Second system extension extension.

[Stan]

You’ve got a serious amount of PV there Tinbum, not to mention battery storage. Are you earning FITs on that or even just on your house?
My mind wanders to having another array, a big one with storage. At present I don’t know enough about how it would island alongside my domestic system and whether I would be risking the existing FIT payments.

[Tinbum]

The pylon have still to be connected so just running on the lead acid at the moment. I need to concrete a floor first for the batteries but I'm still suffering from Long Covid and haven't had a day when I could contemplate doing it. Fits are just on 2 arrays of 4Kw and the rest I keep separate and off grid. I've another 16Kw to go up but the old roof needs new sheets first. The plan is to be totally self sufficient in energy in the end.

[Stan]

That’s what I don’t understand yet. How do you use the power from the off-grid system without affecting the domestic system?

[Tinbum]

Use the off grid system all the time for pretty well everything and then use the on grid for specific things eg heating DHW, dumping to central heating and then battery chargers to charge the off grid system.

[nowty]

I was similar to Tinbum, I used to have roughly half my system as an off grid system to get around the max 3.68kW rules and I would switch selected house circuits between grid and off grid using a patch panel of plug and sockets (no suicide plugs !) and a change over contactor based upon battery SOC. It got pretty complicated, so eventually I re-designed it with the newer G100 export limitation technology when I upgraded to a newer SMA Sunny Island. The system is now far simpler and I can edit settings with a webpage, shame my thread had to die on the old forum with details of all the changes.

The Octopus Go, Go Faster and now the Octopus Intelligence tariffs have made my life even easier as it rivals gas cost on even resistive storage heaters overnight and running my small heatpump on the batteries during the day.

[Tinbum]

Using something like a Lux or Growatt can make it really simple as they could divert all the AC from the grid system to the off grid system batteries. No need for any AC loads on the grid.

[Stan]

Thanks Tinbum, Nowty. I hadn’t realised how radical it would be but it makes sense.
What is the G100 export limitation technology?

[Stinsy]

The interesting point is that even if you have an off-grid setup, you can still charge the batteries from the grid on days when there is perilously little solar.

[Tinbum]

My grid charge last night at 8A per phase.

[nowty]

And my setup yesterday 18th Oct, the Solar generation was forecast to be very bad so I set a 2kW charge for the batteries from the grid during my 5p / kWh 23:30 to 05:30 cheap slot. Also during cheap slot, ran the storage heaters, heatpump for hot water tank and heated floor in kitchen. The regular spikes during the day were for my heatpump running the house heating from the battery bank and a bit more around 18:00 cooking the roast chicken dinner.




And my Octopus Smart meter import for the same day from my Octopus account, out of the total imported leccy of 40.906kWh, only 0.095 kWh was at peak rate. I note there is a slight difference between my SMA energy meter reading and my smart meter reading, don't know why but happy that the smart meter total is lower.