The chart above from the Energy Information Administration (2005) sets out the projected electricity sources in 2003 and in 2025. You can see that the growth in electricity generation is expected to come largely from new coal plants and natural gas plants. In both the United States and Canada there are no national renewable energy mandates. As a result, by the end of 2007 32 states and several provinces had enacted renewable portfolio standards (RPS) or mandates.
In the USA renewable energy portfolio, hydropower is projected to increase from 7.1% of total generation in 2003 to just 5.3% of the total in 20205 (the production is forecast to increase, but at a slower rate than total production). Other renewables account for 5.3% of projected additions to capacity from 2003 to 2025. Generation from non-hydropower renewables are projected to increase from 2.2% to 3.2% in 2025. Biomass, including combined heat and power systems and biomass co-firing in coal-fired plants, is the largest source of other renewable generation in the forecast. Electricity from biomass combustion is forecast to increase from 1.0% in 2003 to 1.4% in 2025.
Hydroelectricity is a process in which flowing water is used to spin a turbine connected to a generator. Hydro was the source for about 7% of U.S. electricity generation in 2006, and 25% of the electricity generated in Canada in 2005. There are two basic types of hydroelectric systems that produce electricity. In the first system, flowing water accumulates in reservoirs created by the use of dams. The water falls through a pipe called a penstock and applies pressure against the turbine blades to drive the generator to produce electricity. In the second system, called run-of-river, the force of the river current (rather than falling water) applies pressure to the turbine blades to produce electricity.
Geothermal power comes from heat energy buried beneath the surface of the earth. In some areas of the country, enough heat rises close to the surface of the earth to heat underground water into steam, which can be tapped for use at steam-turbine plants. This energy source generated less than 1% of the electricity in the country in 2006.
Solar power is derived from the energy of the sun. However, the sun's energy is not available full-time and it is widely scattered. The processes used to produce electricity using the sun's energy have historically been more expensive than using conventional fossil fuels. Photovoltaic conversion generates electric power directly from the light of the sun in a photovoltaic (solar) cell. Solar-thermal electric generators use the radiant energy from the sun to produce steam to drive turbines. In 2006, less than 1% of the nation's electricity was based on solar power.
However, in 2006 the recent addition of central station solar capacity to the grid may herald the beginning of a new wave of large solar power plants over the next four years. The U.S. Southwest region is an ideal setting for solar thermal power. The deserts of Arizona, California, New Mexico, and Nevada have abundant sunshine and scarce rainfall.
Concentrating Solar Power
Concentrating Solar Power (CSP) plants are power plants that produce electricity from steam heated by the Sun’s energy. CSP may be on the brink of significant growth. Although the CSP concept has been around for decades, it was not considered economic and by the late 1990’s was virtually ignored as a feasible electricity technology.
Recently, however, several factors have caused a resurgence of interest in CSP:
- The high cost of fossil fuels;
- Environmental concerns;
- Government incentives and mandates for renewable energy sources, such as renewable portfolio standards (RPS), which require electricity suppliers to source a certain percentage of electricity from renewable energy;
- Technological advances in CSP; and
- Short construction lead time.
Wind power is derived from the conversion of the energy contained in wind into electricity. Wind power, less than 1% of the nation's electricity in 2006, is a rapidly growing source of electricity. A wind turbine is similar to a typical wind-mill. Although wind power has developed rapidly in the United States since 2000, it still did not provide a substantial amount of electricity until 2006, when wind energy produced 27 billion kWh. This represents half the amount provided by biomass, but nearly 83 percent more than the amount provided by geothermal.
Total installed wind capacity increased from 4,417 MW in 2002 to 11,329 MW in 2006, with 2,600 MW of the increase coming during 2006 alone (Table 1.H1). The top five states for wind capacity in 2006 were Texas, California, Iowa, Minnesota and Washington.
Biomass includes wood, municipal solid waste (garbage), and agricultural waste, such as corn cobs and wheat straw. These sources replace fossil fuels in the boiler. The combustion of wood and waste creates steam that is typically used in conventional steam-electric plants. Another method of using biomass to create electricity is through anaerobic digestion, which releases methane through decomposition of the biomass. This methane is then burned to run a generator. Although anaerobic digestion is very common in Germany with over 2,000 installations, biomass accounts for only about 1% of the electricity generated in the United States.
The United States has abundant ocean wave and tidal energy resources. It is estimated that if one-quarter of the U.S. wave resource were harnessed at 50 percent efficiency, the electricity produced would be roughly equivalent to electricity produced from hydropower in 2003. This translates to about 6.8 percent of the total amount of net electricity generated in the United States in 2006.52
While tides are intermittent, they are very dependable, running in one direction for hours and then reversing. Waves are fairly predictable days in advance, making system supply planning somewhat easier than wind projects. However, the ocean environment is very stressful on equipment and until recently very few projects had been undertaken.
Significant growth is expected in Geothermal, Solar, Biomass and Wind energy over this time period in total production capacity and also in terms of percentage contribution from renewables to the total energy picture. The MSW/LFG notation on the chart indicates Municipal Solid Waste and Landfill Gas projects. These projects typically harness the methane that is released as organic waste decomposes in landfills. That methane is then burned to generate electricity.