National Renewable Energy Laboratory (NREL) shows a more accurate picture of solar panel degradation. This study took a look at the degradation rates for almost 2,000 solar systems across the world in a variety of climates and found that monocrystalline panels made after the year 2000 degraded at a rate of just 0.4% - less than half of the 1% rate used in the warranties."

Therefore, I would say the answer is there is little to be gained in regards to degradation to keep the panels slightly cooler.

Most people like me are thinking that producing some hot water as a result of the cooling as a byproduct is the greater benefit.

[Bloodhound]

Originally Posted by Idaho

Must have missed "back of the panel".

When reading, comprehension is the key to understanding.

😂 yes, so is reading !!!

[Bloodhound]

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.

Power needed only to overcome friction loss through the tubing. Upflow assisted by syphon on downflow assuming tubes run full. So minimal power needs.

[Atcowboy]

Originally Posted by pbmaise

I was utilizing German technology and branded panels made in China. I noticed the panels began with nice white colors around the edges and by the first season this had turned to a brownish white.

I noted no performance decrease, however, wasn't taking accurate measurements nor had a controlled laboratory situation.

"A study conducted by The National Renewable Energy Laboratory (NREL) shows a more accurate picture of solar panel degradation. This study took a look at the degradation rates for almost 2,000 solar systems across the world in a variety of climates and found that monocrystalline panels made after the year 2000 degraded at a rate of just 0.4% - less than half of the 1% rate used in the warranties."

Therefore, I would say the answer is there is little to be gained in regards to degradation to keep the panels slightly cooler.

Most people like me are thinking that producing some hot water as a result of the cooling as a byproduct is the greater benefit.

Oh that is interesting information! I guess the rumor mill had me thinking/misinformed that my panels (renogy, with substantially clear airflow paths) were roasting away once my batteries were full. Instead, the outlier would be panels that need that thermal help. Maybe directly mounted/bedded flex panels, especially if the boat spends a significant amount of time in a calm area with little airflow.

I definitely could put the hot water experiment on my to do list.

- AT

[betwys1]

Originally Posted by Idaho

Boats are surrounded by water.

Why not pump up some water to cool the back of your solar panels?

Would the power to the pump use up all the efficiency gain?

Let's do a quickie estimate.

The max solar panel power loss with temperature is 0.25% per degree Celsius on average.
We suppose a 100 watt panel; 20 degC seawater; panel temp in full Sun 35 degC; practical temp reduction 10 degC, leading to practical max power output gain of 10 X 100 X 0.0025 = 2.5 watts.
If I pick a small DC brushless pump using 12 watts, I would need to cool five 100 W panels to break even.

Well! A numerical estimate after five pages of opinion which contained about three postings of useful pointers.

Here's another more optimistic finding:
The average conversion efficiency of solar panels is 15% so each 100 W panel rejects 100 X 100/15 = 660 watts of heat. Suppose half escapes in front and half in back.
A water circulator may collect 10% of the back heat flow - say 30W per 100W solar panel. This is much more than a marginal payback for a person who can plumb an insulated water reservoir.
Moral: forget the max power gain - use the hot water.

Brian W

[sdutton]

There’s a company called DualSun that makes hybrid water cooled solar panels. Create power and use that hot panel to create hot water.
Years ago I remember reading an article about a residential solar panel installation that snaked copper tubes underneath the panels on the roof in order to have solar hot water as well as solar power.

[Paul Elliott]

Originally Posted by pbmaise

"A study conducted by The National Renewable Energy Laboratory (NREL) shows a more accurate picture of solar panel degradation. This study took a look at the degradation rates for almost 2,000 solar systems across the world in a variety of climates and found that monocrystalline panels made after the year 2000 degraded at a rate of just 0.4% - less than half of the 1% rate used in the warranties."

Yes, but isn't this looking at degradation during the panel lifespan, rather than the panel efficiency vs cell temperature we've been discussing here?

What I find interesting is that panel self-heating is worse when the panel is unloaded or lightly-loaded (disconnected, or when the battery has reached full-charge). Self-heating is minimum when the panel is short-circuited.

This information isn't particularly useful, but perhaps counter-intuitive.

[GordMay]

Originally Posted by sdutton

There’s a company called DualSun that makes hybrid water cooled solar panels. Create power and use that hot panel to create hot water...

DualSun ‘SPRING’ ® Hybrid photovoltaic/hot water panels
➥ https://dualsun.com/en/product/hybrid-panel-spring/
➥ https://my.dualsun.com/en/resources/#spring

[patmvcr]

I didn't have the patience to read all of the comments.... but I've often wondered why nobody has developed floating Solar panels. They could be deployed when at anchor.. folded up and put away when under way??? you could have quite a large array....

[LifePart2]

Originally Posted by betwys1

Moral: forget the max power gain - use the hot water.

Brian W

Exactly.

For a long time I have pondered doing this. My idea is to put a sheet of acrylic on top of the panel. Seal the edges all around, and then circulate fresh water through the gap between the panel and the acrylic and down to my hot water tank. With the syphon effect the pumping needs would be very low. There would be some gain in efficiency, so maybe the pumping needs would be paid for.

And there would be as much hot water as one needs!

Certainly much more efficient than using the solar electricity to run an actual water heater.

The only downside I could see was the cost and effort of building the installation, which is why, as yet, I have still not done it.

[pas63]

I didn't read through all 5 pages of this thread but what I did read is why I rarely post anything. You get hundreds of responses from people that have no knowledge but feel the need to respond, smart asses that just want to contribute nothing useful and a lot of people that think they know but don't.

