Wind is the movement of air generated by the earth’s rotation and by the heating of the atmosphere by the sun. The wind resulting is both intermittent and unpredictable. The amount of wind energy available varies with position on the globe and some regions have much better resources than others. Wind atlases can help reveal the best resource regions but site measurements are usually necessary to evaluate a particular wind project. Global wind capacity has been growing steadily since the beginning of the century. Early growth was driven by expansion in Europe but towards the end of the first decade of the century the centre of gravity moved away from Europe with growth in both the USA and China growing rapidly. Europe still has the largest wind capacity but this will soon be overtaken by Asia. Offshore wind, however, remains a European phenomenon with virtually all the global capacity still located in European waters.

Solar energy is the most abundant energy resource on the earth today, with the amount of energy reaching the surface equivalent to 7,500 times annual energy consumption. Solar cells are robust solid state devices that can operate under virtually all light conditions. Their output is greater the higher the light intensity available. Solar intensity varies globally, with the best regions generally close to the equator. Africa, south and southeast Asia, Australia, the southern states of the USA, and central and south America - all have good resources. However, even regions with lower average insolation, such as northern Europe or Japan - can exploit solar photovoltaic technology successfully. Solar cell capacity has grown rapidly in the second decade of the twenty-first century, reaching 137GW at the end of 2013.