Farms and ranches can use anaerobic digesters—also known as biodigesters—to recover methane (biogas) from animal manure for producing electricity, heat, and hot water. Anaerobic digesters not only reduce energy costs but also methane emissions, which contribute to global warming.  Click on the link to learn more.  Source:  energysavers.gov

The Earth's heat, which constantly flows outward from its core, provides an enormous source of energy called geothermal energy.  You can use geothermal energy—no matter where you live in the United States—to heat and cool your home using a geothermal or ground-source heat pump.  If you live in the western United States, you may have the opportunity now or in the future to buy clean electricity from a geothermal power plant.

Also, if you happen to live in an area that has access to a geothermal reservoir of low-to-moderate temperature (68ºF–302ºF) water, you can tap into it for a direct use application. Direct use applications include home heating, greenhouse heating, district heating, and fish farming.

Geothermal Heat Pumps

Geothermal heat pumps (sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been in use since the late 1940s. Geothermal heat pumps (GHPs) use the constant temperature of the earth as the exchange medium instead of the outside air temperature. This allows the system to reach fairly high efficiencies (300%-600%) on the coldest of winter nights, compared to 175%-250% for air-source heat pumps on cool days.

While many parts of the country experience seasonal temperature extremes—from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.

As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.

A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal units. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well.

Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned to you in energy savings in 5–10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop. There are approximately 50,000 geothermal heat pumps installed in the United States each year.  source: energysavers.gov

We have harnessed the wind's energy for hundreds of years—from windmills that pump water or grind grain to today's wind turbines that generate electricity.

If you live on at least one acre of land with an ample wind resource, you can generate your own electricity using a small wind electric system. You can also use a small wind turbine for pumping water.

Wind is created by the unequal heating of the Earth's surface by the sun. Wind turbines convert the kinetic energy in wind into clean electricity.

When the wind spins the wind turbine's blades, a rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. The manufacturer can provide information on the maximum wind speed at which the turbine is designed to operate safely. Most turbines have automatic overspeed-governing systems to keep the rotor from spinning out of control in very high winds.

A small wind system can be connected to an electric distribution system (grid-connected) or it can stand alone (off-grid).

Although mechanical windmills still provide a sensible, low-cost option for pumping water, farmers and ranchers are finding that small wind electric water pumping systems can be more cost effective and versatile.

Small wind electric systems can pump twice the water volume for the same initial investment. And while mechanical windmills must be placed directly above the well, wind-electric pumping systems can be placed where the wind resource is the best.

Typically, 1- to 10-kilowatt wind turbines are used for pumping water. A small wind turbine manufacturer can help you size and design the system, based on the energy output and quantity of water you'll need, the depth of the well, and your wind resource. System design also includes the wind turbine tower and the balance-of-system parts.  Source: energysavers.gov

Microhydropower systems usually generate up to 100 kilowatts (kW) of electricity. Most of the hydropower systems used by homeowners and small business owners, including farmers and ranchers, would qualify as microhydropower systems. In fact, a 10-kilowatt microhydropower system generally can provide enough power for a large home, a small resort, or a hobby farm.  Hydropower systems use the energy in flowing water to produce electricity or mechanical energy. Although there are several ways to harness the moving water to produce energy, run-of-the-river systems, which do not require large storage reservoirs, are often used for microhydropower systems.

For run-of-the-river microhydropower systems, a portion of a river's water is diverted to a water conveyance—channel, pipeline, or pressurized pipeline (penstock)—that delivers it to a turbine or waterwheel. The moving water rotates the wheel or turbine, which spins a shaft. The motion of the shaft can be used for mechanical processes, such as pumping water, or it can be used to power an alternator or generator to generate electricity.

A microhydropower system can be connected to an electric distribution system (grid-connected), or it can stand alone (off-grid).  Source: energysavers.gov

Passive Solar Home Design

Your home's windows, walls, and floors can be designed to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design. Unlike active solar heating systems, passive solar design doesn't involve the use of mechanical and electrical devices, such as pumps, fans, or electrical controls to move the solar heat.

Passive solar homes range from those heated almost entirely by the sun to those with south-facing windows that provide some fraction of the heating load. The difference between a passive solar home and a conventional home is design. The key is designing a passive solar home to best take advantage of your local climate. For more information, see how a passive solar home design works.

You can apply passive solar design techniques most easily when designing a new home. However, existing buildings can be adapted or "retrofitted" to passively collect and store solar heat.

Active Solar Heating

There are two basic types of active solar heating systems based on the type of fluid—either liquid or air—that is heated in the solar energy collectors. (The collector is the device in which a fluid is heated by the sun.) Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air collector."

Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. If the system cannot provide adequate space heating, an auxiliary or back-up system provides the additional heat. Liquid systems are more often used when storage is included, and are well suited for radiant heating systems, boilers with hot water radiators, and even absorption heat pumps and coolers. Both air and liquid systems can supplement forced air systems. To learn more about these two types of active solar heating, see the following sections: Solar Air Heating, Solar Liquid Heating.  Source: energysavers.gov

 Biomass Power

Ever since humans started burning wood or other organic matter to keep warm and to cook food, we've been using biomass energy, or bioenergy. Today we can also use biomass to fuel vehicles, generate electricity, and develop biobased products.

Biomass Energy or Biopower

Biomass electrical generation or biopower is second only to hydropower as a renewable energy source.

