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Thread: Grid connected solar panel, no net meter

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    Grid connected solar panel, no net meter

    Hi folks, Grid connected solar system on roof top in a telephone exchange, free of supply, installation and maintenance cost. The supplier's only charge is on KWH units supplied by solar panel. However, there is no net meter; there is only one regular energy meter on the solar side for billing purpose. My objection is some power would flow to grid for which also we have to pay unnecessarily. But the contractor refuses to install net meter. Is this proposed grid connected solar system cost effective? Thanks.

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    Quote Originally Posted by Sahib View Post
    Hi folks, Grid connected solar system on roof top in a telephone exchange, free of supply, installation and maintenance cost. The supplier's only charge is on KWH units supplied by solar panel. However, there is no net meter; there is only one regular energy meter on the solar side for billing purpose. My objection is some power would flow to grid for which also we have to pay unnecessarily. But the contractor refuses to install net meter. Is this proposed grid connected solar system cost effective? Thanks.
    As I understand it, if your system is grid tied, a normal meter will run backwards if the net flow is to the grid, or it will run slower in the "positive" direction if usage exceeds the solar array's output. More knowledgeable members will correct me if I'm wrong.

    On the assumption that the normal meter doesn't run backwards based on array output, how can the contractor refuse to install a net meter? Here in the US, the meter is actually owned by the power company but the customer owns the meter base. The power company just plugs the meter into your base.

    If you aren't getting credit or payed for the solar you send back to the grid it probably does not make sense to install it. It all depends on the local cost of electricity, capital cost, etc but here in the US it would almost certainly not be worth it under those circumstances.

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    Thanks gadfly56, for your reply. One more detail I want to add is solar tariff is much lower than grid tariff here in India at present. So the proposal is based on 'net benefit'. My question is whether it is realistic in the long run.

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    Quote Originally Posted by Sahib View Post
    Thanks gadfly56, for your reply. One more detail I want to add is solar tariff is much lower than grid tariff here in India at present. So the proposal is based on 'net benefit'. My question is whether it is realistic in the long run.
    Without detailed knowledge of your project costs I'd hesitate to guess. Here in the US, for similar circumstances, it's almost certainly "no". Especially if the feed-in tariff is lower than the grid tariff.

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    If you can be sure that the timing of local loads in the plant is such that the PV will never try to export to the grid, then there is no need for a net metering arrangement.
    You would still get full price reduction in power consumption while the system is producing.
    If the utility allows sell back, but requires a separate meter for reverse flow to implement the feed in tariff, then you need to install whatever the utility wants.
    If you leave an ordinary meter in place it is very likely that it will still run forward for the reverse power flow and you will be *billed* for it.
    A single properly configured digital meter can keep a separate track of forward and reverse flow, keeping both tariff prices separate.

    Sent from my XT1585 using Tapatalk

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    Quote Originally Posted by GoldDigger View Post
    If you can be sure that the timing of local loads in the plant is such that the PV will never try to export to the grid, then there is no need for a net metering arrangement.
    You would still get full price reduction in power consumption while the system is producing.
    If the utility allows sell back, but requires a separate meter for reverse flow to implement the feed in tariff, then you need to install whatever the utility wants.
    If you leave an ordinary meter in place it is very likely that it will still run forward for the reverse power flow and you will be *billed* for it.
    A single properly configured digital meter can keep a separate track of forward and reverse flow, keeping both tariff prices separate.

    Sent from my XT1585 using Tapatalk
    I thought one of the most popular (and dangerous) scams was to hack the meter to make it run backwards. Is that only for the old spinning disk meters, because that's what I think of when someone says "electrical meter".

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    Quote Originally Posted by GoldDigger View Post
    If you can be sure that the timing of local loads in the plant is such that the PV will never try to export to the grid, then there is no need for a net metering arrangement.
    You would still get full price reduction in power consumption while the system is producing.
    If the utility allows sell back, but requires a separate meter for reverse flow to implement the feed in tariff, then you need to install whatever the utility wants.
    If you leave an ordinary meter in place it is very likely that it will still run forward for the reverse power flow and you will be *billed* for it.
    A single properly configured digital meter can keep a separate track of forward and reverse flow, keeping both tariff prices separate.

