New Solar Panels Underperforming – 8kw Inverter, 7.92kw Panels Only Producing 6.7kw Max

Doboman on 14/10/2024 - 20:48

Hi everyone,

I have a solar setup with an 8 kW inverter and panels totaling 7.92 kW. However, during full sun, I only see a maximum output of 6.7 kW. I understand the production curve varies throughout the day, but I expected the spike to be at its highest around midday. I’ve checked, and all panels are in full sunlight at that time.

Do you typically get the exact amount of solar energy that your panels are rated for, or is it common to see less than advertised? Also, I’m curious about the 8 kW inverter – is that overkill for my system size, and would a smaller one be more efficient?

Looking forward to your insights

Thank you
Dobo

Home & Garden Solar Energy System

Comments

  • duk242 on 14/10/2024 - 20:54
    +1

    I've got a 6kW system and usually only get 3-4kW in the peak of the day, has been this way since we bought it…
    My parents place on the other hand, they had a 3kW system that was getting upto 3.2kW (maxing out the inverter)…

    • Doboman on 14/10/2024 - 21:01

      Thank you - that is interesting. For 6 KW to get. 4 KW don't you think something is wrong then ?

      • iDroid on 14/10/2024 - 21:08
        +3

        As far as I understand, the specified wattage is the best case - which would depend on the temperature as well as many other factors.

        My best production "watts" have been achieved on the coldest full sun days.

        • Doboman on 14/10/2024 - 21:30

          Thanks, Yeah As I am in Melbourne its always cold :) we had some good sun. So that was not the case for me.

  • arkie0 on 14/10/2024 - 21:04
    +1

    This should explain it https://www.solarquotes.com.au/101-guides/understanding-sola… - point 3

    Did a solar installer suggest that setup? or did you specifically ask for it? because your inverter is too big, but it will allow for more panels later if you want to expand.

    • Doboman on 14/10/2024 - 21:32
      +1

      Thanks , I don't think anyone understands Solar does until you get one. They sold it saying yeah you can upgrade it later. When I asked them to come & add a panel they said its too expensive to come & add a panel .Story is changed as there is no rebates on getting a one panel. So the cost is too high any way.

  • MrHyde on 14/10/2024 - 21:05
    +6

    The ratio of inverter to solar panels is usually 1.15 to 1.25. So, for 7.92KW in panels; your inverter would give between 6.87 to 6.3 KW - so it seems to be working fine.

    You would get a higher oversized inverter only if you were planning on expanding one day; otherwise an 8KW inverter is a waste.

    • Doboman on 14/10/2024 - 21:33

      That what I thought - Oh well , it is what it is.

  • idontalwaysnotlie on 14/10/2024 - 21:09
    +2

    Its really hard to get the rated output of your solar panels. You have to have them perfectly aligned to the right direction, at the right angle, peak summer radiation and absolutely no shadows. Even a thin shadow like power lines can cut power output by ten percent. Keep an eye on it over the summer and see what you get on a clear day.

    • Doboman on 14/10/2024 - 21:33

      I will , Summer is coming soon :)

    • pegaxs on 15/10/2024 - 08:43

      Keep an eye on it over the summer and see what you get on a clear day.

      And then the panels will get too hot and lose efficiency anyway. My best production is around this time of year. Sun is at the right angle and it's not 35+ degrees every day cooking the panels. The whole system remains relatively cool.

      I find the best times of the year for my panels are from late Feb. to May, and then late August to about mid Nov. The days are long enough, the sun is about the right angle/height and the days arent that hot that they cook the panels and inverter into being inefficient.

  • JIMB0 on 14/10/2024 - 21:46
    +1

    It seems about right for this time of year. You can look at pvoutput.org and compare your system to others in your area.

    • Doboman on 14/10/2024 - 21:48

      nice one - thank you

  • dvd107 on 14/10/2024 - 21:58

    Are you export limited to 5kW?

    • Doboman on 14/10/2024 - 22:04

      Don't think so I can see it did export today close to or just made 6 kwh. No one was at home to use power.

