Clean energy
Clean energy refers to energy sources that generate little to no carbon dioxide (CO2) emissions or other pollutants, thus contributing less to global warming. Key examples include solar energy, wind power, and hydropower. Solar energy can be harnessed through photovoltaic cells that convert sunlight into electricity and solar thermal systems that generate heat. Wind power involves converting wind energy into electricity using turbines, which have seen significant technological advancements, particularly in Europe and the United States. Hydropower is the most widely utilized clean energy form, involving the generation of electricity from high-pressure water flow through turbines.
The significance of clean energy lies in its potential to mitigate climate change, as countries strive to reduce reliance on fossil fuels. While clean energy technologies have historically been more expensive, rising concerns over climate change and fluctuating fossil fuel prices have accelerated their adoption. Nevertheless, some clean energy solutions, like hydropower, can have environmental impacts, such as greenhouse gas emissions from decaying plant material in flooded areas. As the world progresses toward sustainability, clean energy is increasingly seen as essential for meeting global climate targets, with ambitious goals set for renewable energy contributions in the coming decades.
Subject Terms
Clean energy
Definition
Clean energy refers to any energy source whose use does not emit carbon dioxide (CO2), or other pollutants or that contribute to global warming. Examples of clean energy include solar energy, wind power, and hydroelectric power. Nuclear power is considered by some to be clean energy (it does not emit CO2), but opponents point to the risk of radioactive contamination that it carries. Natural gas is essentially nonpolluting but emits CO2 when burned. (Because methane has a much greater than does CO2, burning it reduces the total amount of CO2 equivalent GHG in the world, despite generating a GHG.)
Solar power (or solar energy) is energy given off by the sun. Humans harness only a tiny fraction of this energy (less than 0.0001 percent), as it is diffuse, is very difficult to trap, and can vary with seasonal and weather conditions. Photovoltaic and solar thermal technologies are the solar technologies most widely used for contemporary power generation. In a photovoltaic process, solar energy is used to generate electricity. Photovoltaic cells, or solar batteries, can be found in many home appliances, including calculators and watches. Each photovoltaic cell consists of two layers. When sunlight strikes the solar cell, electrons from the lower layer move toward the upper surface, creating an electrical potential between the layers. This potential provides an electrical current. Electrons from the upper layer flow through an electrical device (for example, a small motor) back to the lower layer, thus providing energy for the device. These cells can be arranged into panels that generate enough electricity to power an entire family house.
Another solar technology, known as a solar thermal system, uses sunlight to generate heat. These systems are very popular in warm, sunny climates and have been used to provide hot water for homes and factories for decades. A typical solar collector for heating water consists of a shallow box with a plastic top and a black bottom. Glass or plastic tubes filled with water run through the inside of the box. The black bottom absorbs light and conveys the heat to the water within the tubes; the clear top of the box prevents heat from escaping. This technology can also be used to generate electricity, using a technology called concentrating solar power. This technology deploys thousands of dish-shaped solar concentrators attached to an engine that converts heat to electricity.
Wind power is the conversion of wind energy into useful forms of energy, mainly electricity. The design of wind turbines is based on wind-driven propeller blades. Turbine design has recently improved, allowing much more electricity to be generated at competitive prices. In the early 2020s, Europe was the world’s number one user of wind power, followed by the United States. Hydropower is the most widely used form of clean energy. In hydropower dams, water under high pressure flows through turbines and generates electricity.
Significance for Climate Change
In order to reduce global warming, the United States and other countries are making a major commitment to develop clean energy sources that generate little or no CO2. For decades, clean energy technologies were too expensive to compete with fossil fuels. Concerns about global warming, coupled with the high prices of oil, have pushed forward the use of clean (or green) energy technologies. In the first years of the twenty-first century, clean energy supplied less than 7 percent of the world’s energy consumption, but the potential of such technologies was enormous. The amount of solar energy reaching Earth exceeds by six thousand times humanity’s global energy consumption. In the United States, the potential for the expansion of wind power is enormous as well, especially in the windy Great Plains area. In the early 2020s, hydropower already generated about 17 percent of the electricity used around the world.
The operation of wind turbines and solar power stations does not consume and does not produce GHG emissions. However, wind turbines and solar panels require the use of some fossil energy during construction and transportation. These initial CO2 emissions are not significant compared to the environmental benefits of using clean wind and solar power. Wind turbines and solar panels do not require of land, so they do not interfere with forests’ ability to sequester CO2. In addition, land beneath wind turbines can be used for farming. Turbines may also be placed offshore.
Solar photovoltaic cells and collectors can be installed on the roofs and walls of homes and offices, as well as in the desert. Wind power is one success story involving the use of clean energy to reduce CO2 emissions; the number of wind turbines used for the generation of electricity increased dramatically in the first decades of the twenty-first century. Prices for wind power decreased until they were very close to the price of electricity generated by burning coal, a major CO2 producer. This decrease in price may allow replacing coal power with wind-generated power in the future. According to US Energy Information Administration (EIA) statistics, wind power's share of total US electricity generation increased from below 1 percent in 1990 to approximately 11 percent in 2023. Meanwhile, supportive government policies in several European countries, as well as technical improvements, helped drive strong growth in wind energy at the global level as well. One major growth market was China, which directed significant investment into becoming the leading generator of wind-powered electricity in the world. However, while many environmentalists applaud the non-polluting nature of wind-power generation, some people complain that the devices themselves are a blight on the landscape. Offshore wind farms, with turbines sitting in the shallow water of the ocean, have been especially controversial for this reason. Local residents' objections to the effect on the view and, in some locations, concerns about the possible impact on tourism have blocked attempts to build offshore wind farms in a number of countries.
Hydropower is also ideal for clean electricity generation. It does not produce CO2 directly. However, hydropower stations are criticized because they change the environment indirectly, in a way that may produce substantial amounts of both CO2 and methane, a very powerful GHG. The water trapped in flooded areas directly upstream of hydropower dams contains a large amount of decaying plant material. This plant material is metabolized by microorganisms, leading to the formation of CO2 and methane. However, hydropower technologies such as tidal energy exist that do not generate GHG emissions during use. Tidal power uses the energy generated by the daily ebb and flow of ocean tides. This energy is derived directly from the gravitational pull of the moon and, to a lesser extent, the sun. Large tidal power plants exist in France, Canada, and the United States, among other locations.
By the second decade of the twenty-first century, renewable energy sources came to be recognized as critical for the sustainability of Earth’s at-risk climate. Projections indicated the demand and growth for renewable energy sources would accelerate through the decade. These would facilitate cleaner manufacturing, types of fuels, availability, and initiatives such as offshore wind projects. Private investment in clean energy sources was also projected to increase greatly.
Nonetheless, the adoption rate has struggled to keep pace with global climate goals. In January 2023, the United Nations secretary-general Antonio Guterres remarked that the 2015 Paris Agreement objective of preventing global temperature rise from exceeding 1.5 degrees Celsius was falling out of reach. Guterres stated that renewable energy needed to account for 60 percent of global electricity by 2030 and 90 percent by 2050 to meet objectives. Meanwhile, the IEA reported in 2023 that significant progress had been made, with renewable electricity accounting for 30 percent of global electricity generation by 2022, while acknowledging that more innovation was needed to meet international climate goals.
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