solar energy conversion rate

[autogda]

HOT days of 100F+: solar energy conversion rate be increased with cooling applied to panels. Is it worth the effort? Allocate some panel power for pump power & heat sinks mounted on panels. Maybe use cpu/gpu cooling pump and heat sink system. Use large amount of water. cool water lower output and upper for input. Can the effort of cooling be better overall power output relative to do nothing?
Be an interesting experiment.

 

[BentleyJ]

The datasheet for each particular solar panel lists the Voltage/Temperature coefficient. It wouldn't be too difficult to calculate the voltage drop of a panel at 40 degrees C instead of the STC value given at 25 C. My guess it's not worth the effort of constructing & maintaining the cooling system. Then there is the initial cost of the equipment and the water usage. What is the payback period?

 

[45North]

What about thermal shock?
If you cool glass (which PV panels are made of) too fast it will shatter!

 

[wattmatters]

Meh. Cheaper just to add a panel or two if you are worried about temp induced losses.

 

[autogda]

I agree with adding a panel.

 

[bradley.cantrell]

I have been thinking about doing exactly this. My primary goal is to extend the life of the cells by keeping them at a cooler temp. 45 North brought up a very interesting thought regarding temp shock and fracturing the cells. I would think this could be overcome by running the cooling systems earlier in the day before the panels get excessively hot. My understanding is the reason panels lose energy production is from years of excessive surface temps (150F ish?) and then cooling down at night causing micro fractures in the PV material. I would think that this could be avoided or delayed by maintaining cooler temperatures consistently?
Here is the plan. I live in the Panhandle of Florida where it gets very hot more often than cold. I am building a 15KW array and since I have eight acres to play with, I was planning on running a 1,000 ft coiled ground loop which would be something around 3000 ft of waterline (Im guessing?) to cool the system. I am going to have to find a plastic water pan that can be glued to the underside of each panel. Inside each pan, water will completely fill the cavity entering from the top and exiting through the bottom. I need to experiment with water nozzle patterns and see if they are even effective when submerged. But a nozzle with a fan pattern to create max water movement across the panel is the idea. Each panel will be reinforced under the pan to prevent sagging or weight stress on the panels. If there was a large heat sync between the panel and the pan, I would imagine heat exchange would be much more effective...but only testing will tell. Water pump would be connected to a photocell to kick on when the sun comes up and off when it sets.
Is it cost effective? Time will tell. Cost of PE pipe + excavator rental + water pans + water pump = hopefully < $3K and extends the life of the panels to 50 years and maybe increases PV output/efficiency? Or have I just lost my mind? Thoughts?

 

[Solar Guppy]

Florida isn't really hot, we are are tempered by the Gulf of Mexico, place like AZ,NM and the like are easily 25F hotter, it may feel hotter, but that is a humidity thing and the way humans regulate body temperatures.

Pump costs and electricity to run far outweigh the tiny increases in energy produced, there is no data I know of that shows lower temperatures to cell increases lifetime.

As for timing, that doesn't do anything, there is little mass in a solar panel, for example you can hose one down and within a few minutes its back to whatever temperature the panel would have been without the cooling from water.

You haven't lost your mind, but solar has been widely installed in all sorts of climate for decades, and liquid cooling isn't used, it is always cheaper to just add panels to compensate for lower production in heat if one actually is generation limited for the application.

 

[bradley.cantrell]

I have lived all over the world and hot is hot. It was hot in the Pacific, hot in West Texas, Hot in Afghanistan (and cold), hot in Iraq (also gets cold!) and hot in Florida. The humidity just makes it suck more. I love Florida AKA Lower Alabama BTW.
I did some math and as much as I don't want to agree because building a geothermal cooling system to maximize panel production is really cool because I am a nerd like that...It does seem easier to just replace a couple of panels every 10 years to make up for the rate of decay. So if someone didn't have the ability to keep their panels at cooler temps via a liquid heat exchange system, then panel swapping would work to maintain power production with the understanding that it comes with a cost and it isn't very difficult in most cases.
On the other side of that coin, if we had the ability to keep panels cool via geo thermal heat exchange and it were cost effective (DIY in my case and for most people installing panels on their roof isn't), we could expect only a 15% loss of power production at the 50 year mark. Thats an annual loss of .025% vs .05%. This is assuming there is enough ground loop or well distance to actually pull heat off the panels and keep them closer to standard testing conditions (77F/25C). That is a boat load of heat exchange considering how hot panels get, but if done properly it would work.
There are studies that show the rate of decay of panels in standard atmospheric conditions which is .5% - .8% per year and it is caused by multiple factors, heat being one of the largest ones. So reduce the heat, reduce cell fracturing, panels last longer. Again, this is assuming there is enough ground loop to achieve appropriate heat exchange. Does power production go up by keeping them cool, yes but the objective is max power output over time/reducing the rate of decay. Not just more power.
In conclusion, I think the question to ask is how much does it cost initially to setup a cooling system vs panel swapping every ten years. Keep in mind, the price of solar panels will only go higher with time. IMO, a solar power system that requires zero maintenance over 50 years (excluding inverters and batteries biting the dust), thats a pretty good deal.

