But the electricity will be used to power all sorts of appliances, most of which generate heat. So I don't think there will be a noticeable difference on a plan

But the electricity will be used to power all sorts of appliances, most of which generate heat. So I don't think there will be a noticeable difference on a planetary scale unless you use most of the electricity to ship energy out to space. If there is any change to the global temperature, it will probably be due to the albedo change (amount of sunlight that gets reflected off all those shiny panels of glass).