drip irrigation to cool panels?

rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
Be nice cause I'm a noobie and this is probably a dumb idea, but has anyone hooked up a drip irrigation system to the top of PV panels that are on the ground?
like photo below?

55 Gallon rain drums are $10 off craigs list, PVC pipe and joints might be another $30? and $100 for a sump pump?
c8d28ec372.jpg

Comments

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    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
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: drip irrigation to cool panels?
    Be nice cause I'm a noobie and this is probably a dumb idea, but has anyone hooked up a drip irrigation system to the top of PV panels that are on the ground?
    like photo below?

    55 Gallon rain drums are $10 off craigs list, PVC pipe and joints might be another $30? and $100 for a sump pump?
    c8d28ec372.jpg

    I've seen a couple examples of where this has been tried, but the improvement in performance doesn't justify the energy and water requirements to operate it.
    Note that you'll have to clean your panels more frequently, because as the water evaporates it will leave the minerals behind coating the glass on your panels. These mineral deposits are a pain in the ass to clean off.

    I'd thought about a similar panel cooling idea, running copper pipes along the back of the panels with heat spreaders, like they use for sub floor heating. Then circulate water from a larger holding tank or pool.

    However, it's not worth the effort.
    You'll probably only see a 5% improvement in power output and it will take most if not all of that to run the pump.

    Combined with your idea for using mirrors, this might be beneficial but I don't think it would be cost effective.
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    I live near Charlotte, NC. in the summers we get temperatures around 95 F frequently. I imagine the temperature of the black panels would be 140 F or so on days like that.

    What is the performance difference between 140F panels and 85 F panels?

    I'm sure somene has put a hose or sprinkler to clean off their panels and seen how much it improves?

    Just curious what kind of power losses we are talking about?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: drip irrigation to cool panels?

    One of the biggest problems with cooling panels in order to increase efficiency is that panels are made of glass, and glass doesn't conduct heat very well. So you have a heat build up on the silicon wafers which travels poorly through the glass before it gets to the outside where it can be dissipated. To over come this inefficiency of heat transmission there has to be a significant increase in temperature differentiation between the wafers and the outside air. To put it simply, it has to be very cold around the panels in order to take away enough heat from the electricity producing part to make any significant improvement.

    Even panels in "cool" air generate heat inside and drop in power. The superconductivity you hear about is a result of very cold temps. Any type of radiant or evaporative cooling will not decrease internal panel temps sufficiently to make the effort worthwhile. You simply can't get enough temperature differentiation.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    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.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: drip irrigation to cool panels?
    I live near Charlotte, NC. in the summers we get temperatures around 95 F frequently. I imagine the temperature of the black panels would be 140 F or so on days like that.

    What is the performance difference between 140F panels and 85 F panels?

    I'm sure somene has put a hose or sprinkler to clean off their panels and seen how much it improves?

    Just curious what kind of power losses we are talking about?

    85F = 29.4C and 140F = 60C. Most crystalline Si module manufactures quote a temperature coefficient of Voc (heat performance degradation) of about -0.30 to -0.40%/degree C above STC (25C). Assuming the middle of this range:

    29.4C - 25C = 4.4C, (4.4)(-0.35) = 1.5% degradation @ 85F
    60C - 25C = 35C, (35)(-0.35) = 12.25% degradation @ 140F

    Approximately, of course.

    One thing to consider is that these numbers refer to cell temperature. Cooling the glass front on a module does not necessarily translate to lowering cell temperature by the same amount. Also, when the ambient temperature is 85F, in direct sunlight the cell temp is considerably higher.
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    http://www.youtube.com/watch?v=uOeKytIHp2g

    interesting video showing real world preformance increases of cooled panels using water/hose.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: drip irrigation to cool panels?
    interesting video showing real world preformance increases of cooled panels using water/hose.

    Note of caution: do not rely on Youtube videos as a source of accurate information.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    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
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: drip irrigation to cool panels?

    The issue with the video is the first reading of 3450 watts was at 1:00pm which is before solar noon and after the cool down you have two effects

    First is the voltage increase, this is expected
    Second is the increase in irradiation as your closer to solar noon

    Quick math shows
    3450 watts at 270v is 12.7 amps
    3990 watts at 300v is 13.3 amps

    so to calculate the increase to lower temperatures you have the 30V difference, cooling panel will not increase the current only the voltage

    The 3450 reading would increase to 3810 , the remainder is due to being closer to solar noon which is about 9.5% ( voltage increase ) vs 13.5% ( voltage and time ) pretty big difference

    Regardless, its just what panels do and it will always be cheaper to add panels to compensate for hot climates vs some system to cool the panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: drip irrigation to cool panels?
    peakbagger wrote: »
    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

    No one ever said evaporative cooling doesn't work. But it has been quite clearly explained why you shouldn't expect much improvement in solar panel output from it.

