2

So here is my situation. I am using a lot of electricity out of a couple specific outlets, 24/7. I want to install some solar panels, an inverter, and have these outlets (or possibly the whole house if I have enough power) run off solar as much as possible, to reduce the electrical bill... Without having a 2 way meter and no net metering is available.

I of course want to make sure no electricity is feeding back to the grid, if I am producing excess power, as I would just be charged for it, not credited for it because there is not a 2 way meter. Also I want to ensure there is priority that it is always pulling from the solar first, if possible, then pulling from the grid secondary for anything extra it needs if I am not producing enough power to meet demand. Also I want to have a setup without using solar backup batteries for the inverter, because batteries are definitely the biggest expense, the solar panels by themselves are very affordable.

I am trying to imagine a solution and don't really know what kind of products are available.... But I am thinking the only solution would be some sort of device.... Like a solar inverter maybe... That also has a connection to my grid power going into the solar inverter, and the solar inverter has the function that it will always supply power from solar first, but will just pass through to the grid power for other power requested in excess of the the available solar. Then just wire up the power lines I want to go to the inverter instead of the grid fuse box.

Again, I don't know too much about this type of thing, please help me find the best solution possible.

Secondary question/afterthought is, if I had solar being produced, and it was never enough to meet my demand and I always had to pull a little from the grid, so I didn't need to worry about extra energy feeding back to the grid, is there an easier way to do this by like... Just mechanically connecting the solar inverter to the fuse box... But then how or in what way would you control or determine where the electricity is being pulled from? I would assume if there are 2 sources of power just mechanically connected, it would pull equally from both the inverter and grid line? How would you ensure it always pulls from the inverter first before pulling out of the grid?

Thank you!

6
  • as I would just be charged for it, not credited for it because there is not a 2 way meter. Are you sure that you'd be charged? Can you provide your country and the name of your electric utility? I'm not aware of anywhere that it's legal to charge people for excess solar generation per kWh.
    – LShaver
    Commented Jun 1, 2022 at 0:24
  • 1
    I don't think it's about if it's legal or not, more of a technical limitation. The meter is dated 1991. I have read this in many places that these meters can only detect the current, and have no way to determine the direction of the current. Anywho it is in Alberta, Canada. Enmax is the electrical provider.
    – Knr
    Commented Jun 1, 2022 at 2:27
  • I looked at Enmax's website and they indicate you'd get a credit for excess solar (see microgeneration). I'd recommend calling them to ask -- when you apply for solar interconnection, they may verify if your meter is compatible and upgrade it if necessary.
    – LShaver
    Commented Jun 1, 2022 at 12:33
  • Yeah I already looked into it and it's just not a very good deal, they force you to use one of their contractors, make you pay them to install your own solar panels, etc. It's just a big money black hole. I just want to try and understand how to do, what I am trying to do.
    – Knr
    Commented Jun 2, 2022 at 2:36
  • 1
    Either way, if there's no charge for exporting power, then there's really no difference from your perspective between limiting your export and just letting the excess go back to the grid. Besides, export limiting would require some electronics and programming that cost money and can break, so if you skip this step you will likely save time/money. You'll just have to live with the fact that the utility is getting a bit of free power from you!
    – LShaver
    Commented Jun 2, 2022 at 3:15

2 Answers 2

2

On the Enmax website they have a page that shows how to read your meter.

There is a link there "How to find your electric meter number" enter image description here

This overlays a picture of the electricity meter

enter image description here

Is this your meter ? If so, it looks like it will spin backwards or, in a worst case, remain static, as you feed back to the grid.

But if you want to avoid that scenario then it's always possible to install a dump load to make sure nothing gets exported.

Take for example the EDDI Hot water diverter. What this does is monitor the flow of electricity out of the house and switch on a load to eat up that exported electricity. This was typically connecte to an electric immersion heater so that the excess PV (i.e. not being used in the circuits of the house) is used to heat water instead of exporting.

As for how the circuits know which electricity to take my default, well it just works. The local electricity , from PV, will be used first and the grid will automatically make up any shortfall from the PV. I think that the inverter generates AC at a voltage slightly above the grid voltage and this is what makes it more "attractive" if you will.

1

From Wikipedia:

This exported energy may be accounted for in the simplest case by the meter running backwards during periods of net export, thus reducing the customer's recorded energy usage by the amount exported. This in effect results in the customer being paid for his/her exports at the full retail price of electricity. Unless equipped with a ratchet or equivalent, a standard meter will accurately record power flow in each direction by simply running backwards when power is exported

Either your meter has a ratchet or doesn't.

If it has a ratchet, it is run forwards only by electricity you get from the grid. If you use less than you produce, the meter would want to run backwards but can't due to the ratchet.

If it doesn't have a ratchet, you already have net metering!

This applies to mechanical meters. Digital meters measure the strength and direction of current, so the distinction between net metering and no net metering is simply done in software: a "software ratchet" so as to say.

About the only thing that can go wrong is if you have multi-phase electricity with imbalance between the phases. In this case, it's possible each phase is measured separately with a separate ratchet. It it's so, then it's possible you produce:

  • 1 kW in phase 1
  • 1 kW in phase 2
  • 1 kW in phase 3

If you now use:

  • 0 kW in phase 1
  • 2 kW in phase 2
  • 0 kW in phase 3

...the grid is feeding to you

  • 0 kW in phase 1 (1 kW in the other direction)
  • 1 kW in phase 2
  • 0 kW in phase 3 (1 kW in the other direction)

...then you produce 3 kW, consume 2 kW, but still have to pay for 1 kW of electric power because of phase imbalance.

To find out how phase imbalance is handled, you can ask your electricity company.

7
  • "It's possible each phase is measured separately with a separate ratchet." I don't believe this is true. Blondel's theorem was developed in 1893, which states that for a system of n wires, n-1 wattmeters are needed. So a three phase system uses three wattmeters (referencing the neutral) to measure a single total value -- it would cost more to build a meter with three separate ratchets...
    – LShaver
    Commented Jun 6, 2022 at 2:17
  • ... and if you look at an old electric meter there's a single big wheel in the middle, which is where the ratchet would be.
    – LShaver
    Commented Jun 6, 2022 at 2:17
  • 1
    It is technically possible for a digital meter with remote monitoring capability to alert the power company if you feed even a small amount of power back to the grid for any amount of time. I don't know if any meter actually does that or, if any power company watches for that, but the potential is there for you to get into some kind of trouble if you feed back power without having secured permission to do so. Commented Jun 21, 2022 at 20:00
  • With digital meters, the ratchet is just a software feature. Thus, it's as easy to implement three separate digital ratchets than just one digital ratchet. Of course with analog meters, having separate ratchets adds cost.
    – juhist
    Commented Jul 4, 2022 at 16:34
  • 1
    Second, digital meters don't use a "ratchet" in the same sense as analog meters. On an analog meter, if the meter starts to run "backwards", the ratchet engages, and the information about how much power went backwards is lost. Digital meters, instead, have separate "buckets", one for measuring power used, and one for power generated -- so the data about time the meter went backwards is not lost. The utility can then see both quantities, and they are only combined at the end for billing purposes.
    – LShaver
    Commented Oct 31, 2022 at 18:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.