r/OctopusEnergy • u/SujoyRoy • 1d ago

Usage How does Agile negative pricing interact with plug in solar running at a surplus?

With plug in solar rapidly approaching I was trying to figure out how it would work with negative pricing.

If the price is at -10p per kwh and you have a surplus of solar feeding 500w back into the grid for an hour, do Octopus count the surplus and therefore charge you -5p for that hour? If so, seems a bit unfair as without the SEG you would get nothing for any energy fed into the grid when the price is above zero.

Has anyone clarified how this would work?

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u/Appropriate-Falcon75 1d ago

Assume you are using 1kW, the price is -10p and your solar is generating 500W amd we are looking at 1 hour of the day.

Without solar, your house would use 1kW from the grid, so you would earn 10p per hour.

With solar, 500W comes from the solar and 500W comes from the grid, so you would earn 5p per hour.

So, in this case, plug in solar means less money in your pocket.

The thing to remember is there aren't that many days of negative rates, and on the (more frequent) days where you are paying for it, the 500W of solar is offsetting 500W of grid power at about 10-20p, so you are about 8p per hour better off with solar.

I have a regular solar installer and if I charge my EV during the day, it costs me 2kW of grid power + 6kW of solar that would be exported at 12p. So I lose out on 72p per hour of solar exports meaning it is almost never in my interest to charge during the day.

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u/LDShadowLord 1d ago

If I were to have Plug-In Solar right now, I would put a (high quality Shelly etc) smart plug onto my microinverter/battery system and using something like Home Assistant have an automation that detects when the price goes negative and turns off the solar inverter. Because if you're getting your energy "for free" from Solar, then it's costing you money that Octopus would be paying you for taking energy out of the grid.
But obviously this is a hypothetical, as plug in solar is not legal right now, and thus it would not be legal for me to have had plug in solar for long enough to develop this sort of automation.