Mechanical energy nonconservative forces, like frictional forces, will be present, but often they are of negligible values and the mechanical energy's being constant can therefore be a useful approximation. In elastic collisions, the mechanical energy is conserved but in inelastic collisions, some mechanical energy is converted into heat. The equivalence between lost mechanical energy (dissipation) and an increase in temperature was discovered by James Prescott Joule. Many devices are used to convert mechanical energy to or from other forms of energy, e.g. an electric motor converts electrical energy to mechanical energy, an electric generator converts mechanical energy into electrical energy and a
Energy policy of China has the goal of achieving an integrated nationwide grid in the period between 2015 and 2020. In 2015, China generated 73% of its electricity from coal-fired power stations, which has been dropping from a peak of 81% in 2007. China is the world's leading renewable energy producer, with an installed capacity of 152 GW. China has been investing heavily in the renewable energy field in recent years. In 2007, the total renewable energy investment was $12 billion USD, second only to Germany. In 2012, China invested $65.1 billion USD in clean energy (20% more than in 2011), fully 30% of