Renewable Energy
Our sun plays a vital role in producing many different types of available renewable energy. Although, our ability to effectively harness and utilize some of this energy will vary depending on climate conditions, season, time of day, as well as location. Sunlight, or solar energy, is a direct output of the sun's energy, and is used for sustaining life here on earth. Solar energy can be harnessed to support our much of heating and cooling needs, as well as generate electricity to support many of our other energy needs.
Wind too, is also a result of the sun. The sun's heat is responsible in part, for the wind conditions that occur around the earth. Wind energy is typically harnessed by using wind turbines, which can also generate electricity to support our growing energy needs.
Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from renewable resources including; solar, wind, ocean, hydropower, biomass, geothermal resources, as well as hydrogen.
Renewable energy is in contrast with the today's energy resources (e.g., coal, oil, gas, etc.) that primarily utilize fossil fuels. Today, fossil fuels combined make up the largest component of the total energy resources to support energy consumption in the United States. This condition contributes significantly to an increasing and alarming carbon footprint in our atmosphere, which will have serious long-term effects for the environment, as well as social, economic, and political stability in the world.
Renewable-energy technologies can be broadly classified into four categories:
- Mature technology with established markets in at least several countries: large and small hydro, woody biomass combustion, geothermal, landfill gas, crystalline silicon PV solar water heating, onshore wind;
- Mature technology with immature markets in a small number of countries: municipal solid waste-to-energy, anaerobic digestion, biodiesel, co-firing of biomass, concentrating solar dishes and troughs, solar-assisted air conditioning, mini- and micro-hydro and offshore wind;
- Under developed technology having small-scale commercial application with potential for wider market introduction: thin-film PV, concentrating PV, tidal range and currents, wave power, biomass gasification, and solar thermal towers;
- Research technology stage: organic and inorganic nanotechnology solar cells, artificial photosynthesis, biological hydrogen production involving biomass, algae and bacteria, and ocean currents.
The most mature renewable technologies (large hydro, biomass combustion, and geothermal) have been able to compete in today's energy markets without policy support. Solar water heating, solar PV in remote areas, and wind farms are also competitive today based on location.
The following chart identifies the renewable energy component as a subset of the total primary energy components consumed in the United States during 2010.
The use of renewable is on the rise. In 2008, the renewable slice of the energy pie was 7%. Today, the key contributors for renewable include; Solar, Geothermal, Wind, Biomass, and Hydropower. Following is a brief review of each of these renewable energy sources;
Solar
Solar is broken down into the following 2 specific technology areas;
- Photovoltaic (PV)
- Concentrating Solar Power (CSP)
Photovoltaic cells (solar cells) convert sunlight into electrical energy. There has been much success with the use of crystalline silicon cells to support PV technologies, and are the most common PV cells in use today. These cells can be combined into modules and arrays to create a PV system, which can produce a higher power output than that of single PV cells. The PV systems can be interconnected to other PV systems to produce even more power to support both small and large electric power needs.
Concentrating Solar Power utilizes mirrors to reflect and concentrate sunlight onto receivers and convert it to thermal energy. The heat from this process can be utilized in a heat engine or be used to produce steam to run a steam turbine to produce electricity via a generator. CSP is a renewable energy source to help meet our nation's demand for electricity.
Geothermal
Geothermal energy is produced by heat from the earth. Geothermal energy is a large, underused heat and power resource that emits little or no greenhouse gases. In addition, geothermal resources are abundant in the earth's crust, and the production of electricity from geothermal energy is a reliable process. Geothermal resources are tapped by drilling deep wells into underground reservoirs to tap steam and very hot water that can be brought to the surface and used as a renewable energy source to help meet our nation's demand for electricity.
Wind
Wind energy can be used for purposes such as generating electricity and pumping water. A variety of technologies can be utilized to collect and convert the wind's energy into electricity for use to support stand-alone applications, interconnected to a utility power grid, or even combined with a Photovoltaic (PV) system. Large-scale energy production using wind can be achieved through the use of many wind turbines configured closely together (referred to as a wind farm) that interconnects with the power grid.
Biomass
Biomass continues to be the world's major source as a renewable resource of hydrocarbons for use as a source of heat, electricity, liquid fuels and chemicals. In fact, according to the preceding chart regarding the U.S. Primary Energy Consumption for 2010, biomass-based renewable energy sources constituted 53% of all renewable energy consumed in the United States.
Biomass sources include forest, agricultural and livestock residues, organic matter such as plants, as well as the organic component of municipal and industrial wastes. Biomass resources have been in use for thousands of years. For example; wood has been used to provide heat mankind for thousands of years. Through evolving biomass technologies, these resources can now be used to produce fuels, chemicals, and power to support our growing energy needs.
Hydropower
Hydropower is the most common and least expensive source of renewable electricity in the United States today. According to the Annual Energy Review for 2010 by the U.S. Energy Information Administration, hydropower resources constituted about 31% for all renewable electricity generated in the United States.
Hydropower technologies use flowing water to create energy that can be captured and turned into electricity. Both large and small-scale power producers can use hydropower technologies to produce clean electricity.
Hydrogen
Most commercial hydrogen production today is based on steam reforming of methane, but electrolysis of water (especially using carbon-free electricity from renewable or nuclear energy) or splitting water thermo-chemically may be viable approaches in the future. Realizing hydrogen as an energy carrier depends on low-cost, high-efficiency methods for production, transport and storage. Hydrogen has potential as an energy-storage medium for electricity production or transport fuel when needed.
The prospects for a future hydrogen economy will depend on developing competitively priced fuel cells for stationary applications or vehicles, but fuel cells are unlikely to become fully commercial for at least a decade.
