In October 2018, the American Council for an Energy-Efficient Economy (ACEEE) released its annual "State Energy Efficiency Scorecard." The scorecard concluded that states and electric utility companies are continuing to expand energy efficiency measures in order to meet clean energy goals. In 2017, the U.S. spent $6.6 billion in electricity efficiency programs. $1.3 billion was spent on natural gas efficiency. These programs resulted in 27.3 million megawatt hours (MWh) of electricity saved.[160]


Any solar PV system that’s tied to the grid will use a bi-directional meter. When you use electricity from the grid, you’ll see your meter move forward. But when your solar PV system produces electricity, any excess will go back into the grid and your meter will move backward. This is called “net metering,” and the utility company will credit your bill for the excess electricity generated.
Over $1 billion of federal money has been spent on the research and development of hydrogen and a medium for energy storage in the United States.[150] Both the National Renewable Energy Laboratory[151] and Sandia National Laboratories[152] have departments dedicated to hydrogen research. Hydrogen is useful for energy storage, and for use in airplanes and ships, but is not practical for automobile use, as it is not very efficient, compared to using a battery — for the same cost a person can travel three times as far using a battery electric vehicle.[153]
Climate change and global warming concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization.[10] New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors.[24] According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world's electricity within 50 years, reducing the emissions of greenhouse gases that harm the environment.[25]
Some of the second-generation renewables, such as wind power, have high potential and have already realised relatively low production costs. At the end of 2008, worldwide wind farm capacity was 120,791 megawatts (MW), representing an increase of 28.8 percent during the year,[30] and wind power produced some 1.3% of global electricity consumption.[31] Wind power accounts for approximately 20% of electricity use in Denmark, 9% in Spain, and 7% in Germany.[32][33] However, it may be difficult to site wind turbines in some areas for aesthetic or environmental reasons, and it may be difficult to integrate wind power into electricity grids in some cases.[10]
Reliance on rare earth minerals for components has risked expense and price volatility as China has been main producer of rare earth minerals (96% in 2009) and had been reducing its export quotas of these materials.[56] In recent years, however, other producers have increased production of rare earth minerals and China has removed its reduced export quota on rare earths leading to an increased supply and decreased cost of rare earth minerals, increasing the viability of the implementation of variable speed generators in wind turbines on a large scale.[57]
The array of a photovoltaic power system, or PV system, produces direct current (DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to certain desired voltages or alternating current (AC), through the use of inverters.[4] Multiple solar cells are connected inside modules. Modules are wired together to form arrays, then tied to an inverter, which produces power at the desired voltage, and for AC, the desired frequency/phase.[4]
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