The demand for energy has led to a constant search for alternative sources of energy, apart from fossil fuel. Solar energy is an alternative source of energy, but it is not the only alternative energy source. Indeed, there are other ways to produce energy than solar panels, which may either be renewable or nonrenewable.

Biofuels

Biofuels are the direct opposite of fossil fuels because this type of fuel is derived from recently living organisms, as opposed to fossil fuels, which derives from organisms that died millions of years ago. Biofuels are divided into three categories: first generation, second generation and third generation. First-generation biofuels are derived from edible starches and sugar. Second-generation biofuels are derived from non-edible plant materials, and third-generation biofuels are derived from algae and other types of microbes. Biofuels are considered renewable sources of energy because their sources can be regrown.

Coal

According to Chevron, coal is used to produce about 27 percent of the world’s total energy use. Its website states that coal is used to produce 45 percent of the electricity in the United States. This energy source is important because, according to statistics from Chevron, the world's coal consumption is expected to increase by about 60 percent between 2008 to 2035.Coal is used in various industrial processes like cement manufacturing, steel production and the generation of electricity. Coal is a nonrenewable source of energy and also an environmentally unfriendly source of energy, as it is one of the biggest sources of greenhouse emissions. The U.S. Environmental Protection Agency (EPA) reports that one-quarter of the world's coal reserves are in the United States and that more than half of the electricity consumed by Americans is derived from coal power.

Natural Gas

Natural gas was dismissed as a useless byproduct of crude oil production in the past. Back then, natural gas was dispersed into the atmosphere through a process known as gas flaring. It was not until the second half of the 20th century that the true benefits of natural gas were discovered. Now, natural gas is used to produce 23 percent of the world's energy, according to Chevron. This source of energy is nonrenewable because it is derived from fossils; however, it is one of the cleanest conventional energy sources because it produces very low levels of greenhouse gas emissions in comparison to heavier hydrocarbon fuels like coal and oil.

Wind Power

Wind power is the process of converting wind energy into usable forms, like electricity or mechanical energy. This usually is achieved through the use of wind turbines. There are wind farms that are specifically made for the creation of wind energy. Usually, they are connected to local power transmission networks, through which electricity is transmitted, and may be provided to isolated areas. This source of energy is renewable and has a very low environmental impact.