I've got solar panels, which can generate 7kW peak (in practice, measured on the output of the inverter) but I'm capped at 5kW export to the grid*. So if I'm not using (much) power in the late morning, there's 2kW of sunlight going to waste. I have a 5kWh battery but in summer that fills up pretty quickly.†
But I also have a hot water cylinder (heated by a gas boiler), with a vacant position for an immersion heater. So I'd like to put in a 1-2kW immersion heater.‡ I don't use much hot water in the summer (already preferring to use my electric shower off the battery).
Running a dedicated circuit would be prohibitively expensive and/or require a fair bit of decorating. Connecting to the upstairs ring main would be easier, though still not trivial; I could do a fair bit of the work myself even if I needed an electrician to make the final connections. The only circuits coming into the airing cupboard near the HW cylinder are the upstairs lights (also serving the burglar alarm) and the central heating. Both are fused at 5A. The lighting circuit is obviously out of the question, and I'm assuming that even for 1kW (4.3A) the boiler circuit is too.
The inverter and battery are in the loft. Running cables from there to the airing cupboard would be really easy if it's allowed. I'd even consider adding a socket or two if I could.
So what is actually required for connecting an immersion heater to the mains, specifically a low-power one.
* This is on G99 paperwork, where the electricity distributor decides how much I can export. Had I known in advance that I'd be capped at 5kW I would have got all this sorted out by the installers
† I have, to some extent, optimised my charging by telling the system not to charge the battery in the early/mid morning but to export that power instead. Otherwise the battery is full before I hit peak generation. The battery can charge at up to 2.5kW when it's not too full, tapering above about 80%.
‡ Which would be connected via a smart switch that I can automate based on data from my inverter, probably in addition to a conventional switch as a cut-off
