As a fun project I have built a solar and wind powered sound system, which I take out and about to camping expeditions and the like.
It’s built from a 12V car amplifier and a bunch of recycled studio monitor speakers. The wind turbine can generate up to 300W of power and the solar panel up to 130W of power. I also have a pedal generator which can be used with a mountain bike and an enthusiastic human to take it up to 11 when required.
I use around 650Ah of deep cycle battery capacity, which will run the amplifier and also some LED disco and ultraviolet lights, to add a bit of atmosphere.
A laptop computer provides the tunes!
There is an article over at The Big Green Idea giving a full run-down on how to build this system, with a schematic.