The technologies listed here align with the Energy Policy Act of 2005, which defines renewable energy as "electric energy generated from solar, wind, biomass, landfill gas, ocean (including tidal, wave, current, and thermal), geothermal, municipal solid waste, or new hydroelectric generation capacity achieved from increased efficiency or additions of new capacity at an existing hydroelectric project."
Federal agencies should consider the following questions when reviewing technology options.
- What are my energy goals?
- Which kind of energy do I use?
- Why do I need the energy?
- How much power do I use or need to produce?
- Which renewable resources are available at my location?
- Is space available for installation (e.g., rooftop, open land, existing facility, or new construction)?
- What is my budget?
- Which resources are available for operations and maintenance?
Photovoltaic (PV) cells convert sunlight into electricity. Systems typically include a PV module or array made of individual PV cells installed on or near a building or other structure. A power converter converts the direct current electricity produced by the PV cells to alternating current electricity. A typical photovoltaic cell converts approximately 10% of the solar energy striking its surface into usable electricity.
Visit the U.S. Department of Energy's (DOE) Solar Energy Technologies Office for in-depth information about solar energy basics and technologies.
Concentrating Solar Power
Concentrating solar power (CSP) technologies produce electricity by concentrating the sun's energy using reflective devices, such as troughs or mirror panels, to reflect sunlight onto a receiver. The resulting high-temperature heat is used to power a conventional turbine to produce electricity. CSP systems are used to generate a large amount of electricity and require large amounts of land to deploy.
There are three types of concentrating solar power technologies:
- Linear concentrator systems collect the sun's energy using long rectangular, U-shaped mirrors. The mirrors are tilted toward the sun, focusing sunlight on tubes that run the length of the mirrors. The reflected sunlight heats a fluid that flows through the tubes. The hot fluid is then used to boil water in a conventional steam-turbine generator to produce electricity.
- Dish/engines use a mirrored dish similar to a very large satellite dish. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator, which is used to produce electricity.
- Power towers use a large field of flat, sun-tracking mirrors, known as heliostats, to focus and concentrate sunlight onto a receiver on the top of a tower. A heat-transfer fluid heated in the receiver is used to generate steam, which is then used in a conventional turbine generator to produce electricity.
Review NREL's concentrating solar power resource maps.
Solar Hot Water
Although a variety of solar hot water systems are available, the basic technology is simple. A collector absorbs and transfers heat from the sun to water, which is stored in a tank until needed. Active solar heating systems use circulating pumps and controls, which are more expensive but are also typically more efficient. Passive systems work without added equipment.
Solar hot water systems can be cost-competitive when they reduce electricity consumption tied to hot water generation. A typical solar hot water system reduces the need for conventional water heating by two-thirds.
Visit DOE's Solar Energy Technologies Office for in-depth information about solar energy basics and technologies.
Use the FEMP Solar Hot Water System Calculator to estimate what size of solar system will work best for your federal facility and how much it will cost.
Solar Ventilation Preheating
Solar ventilation preheating (SVP) systems preheat air as it enters a building to lessen the energy burden of heating applications. In SVP systems, a transpired collector (a dark, perforated metal wall) is installed on the south-facing side of a building to create an approximately 6-inch gap between it and the building's structural wall. Outside air is drawn through the holes and is heated by the wall's warmth. As air rises in the space between the wall and the collector, it is drawn into the building's air duct system, usually via a fan, to heat the building. Solar ventilation preheating systems are approximately 75% efficient, making SVP the most efficient solar air-heating application available today.
Visit DOE's Solar Energy Technologies Office for in-depth information about solar energy basics and technologies.
Federal agencies can harvest wind energy to generate electricity or mechanical power (e.g., windmills for water pumping). To generate electricity, wind rotates large blades on a turbine, which spin an internal shaft connected to a generator. The generator produces electricity, the amount of which depends on the size and scale of the turbine. Multiple wind turbine sizes are available and widely implemented across the federal sector.
Visit the DOE's Wind Energy Technologies Office to learn more about wind energy basics and technologies.
Review NREL's wind resource maps.
Use FEMP's On-site Wind Energy Project Feasibility Checklist when considering an on-site wind energy generation project.
Download FEMP's On-site Wind Turbine Installation Technical Specification template.
Geothermal energy is produced from heat and hot water found in the Earth. Geothermal resources can be drawn through several sources, which can be at or near the surface or miles deep. Geothermal systems move heat from these locations to locations where it can be used more efficiently for thermal or electrical energy applications. The three typical applications of geothermal energy are:
- Geothermal heat pumps use the ground, groundwater, or surface water as a heat source and heat sink as opposed to ambient air. Typical resource temperatures range from 40° to 100°F (4° to 38°C).
