What factors determine the size of a solar PV system?

Solar system sizing considers: energy consumption (kWh/year to offset), available roof/ground area, solar resource (peak sun hours), panel efficiency and orientation, shading from trees or buildings, budget constraints, utility interconnection limits, and future energy needs (EV, heat pump). System size is expressed in kWp (peak kilowatts under STC). A typical residential system is 5-10 kWp. Annual yield estimation: kWp x peak sun hours x system efficiency (typically 75-85%) x 365 days. Over-sizing is limited by net metering caps and economics.