In answer to the original question -> https://www.custommarineproducts.com...for-boats.html

[blueskymessenge]

Let’s do some real facts with real testing. Having bought recent panels and run some real-life tests on them let’s look at some actual facts and figures from testing. First the panels are 135W and are PET, Flexible Solar Panel 18V Module Monocrystalline supposedly marine (but at the price $100, they are near disposable every few years). Size: 1129*670mm (44.5”x26.4”), supposedly assembled from SunPower cells and advertised falsely on eBay as 350w. Real testing using a Victron 250/100 MPPT shows them as 135W which corresponds directly to the proper power for this size and number (9x4=36) of cells and the actual panel size. I am sure they are of dubious China quality. You can be purchase these for a mere $80 at this site: https://www.yyw.com/product/Polyprop...-_p602561.html or via eBay (looking for 350w panels). Having run a number of these through their paces they do get very hot. BTW if you do buy a bunch of these or other cheap China panels, plan on changing their bypass diodes as they come with a single petty 40v Schottky diodes. Hooking 5 panels or 10 in series (as I will do to max out the MPPT and allow much smaller wiring) of these 18v means you need Schottky diodes upwards 250v. In this case buy some 20A10 which are a 1000v with a reasonably small reverse current (20A10 BOJACK will do). Having a single panel bypass diode on a sailboat with this many panels in series delivers some reasonable charging results and the loss a panel or two from shading with such bypass arrangements, seems to work well.
Actual testing on a bright, cloud-free day, at noon with 5 panels connected in series showed them starting 75°F peaking under heavy (max MPPT) load rising temp to about 190°. These solar panels do have a power loss of about 0.25% per degree Celsius on average. So prior commentors’ guesses wrong, that’s 190F-75F=115F temp (=46C shift) ; which is just over 11% due to heat loss. This corresponded to the actual recorded Victron MPPT power loss which it graphs quite nicely. The MPPT showed power dropping from the initial watts per panel of 115w to just over 100w when they maxed out on the temp.
I did not angle the panels which might have gotten another 15watt out of them, but the wattage drop due to temperature change is noticeable and a bit disconcerting. I covered the panels, let them cool and repeated the test a second time with nearly identical results. It only took about 15 minutes for the panels to max out on their temperature when fully loaded. Oddly, the earlier comment about no load also appeared to be true, as under no load the panels got nearly just as hot and just as fast.
The 15w loss I measured is more than enough to justify cooling the panels using a 12v 3.6W Ledgle brand fountain pump which puts out 240L/H (64 gal/hr) and has a 9’ max head lift. If the cooling loop is sealed and the input and output levels are both water level then the head lift is actually near 0’ (assume both lines run under the waterline and once primed the weight of the input side and output side are equal so virtually no lift, only circulation pressure resistance).
As a result of the latter, I am contemplating gluing them, as RV campers have done, on top of some LEXAN Thermoclear 1/4 in. Clear Multiwall Polycarbonate Sheet (Homedepot). These sheets will support full body weight as they are channeled with ~6mm rectangular channels (a honey comb rigid material). https://www.homedepot.com/p/LEXAN-Th...MMCL/205202473 . I have yet to run the test with just air flow as these were going to be mounted on my biminis. My hope, as RVers have shown, is that the air channels under the panels with movement provides ample cooling to warrant the minor cost of the polycarbonate sheet. But since the discussion has gone this far, sealing alternate ends of the polycarbonate and shoving a tube in and out of each panel and using water cooling certainly is justified by the wattage gained.
The earlier argument made about panels putting out more than your battery bank can absorb is most valid, but most of the larger cruisers, switching to LiPo house banks and adding more refrigeration and/or A/C or inverters supporting whatever devices…, well most of us, as I can show, will eat a full 2.5k watt per day, -- and to get that back on most sunny days will really take as much of the panel as she’ll give.
I’ll post more about my experiment with the polycarbonate air test. And if I do a water test, I’ll post again as to what the results showed.

[tdotson]

I think you guys are missing the point. It is not a mater of whether the panels will be more efficient, how about hot water for showers without ever running your engine? I have spent a week at anchor and did not start my engine or generator once and had all the hot water we needed.

When I installed my solar I bought from Custom Marine Products their solar water heater. This is a copper coil that mounts on the back side of the fixed panel. I then added solar insulation and caped it off with what looked like plastic cardboard (often used for outdoor signs). I then T’d into my hot water lines at the water heater. Add a small pump and some 1/4 in tubing with some ball valves here and there. The system comes with a temperature probe that reads the temperature of the panel and turns on the pump when the panel gets hot. I have seen the panel drop by 30 degrees and will give me water in the 110 range on a sunny day. One problem, if the panel temp drops below the water temp, it will start cooling the water. I added a timer so that it shuts off as the sun sets.

When we are motoring I shut the system off so I am not pumping hot water to my panel.

It sounds complicated but I did it myself. The good folks at Custom Marine Products talked me through it and I could not be more pleased .

[HeywoodJ]

The heating water for your shower argument may result in less power from your solar installation. Open-loop cooling from the sea will almost certainly result in more power. But closed loop in your domestic hot water system could result in less power. While you are getting up to maximum water temperature you should certainly see improved electrical production. But once you reach that temperature you now have something on the back of your panel blocking heat dissipation. And if it is the CMP product you've added insulation below the heat exchanger, further reducing heat transfer to the air from the back side of the panel. If you're already at the point where your batteries can't accept all you produce then probably no loss. But if you are still in bulk then the increased heat once the domestic water is hot will reduce power output. Timing of when that all happens will tell whether you come out ahead or behind.

Solar modules are designed to lose heat from the back of the module. They are designed with air flow there in mind. And with backsheets that perform specific functions. Not allowing unused energy to pass through the backside, and not allowing air flow are detrimental to cooling of the panels as designed. Can it be done? Yes. Is it as simple as slapping something on the back of an existing module? Not likely.