Tribrids are the third generation of alternative propulsion vehicles. Second generation are the bivalent hybrid vehicles with turbines. Tribrids are hybrids that obtain additional energy from the ambient environment (solar panel, windmill or sail). An example is a velomobile with an electric power-assist motor and additional on-board solar cells. Under this definition, 2010 Toyota Prius hybrids equipped with an optional solar panel are tribrids.