drip irrigation to cool panels?

Re: drip irrigation to cool panels?

I suspect that a number of things would happen to varying degrees. First, the water ont he panels will reduce insolation to some degree. Second, much of the water is going to evaporate on hot panels, and third, the energy cost of pumping the water will most likely negate any benefit.

There are some threads here about commercial hybrid systems that cool the back of PV and use the heat for DHW. Try a search on this forum.

Tony

Re: drip irrigation to cool panels?

And don't forget the mineral buildup that will take place as the water evaps and leaves the minerals behind, caked on, blocking light, and VERY difficult to remove, often requiring an acid to dissolve. Steam distilled water shouldn't leave any buildup, but who knows what it may have been in contact with before you got it. And considering the cost, it might be cheaper to run a small generator.
Good idea, but I fear the cure would be worse than the disease.

Re: drip irrigation to cool panels?

Note of caution, do not rely on information obtained on internet forums .

If the panels are in an area with a low relative humidity, evaporative cooling does work. It would be less effective in eastern areas that end to have high relative humidities. The gas turbine industry uses it extensively. Best case is that if everything is perfect, you may get within 10 degrees of the wet bulb temp. Unfortunately, I dont think conventional drip irrigation would be the best way, I expect you would get more effective evaporation with a fine mist which most likely will require a high presure pump

I sure wouldnt spend a lot of money but it sounds like a fun experiment

Re: drip irrigation to cool panels?

That was one. I think there are some threads here if one wishes to do a search.

t

Re: drip irrigation to cool panels?

rollandelliott wrote: »

Cool. What kind of measurements should I take to correctly test this sort of set up? Also anyone know of an automatic valve that would turn the water on to fill up a tank and turn it off when it was full?

Sure it's called a "Float valve" There is one in almost every toilet, they are also used in swamp coolers, stock tanks, etc.

I'm guessing I'll need to buy a surface thermometer? Recommendations?
Note time of day, location and sun conditions.
For evaporative cooling effect I guess I'd need to measure the humidity and wet bulb temperature as well.

You could measure temperature, but why? What you are trying to do is to boost the output from your panels right? Why not just measure their output to see if it makes any difference.
Simple way to do this, on a clear cloudless day, start with the emitters turned off and measure the output of your array for 1 hour before solar noon. At solar noon turn your emitters on and measure the output for 1 hour after noon.
See if your power increases.

Based on my experience with both swamp coolers and my array, I'm guessing you'll see maybe 1-2% increase in power.

But real world data/measurements trumps guesses and calculations every time.

http://www.zoellerpumps.com/ProductPerformance.aspx?ProductID=90
1/3HP pump is about 250watts.
Assume 200Gal Capacity tank.
Assume 10 drip emitters per panel at 1gallon per hour =10Gallons per hour/panel
For 20 panels that is 200Gallons per hour.
Flow rate with 10 feet of water head (estimate height/head between supply and collection tank is 30GPM, see flow chart on web page.
which means pump will be running 8 minutes every hour, approximately.

I don't think that is going to work. with only 10 feet of head you're only going to see about 4 psi at the emitters. Drip emitters normally need 10-15 psi.
You'll need around 30 feet of head.

I use drip emitters for my vegetable garden. I've tried using them with my rainwater system that provides about 8 feet of head. However, I'd only get about about 1/5 or less of the rated output from the emitters at this low pressure.

So another option might be to use 4 gallon per hour emitters (if you can find them) or just use twice as many 2 gallon per hour emitters.

With that many emitters, your going to see a fair bit of pressure drop due to the tubing. You might need a bit more height to compensate.

I'm betting the mineral build up will be significant. I use swamp coolers during the summer and even with purge pumps (dumps out the water every 8 hours) and adding chemicals to keep the scale in solution I still see about 1/4" of buildup over 3-4 months.

There are chemicals that can dissolve this, but I'd check to make sure they don't eat away at any of the parts on the panels (aluminum, seals, etc.)