      • wannagrababargain on 15/10/2024 - 09:18

        Export is limited by power, not energy. Every distributor in Victoria requires 5kW export limit which would have been installed by your solar installer. If you have energy monitoring you should be able to see your real time generation and export from your inverters app or web portal. Your max generation would be limited by 5 kW + Whatever you're self consuming at the time. To see if you're clipped to that limit try drawing a lot of power in the middle of the day during full sun (put on the kettle and toaster) and see if the total generation amount goes up.

  • cloudy on 14/10/2024 - 22:33

    Not sure if i missed, but is it N facing? and whats the angle of the panels?

  • GordonD on 15/10/2024 - 08:29

    The output of panels goes up with more intense sunshine, and down with temperature.

    Panels will produce more power when there is brighter sunshine, which occurs when the sun is in the direction the panel is pointing, which may or may not be midday. And for any given intensity of sunlight, they'll produce less power at higher temperatures. They are rated at 25C, I believe. That's panel temperature, not air temperature.

    So in spring and autumn when the sun is less bright than in mid-summer, but the lower air temperature is keeping the panels cooler, they'll produce most power at midday if they are facing north. But in mid-summer the higher temperature will mean the midday peak is not as high, and output may even be higher in the morning.

  • pegaxs on 15/10/2024 - 08:37
    +1

    Well, wait until you hear about thermal losses… Or wait about 5 or so years and it's down to about 80~90% efficiency.

    I have a north facing system at about 40 degrees that extends around the western side of the roof and the best I can get from my "7.2kW" system, is about 5 to about 5.2kW… At the right time of year. It never made over 6.5kW even when the system was brand new. Sun hits at slightly the wrong angle, the weather is too hot causing panels to heap up. resistance in wiring. System getting older (almost 10 years). It all adds up.

    7.92kW is what your system will produce "on paper", not in real work applications. If you wanted 7.92kW, you should have made an over allowance and gone to about 9kW

  • caboose on 15/10/2024 - 08:54
    +1

    As others have said you'll only get the rated output under certain conditions - you'll probably see it maxed out with cloud edge effect where the sun is peaking through some clouds, but you will not see it under regular sustained sunlight.

    So the behaviour looks fine.

  • highon2str on 15/10/2024 - 09:48
    +1

    You'll have a good idea where your output is at if you compare your output to similar systems (size, orientation) around your postcode, on pvoutput.org.

  • lgacb08 on 15/10/2024 - 11:34
    +1

    To get an idea of whether your system has maxed out at this time of the year or not you will have to log into the inverter web interface and check the current curve of each string, if they are in perfect bell shape and the voltage curves remain fairly consistent then it's fair to say that's all you'll get. Depending upon string orientation your system might never see them hitting peak.

  • Drakesy on 15/10/2024 - 11:40
    +1

    Location: Victoria.

    Checks out

    Mine only tend to max out during the day around October this year.

    Although you may have a bad panel (highly unlikely though.)

  • netjock on 15/10/2024 - 12:11
    +1

    All the above is correct. In summary.

    If you wanted 8kw you would need to have more than 8Kw of panels due to loss from angle of roof, thermal efficiency.

    To hit 8kw you would also need to be in ideal conditions. I'd suggest to read the data sheet on your panels. Also you inverter is usually 99.8% efficient so you would never hit exactly 8 and you will never go over.

    You are better off in comparing the overall total output of your system with other people with the same system in the same suburb to see whether you actually have a problem.

  • Lunarboogie on 15/10/2024 - 19:33

    I'm considering installing solar, so this is hugely interesting.

    Out of curiosity, is 8kw a good size for an average family of 4? I know there are many variables but just looking to get a general idea.

    • Doboman on 15/10/2024 - 22:44

      It like your health from what I learnt. Every one is different. This is my personal view.
      If you thinking of getting a EV then 8 KW is not enough other wise it's ok. If I knew what I know now I would have got the most panels I could afford.
      Also check your KW when you have AC , EV on charge , oven etc.. to see highest you will use. This will indicate you what you need. Again if you get a battery the whole story changes. Good luck.

      • Lunarboogie on 16/10/2024 - 11:24

        Thanks. This is in line with what I've heard elsewhere and from what I've read. Go as big if you can afford it.

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