microgeneration, small-scale generation of heat and power designed to suit the needs of communities, businesses, or residences. Microgeneration relies on power produced at a generation facility that is smaller than an industrial-scale power plant that serves a city or region. Power is produced locally rather than at great distances away, and thus transmission lines are shorter, resulting in less power lost during the distribution process. Microgeneration often has a smaller carbon footprint and less environmental impact than industrial-scale generation since it relies more on alternate energy sources such as biomass, solar cells, wind turbines, hydrogen fuel cells, and hydroelectric power.

Process

Microgeneration uses a variety of technologies. In addition to a connection to a country’s electrical grid (electrical power distribution network), if applicable, there must be a power plant and infrastructure for the storage and conversion of energy. The energy-storage apparatus is necessary for efficiency and to make surplus energy available when the demand is greater than the supply being generated. Battery storage is a common solution, but hydrogen fuel cells, flywheel energy storage, and pumped hydroelectric energy storage are also used. Power-conditioning equipment is used to convert energy from direct current to usable alternating current. Surge protectors, switches, and groundings constitute the necessary safety equipment, while meters monitor power consumption, power fed into the grid, and energy storage.

Microgeneration systems vary greatly from locale to locale. For instance, in the urbanized developed world, a residence or business may keep its connection to the traditional power grid but operate some alternate means of power generation, so that it draws from the grid only when additional power is needed or when the microgeneration system is being repaired. Retaining a connection to the grid also allows the delivery of surplus power from microgeneration back to the utility.

Microgeneration is necessary for autonomous buildings, which operate independently from the local infrastructure. (Those buildings are separated from the electrical and natural gas grids, communication systems, water systems, and sewage-treatment systems.) In some parts of the world, the principal benefit to autonomy is not environmental responsibility but the ability to continue functioning when the national or regional grid is unreliable. In the developed world an autonomous residence is sometimes called “a house with no bills.” Because start-up costs are high, microgeneration must be planned carefully and thoughtfully to be economically feasible, but certain technologies such as wind turbines and solar panels have benefited from economies of scale (a reduction in a technology’s cost as its production increases).

Net metering

Microgeneration adopters experience cost savings by using less energy from the grid, and those who create surplus power can make a profit by selling excess electricity back to local electrical utilities. In the United States, under the 2005 Energy Policy Act, all public electric utilities are required to make net metering available to customers on request. The process of net metering credits the bills of nonutility net energy producers when they add electricity to the grid, which reduces the amount they pay for electricity. It records energy inflows and outflows and bills customers only for the difference between the amount used and the amount produced. Whether or not credits in the customer’s favour—when more energy has been generated than consumed—roll over to the next billing cycle varies from state to state. In most states, credits roll over from month to month; however, some states provide annual credits instead. State laws also vary on whether electric utilities can limit the percentage of subscribers who are signed up for net metering, whether there is a power limit on energy inflows, and how customers whose accounts end the billing year in a credit are compensated.

The legal environment relevant to microgeneration also varies. In the United States there are federal and, in many cases, state income tax credits available for the use of renewable energy; however, some of those programs are controversial because they effectively transform the tax credit into an increased tax burden paid by people who do not use microgeneration. In addition, many utilities feel threatened by net-metering programs because they typically herald losses in revenue; microgeneration adopters use less utility-produced power, and net-metering laws compel utilities to buy power from them.

In the United Kingdom the Microgeneration Certification Scheme (MCS) covers all microgeneration technologies. MCS was the foundation of the country’s Low Carbon Buildings Programme, which rewarded green buildings with government grants to offset their initial costs.

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Also called:
alternative energy
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renewable energy, usable energy derived from replenishable sources such as the Sun (solar energy), wind (wind power), rivers (hydroelectric power), hot springs (geothermal energy), tides (tidal power), and biomass (biofuels).

At the beginning of the 21st century, about 80 percent of the world’s energy supply was derived from fossil fuels such as coal, petroleum, and natural gas. Fossil fuels are finite resources; most estimates suggest that the proven reserves of oil are large enough to meet global demand at least until the middle of the 21st century. Fossil fuel combustion has a number of negative environmental consequences. Fossil-fueled power plants emit air pollutants such as sulfur dioxide, particulate matter, nitrogen oxides, and toxic chemicals (heavy metals: mercury, chromium, and arsenic), and mobile sources, such as fossil-fueled vehicles, emit nitrogen oxides, carbon monoxide, and particulate matter. Exposure to these pollutants can cause heart disease, asthma, and other human health problems. In addition, emissions from fossil fuel combustion are responsible for acid rain, which has led to the acidification of many lakes and consequent damage to aquatic life, leaf damage in many forests, and the production of smog in or near many urban areas. Furthermore, the burning of fossil fuels releases carbon dioxide (CO2), one of the main greenhouse gases that cause global warming.

In contrast, renewable energy sources accounted for nearly 20 percent of global energy consumption at the beginning of the 21st century, largely from traditional uses of biomass such as wood for heating and cooking. By 2015 about 16 percent of the world’s total electricity came from large hydroelectric power plants, whereas other types of renewable energy (such as solar, wind, and geothermal) accounted for 6 percent of total electricity generation. Some energy analysts consider nuclear power to be a form of renewable energy because of its low carbon emissions; nuclear power generated 10.6 percent of the world’s electricity in 2015.

Combination shot of Grinnell Glacier taken from the summit of Mount Gould, Glacier National Park, Montana in the years 1938, 1981, 1998 and 2006.
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Growth in wind power exceeded 20 percent and photovoltaics grew at 30 percent annually in the 1990s, and renewable energy technologies continued to expand throughout the early 21st century. Between 2001 and 2017 world total installed wind power capacity increased by a factor of 22, growing from 23,900 to 539,581 megawatts. Photovoltaic capacity also expanded, increasing by 50 percent in 2016 alone. The European Union (EU), which produced an estimated 6.38 percent of its energy from renewable sources in 2005, adopted a goal in 2007 to raise that figure to 20 percent by 2020. By 2016 some 17 percent of the EU’s energy came from renewable sources. The goal also included plans to cut emissions of carbon dioxide by 20 percent and to ensure that 10 percent of all fuel consumption comes from biofuels. The EU was well on its way to achieving those targets by 2017. Between 1990 and 2016 the countries of the EU reduced carbon emissions by 23 percent and increased biofuel production to 5.5 percent of all fuels consumed in the region. In the United States numerous states have responded to concerns over climate change and reliance on imported fossil fuels by setting goals to increase renewable energy over time. For example, California required its major utility companies to produce 20 percent of their electricity from renewable sources by 2010, and by the end of that year California utilities were within 1 percent of the goal. In 2008 California increased this requirement to 33 percent by 2020, and in 2017 the state further increased its renewable-use target to 50 percent by 2030.

Noelle Eckley Selin The Editors of Encyclopaedia Britannica