since ancillary services are typically provided by controllable fossil-fuel generators, future carbon-free electrical grids that contain high percentages of solar and wind must rely on other forms of controllable power generation or consumption. one of the most well-known examples of this is vehicle to grid technology. in this case, distributed electrical vehicles connected to the grid can be controlled together to act as a single virtual power plant. by selectively controlling the rate at which each individual vehicle charges, the grid sees a net injection or consumption of energy as if a large scale battery was providing this service.