Sustainable energy is energy that can potentially be kept up well into the future without causing harmful repercussions for future generations. A number of types of energy can be thought of as sustainable, and many governments promote their use and the development of new technologies that fit within this model. Increasing rates of energy consumption around the world have led to a corresponding rise in concerns about where the energy comes from and if it will become more scarce.
Several factors go into making energy sustainable. The first is whether or not the current use of the energy is something that could potentially persist into the future, which leads many forms of renewable energy to qualify as sustainable. People can generate energy from windmills, ocean waves, and the sun without running out of energy and resources, making these methods sustainable for use by future generations. By contrast, fossil fuels are not treated as sustainable because the Earth's supplies of crude oil will eventually run out.
Another consideration is energy efficiency. Some forms of renewable energy, for example, take quite a lot of effort to actually generate, meaning that almost as much energy goes into their production as the sources themselves generate. Energy efficiency can also be used to describe the technologies that use energy, such as homes, cars, and businesses. Increased efficiency in the way energy is used makes sustainable energy stretch further.
Many people also feel that the environmental impact an energy source has is another facet of whether or not it is considered sustainable, which is why sources like nuclear power are often not treated as such. Although it meets the demands of renewability and energy efficiency, nuclear power can have a negative impact on the environment. Likewise, some of the methods used to produce solar panels, wind turbines, and other technology to convert renewable sources into energy are polluting, leading to concerns that such technology merely moves the pollution to a different place, making it unsustainable.
Another factor important to some people in the energy field is independence. Some critics argue that energy is not sustainable if a nation is forced to rely on another country to meet its energy needs, even if that energy is renewable, non-polluting, and efficient. For example, if the United States relied heavily on Canadian wind farms, this would violate the criterion of energy independence. Being able to meet one's own energy needs as a nation is an important part of sustainable energy in the eyes of some people who are concerned about the intersection of energy and politics.