The Boy That Cried PV Extension

[Mart]

Regarding coils, for a resistive tank, I was thinking 1kW at the top, and a 3kW at the bottom, to heat from cheap rate over night.

Happy to heat the tank during the day. As explained, if I'm already using the oil rads to heat from leccy, then being able to distribute that heat a bit more evenly via the rads (upstairs CH circuit?) seems to be the same energy to me. Plus the water tank being a large store of energy from cheap rate.

Bear in mind that we use about 100kWh of gas per month for DHW and oven. So that suggests to me less than 3kWh (per day) for DHW especially with boiler inefficiencies, as even in the winter now, the boiler is operating from cold. Wifey and I take quick showers, probably less than 5mins, and no bath, the room is too small.

So that HW tank (resistive or HP) could store 10kWh+ (I'm not sure, just guessing) of energy from cheap rate, so more than we need, but even if we have to top up during the day for heat, that's what we are doing already.

Hope that makes sense. Just trying to find out if the product description of small central heating system, is what I have upstairs. From there that would seem to answer/solve the upstairs issue, no need to get an immersion heater for the bathroom towel rad. I do share your concerns about a HPHW tank lasting, but that would help even more with daytime top up, as the COP would lower demand on the batteries.