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Sustainable energy facts for kids

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Micro WindMill
A 01 KiloWatt Micro Windmill for Domestic Usage

Sustainable energy involves both energy efficiency and renewable energy. Both resources help to stabilize and reduce carbon dioxide emissions.

Efficient energy use allows energy demand to slow so that rising clean energy supplies can make big cuts in fossil fuel burning. If energy use grows too fast, renewable energy development will chase a receding target. Likewise, unless clean energy supplies come online rapidly, slowing demand growth will only begin to reduce total emissions; reducing the carbon content of energy sources is also needed.

Any serious vision of a sustainable energy economy thus requires major commitments to both efficiency and renewables.

Renewable energy sources

Renewable-energy-consumption-1965-2016
Rise in renewable energy consumption from 1965 to 2016

When referring to sources of energy, the terms "sustainable energy" and "renewable energy" are often used interchangeably, however particular renewable energy projects sometimes raise significant sustainability concerns. Renewable energy technologies are essential contributors to sustainable energy as they generally contribute to world energy security, and reduce dependence on fossil fuel resources thus mitigating greenhouse gas emissions.

Solar power

In 2018, solar power provided around 3% of global electricity. Solar electricity production uses photovoltaic (PV) cells to convert light into electrical current. Photovoltaic modules can be integrated into buildings or used in photovoltaic power stations connected to the electrical grid. They are especially useful for providing electricity to remote areas. Although generally warranted for 25 years it is claimed that an average solar panel will last 40 years and almost all of it can be recycled.

Currently, photovoltaic (PV) panels only have the ability to convert around 24% of the sunlight that hits them into electricity. At this rate, solar energy still holds many challenges for widespread implementation, but steady progress has been made in reducing manufacturing cost and increasing photovoltaic efficiency. In 2008, researchers at Massachusetts Institute of Technology (MIT) developed a method to store solar energy by using it to produce hydrogen fuel from water. Such research is targeted at addressing the obstacle that solar development faces of storing energy for use during nighttime hours when the sun is not shining.

Large national and regional research projects on artificial photosynthesis are designing nanotechnology-based systems that use solar energy to split water into hydrogen fuel and a proposal has been made for a Global Artificial Photosynthesis project.

Research is ongoing in space-based solar power, a concept in which solar panels are launched into outer space and the energy they capture is transmitted back to Earth as microwaves. A test facility for the technology is being built in China.

Flipped MIT Solar One house
MIT's Solar House#1 built in 1939 used seasonal thermal energy storage (STES) for year-round heating.

Solar heating

Solarpipe-scheme
Sketch of a Parabolic Trough Collector

Solar heating systems generally consist of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage, and a reservoir or tank for heat storage and subsequent use. The systems may be used to heat domestic hot water, swimming pool water, or for space heating. The heat can also be used for industrial applications or as an energy input for other uses such as cooling equipment. In many climates, a solar heating system can provide a very high percentage (20 to 80%) of domestic hot water energy. Heat can be stored through thermal energy storage technologies. For instance, the summer heat can be stored for winter heating. Similar principles are used to store winter cold for summer air conditioning.

Wind power

Global Wind Power Cumulative Capacity
Wind power: worldwide installed capacity

In 2018, wind power provided approximately 6% of the global electricity supply. However, it may be difficult to site wind turbines in some areas for aesthetic or environmental reasons. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore.

After about 20 years wind turbine blades need replacing with larger blades, and research continues on how best to recycle them and how to manufacture blades which are easier to recycle.

Hydropower

Among sources of renewable energy, hydroelectric plants have the advantages of being long-lived—many existing plants have operated for more than 100 years. Also, hydroelectric plants are clean, have few emissions and can compensate for variations in wind and solar power. Criticisms directed at large-scale hydroelectric plants include: dislocation of people living where the reservoirs are planned, and release of greenhouse gases during construction and flooding of the reservoir.

Nishidaira Dam
Hydroelectric dams are one of the most widely deployed sources of sustainable energy.

However, it has been found that high emissions are associated only with shallow reservoirs in warm (tropical) locales, and recent innovations in hydropower turbine technology are enabling efficient development of low-impact run-of-the-river hydroelectricity projects. Generally speaking, hydroelectric plants produce much lower life-cycle emissions than other types of generation.

In 2015, hydropower supplied 16% of the world's electricity, down from a high of nearly 20% in the mid-to late 20th century. It produced 60% of electricity in Canada and nearly 80% in Brazil. As of 2017, new hydropower construction has stopped or slowed down since 1980 in most countries except China.

Biomass

Sugarcane plantation to produce ethanol in Brazil
A CHP power station using wood to provide electricity to over 30.000 households in France

Biomass is biological material derived from living, or recently living organisms. As an energy source, biomass can either be burned to produce heat and to generate electricity or converted to modern biofuels such as biodiesel and ethanol.

