The peak generation of power is on a cool, clear day when the sun is perpendicular to the solar array. Clouds, seasonal changes in the angle of the sun, array soiling, roof orientation, and any incidental shading may impact on the performance.
For example, a typical energy efficient home is defined as consuming 7.5kWh per day, and would require a 2kw system to cover some or all the energy consumed.
A typical conventional home consumes 18kWh per day and would require a 5kw system to cover all the energy consumed.
A system can be installed to produce all or a percentage of the energy you consume.