It's not any more efficient, but there is actually a technology that has been around for a while which lets you store heat energy during off-peak hours and use

It's not any more efficient, but there is actually a technology that has been around for a while which lets you store heat energy during off-peak hours and use it during peak hours: electric storage heaters. They look like large baseboard heaters, and inside have a bunch of ceramic bricks which can store a lot energy. During off peak periods the heaters can 'charge', i.e. heat up the bricks, then after that the heat is slowly released over time. Modern versions have a small fan to assist releasing heat, controlled by a thermostat or other smarts. The thing is though, these can store a lot of energy. My parents had a new one installed last year which stores 24 kWh of heat: https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retention-storage-heaters/ https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retenti... Potentially these (the charging can be controlled by a smart meter) could have reduced the electricity demand during peak times.