Buy solar panels. Broadly speaking, there are 3 types of solar panels (strictly speaking, photovoltaic cells): amorphous silicon, polycrystalline, and monocrystalline. Amorphous silicon panels are relatively inexpensive, relatively unaffected by small shadows, but are very inefficient in terms of space (for the same power rating, amorphous silicon panels will be larger and heavier). Polycrystalline panels are more efficient, cheaper than monocrystalline, but also less efficient. Monocrystalline panels are the most efficient, but also the most expensive. Output from mono- and polycrystalline panels can be halved or less by even a tiny shadow because of the way individual cells are wired. Mono- and poly-crystalline panels can be purchased these days can under $1 per Watt.[1]