Fossil fuels destroyed by use, I.e. they can be recovered. Alternative source of energy include hydroelectric power, nuclear energy, wind generators and solar panels.
Hydroelectric schemes can only be built in mountains regions where rainfall and rivers are plentiful. Such schemes involve damming rivers which upset the aquatic ecosystems.
Nuclear reactions produce energy. During this process, radioactive wastes are produced. Their disposal poses a dangerous pollution problem. Accidents in nuclear reactors can endanger the future of earth. So people in many countries are opposed to using nuclear energy.
Wind generators and solar panels are not very efficient energy producers. However, future schemes for producing solar energy via solar power satellites are promising. Such schemes would provide us with an inexhaustible supply of energy which would also not cause ant pollution problems.
Wood, oil and alcohol (from fermentation of sugar) could also be used as alternative source of energy. As these are product of photosynthesis, they are renewable. However, arable land has to be used to produce the plants which supply these energy sources. This would be a problem as we do not have land to produce even our food needs.