 

[wattmatters]

A liquid heat exchange system would also require maintenance.

 

[bradley.cantrell]

A liquid heat exchange system would also require maintenanceI

I agree, but minimal IMO. How long do circulating pumps last?

 

[efficientPV]

I think of all those who put every panel they can in series and just let the bypass diodes and controller sort it out. I've seen FLIR photos of panels which are loaded down below their power point voltage. Solar panels are just large crappy diodes. There are always weak cells and they heat up the most. Replacing a panel will just be bad luck. Some day MPPT controllers may be called panel killers. Ten years from now we will all have new better technology to put up. So, it doesn't matter.

 

[42OhmsPA]

I think of all those who put every panel they can in series and just let the bypass diodes and controller sort it out. I've seen FLIR photos of panels which are loaded down below their power point voltage. Solar panels are just large crappy diodes. There are always weak cells and they heat up the most. Replacing a panel will just be bad luck. Some day MPPT controllers may be called panel killers. Ten years from now we will all have new better technology to put up. So, it doesn't matter.

Could you expand on this? I'm planning to run 8s2p 315w Qcells. As long as shading isn't an issue, why would running in series be a negative?

 

[TomC4306]

What about thermal shock?
If you cool glass (which PV panels are made of) too fast it will shatter!

I don't see any panels shattering in my backyard when a popup thunderstorm rains on my 100⁰+ panels.

 

[TomC4306]

A liquid heat exchange system would also require maintenance.

A cheap lawn sprinkler from Walmart or Amazon wouldn't. $6.

 

[wattmatters]

I have 40 panels in 2 sets of 10S2P into each MPPT of my Fronius inverter. It's Australia. It gets hot. They and the inverter do a fine job. When it's hot they are less efficient and generation is lower. Exactly how they are supposed to work.

 

[wattmatters]

A cheap lawn sprinkler from Walmart or Amazon wouldn't. $6.

We've had people on a local forum experiment with rooftop sprinklers in the past and water return systems via the gutters and tank water but the power to run them just wasn't worth it. Adding one more PV panel did a better job.

Water is often just as precious as power here, you don't want to be evaporating it any more than you need to.

Most homes with such rooftop irrigation systems have them built for fire protection (for dousing embers from bushfires), and you won't be using a cheap Walmart type of sprinkler for that. Certainly nothing that can melt in a fire and whatever it is needs to be able to cope with a lot of sun exposure over years.

 

[wattmatters]

Here's some research published this year on one system design:

Design and Implementation of Automatic Water Spraying System for Solar Photovoltaic Module

Photovoltaic (PV) cell has a characteristic of decrease in power beyond a certain temperature. This decrease in power is due to a drop in the open circuit cell voltage. This decreases the efficiency of the PV cell. The objective of this research is to increase the efficiency of PV cells by...

www.hindawi.com

This is by no means unique. There are other PV panels with thermal exchange build in. In general people don't bother because the cost is so high for such a small gain.

In this case they gained a 1% efficiency improvement overall. I dunno about you, but all that effort for 1% efficiency improvement?
Just add an extra panel instead.

 

[PlaneBatteries]

It works - I have 2 strings that really could use more panels and normally wheeze out 5- 6 amps in central florida mid day heat and with sprinklers hitting them I have seen 10+ amps after watering them down for a couple minutes.
I have a 275 gallon rain water catch tank with a 12 volt pump for plant watering and car washing so all the components were in place.

 

[Checkthisout]

Be cool to heat water for bathing with the cooling water.