Our bill are much cheaper in summer for sure, by half the price. Water can cost lots in summer sometimes water bill 100 dollars for watering lawn etc. Last year we did not need to water much as it rained a lot.
I hate to tell you this.... but half the time my green house is heated by candles that I get on sale. I also save wax and make candles too. Although I do have a round energy saving heater, what is that thing called again.... got to go look, and light some candles right now... OK I'm back now, got some pictures, heater is a parabolic dish. It radiates the heat with no fan. Although the heater is more dangerous then candles if you ask me. Green house is drippy with water from roof when I use candles, no danger of fire, been doing this for at least 15 years. I use heater it drys up quick. Heater scares me more than candles. When I build my greenhouse I used 2X4 wood, poly on each side so I have inch and a half of air insulation that way. Then if it is sunny no need to heat during daylight hours as sun heats it quite well. Sometimes it can be minus 17c like last night, but by 10 or 11am I turn off all heat and blow out candles. Well I time the candles to go out, by 11am sun heats even through it's cloudy. If I light tea lights at 6am they go out by 10 am when I am at work.
Then the candles burn oxygen and give off carbon dioxide, which the plants breath in as fertilizer!
I am obsessed with my greenhouse project, been obsessing with it for years. I sit and plant tomatoes and peppers in early spring for garden, used to grow Johns tobacco too, will still grow some in spring for the flowers and they attact hummingbirds. I can sit in my greenhouse in my "birthday suit" ha ha, and get some sun, ha ha ha, and no one can see me cause I just look like a burry pink blob on the other side! Ha ha ha