The number of solar panels needed for a heat pump and an electric car depends on several factors, such as the energy consumption of the heat pump and the electric car, the efficiency of the solar panels, and the available space for the installation of the solar panels. Here are some considerations to determine how many solar panels you need:

1. Energy consumption of the heat pump: The energy requirement of a heat pump can vary depending on the type of heat pump, the size of the house, and the desired heating temperature. Consult the specifications of the heat pump to determine the expected energy consumption. This is often expressed in kilowatt-hours (kWh) per year.

2. Energy consumption of the electric car: The energy consumption of an electric car varies depending on the brand, model, and your driving habits. Consult the specifications of the electric car to find out the estimated energy consumption per kilometer or per year. This is often expressed in kilowatt-hours (kWh) per kilometer or per year.

3. Efficiency of the solar panels: The efficiency of solar panels can vary, depending on the type and quality of the panels. In general, you can assume an efficiency between 15% and 20%. This means that a solar panel can convert about 15% to 20% of the available sunlight into electricity.

4. Available space and location: The available space on your roof or in your garden determines how many solar panels you can install. Also take into account any shadow from trees, buildings, or other obstacles that could affect the yield of the solar panels.

To make a rough estimate of the number of required solar panels, you can follow these steps:

1. Determine the total annual energy consumption of the heat pump and the electric car (in kilowatt-hours, kWh).

2. Calculate the total energy production of a solar panel per year by multiplying the capacity of a solar panel (in kilowatts, kW) by the estimated efficiency and the number of sunshine hours per year.

3. Divide the total energy consumption by the energy production of a solar panel to get a rough estimate of the required number of solar panels.

Please note that this is a simple estimate and other factors may come into play, such as seasonal variations in sunlight and energy consumption. It is advisable to seek professional advice from a certified installer.