Photovoltaic (PV) System Size Calculator
Understanding Photovoltaic (PV) System Sizing
Sizing your solar panel system correctly is the most critical step in transitioning to renewable energy. A system that is too small won't cover your electricity bills, while one that is too large may result in unnecessarily high upfront costs without a proportional return on investment.
Key Variables in Solar Calculation
- Monthly Energy Usage: Look at your utility bills from the last 12 months. Energy usage fluctuates with seasons (HVAC use), so an average is best for calculation.
- Peak Sun Hours: This is not the total hours of daylight. It represents the intensity of sunlight equivalent to 1,000 watts per square meter. Most regions receive between 3.5 and 6.0 peak sun hours per day.
- System Derate Factor: No solar system is 100% efficient. Energy is lost through DC-to-AC conversion (inverters), wiring, soiling (dust), and temperature fluctuations. A standard realistic factor is 0.77.
Example Calculation
If your home uses 1,000 kWh per month and you live in an area with 5 peak sun hours:
- Daily Usage: 1,000 kWh / 30.42 days = 32.87 kWh/day.
- System Size Required: 32.87 / (5 hours * 0.77 efficiency) = 8.54 kW.
- If using 400W panels: (8.54 * 1000) / 400 = 22 Panels.
Solar Sizing FAQ
Should I size for 100% offset?
Many homeowners aim for 100% offset, but if your utility company has poor "Net Metering" policies, it might be more cost-effective to size for 80-90% of your usage.
What if I plan to buy an EV?
Electric vehicles significantly increase home energy consumption. An average EV adds about 250-400 kWh per month to your bill. It is wise to add 2-4 extra panels to your calculation if you plan to go electric soon.