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Calculating savings basics

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  • Calculating savings basics

    Do I have the correct understanding on calculating the savings?

    My electricity is $.10 per 1kWh. If I’m on net metering than my power company will pay me $.05 per 1kWh.
    Let’s say I use 20kWh per day without solar which costs me $2 from the power company.
    Now, I install a solar system that produces 20kWh per day when the sun is shining.
    Let’s say I used 10kWh during the day when the sun was shining and I send the extra 10kWh to grid earning me $.50 credit.
    Now the sun stops shining and I start drawing power from the grid for the 10kWh that I need to power my house.
    I use up my $.50 credit built up from my solar panels to pay for 5kWh. Then I have to pay $.50 for the remaining 5kWh.

    To be 100% covered I will need to buy a system that will produce 30kWh per day.
    Last edited by MaxThisPower; 05-22-2020, 11:47 AM. Reason: Change kW to kWh

  • #2
    You may have it wrong.

    Every instant power flows from the grid to your house, you pay $0.10 / kWh for it.
    Every instant power flows from your array into the grid, you get $0.05 / kWh for it.

    The net-meter has two accumulators. One records when power is going out. The other records when power is going in. The bill has a different rate for each.

    On top of this, you pay to rent the meter. For me, that's a fixed monthly charge.

    If your cynnical, you could say that the power company structures things to squeeze as much money out of you as they can. If you're generous, you could say that the power company maintains the power grid and has to have the generating capacity available whether you use it or not, so they deserve every penny they get.

    Now to your last statement. Not every day is sunny. Winter is worse than summer. To get a full understanding of what you use in a year, look at last year's power bill. To get a full understanding of what your system will produce, use a solar modeling tool like PVWatts.nrel.gov
    Last edited by bob-n; 05-21-2020, 05:26 PM.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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    • #3
      I'd start by learning the difference between a kilowatt (kW), a unit of power, and a kilowatt-hour (kWh), a unit of energy. POCOs sell and bill in units of energy.

      For the rest of the basics of how PV works and net meter basics, download a free but slightly dated edition of : "Solar Power Your Homer for Dummies", a free PDF download.

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      • #4
        Strictly speaking, "Net Metering" is where you swap kWh with the POCO. For every kWh you push into the grid, you get a kWh back at a later time. In other words, you are getting full retail credit for your excess solar power. Its a good deal for solar (actually it is the incentive that fueled the solar industry for years) and the POCOs hate it. What the OP is describing is really "Net Billing" where you get paid one price for your excess generation, and a different price for the power you get from the grid. Yes, under net billing, you need to overproduce in order to break even. The good news is that the cost of solar equipment has come down enough that net billing bias against solar can be overcome.
        BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed

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        • #5
          Originally posted by solarix View Post
          Strictly speaking, "Net Metering" is where you swap kWh with the POCO. For every kWh you push into the grid, you get a kWh back at a later time. In other words, you are getting full retail credit for your excess solar power. Its a good deal for solar (actually it is the incentive that fueled the solar industry for years) and the POCOs hate it. What the OP is describing is really "Net Billing" where you get paid one price for your excess generation, and a different price for the power you get from the grid. Yes, under net billing, you need to overproduce in order to break even. The good news is that the cost of solar equipment has come down enough that net billing bias against solar can be overcome.
          That's exactly what I'm getting at.

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