New 3.84 kW system online

rprr
rprr Registered Users Posts: 14 ✭
in Grid Tie and Grid Interactive Systems #1
We finally got our 3.84 kW system online after almost 2 months waiting.

http://enlighten.enphaseenergy.com/public/systems/5W6a21534

Location: Hawaii, Big Island on the Hilo Side

Some details: We have 16 Sunpower 240 Watt panels with Enphase M210
inverters. Ideally DC output should be 3.84 kW. The maximum rated
output for each inverter is 210 W but I read that it can put out about 5% more which
is roughly 220 W. Thus the ideal total AC output will be 220*16 = 3.5
kW.

Today was a great sun day here. We produced 22 kWh.
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Comments

  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #2
    Re: New 3.84 kW system online

    Congratulations! 22K the very first day, most excellent. You'd think when a new system went on line it would rain for a week. ;) They should put a snack bar at the Enphase website..... you'll be camping out there a lot until the honeymoon is over.
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  • autoxsteve
    autoxsteve Solar Expert Posts: 114 ✭✭✭✭
    #3
    Re: New 3.84 kW system online

    Nice to have you on board!

    You system is a little smaller than what I've had operating for over 3 years and I must say, that you're in for some pleasant surprises in these systems consistent performance and reliability.

    I'll have to look you up when we're on the big island vacationing!
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #4
    Re: New 3.84 kW system online

    Thanks for the welcome.

    Unfortunately, it is not so good today. Sky is totally cloudy and overcast. Output is about half of what it was yesterday :grr
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #5
    Re: New 3.84 kW system online

    I have a question about the total power reported. Yesterday and today the total reported by Envoy/Enlighten is about 40 kWh. However, the utility net meter reports that 33 kWh was sent to the grid. Can the loss in power (17.5%) be this large? Thanks.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #6
    Re: New 3.84 kW system online

    If it is a net meter:
    • 33 kWH Utility Meter - 40 kWH Envoy = -7 kWH used by home
    Or is your home on another meter?

    In general, your various meters are probably around +/- 2% accuracy. So, 40kWH*2%=+/-0.8kWH margin of error (for enphase).

    The Utility Meter could be off in the oposite direction (by 0.66 kWH)--so worst case error could be in the 1.46 kWH range (probably not this bad).

    So, ~7kW difference would seem to be used by the home or some other issue (~210 kWH per month--a fairly low home power usage by US standards).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #7
    Re: New 3.84 kW system online

    BB -- Many thanks.

    Doh...

    The house has only one meter. Over the past two days this is what the meter shows on a rotating basis
    12 --> I assumed that this is received from grid
    33 --> I assumed that this is exported to grid
    99979 --> this makes sense as it started at 00000 and net 21 kWh was exported.

    However, Envoy/Enlighten reports almost 40 kWh generated. I must have used the 7 kWh. Thus my total consumption over the two days was 19 kWh. Is that correct?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #8
    Re: New 3.84 kW system online

    I am not sure how your meter works... But, to take a guess with the numbers you have given. Knowing that your array produced 40 kWH...
    • 12 kWH => power used from grid (when loads less than solar power--heavy loads / at night power consumption)
    • 33 kWH => power shoved to grid (when solar power greater than loads--daylight power production)
    • 40 kWH produced - 33 kWH sent to grid + 12 kWH used from grid = 19kWH home load
    The other register on your meter started at 00000kWH and now reads 99979kWH:
    • 100,000 starting reading - 99,979 kWH next reading = 21 kWH (excess) power generated
    So:
    • 19kWH used by home + 21 kWH excess sold to utility = 40 kWH generated by array
    19kWH used calculated from the various sources sounds very similar to the -99,979 kWH generated [deleted line---Was typing something else as I was figuring out the data -Bill]

    This assumes your meter has three "registers" and they behave in the manner I have guessed... I could very well be all wet.

    It will be interesting to see how your utility calculates the bill (double check, some utilities seem to get the first month or so worth of bills wrong and require complaints to get them right).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #9
    Re: New 3.84 kW system online

    Bill -- Many thanks with your clear explanations. Thus far, I am thrilled with my system.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #10
    Re: New 3.84 kW system online

    The Envoy is a bit optimistic - I think somewhere around 3% based on the numbers others have seen when compared to a utility grade meter.

    There seems to be a rather substantial difference in production between panels - are any of them shaded? It doesn't look like it from the power output charts.
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #11
    Re: New 3.84 kW system online
    drees wrote: »
    There seems to be a rather substantial difference in production between panels - are any of them shaded? It doesn't look like it from the power output charts.
    I did notice that as well. Nothing should be shaded as far as I can tell. I will check over the next week or so and if this different persists, I will try to raise the issue with the installer.
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #12
    Re: New 3.84 kW system online
    drees wrote: »
    There seems to be a rather substantial difference in production between panels - are any of them shaded? It doesn't look like it from the power output charts.


