What is the primary energy source in a vehicle?

The primary energy source in a vehicle, particularly for conventional internal combustion engine vehicles, is gasoline. It serves as the fuel that powers the engine through combustion, generating the energy necessary to move the vehicle. In electric vehicles, however, the storage battery is the primary source of energy, as it stores electricity that powers the electric motor.

Gasoline, propane, and solar panels are alternative energy sources but are not standard for all vehicle types. Gasoline is commonly used in traditional vehicles, while propane may be utilized in some specific vehicles designed for that fuel type. Solar panels are also an emerging technology primarily used in hybrid and experimental vehicles, but they are not the primary energy source for the majority of current vehicles on the market.

Thus, in context to electric vehicles, the storage battery clearly stands out as the correct answer, functioning as the main power source, storing electricity for operation.