The number of solar panels needed to charge a car depends on various factors, including the capacity of the solar panels, the efficiency of the charging system, the energy consumption of the car, and the desired charging time. Here are some steps to make a rough estimate of the number of solar panels you need:

1. Determine the car's energy consumption: Consult the specifications of your electric car to find out the average energy consumption per kilometer. This is often expressed in kilowatt-hours per kilometer (kWh/km). Multiply this by the number of kilometers you want to charge to estimate the total energy requirement.

2. Calculate the required energy: Multiply the total energy requirement by a factor to account for charging losses and the efficiency of the charging system. A typical factor can be between 1.2 and 1.5, depending on the charging system and conditions.

3. Determine the capacity of the solar panels: Solar panels have a certain capacity expressed in watt-peak (Wp). This indicates how much electrical power they can produce under ideal conditions. Note that the actual yield of solar panels can vary depending on factors such as orientation, tilt, and shading.

4. Calculate the number of solar panels: Divide the required energy by the capacity of the solar panels to get a rough estimate of the number of solar panels you need. Keep in mind that this is a rough estimate, and you may wish to install more panels to compensate for variables like fewer sunlight hours on certain days or seasons.

It is important to note that solar panels are usually not directly connected to an electric car but rather linked to the electricity grid. The solar energy is then used to reduce your total energy consumption, including charging the car. The surplus solar energy can also be fed back into the electricity grid or stored in a battery system.

The exact number of solar panels you need can vary depending on your specific needs, available roof space, and local conditions. It is advisable to consult a professional solar panel installer to get a detailed evaluation based on your specific situation.