    Sent from my XT1585 using Tapatalk
    Very helpful reply. One more clarification I request is whether it is possible for undersized solar to feed into grid also in addition to feeding higher owner load demand in parallel with grid. I ask this based on superposition theorem. In that case, will the POCO energy meter, configured in power insensitive mode for example, register an increase in use of energy?

  8. #8
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    Quote Originally Posted by Sahib View Post
    Hi folks, Grid connected solar system on roof top in a telephone exchange, free of supply, installation and maintenance cost. The supplier's only charge is on KWH units supplied by solar panel. However, there is no net meter; there is only one regular energy meter on the solar side for billing purpose. My objection is some power would flow to grid for which also we have to pay unnecessarily. But the contractor refuses to install net meter. Is this proposed grid connected solar system cost effective? Thanks.
    Based on what you've told us, I would not go for this arrangement unless you had good data available on the minimum average load over, say, 15 minute intervals or less, and that load was equal or greater than the inverter max output.

    Also, around here, utilities install net meters, not contractors. What is the utility's opinion where you are? Or does anyone care?

    Quote Originally Posted by gadfly56 View Post
    I thought one of the most popular (and dangerous) scams was to hack the meter to make it run backwards. Is that only for the old spinning disk meters, because that's what I think of when someone says "electrical meter".
    I think the old analog disk meters can be counted on to count downwards when backfed or flipped upside down. Digital meters are a gamble. I will not hazard a guess as to what's typical in India. In the US, many newer net metering schemes require separate accounting of imports and exports - not just the net difference - and so the old analog meters are no longer suitable for that.

  9. #9
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    Quote Originally Posted by Sahib View Post
    Very helpful reply. One more clarification I request is whether it is possible for undersized solar to feed into grid also in addition to feeding higher owner load demand in parallel with grid. I ask this based on superposition theorem. In that case, will the POCO energy meter, configured in power insensitive mode for example, register an increase in use of energy?
    I would say that trying to coordinate higher owner demand with solar production will be a fool's game, not worth the investment necessary to assure it will happen the way you want. Sizing the system small enough to minimize exports is probably the only reasonable way to go. Any money lost on exports because of a low solar tariff or being billed for exports needs to be dwarfed by whatever you're presumably saving by paying the solar supplier's rate instead of the utility's. I suspect the idea will not be practical for a typical residence, only for a business or other large enough compound to have a sizable minimum daytime load.

  10. #10
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    Quote Originally Posted by Sahib View Post
    Very helpful reply. One more clarification I request is whether it is possible for undersized solar to feed into grid also in addition to feeding higher owner load demand in parallel with grid. I ask this based on superposition theorem. In that case, will the POCO energy meter, configured in power insensitive mode for example, register an increase in use of energy?
    1.No it will not be a problem. The theory of superposition tells you that you could have one unit of PV power feeding the load and one unit of POCO power also feeding the load OR one unit of power going out and two units of power coming in from the grid. In either case the meter measures one unit of power *net* going in.
    The purchase tariff for the grid only comes into play when the net power flow is outward.

    2. The very first meters would spin their disk in the opposite direction when the meter was inverted in the socket. That type of meter would work fine if the sale and purchase prices were identical.
    But those meters made power theft easy.

    The next generation included a ratchet so that disk and dials could only go in one direction. That still allowed power theft with the meter standing still.

    The final solution used a double overriding clutch which moved the dials in the same direction regardless of which way the disk spun. This version is totally incompatible with power export.

    3. Some grids do not allow export, so sensing circuitry in the PV system would monitor power flow and throttle the PV or add opportunity loads (like water heating or battery charging) to prevent export.

    Sent from my XT1585 using Tapatalk

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