How do you calculate the solar system capacity?

2010

Energy production from a solar electric (PV) system is a function of several factors, including the following. Our assumptions are shown:

Factor	Assumption
Solar resources	Assumed solar availability: As per PV Watts
Soiling or contamination of the PV panels	Clean, washed frequently: 98% design sunlight transmission
Temperature	25C, calm wind
System configuration (battery or non-battery)	Non-battery
Orientation to the sun	tilted at your latitude, South facing
Shading	None
PV Energy delivered as % of manufacturer`s rating	95%
Wiring & power point tracking losses	9% (91% delivered)
Inverter Efficiency	90%
Total Energy Delivered	95% x 91% x 90% = 78%

System Capacity Required (kW of PV) is calculated as follows:

Annual usage = Monthly Usage x 12 months
KW of PV = (Annual Usage) / (78% x kWh/sq-m/day from Solar Radiance chart x 365 days/year)