Alternative energy is energy derived in such a way that it does not harm the environment or the fuel sourced that it relies on. The debate against common energy solutions such as fossil fuels (petroleum, coal, etc.) that are in use today is an old one. They harm the environment and are a cause of pollution, whereas on the other hand they are non-reusable, that is that they would eventually run out as we have a limited supply of them and they cannot be replaced, hence the need for alternative energy solutions.