By 2050 most of the planet no longer uses fossil fuels for energy, save for those who burn fossil fuels for collectable devices such as Petroleum Age cars and Industrial Era steam engines. All cars produced use electricity for their drive trains, and most private homes and businesses generate their own energy. Personal Power, the engineering philosophy of designing a building to generate its own electricity autonomously, is a common design practice. Large scale Mass Power is still in use as a means of power large devices such as particle accelerators, and acting as a reserve for city electrical grids in the event that more energy is consumed by a building than is made.