The factors that must be kept in mind before choosing a source of energy are:

(a) Ease of extraction: While selecting or choosing a source of energy we must always keep in mind the process involved in the production of the energy from that source. One must also keep in mind the calorific value of the source (in case of fuel). One should also keep in mind the abundance of source in the nature, which implies whether the source is renewable or non-renewable.

(b) The cost of extracting energy from the source is also an important factor in choosing a source. The source may be renewable or physically abundant but the cost of installation may be very high. Hence the expense is also an important factor.

(c) The damage to the environment that the source will cause in the process of extracting energy from it is also an important factor in deciding or choosing the source of energy. The source should cause least pollution, release least harmful gasses and should not harm the environment.

By considering these issues, one should decide what source of energy should be chosen over what.