Wind Energy
Wind power is a vast resource of clean, reliable cost effective electricity. Electricity generated from the wind does not contribute to global warming and acid rain. As part of an electrical system which has a diversity of sources or significant storage capacity, wind turbines can be a valuable source of low cost electricity. The amount of electricity supplied in the future by wind turbines will depend upon the costs of wind power compared to other sources of electricity and the value that society places on reducing atmospheric pollution, rather than the ultimate size of the wind resource. All methods of generating electricity, including wind turbines have some negative environmental impacts and therefore it is important that electricity is used efficiently regardless of source.
Tidal Energy
In coastal areas with large tides, flowing tidal waters contain large amounts of potential energy. The principal of harnessing the energy of the tides dates back to eleventh century England when tides were used to turn waterwheels, producing mechanical power. More recently, rising and falling tides have been used to generate electricity, in much the same manner as hydroelectric power plants.
Tides originate from the motions of the earth, moon and sun. Although ocean tides contain extremely large amounts of energy, it is only practical to generate electricity at sites with exceptionally high tides such as the Bay of Fundy in Atlantic Canada which, at up to 17 metres, has the highest tides in the world. Tidal energy is an essentially renewable resource which has none of the typical environmental impacts of other traditional sources of electricity such as fossil fuels or nuclear power. Changing the tidal flow in a coastal region could, however, result in a wide variety of impacts on aquatic life, most of which are poorly understood.
Geothermal Energy
Geothermal energy is energy recovered from the heat of the earth's core. In nature, geothermal heat shows up in the form of volcanoes, hot springs and geysers. For thousands of years, humans have used naturally occurring hot springs for bathing. More recently, geothermal energy has been used to generate electricity, and to provide heat for homes and industries. Geothermal energy is a versatile and reliable source of heat and electricity which generally produces none of the greenhouse gases associated with the combustion of fossil fuels. Unfortunately, the best geothermal resources are concentrated in areas of volcanic activity and are not widely distributed. California, Iceland, Italy, New Zealand and Japan are all areas where geothermal energy is used on a significant scale.
The high temperatures in the earth's core are a result of heat trapped during the formation of the earth approximately 4.7 billion years ago, as well as the decay of naturally occurring radioactive elements. The rate of heat flow out of the earth is about 5,000 times smaller than the rate of solar energy reaching the earth's surface. Solar radiation therefore controls the surface temperature of the planet; but a few meters below the earth's surface, temperatures are governed by the internal heat of the earth. Geothermal energy is often considered a renewable source of energy. This is not strictly true, because human uses of geothermal generally remove the heat from a location faster than it is replaced. The magnitude of the geothermal resource is so large, however, that on a human time scale it may be considered as a renewable energy source.
Biomass
Biomass, defined as all land and water based vegetation as well as all organic wastes, fulfilled almost all of humankind's energy needs prior to the industrial revolution. All biomass is produced by green plants converting sunlight into plant material through photosynthesis. As recently as 1850, 91% of the total US energy consumption was biomass in the form of wood. Since the industrial revolution, the majority of the developed world's energy requirements have been met by the combustion of fossil fuels such as coal, oil and natural gas. Biomass, however, is still the predominant form of energy used by people in the less developed countries, accounting for 14% of world energy use.
Worldwide concern about global warming and acid rain have prompted many observers in industrialized countries to call for a decreased reliance on fossil fuels. Renewable sources of energy such as wind, solar and hydro power, as well as biomass, are being looked at as alternatives. Conversion of biomass into useful energy carriers is fairly well documented and economical in many cases; but less well understood are the environmental implications of increased use of biomass fuels.