In the developed world, energy use contributes more than any other activity to greenhouse gas emissions, which may cause global warming. This is because most of our energy comes from carbon-based fossil fuels like coal, oil, and natural gas. When we burn these fuels for heat, power, and transportation, the carbon they contain combines with oxygen from the air to form carbon dioxide, the most abundant greenhouse gas. Using energy more efficiently can help to reduce carbon dioxide emissions, but won't eliminate them, so long as we continue to rely on fossil fuels as our energy source to begin with. To eliminate the problem altogether, and achieve a sustainable energy future, we need to use renewable sources of energy, like the wind, the sun, rivers, and oceans. This fact sheets looks at renewable energy.
What is Renewable Energy?
Energy sources which are not used up or depleted by over-consumption are called "renewable". They are naturally replenished, and can either be managed so that they last forever, or their supply is so enormous that they can never be meaningfully depleted by humans. In addition, unlike the fossil fuels, most forms of renewable energy do not release carbon dioxide as a by-product into the atmosphere. Biomass energy (energy obtained from the burning of plant material) does release carbon dioxide, but it is only returning to the atmosphere as much as was removed through photosynthesis during the plant's lifetime. Burning fossil fuels, by contrast, returns carbon dioxide to the atmosphere which has been locked away in the Earth's crust for hundreds of millions of years.
Sources of Renewable Energy
The Sun provides a basic form of energy for all living organisms. It has been shining for nearly 5 thousand million years, and will probably go on shining for at least as long. Solar energy is therefore free and inexhaustible. Converting sunlight into useful forms for human consumption is not exactly free, but with today's technology, it is not nearly as expensive as it once used to be. Sunlight has been used by humans for drying crops and heating water and buildings for millennia - called passive solar heating. A twentieth-century technology is photovoltaics, which turns sunlight directly into electricity.
Air moves around the Earth because of the differences in temperature and atmospheric pressure which exist. This movement of air can also be harnessed as a form of energy, and has been since ancient times. Today, advanced aerodynamics research has developed wind turbines that can produce electricity on a very economic basis. Wind turbines are often grouped together in farms, located in exposed areas of countryside, either near coasts or on hill tops which experience a regularly prevailing wind throughout the year.
Rocks under the Earth's crust contain naturally decaying radioactive materials like uranium and potassium, producing a continuous supply of heat The amount of heat within 10,000 meters of the surface contains 50,000 times more energy than all the oil and gas resources in the world. Geothermal energy taps into the heat under the Earth's crust to boil water. The hot water is then used to drive electric turbines and heat buildings. The areas with highest underground temperature are in regions with active or geologically young volcanoes. These "hot spots" occur at the boundaries between tectonic places where the crust is thin enough to let the heat through. Many of these "hot spots" occur around the Pacific Rim, called the "ring of fire" for all of its volcanoes.
On Earth, water is neither created nor destroyed, but is constantly moved around. Water evaporates from the oceans, forming clouds, falling out as rain and snow, collecting into streams and rivers, and flowing back to the sea. All this movement provides an enormous opportunity to create useful energy. Hydroelectric power uses the force of moving water to produce electricity. Hydropower is one of the main suppliers of electricity in the world, and the main source of renewable energy, but is most often in the form of large dams which disrupt habitats and displace people. A better approach is to use small scale hydro plants.
Biomass is a term we use to describe plant materials and animal wastes used for energy. Plants form the basis of the food chain, on which all life on earth depends. But in terms of energy production "biomass" refers to using tree and grass crops, and forestry, agricultural, and urban wastes. It is the oldest source of renewable energy known to humans. Biomass is a renewable energy source because the energy it contains comes from the Sun. Through the process of photosynthesis, chlorophyll in plants captures the Sun's energy by converting carbon dioxide from the air and water from the ground into "carbohydrates," complex compounds composed of carbon, hydrogen and oxygen. When these carbohydrates are burned, they turn back into carbon dioxide and water, and release the Sun's energy they contain. In this way, biomass functions as a sort of natural store of solar energy.
Use of Renewable Energy
Compared to the use of fossil fuels, the harnessing of energy from renewable sources for mass consumption is still limited. Large scale hydroelectric power contributes about 20% of the world's energy needs. In the UK however, energy from renewables currently contributes only 3% to the total electricity consumed. About half of this comes from hydroelectric power, with about 20% from landfill gas and 10% from wind power. In the UK, the Government is trying to encourage the uptake of renewable energy through the Non-Fossil Fuel Obligation, which requires energy suppliers to purchase some of their electricity from renewable sources.
Barriers to Renewable Energy
One of the major reasons why the use of renewable energy is still relatively limited is its cost compared to fossil fuel generated power. Recently, improved technology has made wind power and biomass energy economically more competitive. The cost of some solar energy designs, however, remains fairly high, and it is unlikely that countries like the UK, with unreliable sources of sunlight, will invest considerable sums of money into developing this resource within the short term future. Furthermore, renewable energy systems can often be locally intrusive: many people object to large numbers of wind turbines occupying the countryside, and emissions from biomass waste incineration have the potential to cause health problems if unmanaged. Despite these barriers, however, renewable energy over the long term is likely to have a secure future, and will continue to provide an increasing proportion of the world's energy needs whilst concerns about the climatic impacts of fossil fuel power generation remain.
Reducing our dependence on fossil fuels such as coal, oil and gas for the production of energy will not be an easy task. Part of the solution will come from a family of diverse energy technologies that share one common thread - they do not deplete or destroy our natural resources. Renewable energy technology taps into natural cycles and systems, turning the ever-present energy around us into usable forms. The movement of wind and water, the heat of the Sun, heat trapped underground, and the carbohydrates in plants are all natural energy forms which can supply our needs in a clean and sustainable way, and in a way that will not change the global climate.