The Sun. Our favourite Earth-dwarfing ball of incandescent gas is the source of a million eco-friendly DIY projects. Not forgetting how human beings are themselves solar powered, there are many ways to use the free energy of sunlight. Work out where you can get the most sunlight, and rig up heat-absorbing materials, mirrors (be safe!) and solar panelling – Treehugger has details on how to do this yourself as cheaply as possible. If you have an old satellite dish in the shed, you’ve got a head start.