The number of solar panels needed for a family of 4 depends on various factors, such as the average energy consumption of the family, the location and orientation of the house, the available roof space, and the efficiency of the solar panels.

On average, a family of 4 consumes about 3,500 to 4,500 kilowatt-hours (kWh) of electricity per year. To make a rough estimate of the number of solar panels needed, you can use the following formula:

Annual energy need / Annual energy output per solar panel = Number of solar panels needed

The annual energy output per solar panel depends on factors such as the efficiency of the panels and the average solar insolation at your location. This can vary, but on average, you can assume about 250 to 300 kWh per year per solar panel.

Let's say, for example, that the family of 4 has an annual energy need of 4,000 kWh and the annual energy output per solar panel is 275 kWh. The calculation would then be as follows:

4,000 kWh / 275 kWh = 14.5 solar panels

Since you can't install half a panel, you would probably want to round up to the nearest whole number. In this case, that would be about 15 solar panels.

Please note that this is a rough estimate, and it is advisable to consult a professional solar panel installer to conduct a more detailed analysis based on your specific situation. They can help you determine the optimal number of solar panels based on your energy consumption, roof space, and other relevant factors.