Wind Power

In a wind power system, wind turns a rotor attached to a turbine which drives a generator. The turbine is mounted on a tower to avoid turbulence and take advantage of the greater wind speeds at higher elevations, and has a "tail" to keep it oriented efficiently. A wind system can connect to the grid (with a sensor to disconnect it during outages) or stand alone, and can be used with photovoltaic solar. A typical home setup might include a 10kW turbine with 23-foot wide rotor, mounted on an 80-foot tower, but a turbine as small as 400 watts with 46-inch wide rotor could be used for special purposes such as pumping water or powering a cabin. Image courtesy DOE/NREL, Credit - Robert Slack

Solar Hot Water

A solar hot water system uses the power of the sun, rather than fossil fuel or electricity, to heat water. The two main parts in a typical system are the solar collector and the storage tank. The storage tank is usually larger and better-insulated than a conventional water heater. Active solar water heaters, the most common system, use electric pumps to circulate water or a heat-transfer fluid through the collectors. Passive solar water heaters use gravity and water's natural tendecy to circulate when heated, making for a simpler system. Solar water heaters usually have a conventional backup system. Image courtesy U.S. Department of Energy

Solar Photovoltaic (PV)

Photovoltaic (or "Solar PV") systems convert sunlight into electricity. PV cells, which can be made of a variety of semiconducting materials and typically produce 1 or 2 watts of power, are connected together to make larger units called modules, which are in turn connected together to make arrays. All the other items in a PV system, which may include mounting/aiming structures, A/C converters, and batteries or a grid connection, are referred to as the "balance of system" (BOS) components. The most common array design is referred to as a "flat-plate system", and responds to both direct and diffuse sunlight (diffuse sunlight accounts for anywhere from 10% of the light on a sunny day up to 100% when it's overcast). They may be mounted in a fixed position or on a tracking device to keep them aimed at the sun. Tracking arrays produce more electricity per unit area of array, but fixed arrays are much simpler, containing no moving parts, and are lighter and less expensive. A "concentrator system", in contrast to flat-plate, uses lenses or reflectors to concentrate the sunlight, allowing it to use fewer and/or smaller cells. However, concentrator systems cannot focus diffuse sunlight, and usually require a tracking system.

Micro Hydropower

Most people are familiar with hydroelectric power, where a river is dammed and the flow turns turbines to generate electricity. Micro hydro is similar, but without the need to alter the waterway's course. If you live near running water, micro hydro can be a very efficient and low-impact source of electricity, and it runs day and night. Peak output will typically be in the winter, when consumption is also likely to be greatest. Micro hydro is very site-specific; the two factors that determine power are head (also called drop, the water's change in elevation) and flow (the amount of water passing through in a unit of time), and it is also important to consider the distance between source and point of use. The physical system will consist of a water intake, a pipe (called a penstock) that brings the water to the turbine, a shutoff valve for maintenance, the turbine and generator, an exit pipe (if the water doesn't exit directly), transmission lines for the electricity, and a battery setup or equipment to provide A/C power. Image courtesy U.S. Department of Energy

Geothermal Heat Pumps

Geothermal Heat Pumps exchange heat with the earth, using the relatively constant temperature a few feet below the surface to achieve greater efficiency than air-source heat pumps. Like air-source pumps, they can heat, cool, and (if equipped) supply hot water, but are quieter, last longer, and require less maintenance. Geothermal systems circulate fluid through looped pipes in the ground, which may be arranged horizontally or vertically, or can use a well or body of water. Geothermal uses 25-50% less electricity than conventional heating & cooling systems, and make it easier to control humidity by maintaining about 50% relative indoor humidity. Geothermal systems are durable and reliable, having relatively few moving parts. Those parts are sheltered inside the building, and the indoor equipment takes less space than a conventional HVAC system. Geothermal systems are also very quiet. Image courtesy U.S. Department of Energy

Did You Know - Only 7.5 percent of total U.S energy consumption came from renewable sources, of that total 94% was from hydropower and biomass (trash and wood incinerators) . U.S. Energy Information Administration.