Car manufacturer Toyota is to add solar panels to some of its vehicles to power their smaller features.According to the Guardian, the next phase of remodelling of the Prius hybrid car will see the addition of solar panels in response to calls for environmentally-friendly cars amid concerns over rising fuel costs.The high-end models of the cars will have features such as air conditioning powered by the renewable resource, although it is thought that it would be difficult to power an entire car using the sun's energy.Difficulties in energy storage and the rising cost of silicon were cited by the source, who wished not to be named, as factors that would stand in the way of fully solar-powered cars."It's more of a symbolic gesture," the source said."It's very difficult to power much more than that with solar energy."A zero carbon initiative is currently being explored by Lotus, which is working on a process to extract CO2 from the atmosphere in order to power vehicles.