1) Traditional energy sources like oil, coal and natural gas have been the principal sources of energy around the world since the 1900s, and are mainly used for electricity and transport. Are they going to run out in the future? When will that be ? How will be survive without them?
3) What do they use? Denmark mainly uses wind power through turbines to mechanically generate power for electricity. Turbines look like giant-size fans placed either on land or in the water. Iceland mainly uses geothermal power - basically the heat coming from the land. Iceland has a high concentration of volcanoes which makes it easy to generate heat.
4) Why should we use renewable energy? For so many reasons, first of all pollution! Oil use produces vast amounts of toxic gases, which makes it extremely polluting. Renewable energy protects our health because it doesn't produce harmful pollution. Secondly, because it is feely available in many forms, any country which has waves, sunshine or wind can benefit from these sources. Renewable energy is an efficient use of natural resources and can be especially useful for developing countries. The question really should be, Why not?