Windmills and hydro-power generators are also sustainable solar resources.
Both are energy sources derived from the sun, although indirectly compared to solar collectors (PV and hot water). Wind is caused by changes in air pressure brought on by different regions of the globe heating and cooling at different rates due to variations in solar exposure. Rain is caused by evaporation, which results from warming and cooling as well; hydro-power comes from rain storage in reservoirs, creeks, and the like.
The two methods are very similar in the way they generate voltages with spinning turbines. The concept is very simple: When you apply a power source to an electric motor, the shaft spins. On the other hand, if you reverse the process and manually spin the shaft of an electric motor, its two wires output power.
The physics goes equally in either direction. Practical designs can be very complex, but at the heart is always the electric motor principle. Inverters are required (just as with solar PV panels) to convert the raw voltages from the rotors into usable power, typically 12VDC because batteries are the norm.
Another style of inverter converts into standard 120VAC household current.
Although solar PV panels and water heater collectors work only when there’s direct sunshine, both wind and water are available at any time of day or night.
Wind, however, can come and go, from minute to minute. Water resources generally don’t vary much over the course of a day, but they can vary over seasons and are also subject to droughts when there may be no power available at all for extended periods.
Hydro power is also a built-in energy storage mechanism because you can make a reservoir from which you can draw water any time you want it. In fact, a reservoir is generally a good idea because it makes pressures constant. Of course, the big problem with hydro power is that you need to be by a river or stream (or dam) to be able to use it. Most people don’t have this luxury, but for those who do, this is an excellent and economical source of solar power.
The good news is that you can get rebates and subsidies for wind and water power the exact same as for PV systems and water heating systems. They’re all solar power and are therefore grouped together in this regard.
In the following sections, I explain the general concepts of using both wind and water power so that you can decide whether they’re viable options for you, and if so, how best to proceed.