Next on my list of big ideas for the house is to install solar water heating. We have radiant floor heat, so solar hot water would heat the whole house with far less gas than we're using now. I'm not so excited about photovoltaics, because they are not cost effective. However, heating water with sunlight is much more direct. Sunlight naturally provides heat and light in abundance but not electricity.
This Saturday, I'll be going to the Solar Fiesta to attend a workshop on solar hot water. Hopefully, I'll find out how to buy and install a system that will pay for itself within 5 years. I think that's reasonable, but I'm not sure.
And if I can pull that off, my next environmentally-minded home project will be composting to reduce our amount of trash. I tried composting when we first moved in, but gave it up because it didn't seem to be working. At the State Fair, I saw a brochure on composting that might help this time around.