When a car is under the sun, the interior is hot. This is due to the interior, especially seats, which are black (or a dark color) so that they heat under sun light and restitute this heat to the air. how much energy is stored in the interior elements ?
Is the car interior hot because the space is little or hot because elements heat a lot ?
You would need to find the specific heat capacity of all the materials inside the car, which might be difficult to get, but as a first estimate you can start with the air in the car. It's specific heat at room temperature is about $c=$1000 Joules/(kg-K). The "stored energy" I assume you are looking for is the amount of energy that would be released by cooling the air to room temperature (20°C). If we assume the heated car is at 40°C, your stored energy would be: $E=mc(40-20)$ Where $m$ is the mass of air in the car that you would find using the volume and density (at 40°C). This would be a good exercise for you to do.
