Home solar output throttling

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Originally Posted by BradC

There's no way to say "the grid voltage is too high, so I'll just supply the house".

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The grid voltage only becomes to high if there is no (or not enough) load and all the inverters in the grid area are trying to force the power being produced into the grid
If you are consuming power when your system is producing its peak power, then there will be no need for it to generate a higher voltage to push it back into the grid, therefore going into over voltage fault mode
As suggested before, if you can set your appliances (dishwashers, washing machine, pool pumps, hot water system etc) to turn on when your solar system is producing its peak power you will alleviate this situation
I have setup for customers Current Transformer Relays to boost a secondary element in there hot water system (standard (upper) element thermostat set at 55-60, secondary (lower) element thermostat set at 65-70)
A couple of years ago but I’m sure this is the current transformer used
Model MSCS | Miniature Current Switch is a low cost solution for monitoring on and off status of light to medium current loads in compact spaces. Applications include BAS, HVAC, small industrial motors, refrigeration, pumps, fans, and lighting. | Dwyer Instruments
With a 24volt control system and contactor

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Gav

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Originally Posted by Gav 110

The grid voltage only becomes to high if there is no (or not enough) load and all the inverters in the grid area are trying to force the power being produced into the grid
If you are consuming power when your system is producing its peak power, then there will be no need for it to generate a higher voltage to push it back into the grid, therefore going into over voltage fault mode

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You'd need a pretty significant load to pull your incoming voltage down such that it is below the threshold at your metering point. You're effectively relying on your lead-in and consumer mains to have sufficient resistance to drop that, and then making sure your inverter isn't pushing it back up to the cutoff.

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Originally Posted by BradC

You'd need a pretty significant load to pull your incoming voltage down such that it is below the threshold at your metering point. You're effectively relying on your lead-in and consumer mains to have sufficient resistance to drop that, and then making sure your inverter isn't pushing it back up to the cutoff.

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The idea is not to pull down the incoming voltage, it is to use the power that your solar system is producing Incoming voltage should not be at the threshold as the inverters on neighbouring solar systems will (should) have shut down
It is your own inverter trying to push the power into the grid
If your solar system is always cutting out on over voltage fault then in my opinion you have wasted your money on a system that is producing too much power that you are not using, maybe money better spent on LED lighting to lower your power usage when your solar system isn’t producing power (night time)

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Gav

I put this here as a general observation for those that are involved with PV systems. This article is not recent, so the over voltage problem is not new., or an unknown fact. Basically, what is being said is that the inverters will require voltage regulation using the grid voltage as a reference to control the inverter output voltage.

The voltage level stability of a grid (at the local transformer) cannot be maintained at a steady linear level just by tap changing. On the other hand, voltage regulation of an inverter can be controlled to match the grid voltage in a linear fashion electronically. In simple terms, the output load of the inverter, just as with a engine driven generator, has to be matched to the grid voltage to limit the load on either source.

(PDF) Voltage regulation via photovoltaic (PV) inverters in distribution grids with high PV penetration levels (researchgate.net)

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Originally Posted by Graeme

The inverter, if correctly configured, will throttle back to effectively produce nothing rather than shut-down, then ramping up quite quickly as the voltage drops either by loads from household appliances or the grid voltage drops. My inverter had incorrectly had its voltage limits changed by the installer attempting to account for a 5-6V drop between the inverter's sensor at the meter box and at the inverter itself some 20m away, but the incorrect parameters caused the inverter to shut-down within 1 second of the voltage hitting the disconnect limit seen at the meter box which then took a few minutes to restart.

After I discussed my suggested voltage limits with the local Essential Energy inspector, the installer reset most of the voltage limits to my suggestions and in 18 months the inverter has only dropped-out once.

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My inverter (Fronius Primo) with 5.2kW panels has an internal limit set by the installer to limit grid feed in to 4kW. I think this is separate to the ultimate shut down setting if the grid voltage goes too high.
It also switches a relay to connect the HWS in at the element wattage (3.2kW). So the inverter rarely reaches the 4kW feed in limit anyway.
Terry

Yes, the export limit is unrelated to voltage. For Essential Energy in NSW the single phase limit is 5kw but my installer wanted to set mine lower for no good reason but set it to my requested 5kw. I also requested access to allow load management changes so now I have full load management and export configuration control via the web page.

Mine's a Primo 8.2 with 8kw of panels that often gets to 8.3kw on bright, cool days when the 3.6kw HWS is heating. I usually have ON set to very slightly under 5kw to delay switching on as late as possible to maximise export for the day.

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Yes, the export limit is unrelated to voltage.

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There may well be an export limit in Kw's set by the grid provider, but the voltage IS what is "pushing" the amps into the grid. It is no different than any other electrical source feeding a load. The "generator" (be it whatever) voltage output has to exceed that of the grid, or plain and simple, amps cannot flow into the grid if isn't. It is by how much the voltage exceeds that of the grid that regulates how much current can flow.

But throttling back because the export limit has been reached has nothing to do with any voltage limit.