- Direct-use application systems use hot water directly for space conditioning or process heat. This approach is most appropriate for low- to moderate-temperature hydrothermal resources.
- Steam and binary geothermal power plants leverage heat from geothermal resources to drive turbines, which produce electricity.
Geothermal resources make a significant contribution to renewable energy production. Because many geothermal resources are located on federal lands, it is not surprising that 46% of the geothermal electricity generated is from resources on federal lands.
Visit DOE's Geothermal Technologies Office to learn more about geothermal energy basics and technologies.
Review NREL's geothermal resource maps.
Biomass energy is fuel, heat, or electricity produced from organic materials such as plants, residues, and waste. These materials come from several sources, including agriculture, forestry, primary and secondary mill residues, urban waste, landfill gases, wastewater treatment plants, and dedicated energy crops. Biomass energy takes many forms and can have a wide variety of applications:
- Direct firing to produce electricity
- Cofiring with fossil fuels for electricity
- Direct firing of boiler for heating
- Direct firing for combined heat and power (CHP)
- Gasification for CHP
- Conversion into liquid fuels.
Visit the DOE's Bioenergy Technologies Office to learn more about biomass energy basics and technologies.
Review the NREL's biomass resource maps.
Landfill gases constitute a viable energy resource created during waste decomposition. Most communities have landfills. These resources can be tapped to generate heat and electricity. As organic waste decomposes, biogas that is roughly half methane, half carbon dioxide, and small amounts of nonmethane organic compounds is produced. The methane can be collected, converted, and used as an energy source instead of being released into the atmosphere or flared.
The collected methane can be burned to generate thermal energy for heating applications. It can also be burned to create steam, which can then be used to drive a turbine that generates electricity. Using methane in these applications helps keep it out of the atmosphere and thus reduces air pollution.
Visit the DOE's Bioenergy Technologies Office to learn more about landfill gas energy basics and technologies.
Review the NREL's biogas resource maps.
Municipal Solid Waste
Municipal solid waste, also known as waste-to-energy, generates electricity by burning solid waste as fuel. This generates renewable electricity and incinerates landfill and other municipal waste products such as trash, yard clippings and debris, furniture, food scraps, and other discarded items. The United States currently uses two waste-to-energy facility designs:
- Mass burn, which is the most common technology, combusts municipal solid waste much like fossil fuels and other direct combustion technologies to generate steam, which drives a turbine to generate electricity
- Refuse-derived fuel facilities process municipal solid waste before incineration, which typically includes shredding and removing metals and other sorting activities.
Incinerating municipal solid waste generates energy and reduces waste volumes by as much as 90%. Ash disposal and air-polluting emissions are the primary environmental impacts. Effective environmental management is needed to remove toxins before combustion to minimize pollutants.
Visit the DOE's Bioenergy Technologies Office to learn more about municipal solid waste energy technologies.
Hydropower and Ocean
Hydropower has been used for centuries to power machinery, but the application most commonly associated with hydropower is electricity production through dams.
Ocean energy refers to various forms of renewable energy harnessed from the ocean. The two primary types of ocean energy are:
- Mechanical energy, which is derived from the earth's rotation. The rotation creates wind on the ocean surface that forms waves; the gravitational pull of the moon creates coastal tides and currents. This motion creates energy that can be captured and converted to electric power.
- Thermal energy, which is derived from the sun. The sun heats the surface of the ocean while the depths remain colder. This temperature difference allows energy to be captured and converted to electric power.
Specific factors must be in place for hydropower and ocean energy technologies to be viable for federal applications.
Visit the DOE's Water Power Program to learn more about hydropower and ocean energy basics and technologies.
Review the NREL's marine and hydrokinetic resource maps.
Energy storage technologies can charge energy from an external source and discharge it at a later time. Energy storage can enhance the value of renewable energy technologies. Broadly speaking, energy storage technologies are classified by the type of energy they store:
- Mechanical (e.g. pumped hydropower, compressed air, flywheels)
- Electrochemical (e.g. batteries)
- Electrical energy (e.g. supercapacitor, superconductor)
- Thermal energy (e.g. various materials).
New installations are increasingly using electrochemical battery storage technologies, although pumped storage hydropower systems have dominated in the past. Energy storage systems can be interconnected at various levels of the power system (e.g., in front of the meter, behind the meter, and off grid).
Various DOE program offices are doing research on integrating storage technologies. Visit DOE's Energy Storage Program and NREL's Energy Storage Research for more in-depth information about energy storage basics and technologies.
Review the DOE Office of Electricity Global Energy Storage Database for information about grid-connected energy storage projects and relevant state and federal policies.
Get training on energy storage technologies.
Download FEMP's Battery Storage Technical Specifications template and the Battery Energy Storage System Procurement Checklist, which provides a standard set of tasks, questions, and reference points to assist in the early stages of project development.