[andoma]

Our house have geothermal heating (heatpump conncted to 160m drilled hole, pretty common in Scandinavia). The heatpump supports having a coolant loop for cooling the house in the summer. Thus the heat pump pretty much exchanges heat from the house to the well (heating it up ever so slightly). It would certainly be possible to insert a resistive dummy load on that loop and just store that heat in the bedrock as well.

[frabert]

This! Or, if you don't have geothermal heating but have an electric water heater, maybe temporarily increase the temperature it goes to: maybe it's normally set to go to 65C, then when you detect that you have negative prices and your batteries are full and your water already hot, maybe heat the water to 70C and store that little bit of extra energy as heat! If you have thermostatic valves in your bathrooms, you won't even notice the difference except by the fact that your water heater now can apparently hold a little bit more water than usual :)

[john61]

I have a heat pump for hot water and calculated this with an offered floating energy tariff. It is not economical because the high net tariffs are not floating but fixed per kwH and negative / very low prices are seldom here and only for a short period of time available.

[cogman10]

Assuming regular negatives (more than once a day) you could also tie the heating to the grid prices with maybe an hour buffer around your high water usage times to make sure you are up to temp.

Modern water heaters will keep temp for a shockingly long period of time.