For 20kWh per day, you will require a minimum of 5kW solar system which by exploiting solar energy for four hours can produce 20kWh electricity. But with a 5kWh solar power system, you may not get 2okW power every day, especially during cloudy and rainy days when the production may slump to 10kW per day or even less. However, the same set-up may produce up to 30kWh of power every day during the sunny days of summer. However, the average electricity generation from a 5kW solar system over one year would be around 20kWh.