photovoltaic system calculator

How this photovoltaic system calculator works

A photovoltaic (PV) system converts sunlight into electricity. The goal of sizing is simple: install enough panel capacity to produce the amount of energy you need over a year, while accounting for real-world losses.

This calculator uses your monthly electricity consumption, local peak sun hours, expected system losses, and panel wattage to estimate:

• Required solar array size in kW
• Estimated panel count
• Projected annual energy production
• Suggested inverter size range
• Approximate roof area required

Input fields explained

1) Monthly electricity use (kWh)

This is usually found on your electric utility bill. If your usage fluctuates seasonally, use a yearly average for better results.

2) Peak sun hours per day

Peak sun hours are not daylight hours. They represent equivalent full-intensity sunlight. A location with 5 peak sun hours means your panels receive the energy equivalent of 5 full-power hours per day on average.

3) Panel wattage

Modern residential modules are often in the 380W to 550W range. Higher wattage reduces panel count, though roof geometry and layout still matter.

4) System losses

Real systems lose energy due to inverter conversion, temperature, wiring, dust, and mismatch. A common planning assumption is 14% to 25%.

5) Target energy offset

Not every homeowner wants 100% offset. You might intentionally size smaller (for budget) or slightly larger (if adding an EV or heat pump).

Quick example

Suppose your home uses 900 kWh/month, site sun is 5 peak sun hours/day, losses are 20%, and panels are 450W. You can expect a required array around the mid-7 kW range, which is often around 16 to 18 panels depending on rounding and design constraints.

Important design factors beyond this calculator

• Roof orientation and tilt: South-facing (in the northern hemisphere) often yields best output.
• Shading: Trees, chimneys, and nearby buildings can significantly reduce production.
• Local code and utility rules: Interconnection limits and net-metering policies vary.
• Future loads: EV charging, electric water heating, and HVAC upgrades increase demand.
• Battery storage goals: Backup design is a separate calculation from annual energy sizing.

Financial planning tips

Estimate total installed cost

Multiply system size by local cost per watt, then apply incentives (tax credits, rebates, SRECs where available). Compare financing options against expected electricity inflation.

Compare payback and long-term savings

A simple payback estimate is useful, but net present value (NPV) and internal rate of return (IRR) give a better investment picture for long-lived assets like solar.

Final note

This tool provides a practical first-pass estimate, not a stamped engineering design. Before purchase, request a professional site assessment including shade analysis, structural checks, and utility interconnection review.