Solar Feed In - Checking my iusage of Solar vs Feed In

Ldanjerman on 23/02/2022 - 12:04

I have bought a new house with Solar. My inverter says I am producing up to 30Kwh per day on good sunny days. We obviously use a portion of that in the house reducing our electricity bill but also some will be fed into the grid and I get a FiT for that.

My query is how do I check what I am using from it. The information I have is this:

Et = Etoday from Inverter = Daily total for Inverter output
Eall = Eall from Inverter = Cumulative total for Inverter output (multiple readings a day apart give delta)

U = Usage from Grid from Elec meter = Cumulative total (multiple readings a day apart give delta)
F = Feed in to Grid from Elec meter = Cumulative total (multiple readings a day apart give delta)

Now, If i want to check how much I am using internally of my solar, I would compare how much I have generated over a period from Eall and then subtract the amount I have piut into the grid from F for the same period (using multiple readings to get the Delta).

My challenge is that I see the F value as too low compared to the Eall for the period and I doubt we are using the vast majority of the solar we generate. How do I check that manually? Clip on power meter around the cable?

Thanks
Dan

Home & Garden Solar Energy System

Comments

  • dogboy on 23/02/2022 - 12:28
    +2

    Get a smart meter. Does all that for you.

  • SBOB on 23/02/2022 - 12:41
    +2

    Per delta interval
    Self usage per delta interval = Eall (delta) - F(delta)

    Anything the inverter makes, that doesn't get fed to grid, is internal usage (ignoring small losses, close enough to be irrelevant for your calcs)

    Need to also ensure same units (kWh or Wh)

    A smart meter from your inverter manufacturer will do this calculation for you also.

    • danjerman on 23/02/2022 - 18:23

      Thanks. I agree thats how I calculate it. My calculations are showing that Eall (delta) is 857 KWh for a 38 day period but F(delta) is 129 KWh for the same period. I'm therefore using 728 KWh of my solar myself, an average of 19.15 KWh. I've also taken 1165 KWh from the grid in this time or 30.65 Kwh / day on average totaling a household usage of 50KWh a day.

      I don't think I use that much. Its double what we used in our last house. This house is bigger, granted but I want to confirm that these figures make sense.

      Therefore, I want to confirm how much of my own Solar I use by measuring it going into the house if that is possible.

      From yours and other replies, it sounds like a smart meter is the way forward either on the supply or solar inverter.

      I'll investigate further.

      Cheers
      Dan

      • danjerman on 23/02/2022 - 18:26

        I may switch off the house one day at the consumer unit and see if the Eall (delta) increases by the same amount as the F(delta) for the day. That might be a valid test.

      • SBOB on 23/02/2022 - 18:57
        +1

        Eall (delta) is 857 KWh for a 38 day period

        This seems fairly high for a 3kw 10 year old system.
        (If it's right you've got a very well performing system)

  • AndyC1 on 23/02/2022 - 12:47
    +1

    What are the values and the discrepancies over say a week? Also look at % as there will be some loses, but they should be in the 1 to 3%.

    • danjerman on 23/02/2022 - 18:23

      Thanks. I just posted some figures in the reply above.

  • knasty on 23/02/2022 - 15:31
    +1

    Don't most inverters have an app that does this? My Solaredge inverter shows me the live and historic data for production, usage, import, export etc.

    • danjerman on 23/02/2022 - 18:25

      My solar is a 3kw system installed over 10 years ago. I am on a 44c FiT guaranteed until 2028 apparently. This is why I'm keen to understand these figures properly.

      My Inverter is a Growatt Sungold 3000. Does anyone know if this is too old to get a smart meter or app that works with it? Any recommendations?

      Thanks
      Dan

    • JIMB0 on 23/02/2022 - 20:34
      +1

      You need to add an extra meter to measure how much the house is using.

  • lgacb08 on 23/02/2022 - 22:03
    +2

    with that much premium fit you have, it's best just to turn off all circuit when the sun goes up and go to work/shopping and use bugger all after you get home to take hot shower/run your dryer or hot spa.

  • VQLD on 11/10/2023 - 12:58

    you can add 3rd party power monitoring (e.g. Shelly)

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