Alternative Energy Storage
You could collect a lot of lumber (like >50kg), tie it all together and throw a long rope over a big tree branch. Then using several winches lift up all the lumber high in the air, and then utilise the energy of the timber slowly descending towards the ground. The winches would convert high torque to low torque but with a very long rope, which would be a good way to drive a dynamo.

Just thinking alternatively... :)