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Lost in the mix are the biofuels, fuels made from biological ingredients instead of fossil fuels. These starting ingredients can range from corn to soybeans to animal fat, depending on the type of fuel being made and the production method.

Ethanol, for instance, is an alcoholic biofuel easily distilled from sugary or starchy plants. It has been used to power cars since Ford’s Model T and, blended into conventional petrol, constitutes about 10% of the fuel burned by America’s vehicles today.

Photovoltaic cells are made of at least two layers of semiconducting material. The first layer has a positive charge; the next layer has a negative charge. When sunlight strikes the cell, the semiconducting material absorbs photons from the light. This process frees electrons from the negative layer, which move to the positive layer. This flow of electrons constitutes an electric current, which can be captured in a circuit connecting the two layers. The electricity generated by a photovoltaic cell can be used directly, stored in batteries or sold back to a utility company.

Solar power is different: although it too uses a lot of space, solar panels can be very well integrated into the urban environment, so they have virtually no impact on land use and cause very little visual pollution.