The basic idea of the storage radiator is to heat up with off-peak electric, and to then release the energy when required, other than the central cupboards with circulating fans, which could stay hot for a week, the after build version were never really a success. It would not retain the energy well enough, so would often get cold before the off-peak was available to recharge them.
The tariff was called Economy 7, and there were a host of ways to use it, from the original white meter, to the modern smart meter, and sometimes the heater turned the supply on/off with a sensing signal, and sometimes the electric meter turns it on/off. There was an Economy 10 where one got a midday boost, but today we have a whole host of names for off-peak power, aimed at EV chargers (often 5 hours but sometimes 7 hours) and solar panel users with storage batteries (can be as low as 3 hours) and some three stage, off-peak, standard and peak, the latter often 4 pm to 7 pm.
The off-peak charge can also vary a lot, from 6p per kWh to 16p per kWh, it would make sense if the shorter the charge time was the cheaper it was, but that does not seem to be the case, 3 hours at 15.45p per kWh for solar panel users and 7p per kWh for 6 hours 23:30 to 05:30 and although one gets a promise they will buy excess solar, often suppliers drag their feet, so after 18 months still nothing.
So the comparison websites are useless, at least that is what I found, and so much depends on your personal lifestyle. Having a hot home 9–5 when you're not there is a bit useless, and heat pumps may be good, but they are large lumps, so many find a simple panel heater is more appropriate for their needs.
I can see with my house how fast it cools,
I can see midnight until 7 am room cools 3ºC
and I can see what other rooms do, how fast they heat and cool when the heating turns on and off. But most people have little idea of heating and cooling speeds, so to work out how much needs to be stored, is near impossible, we have considered a storage radiator, or at least an oil filled radiator, as often around 1 to 3 pm we are giving away electric. Autumn and Spring, yes it would likely work well. But Winter not enough solar, running a heat pump to cool the home great, but to heat it, so much depends on how well insulated.
