PEC Solar Financial
System size, energy production, monthly savings, and payback period — the methodology behind the Solar System Sizing & Savings calculator, explained in full.
The PEC tab's Solar System Sizing & Savings calculator sits a layer above the pure electrical calculators — it's a system-level sizing and financial estimator, not a code-compliance check. Here's exactly how it works.
Daily Energy (kWh) = System kWp × Peak Sun Hours × System Efficiency
Peak Sun Hours represents the equivalent number of hours per day the sun delivers standard 1000 W/m² irradiance — a proxy that captures a location's actual solar resource, not just daylight hours. System Efficiency accounts for real-world losses: inverter conversion loss, cable resistance, panel soiling, and temperature derating, typically landing well under 100%.
Monthly Savings = Daily kWh × 30 × Electricity Rate
This assumes the household or business actually consumes what the system produces, either directly or through net metering credit — a system that overproduces relative to consumption without export capability won't realize this full savings figure.
Panel and inverter counts use a standard 1:1.3 DC-to-AC oversizing ratio — a common industry practice where the DC array is sized somewhat larger than the inverter's AC output rating. This improves energy harvest during non-peak sun hours (early morning, late afternoon, overcast periods) without requiring a proportionally larger, more expensive inverter.
Payback Period (years) = Total System Cost ÷ Annual Savings
This is a simplified payback calculation — it doesn't account for panel degradation over time, electricity rate escalation, or financing costs. Treat it as a first-pass estimate for comparing system sizes, not a bank-ready financial projection.
It doesn't replace an actual quotation with real, current equipment pricing, site-specific shading analysis, or a formal load study. It's meant to answer "is this roughly worth pursuing?" quickly, before committing to the more detailed work a real installation requires.
Run your own numbers in the Solar System Sizing & Savings calculator on the PEC tab.