wongfeihong187
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Why I'm not generating full capacity?

Mon Nov 24, 2014 10:04 am

Hello all. New to solar so this may be a dumb question. I finally got my LG 300's installed last week and am finally producing my own electricity! Question, my system is rated to be 5.4kwh but I'm finding that at peak times of the day I'm only generating 4.3 kwh? why is this? Thanks for all you solar gurus who know this stuff :)

NeilBlanchard
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 10:13 am

Your system may be rated 5.3 kW - note the lack of the 'h'. That means that if it is exposed to full sun for one hour, it should in theory produce 5.3kWh. It sounds like very cloudy day? Or, possibly you have micro inverters that are limiting the output of your (300W?) panels to ~210W?

I asked my nephew, who works installing solar panels, and he said they are now using a new type of central inverter (instead of the micro inverters) that works at the full output of the panels, and has the panels connected in small groups, so that if a shadow hits a panel(s) it only drops that groups' output. In previous older systems, the central inverter dropped the entire array's output if too much shadow hit a panel or panels.

wongfeihong187
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 10:33 am

Thanks Neil. I'm using a single inverter (Sunnyboy 5000tl), but on two strands with 9 panels tied to each (total of 18 panels). Nope, it's sunny without a clouds in San Diego all weekend.

woodgeek
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 10:35 am

Because its November, and the sun is low in the sky. Check back in June.

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RegGuheert
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 11:32 am

PV panels are rated under very specific conditions: 1000W/m^2 of sunlight and 25C CELL temperature.

I can think of six things other than clouds that will limit your output below the rating of your PV panels:

1) The sun is not in the boresight of the array. That only happens during certain times of the year and even then it only happens at a particular time of day. Typically it occurs in Spring and Fall, but it depends on the slope and azimuth of your roof.
2) Dust or dirt on your panels can block some of the light from getting to the PV cells inside. This is not likely a problem with your system, yet.
3) The PV panels are warmer than 25C. PV panels get less efficient at converting light into electricity as they warm up. Since the PV panels heat up when the sunlight hits them, nameplate production typically only occurs if the outside temperature is quite cold, like in wintertime.
4) Solar inverters are not 100% efficient, so about 5% of the electricity produced by the PV panels is converted into heat in your inverter.
5) The wiring in your system is not 100% efficient. With microinverters the wiring losses are mostly in the AC wiring and with central inverters it is mainly in the DC wiring. 300Wp panels couple to a central inverter may result in ~3% wiring loss.
6) Most inverters, including yours, have a limit on the amount of power they can process. This power level is typically LOWER than the power rating of the PV panels, for the reasons listed above. In your case, you should not expect to EVER see more than 5000W from your system due to the limit of your inverter. But this is not what limited your production over the weekend. Likely your inverter will never limit the production of your system.

All that said, there are two things which CAN cause a PV system to produce MORE than its nameplate power (in cases where the inverter is NOT the limiting factor):

1) Being at high altitude where the amount of sunlight striking the panels is more than 1000 W/m^2.
2) Temperatures cold enough to increase the production enough to overcome the efficiency losses in the wiring and the inverter.

Neither of these apply in San Diego.

Can you please provide a link to your system so that we can observe the production (and perhaps see pictures)?
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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wsbca
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 11:48 am

wongfeihong187 wrote:Thanks Neil. I'm using a single inverter (Sunnyboy 5000tl), but on two strands with 9 panels tied to each (total of 18 panels). Nope, it's sunny without a clouds in San Diego all weekend.


As noted in a couple of other posts, it's not the right time of year in San Diego for full production - the angle of the sun is too low. If you've got a good roof orientation your peak production will come in June/July/August. Another thing you'll notice, more during that time but even now, is that heat is an enemy - it increases resistance and lowers production. So you may find that on otherwise identical sun angle days, if the ambient air temperature is higher or there is less cooling from the wind, you'll produce less (than your rating, and/or compared to a cooler day).

As an example, my array is rated 3440w DC, which converts down to about 2960 AC. We have a 3000w inverter, which clips at 3060 watts, even if the panels are making more than that (which they do, on a perfect day (cool and with perpendicular sun angle). In the right conditions at the right time of year we'll make 3000+ watts at the peak of the daily production curve, but only for a fairly brief period.

Our peak production on a steady sunny day ranges from around 2200 at the winter solstice to consistently touching the max rating in/around June. On a more volatile day (intermittent clouds) at other times of the year it will spike up to the full rating now and then when the clouds cool the panels and then briefly move out of the way, but if it's a clear day the combination of low sun angle and heat will keep the max constrained throughout the day.
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RegGuheert
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 12:08 pm

wsbca wrote:If you've got a good roof orientation your peak production will come in June/July/August.
That would be peak daily ENERGY production.

Peak instantaneous POWER production, which is what I believe OP is asking about, should occur on cold days near the winter solstice in San Diego, assuming a South-facing roof with about 7/12 pitch or steeper. Very shallow roofs may have peak power production at different times of the year, but they are likely to NEVER drive the inverter to its output limit.
RegGuheert
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10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

NeilBlanchard
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 1:05 pm

Also, what angle are the panels? The ideal angle is roughly equal to the latitude. If they are flatter than that, then they will do better in the summer, and if they are steeper, then they will get more in the winter, than otherwise. If they are producing ~ bit over 80% of their maximum, that is pretty good for this time of year.

wongfeihong187
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 3:00 pm

NeilBlanchard wrote:Also, what angle are the panels? The ideal angle is roughly equal to the latitude. If they are flatter than that, then they will do better in the summer, and if they are steeper, then they will get more in the winter, than otherwise. If they are producing ~ bit over 80% of their maximum, that is pretty good for this time of year.


Oh I don't know the angle of my panels, but they follow the roofline and facing sun all day (majority of the day). Good to know that I'll get at least close to 5.4kw during the summer. I"m just hoping my next month's electricity is offset by the panels (I just put up my Christmas lights this weekend too).

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RegGuheert
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Re: Why I'm not generating full capacity?

Mon Nov 24, 2014 3:06 pm

wongfeihong187 wrote:Good to know that I'll get at least close to 5.4kw during the summer.
You will be farthest from 5.4kW during the summer unless your roof is VERY flat. You will never get much beyond 5.0kW, which is the point at which your inverter will limit the output.
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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