Too bad you don't live close to a river. A paddle wheel generator would be semi easy to rig up. Where did you get 1.8kW? I's that a daily or hourly estimate?
that should be an hourly estimate. 1.5 kw is easy to produce with nothing but a wind turbine and solar panel arrangement. keep in mind how much you get as far as wind a sun goes.
my home in greece will soon be outfitted with a 1kwh wind turbine and a 1kwh solar panel arrangement. in greece the sun is blazing and the days throughout the year are 95% clear with zero clouds in the sky. the wind blows like a hooker blows your cock desperately for that crack money. the European community will usually pay you double the price of electricity that you put in. so if you spend 100 euros a month, and you pump it in at equal rate of consumption, you will get about 200 euros back every month.
geo thermal heat piping works on the concept that a certain number of meters down underground, the temperature will always be 50 degree no matter what. usually using a fluid such as water, it gets cycled through the ground pipes and come up at 50 degree F, and when it cools off, it gets lowered into the ground again to heat up or cool off.
cooling a garage is going to be very difficult. for one, they are usually designed to not hold their temperature at all. the ceilings are far too high ( the hot air gets trapped ) and the cement floor is ciller in the winter time because its soo frigin and its like a friggin icecube in your water. i suggest putting a later of outdoor carpeting or that matting that is usually black, comes in giant puzzle pieces, and just lay them all over the floor. also, if your garage door faces the sun in the morning, paint it black. it will heat up nice.