Power and Energy Basics in Solar PV Systems

What is Electrical Energy?

Electrical energy is the total work an electrical system can perform over time. It is typically measured in kilowatt-hours (kWh). The formula to calculate electrical energy is:

Energy (kWh) = Power (kW) × Time (hours)

For example, a 1-kW appliance running for 5 hours consumes:

1 kW × 5 hours = 5 kWh

What is Electric Power?

Electric power is the rate at which energy is used or generated in a system, measured in watts (W). The basic formulas are:

DC: P = V × I
Single-phase AC: P = V × I × pf
Three-phase AC: P = √3 × V_L × I × pf

Solar Power and Energy Generation

In solar systems, power generation varies throughout the day, starting at zero in the morning, peaking around noon, and dropping again in the evening, following a curve similar to a sine wave. Therefore, we can’t simply multiply peak power by daylight hours to estimate energy production. A typical 1 kW system in India generates around 4 units (kWh) per day.