1 kw per square meter

StevenB
StevenB Solar Expert Posts: 71 ✭✭✭✭
in Solar Beginners Corner #1
I read that the sun's energy produces 1000 watts per square meter of surface. If that's correct then a theoretical 100% efficient panel operating under 100% conditions is limited to 1kw/sq m?

So other than clear sunlight, at a direct angle, and acceptable ambient temperatures........what are the variables in the panels themselves that I should be aware of when considering a purchase?

Since my few current panels are ground mounted (and battery hybrid), I intend to add to them as my budget allows. What should I know about adding future panels, if my current choice model is discontinued or improved technology makes sense to change panel type? I assume it's not good to mix panel types on a single controller.....so is it just a matter of using a separate controller when adding panels of a different type?

I'm looking at adding with REC 220's.....I've been told they are good panel with a likelihood of maintaining over time as a product version. I'm going to add 6 the first go around, and Xantrex sizing tool says I can put 3 modules together on as many as 5 strings.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #2
    Re: 1 kw per square meter

    That is about the accepted answer.1000 w per sq/m
    Main thing to look for with panels is output voltages and current ratings ,, its important to only connect ones that are very closely rated or the system only operating at what ever is the lowest rated panel. that is not 100% accurate in every way but close enough to go by..
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: 1 kw per square meter

    Mixing panels is not the best solution,, but there is nothing wrong with it,, as long as they are close on Vmp. Any parallel string will "default" to the lowest Vmp in the string, leading to potential losses of efficiency. (This if I understand Bill's explanation correctly!)

    I myself have a hodge podge of 3 different panel systems on a string of only 5 panels!

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #4
    Re: 1 kw per square meter

    And to clarify my earlier less that clear remarks...

    The power curve is flat enough that if the panels are within ~10% of each other for Vmp/Imp--you will not lose very much energy overall.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #5
    Re: 1 kw per square meter
    StevenB wrote: »
    I read that the sun's energy produces 1000 watts per square meter of surface. If that's correct then a theoretical 100% efficient panel operating under 100% conditions is limited to 1kw/sq m?

    I believe that number is for a square meter "at the equator" at "solar noon".

    Other places at other times will be less. Even at the equator at any time other than solar noon the insolation will be less.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: 1 kw per square meter
    dwh wrote: »
    I believe that number is for a square meter "at the equator" at "solar noon".

    Other places at other times will be less. Even at the equator at any time other than solar noon the insolation will be less.

    Not always less depending on time of day/ latitude etc. You could have better insolation on the tropic at the solstice than at the equator on the same day. I do believe that we are picking nits however.

    Tony :p
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #7
    Re: 1 kw per square meter
    icarus wrote: »
    Not always less depending on time of day/ latitude etc. You could have better insolation on the tropic at the solstice than at the equator on the same day. I do believe that we are picking nits however.

    Tony :p

    I stand corrected. Somewhat corrected that is, there is still that annoying squeal from the brakes. :D
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #8
    Re: 1 kw per square meter

    Silicon panels with 13-14% efficiency are about state of art. Hubble space telescope has GaAs panels that are about 25% efficient (and cost very big bucks).

    The higher the panel temperature the worse the efficiency because the parasitic diode voltage drops at at about -2.5 mV per deg C. Most panel power is spec'd at 70-80 degs F which is usually a lot lower then normally seen. (at least in FLA). Each silicon cell operates between 0.35v (hot) to 0.55 vdc (cold). This is slightly below the voltage where the parasitic diode starts to significantly conduct. The MPPT controller's job is to find this variable 'sweet spot' no matter what the panel temperature and solar flux is.

    Then there is humidity haze, smog, and dirt build up on panel. In morning and afternoon there is more atmosphere to penetrate due to look angle.

    Bottomline, there are a lot of ever changing variables.
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