    When I got my 230 watt panels each one was marked showing the power that it put out. I bought mine in two batches. The first 15 were between 229 and 234 watts each, the second batch of 15 ran a little higher at 233 to 237. You do seem to have a larger variance, but perhaps that's normal for those panels. Did you notice if they were marked from the factory?

    While we are here..... this is where the Enphase makes extra power. In a "normal" system, you would lose most (all?) of the output above the lowest panel.

    I attached a couple of screens shots for you in case you want to show the installer. At 13:45 the first day you had what I'm guessing were a couple of odd clouds. Again, for those few moments you'd have lost wattage from the entire array if not for the Enphase. Fun stuff!
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #13
    Re: New 3.84 kW system online

    Frxddy -- Thanks very much for the screenshots. I will definitely show them to the installer. Unfortunately, I was not present when the installer came so I don't know if those were marked. I had never thought about any advantages the Enphase would have with clouds. I live in a place where clouds come and go all the time.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: New 3.84 kW system online
    Frxddy wrote: »

    While we are here..... this is where the Enphase makes extra power. In a "normal" system, you would lose most (all?) of the output above the lowest panel.

    how do you figure that? i believe, if my memory serves, solar guppy made tests and small variations in voltage and current are not lost in a series string and he did that with pvs that were essentially different pvs. sg, please clarify what i'm remembering here.
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #15
    Re: New 3.84 kW system online
    niel wrote: »
    how do you figure that?

    From reading. (I did leave a question mark in there.) But, Tt be clear, what I meant was with a central inverter if all panels are putting out 150 watts, then a shadow covers one panel making it produce 100 watts, then all panels will now produce 100 watts. The question mark was because I'm not sure if it's actually exactly the full drop for every panel.

    Here is a quote from an article at: http://www.solartown.com/learning/solar-panels/choosing-between-a-central-inverter-and-a-micro-inverter

    Quote: "There are also many negatives that go along with a central inverter. One weakness is that when one module in a solar array is slightly shaded, its energy output can drop 50%. When this occurs the output from the entire array can also drop 50%--just because of one shaded module."

    With some web searching you will find this same information from many sources. This is the one reason that micro inverters claim an increase of 5% to 25% over a central inverter. 25% is probably optimistic, but certainly there is some advantage. As clouds pass over an array a micro inverter system has the advantage of each panel being a separate system.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
    Re: New 3.84 kW system online

    no, that won't be the case unless each pv has an equal shadow to drop the same power in each pv. the shadowed pv will be either partially or totally bypassed, by way of the bypass diodes in it, with the remaining pvs allowed to continue producing their nominal power that is allowed to pass through these bypass diodes unimpeded excepting a small voltage drop for each diode it passes through.
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #17
    Re: New 3.84 kW system online

    Yes, by pass diodes help, but only a certain amount. Here's another quote & website:

    http://www.renewableenergyworld.com/rea/news/article/2009/02/shade-happens-54551

    " Just 10% shading of a solar array can lead to a 50% decline in efficiency..... the typical installation is equipped with "bypass diodes." These reroute the current around the underperforming cells. The catch is that rerouting the current loses not only the potential energy from these cells, but also lowers the entire string's voltage."

    From all I've read, by using micro inverters, if you have 10% shading, you lose 10% power, but with a central inverter the loss is much greater. I don't want to quote anything from a microinverter manufacturer website as it could easily be taken as "hype", but for any of those websites better efficiency dealing with shadows is a major selling point.

    I am new to this and I do want to know the facts. If I and the many articles I've read are totally off base, please show me the source of more accurate information.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #18
    Re: New 3.84 kW system online

    It sort of depends... With central inverters and large wattage solar panels, it is possible to put all panels in series. In this configuration, shading of one panel will not usually do any more than kill just the output from that one panel.

    If you have parallel strings (say to strings of 10x each) and shade 2 panels on just one string, you could lose the entire output of that one string from shading.

    But, in general, try to keep shading to a minimum on your array. It does really kill output (remember, that a 1/2 shaded panel on a micro inverter will probably output no power either).

    At this point, I am not sure I am going to go down the road of micro inverter+solar panel vs central inverter reliability.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #19
    Re: New 3.84 kW system online
    BB. wrote: »
    If you have parallel strings (say to strings of 10x each) and shade 2 panels on just one string, you could lose the entire output of that one string from shading. My point exactly. This does not occur with micro inverters

    But, in general, try to keep shading to a minimum on your array. It does really kill output (remember, that a 1/2 shaded panel on a micro inverter will probably output no power either). Again, exactly my point, using micro inverters shading of one panel effects only that one panel.
    -Bill

    Glad we got that settled. *smile* I was starting to worry that everything I'd read was wacky!
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #20
    Re: New 3.84 kW system online

    the system looks great man, Can't wait to get mines up and running, almost 4kw, awesome so jealous. lol
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