Why I'm not generating full capacity?

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wongfeihong187

Well-known member
Joined
May 14, 2014
Messages
60
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 :)
 
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.
 
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.
 
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)?
 
wongfeihong187 said:
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.
 
wsbca said:
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.
 
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.
 
NeilBlanchard said:
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).
 
wongfeihong187 said:
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 said:
wongfeihong187 said:
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.

This prediction seems a little misleading to me - though his inverter will indeed likely clip at some point in the middle of the day in summer months (unless it's hot), his total daily production will definitely be highest in those months, which is what I think he's really concerned about. And unless his orientation is really odd, his peak instantaneous production will be lower in the winter as well. For example, our fairly steeply angled roof faces WSW - right now our peak is about 2400w at best orientation on a 3.44kWDC/3kWAC rated system. In the summer we are right up close to the rating in steady state (and clipping when intermittent clouds cause temperature swings).

Maybe all you are saying is that his 5KW inverter will always clip at ~5100w, which it will, but I'm confused by the "farthest from 5.4 during summer" statement.
 
Here's a good link that explains how steeper tilts (mostly) peak in the colder months: http://solarpaneltilt.com" onclick="window.open(this.href);return false;
 
I frequently get more than rated output from my grid-tied array (2.46kw with Enphase microinverters). Usually it happens in March, but I also exceeded 2 1/2 kw peak a couple of times in the last month which was a surprise to me.
 
Hello all, still not producing anywhere where I should be (5.4 kw). Here's a snap shot of my system, taken at 1:30pm on a cloudless day:

PV System Overview | Chu's Household

PV System Data
Current power
3399 W Energy and Power »
Current PV system status


PV System Logbook »
Energy
6035 Wh
Today Total: 975.74 kWh

CO2 avoided
9.3 lb
Today Total: 15 cwt

PV system information
PV system power:
5300 Wp
Commissioning:
11/30/2014 PV system profile »
Weather for San Diego
62 °F
Cloudless Tomorrow »

Location
92127 San Diego
UNITED STATES
Enlarge map »

DayMonthYearTotal

< Day Day >
 
wongfeihong187 said:
Hello all, still not producing anywhere where I should be (5.4 kw).
As I've stated previously, your system will NEVER produce 5400W and should only ever get just above 5.0 kW peak. If you expect to EVER see 5.4 kW from a system containing 5.3 kWp of PV connected to an inverter with a 5.0 kW peak output you are setting yourself up for disappointment.

For reference, I have a 12.5 kWp system which can never produce more than about 11.0 kW due to the limitation of the inverters. Even then it can only happen during certain times of the year. I have never seen more than 10.9 kW.

Since you are now closer to the winter solstice than you were when you first posted in November, it is not surprising that your peak production is lower today than on November 24.

But since you will not tell us how steep your roof is, we cannot tell you if the change is reasonable or not.
 
wongfeihong187 said:
Hello all, still not producing anywhere where I should be (5.4 kw). Here's a snap shot of my system, taken at 1:30pm on a cloudless day:

PV System Overview | Chu's Household

PV System Data
Current power 3399 W Energy and Power »

It's the dead of winter - sun angle is too low. As a point of reference, my 3.4kwDC rated (2.99AC, 3kw inverter) panels, which face WSW at a fairly typical roof angle topped out at a lowly 2200 W today, also in San Diego. Pretty similar percentage to what you are seeing. In May-June, unless it's really hot, I'll be making 3060 at midday (at which level the inverter will be clipping).

To put it another way, right now I'm making between 12 and 13 kwH total on a clear day. On optimal days in the late spring I will make 23 or more.

The sunlight has to be coming in nearly perpendicular to your panels for them to operate at their rating. When that will most nearly happen depends on exactly which way your array points, and at what angle, but your installer hopefully oriented the array for the best overall (year around) performance given the limitations of your roof. That means it won't be at its maximum during these shorter days (if it was, you'd be giving up more total production during longer days). Be patient.

Your annual production is going to end up looking something like this:

35btw0k.png
 
I really like my microinverters. I have an array of 12 panels each rated at 205 watts, using 215 watt Enphase microinverters. The panels are ground mounted on an adjustable tilt mount. Today the high outside temp in the shade by the garage reached minus 6 degrees F. My panels put out 225 watts each for over 3 hours--the 215 watt Enphases clip at 225 watts.
BUT I am sure that my low temperature here had a lot to do with it. I don't think you willl ever get that kind of low temp boost in energy output in California! And my adjustable tilt makes a difference, too, but not as much as those low temps and the reflective snow on the ground.
 
wongfeihong187 said:
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 :)
There are a few variables, time of year for one. This time of year my solar array is only about 80% efficient against rated maximum. You are getting pratically the same efficiency as me, so you are actually doing quite well.

The other is wiring of the panels and charger controllers. The closer the charger controller is to your battery/inverter, the better. It helps to keep the line voltage from the panels high before it is step down for use. If your charger controller is too close to your panels and the source draw is far away, you lose a lot of wasted energy in the form of low heat. Without a lot of details about your setup, I am just kind of guessing at some common reasons for you.
 
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