I'm on an electricity tariff with dynamic pricing. The last week has been pretty rough in fairness, but generally it's really rewarding on most days and sometimes, on days like this, it's amazing.
Based on my past calculations, whenever the cost is below ~20p, I'm paying less for heating than I would with a gas boiler. Where the cost of energy is negative, I'm essentially getting paid to use surplus energy.
In fairness, most people here pay about 24p/kWh which is about 32¢/kWh and on my tariff sometimes prices will peak at 45p (about 55¢) so we're not too far behind!