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  • Reverse Energy Detection

    I have a 40kWp solar pv system and I want to measure how much electricity is being used in the building before being exported. I don't want to instal an export meter which I have to pay someone to read. I've been told it's legal to install a 'private wire' on the cables just before it enters the buildings main junction box and so out. But how is this actually done? What meters could I install on the supply so I can compare what is being generated with what is being exported?

  • #2
    Hello goodneighbour and welcome to Solar Panel Talk

    It sounds like you need two meters. One measuring what you generate and the one that the POCO supplies. The POCO meter will be programmed to handle both in and out going kwh. Based on what each meter measures you will then need to do the math to determine how much of what you generate is exported.

    If you want a completely automated system you will need to get with an electrical resource to design, install and program the system to provide you the data you want.

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    • #3
      Originally posted by goodneighbour View Post
      I have a 40kWp solar pv system and I want to measure how much electricity is being used in the building before being exported. I don't want to instal an export meter which I have to pay someone to read. I've been told it's legal to install a 'private wire' on the cables just before it enters the buildings main junction box and so out. But how is this actually done? What meters could I install on the supply so I can compare what is being generated with what is being exported?
      you can add CT type meters to the wires, usually inside the MSP (main service panel).
      There are options that work with many inverters to calculate generation and consumption or you can use a supported system with pvoutput.org
      You didn't mention the inverter you have but most that have online monitoring have a consumption meter option.
      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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      • #4
        You could look at installing something like a TED 5000. And get nice graphs and everything automatically on the same time scale and all in one spot.

        But as others have said your inverter likely has a meter built into it.
        So you can use that plus the regular POCO meter to see what's used locally vs. exported.
        Because POCO_meter = local_usage - inverter_meter

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        • #5
          Originally posted by goodneighbour View Post
          I have a 40kWp solar pv system and I want to measure how much electricity is being used in the building before being exported. I don't want to instal an export meter which I have to pay someone to read. I've been told it's legal to install a 'private wire' on the cables just before it enters the buildings main junction box and so out. But how is this actually done? What meters could I install on the supply so I can compare what is being generated with what is being exported?
          Your inverters and PoCo billing already provide the numbers. But I added this feature. More breaker positions
          were needed, so I added a second distribution box. It is fed from the first, through this bi directional spinning
          disc meter. All my heavy KWH loads and PV output are on the new box. When panels build reserve, the meter
          runs (really fast) forward. After sunset the meter unwinds the other direction, depending on load. Noting the
          reading at time of my annual net metering reset, I can see about how much reserve there is left.

          These meters are cheap and accurate, if you can do the wiring. There are a lot of breakers in my original
          box not measured, but they are connected mostly to very light circuits that are not on much. Here they
          amount to about 5KWH a day, which I can subtract from indicated reserve to be pretty accurate. Many of
          these meters have reversing gears to only count upward, but that is easily defeated. Bruce Roe

          BiDirMtr.JPG
          Last edited by bcroe; 01-11-2019, 05:28 PM.

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          • #6
            Hi, thanks for all of that, very helpful. The inverters (we have 2) are SMA Sunny Boy 15000TLd but I'm not sure whether (or how) they might be configured for RED. As for the TED5000, I can see how it can measure electricity being supplied and used in real time but not necessarily how much is coming from the panels and how much from the grid. Or am I missing something?

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            • #7
              Originally posted by goodneighbour View Post
              Hi, thanks for all of that, very helpful. The inverters (we have 2) are SMA Sunny Boy 15000TLd but I'm not sure whether (or how) they might be configured for RED. As for the TED5000, I can see how it can measure electricity being supplied and used in real time but not necessarily how much is coming from the panels and how much from the grid. Or am I missing something?
              I use a TED Pro but used to have the 5000. You need to MTUs and sets of CTs. You measure production with one set, by measuring what comes out of the inverters.
              you then measure the grid to your home,this one is NET. Configure the ted and it does the math. You can also send the data to pvoutput and it also does the math.
              Last edited by ButchDeal; 01-13-2019, 09:47 PM.
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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              • #8
                Originally posted by goodneighbour View Post
                Hi, thanks for all of that, very helpful. The inverters (we have 2) are SMA Sunny Boy 15000TLd but I'm not sure whether (or how) they might be configured for RED. As for the TED5000, I can see how it can measure electricity being supplied and used in real time but not necessarily how much is coming from the panels and how much from the grid. Or am I missing something?
                The TED5000 (and other similar meters) will measure how much current is flowing through a wire and what the voltage is where it's hooked up. And current * voltage = watts. Then look at watts over a period of time and you have energy (kwh)
                The TED5004 is the model I have. It came with four pairs of CTs (things you clamp around wires to measure the current in that wire). With that set of 8 I can measure four different 220V circuits. So I can measure the connection to the solar inverter, and 3 connections going to subpanels.

                Conservation of energy guarantees that energy coming into the breaker box == energy going out of the breaker box.
                So I don't have to measure directly what goes to/comes from the grid. Because I can know that if 0.1kwh came in from the inverter and 0.2kwh was consumed locally I must have gotten 0.1kwh from the grid. Or if at another time I measure that 0.5kwh came in from the inverter and 0.3kwh consumed locally by my appliances then 0.2kwh must have gone out to the grid.

                These types of meters are made by people who know that a large part of their market is people doing solar. So most of them have built in nice graphs that allow you to easily see production vs. local consumption using metering on just 2 of the 3 (and does the calculation for you on the 3rd)

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