Biomass is extremely versatile and one of the most-used sources of renewable energy. It is available in many countries, which makes it attractive for reducing dependence on imported fossil fuels. If the production of biomass is well-managed, carbon emissions can be significantly offset by the absorption of carbon dioxide by the plants during their lifespans. However this "carbon debt" may be paid back too late, or (especially in the United States) not properly accounted for. If the biomass source is agricultural or municipal waste, burning it or converting it into biogas also provides a way to dispose of this waste. Bioenergy production can be combined with carbon capture and storage to create a zero-carbon or negative-carbon system, but it is doubtful this can be scaled up quickly enough.

If biomass is harvested from crops, such as tree plantations, the cultivation of these crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilizers. In some cases, these impacts can actually result in higher overall carbon emissions compared to using petroleum-based fuels.

Biofuels

Sao Paulo ethanol pump 04 2008 74 zoom
Neat ethanol on the left (A), gasoline on the right (G) at a filling station in Brazil

Biofuels are fuels, such as ethanol, manufactured from various types of biomass, such as corn or sugar beet. Biofuels are usually liquid and used to power transport, often blended with liquid fossil fuels such as gasoline, diesel or kerosene. As of 2020 which are sustainable biofuel is being debated.

Cellulosic ethanol has many benefits over traditional corn based-ethanol. It does not take away or directly conflict with the food supply because it is produced from wood, grasses, or non-edible parts of plants. Moreover, some studies have shown cellulosic ethanol to be potentially more cost effective and economically sustainable than corn-based ethanol. As of 2018, efforts to commercialize production of cellulosic ethanol have been mostly disappointing, but new commercial efforts are continuing.

Use of farmland for growing fuel can result in less land being available for growing food. Since photosynthesis is inherently inefficient, and crops also require significant amounts of energy to harvest, dry, and transport, the amount of energy produced per unit of land area is very small, in the range of 0.25 W/m2 to 1.2 W/m2. In the United States, corn-based ethanol has replaced less than 10% of motor gasoline use since 2011, but has consumed around 40% of the annual corn harvest in the country. In Malaysia and Indonesia, the clearing of forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for endangered species. In 2015, annual global production of liquid biofuels was equivalent to 1.8% of the energy extracted from crude oil. It has been suggested that, due to the limited quantities that can be sustainably produced, it should all be aviation biofuel: because unlike other forms of transport long-distance aviation cannot be powered by batteries, hydrogen, ammonia or fuel cells.

Geothermal

West Ford Flat Geothermal Cooling Tower
One of many power plants at The Geysers, a geothermal power field in northern California, with a total output of over 750 MW.

Geothermal energy is produced by tapping into the thermal energy created and stored within the earth. It arises from the radioactive decay of an isotope of potassium and other elements found in the Earth's crust. Geothermal energy can be obtained by drilling into the ground, very similar to oil exploration, and then it is carried by a heat-transfer fluid (e.g. water, brine or steam). Geothermal systems that are mainly dominated by water have the potential to provide greater benefits to the system and will generate more power. Within these liquid-dominated systems, there are possible concerns of subsidence and contamination of ground-water resources. Therefore, protection of ground-water resources is necessary in these systems. This means that careful reservoir production and engineering is necessary in liquid-dominated geothermal reservoir systems. Geothermal energy is considered sustainable because that thermal energy is constantly replenished.

Geothermal energy can be harnessed to for electricity generation and for heating. Technologies in use include dry steam power stations, flash steam power stations and binary cycle power stations. As of 2010, geothermal electricity generation is used in 24 countries, while geothermal heating is in use in 70 countries. International markets grew at an average annual rate of 5 percent over the three years to 2015.

Geothermal power is considered to be a sustainable, renewable source of energy because the heat extraction is small compared with the Earth's heat content. The greenhouse gas emissions of geothermal electric stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal-fired plants.

Marine energy

Marine energy is mainly tidal power and wave power. As of 2020, a few small tidal power plants are operating in France and China, and engineers continue to try and make wave power equipment more robust against storms.

Non-renewable energy sources

Nuclear power

Nuclear Power Plant Cattenom
Cattenom power plant outside Metz is the largest nuclear power plant in France, as of 2011.

Nuclear power plants have been used since the 1950s to produce a steady supply of electricity, without creating local air pollution. In 2012, nuclear power plants in 30 countries generated 11% of global electricity. The IPCC considers nuclear power to be a low-carbon energy source, with lifecycle greenhouse gas emissions (including the mining and processing of uranium), similar to the emissions from renewable energy sources.

There is considerable controversy over whether nuclear power can be considered sustainable, with debates revolving around the risk of nuclear accidents, the cost and construction time needed to build new plants, the generation of radioactive nuclear waste, and the potential for nuclear energy to contribute to nuclear proliferation.

There are potentially two sources of nuclear power. Fission is used in all current nuclear power plants. Fusion is the reaction that exists in stars, including the sun, and remains impractical for use on Earth, as fusion reactors are not yet available.

Thorium is a fissionable material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation and reduced plutonium and actinide production. Therefore, it is sometimes referred as sustainable.

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