Most electricity generated using biomass today is by direct combustion using conventional boilers. These boilers burn primarily waste wood products generated by the agriculture and wood-processing industries. When burned, the wood waste produces steam, which is used to spin a turbine. The spinning turbine activates a generator that produces electricity. Many coal-fired power plants also add biomass to their coal-burning process (i.e., co-firing) to reduce the emissions produced by burning the coal.

Biomass can also be gasified prior to combustion. Gases generally burn cleaner and more efficiently than solids, which allows removal of toxic materials. Gasification also makes it possible to use biomass in combined-cycle gas turbines, such as used in the latest natural gas power plants. Using gasification, these natural gas power plants can achieve much higher efficiencies. Small modular biomass gasification systems are well suited for providing isolated communities with electricity.

In addition, the decay of biomass in landfills produces gas (primarily methane) naturally, which can be harvested and burned in a boiler to produce steam for generating electricity.  source: energysavers.gov

Some of the oldest ocean energy technologies use tidal power. All coastal areas consistently experience two high and two low tides over a period of slightly greater than 24 hours. For those tidal differences to be harnessed into electricity, the difference between high and low tides must be at least five meters, or more than 16 feet. There are only about 40 sites on the Earth with tidal ranges of this magnitude.

Currently, there are no tidal power plants in the United States. However, conditions are good for tidal power generation in both the Pacific Northwest and the Atlantic Northeast regions of the country.

Technologies

• Barrage or dam

  A barrage or dam is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity.

• Tidal fence

  Tidal fences look like giant turnstiles. They can reach across channels between small islands or across straits between the mainland and an island. The turnstiles spin via tidal currents typical of coastal waters. Some of these currents run at 5–8 knots (5.6–9 miles per hour) and generate as much energy as winds of much higher velocity. Because seawater has a much higher density than air, ocean currents carry significantly more energy than air currents (wind).

• Tidal turbine

  Tidal turbines look like wind turbines. They are arrayed underwater in rows, as in some wind farms. The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph). In currents of that speed, a 15-meter (49.2-feet) diameter tidal turbine can generate as much energy as a 60-meter (197-feet) diameter wind turbine. Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).

Environmental and Economic Challenges

Tidal power plants that dam estuaries can impede sea life migration, and silt build-ups behind such facilities can impact local ecosystems. Tidal fences may also disturb sea life migration. Newly developed tidal turbines may prove ultimately to be the least environmentally damaging of the tidal power technologies because they don't block migratory paths.

It doesn't cost much to operate tidal power plants, but their construction costs are high and lengthen payback periods. As a result, the cost per kilowatt-hour of tidal power is not competitive with conventional fossil fuel power.  Source: energysavers.gov

Wave power devices extract energy directly from surface waves or from pressure fluctuations below the surface. Renewable energy analysts believe there is enough energy in the ocean waves to provide up to 2 terawatts of electricity. (A terawatt is equal to a trillion watts.)

Wave power can't be harnessed everywhere. Wave-power rich areas of the world include the western coasts of Scotland, northern Canada, southern Africa, Australia, and the northeastern and northwestern coasts of the United States. In the Pacific Northwest alone, it's feasible that wave energy could produce 40–70 kilowatts (kW) per meter (3.3 feet) of western coastline. The West Coast of the United States is more than a 1,000 miles long.

Technologies

Wave energy can be converted into electricity through both offshore and onshore systems.

Offshore Systems

Offshore systems are situated in deep water, typically of more than 40 meters (131 feet). Sophisticated mechanisms—like the Salter Duck—use the bobbing motion of the waves to power a pump that creates electricity. Other offshore devices use hoses connected to floats that ride the waves. The rise and fall of the float stretches and relaxes the hose, which pressurizes the water, which, in turn, rotates a turbine.

Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funneling waves through internal turbines and then back into the sea.

Onshore Systems

Built along shorelines, onshore wave power systems extract the energy in breaking waves. Onshore system technologies include the following:

• Oscillating water column

  The oscillating water column consists of a partially submerged concrete or steel structure that has an opening to the sea below the waterline. It encloses a column of air above a column of water. As waves enter the air column, they cause the water column to rise and fall. This alternately compresses and depressurizes the air column. As the wave retreats, the air is drawn back through the turbine as a result of the reduced air pressure on the ocean side of the turbine.

• Tapchan

  The tapchan, or tapered channel system, consists of a tapered channel, which feeds into a reservoir constructed on cliffs above sea level. The narrowing of the channel causes the waves to increase in height as they move toward the cliff face. The waves spill over the walls of the channel into the reservoir and the stored water is then fed through a turbine.

• Pendulor device

  The pendulor wave-power device consists of a rectangular box, which is open to the sea at one end. A flap is hinged over the opening and the action of the waves causes the flap to swing back and forth. The motion powers a hydraulic pump and a generator.

Environmental and Economic Challenges

In general, careful site selection is the key to keeping the environmental impacts of wave power systems to a minimum. Wave energy system planners can choose sites that preserve scenic shorefronts. They also can avoid areas where wave energy systems can significantly alter flow patterns of sediment on the ocean floor.

Economically, wave power systems have a hard time competing with traditional power sources. However, the costs to produce wave energy are coming down. Some European experts predict that wave power devices will find lucrative niche markets. Once built, they have low operation and maintenance costs because the fuel they use—seawater—is free.  Source: energysavers.gov