Octopus do an 'agile' tariff that changes every half hour with the possiblity of prices turning negative (maybe once for half an hour a year by the looks of the data)...might be worth a look but for me the go tariff works out, the agile tariff only went below 5p per kWh for 46 half hour periods in a year so hardly a saving... whereas it went above 30p per kwh for 731 half hour segments so not going to be cheaper me feels then...plus only getting 4 hours a night at and 5p on the go tariff is more then sufficient and if I'm going away and need to fully "tank"I just plan ahead a day or 2...no problems.