How much kW output per day is produced from a 4-kW solar power system?

The total output per day of a solar power system depends on the size of that system and the amount of direct sunlight it receives. A 4-kilowatt (kW) system will produce 4 kW of solar power under direct sunlight. That same system, under an average five hours of sunlight per day, will produce 20 kilowatt-hours of solar energy each day and 7,300 kWh per year.

However, calculating actual system output is usually not so simple. A number of factors affect output, including wiring losses, shading, inverter efficiency, orientation to the sun and the fact that photovoltaic panels deliver an average of 95% of the power rating given by the manufacturer. According to Solar-Estimate.org, total losses from inefficiencies (assuming an unshaded, clean array) are 22%, meaning that 78% of the solar system's rated power is actually delivered to the source, your home.

Therefore, that 4-kW system described above, creating 20 kWh of energy per day, would actually deliver 15.6 kWh of solar energy each day (5,694 kWh per year). That is 468 kWh per month, about half of what the average American home consumes. However, a well-sealed, insulated, energy-efficient and energy-conserving home can use much less and realize much more effect from its solar power system.