Solar Power Output Help

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Hello,
If I have 12- 72 watt panels, each made up of 40 cells @ 1/2 volt each and 1.8 watts per cell, 3.6 amps, 20 volts, 72 watts per panel and all panels hooked up in series. I then send my power via 2- 4/0 THHN wires to a 100 amp disconnect and then into a 40 amp circuit breaker, from there into 3- 400 watt grid tie inverters, what would be my expected watt output going into my home be?
The reason I ask is on the best of sunny days I am only getting 240 watts output from my grid-tie inverters. Now my amps are between 40 and 43 amps, I know this because I am using a kill-a-watt meter to check output. I thought I my watt output would be around 700 to 800 allow for efficiency loss in the inverters.
Can you shed some light on this for me?

Thanks in advance,
Shane
:D
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Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: Solar Power Output Help

    It sounds like you are using homemade panels coupled to non listed "grid tie" inverters.

    With the homemade panels there is little way of knowing what they are likely to put out. Personally, there are better measuring devices out there for panel output rather than a Kill-a watt. For example, if you were to measure the current output of each PV and know what the voltage out put is, you could then calculate what it is really putting out as opposed to what you think it should.

    I might add that the out put of a good, name brand panel rarely nears 100% of rated, 80% is closer to an average. I would guess that a home made panel the out put would drop even further, maybe closer to 50%.

    Please describe your system a bit more in depth.

    Tony

    PS. If you take a normal panel efficiency of 80%, 864 watts of panel might put out ~ 690 watt, run that into a 80% ef inverter you might see on an ideal day ~ 550 watts. So I am guessing that your panels are probably not putting out nearly what you think they are, and the inverters are probably eating a lot as well.

    You do realize that these no listed components are illegal to be connected to the grid? They present a danger to you and to the utility, and would most likely void your insurance if there ever was a fire.

    T
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Solar Power Output Help

    These sound like homemade panels. Yes?

    If "yes" your expected output will be zero with a grid-tie inverter because it is not legal to connect them.

    Otherwise twelve 72 Watt panels would be 864 Watts, or about 665 Watts after typical derating is considered. This might be enough to run two 400 Watt GT inverters, but not three. You also would need three separate arrays for three separate inverters; you can not parallel the DC inputs. The input Voltage to the inverter must be above its "on" threshold too. You should not be seeing 40 Amps current out of an 800 Watt array wired for 240 Volts. 4 Amps maybe.

    I suspect this is an illegal "guerrilla" install. It isn't wired right and it isn't functioning right. If all that's happened is a few burned out panels or fired inverter consider yourself lucky.

    Sorry, Shane, but it sounds like a total mess that should be tossed.
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #4
    Re: Solar Power Output Help
    spotter wrote: »
    Hello,
    If I have 12- 72 watt panels, each made up of 40 cells @ 1/2 volt each and 1.8 watts per cell, 3.6 amps, 20 volts, 72 watts per panel and all panels hooked up in series. I then send my power via 2- 4/0 THHN wires to a 100 amp disconnect and then into a 40 amp circuit breaker, from there into 3- 400 watt grid tie inverters, what would be my expected watt output going into my home be?
    The reason I ask is on the best of sunny days I am only getting 240 watts output from my grid-tie inverters. Now my amps are between 40 and 43 amps, I know this because I am using a kill-a-watt meter to check output. I thought I my watt output would be around 700 to 800 allow for efficiency loss in the inverters.
    Can you shed some light on this for me?

    Thanks in advance,
    Shane
    :D

    Where did you find a 40 amp DC circuit breaker rated for 400+ VDC? I've been looking for something like that.

    Also where the heck are you seeing 40 amps? That shouldn't happen anywhere in the circuit you described. I can't see how you be seeing anything more than 1/10 of that.
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