In the UK there is a provider than bills the "live" electricity price using smart meters, (in reality I think it's 30 min chunks but close enough). Sometimes at

In the UK there is a provider than bills the "live" electricity price using smart meters, (in reality I think it's 30 min chunks but close enough). Sometimes at low demand and high wind and solar output prices go negative. https://www.energy-stats.uk/octopus-agile-london/ https://www.energy-stats.uk/octopus-agile-london/. I think the all time low was -10p/kWh. Most of the time it's around -3p though when it does go negative. Assuming you had a 20kW (massive) heater you'd only make maybe £1-5/day running it when the prices are negative, which isn't hugely often ATM. So probably not economical, yet.