    And if you think the information provided on this forum is unreliable you don't "surf around" much! :p
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    Obviously some videos are opinionated, but so are the posts on this forum.

    his video however is pretty stragiht forward and I'm puzzled why anyone would flag it as being potentially inaccurate.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: drip irrigation to cool panels?
    Obviously some videos are opinionated, but so are the posts on this forum.

    his video however is pretty stragiht forward and I'm puzzled why anyone would flag it as being potentially inaccurate.

    Read Solar Guppy's post.

    For a test of this type to be valid you'd have to use a controlled light source, which the sun isn't. That way you could be sure that the panels were under the exact same irradiation under both circumstances.

    My comment was aimed at Youtube videos in a more general way. And yes posts on this forum are opinionated; generally biased towards the laws of physics, years of experience, and practical applications. We do not like to see people get fooled, ripped-off, or waste a lot of time/effort/money.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: drip irrigation to cool panels?
    icarus wrote: »
    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

    Tony, you mean this:

    http://www.sundrumsolar.com/

    It would be interesting to find out if anyone has tried this.

    John
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: drip irrigation to cool panels?

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

    t
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    Are there any photos of the sun drum unit's and how they thermally suck off the heat from the panels? It would be neat to see!

    Since no one has tried this when I get my PV system installed I'll try to hook up a drip system and see how well it works and report back. I think it will work better than many theorize on this thread.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: drip irrigation to cool panels?

    Here is a google search for SunDrum on our forum:

    http://www.google.com/search?q=sundrum+site%3Awind-sun.com

    That is the same as typing into Google:
    • sundrum site:wind-sun.com
    Very handy on many sites to use Google search when the site search tools are a little more basic.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: drip irrigation to cool panels?

    Here is about 60 pages on someone else's attempt to do sort of what you are considering. He hasn't check back in a couple of years so my guess it it didn't work out too well.

    http://forum.solar-electric.com/showthread.php?t=5185&highlight=water+cool+panel
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    Thanks for the link, but whether someone reports back or not has nothing to do with whether the project was successful, Besides, They could obviously lie about the results as well, or fabricate data, etc.

    It might cost $20 and a few hours of time to test, a 50 gallon drum and some pvc pipe is all that is needed. A sump pump can be bought if the data concludes it is worthwhile.....nothing that expensive nor complicated and will satisfy the tinker er in me. Might just put a 5 gallon bucket on top of my car's windshield and see how much the glass cools down to start off with.

    but I can see why people never try, too many posts say it won't work, that a sump pump running 10 minutes a day will negate any gains, that mineral deposits will build up to fast, etc, etc. Possible, but unlikely IMHO.

    Cheers to all those that test their hypothesis :)
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: drip irrigation to cool panels?

    We await your results,,

    Tony
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    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? I'm going to need some sort of replenishing water since a lot of water will be evaporating off the panels.

    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.

    Measure before and after temperatures
    Also measure Watts that are displayed on inverter before and during cooling?

    Is my calculation below for energy used by pump correct?

    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.

    Assume 10 hrs per day run time which means 80 minutes per day =1.33 hrs.

    250watts x 1.33 hrs = 332.5 Watt hrs.

    That is approximately the amount of energy produced by one 215 Watt panel in 1.5 hours. Start up energy will make it less effcient. Which is around 1.5% of the total arrays' output. Replenishing valve will take some energy as well, but not much.

    Of course buying a kilowatt meter would be more accurate

    What remains to be seen is maintenance issues, mineral build up, etc...

    Anything else I am missing?
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: drip irrigation to cool panels?

    Measure the panel voltage and current.

    Also these measurements should be done on a modern mppt type controller.

    Cooling the panels only will increase voltage, and reduce current by a little bit.

    Any other changes will be the results of other variables such as controller algorithms, changes in solar radiation and such.

    You might want to have a similar your panel connect to a logging amp meter. A dead short panel's current is pretty much equal to solar radiation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: drip irrigation to cool panels?
    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.)
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: drip irrigation to cool panels?
    BB. wrote: »

    You might want to have a similar your panel connect to a logging amp meter. A dead short panel's current is pretty much equal to solar radiation.

    -Bill

    Umm, doesn't that drastically increase the temperature of the panel? You're basically turning all of your generated power into heat in the panel.
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: drip irrigation to cool panels?

    "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. "

    Thanks for the other tips, but I'm not using drip emitters. I'm going to be drilling holes in PVC pipe that drip the water out, very low tech.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: drip irrigation to cool panels?
    Peter_V wrote: »
    Umm, doesn't that drastically increase the temperature of the panel? You're basically turning all of your generated power into heat in the panel.

    Actually, for crystalline solar cells, the current is slightly positively affected by increased temperatures... For a generic Mono-Crystalline panel:

    Temperature coefficient of Isc (0.065±0.015)%/ºC

    Current is pretty stable for temperature (about 1/10th that of change in voltage).

    And Isc is ~ 1.1*Imp ... So, since Isc is only slightly higher than Imp--there is not much difference in dissipated power (approximately 20% more power because of Isc measurement--but that is still compared to ~80%+ of heat absorbed directly from the sun) in a solar panel between a panel running at Imp vs Isc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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