Solar resource and peak sun hours
Peak sun hours (PSH) converts site irradiance into an average daily energy value. Many urban and industrial sites fall near 3.5–6.0 kWh/m²/day, while high‑resource regions can exceed that range. Because yield scales linearly with PSH, confirm it from a solar map, feasibility study, or measured dataset before using the results in budgets.
Performance ratio and loss budgeting
Performance ratio (PR) summarizes real‑world losses from temperature, wiring, soiling, shading, mismatch, inverter conversion, and downtime. Early estimates often use 70–85% depending on roof complexity and maintenance. Common starting values include temperature loss 6–12%, soiling 1–6%, wiring 1–3%, mismatch 1–2%, shading 0–10% (site‑dependent), downtime 0.5–2%, and inverter efficiency 96–99%. Use detailed losses when you need transparent assumptions for reviews.
Orientation, tilt factor, and optional gains
The tilt/orientation factor adjusts for geometry and layout constraints common on construction sites. A well‑aligned fixed roof array may be near 0.95–1.05, while constrained azimuth or low tilt can drop below that. Optional gains capture design choices: tracking can add 10–25% in suitable layouts, and bifacial gain often lands around 2–15% with reflective surfaces and elevated racking.
Financial metrics for project decisions
Energy converts to gross savings using the tariff, then net cashflow subtracts annual O&M. Multi‑year projection applies degradation and tariff escalation, and discounting produces NPV for capital planning. LCOE provides a cost per generated kWh, useful for comparing PV options against anticipated utility pricing and for aligning with internal hurdle rates.
Construction workflow and quality checks
Run three scenarios: base, conservative, and upside. Stress shading and soiling to quantify risk, then validate capacity factor and PR against similar completed projects. Export CSV for spreadsheet review and PDF for client submittals. Record PSH source, tilt factor rationale, and loss assumptions so stakeholders can audit the estimate quickly.
| Parameter | Example A | Example B | Example C |
|---|---|---|---|
| System size (kW DC) | 20 | 75 | 150 |
| PSH (kWh/m²/day) | 4.6 | 5.2 | 5.8 |
| Tilt factor | 0.98 | 1.00 | 1.03 |
| Availability (%) | 98.5 | 99.0 | 99.2 |
| PR / performance used (%) | 76 | 78 | 80 |
| Tariff (per kWh) | 0.14 | 0.16 | 0.18 |
| Degradation (%/yr) | 0.7 | 0.6 | 0.5 |
Peak sun hours represents average daily solar energy as an equivalent number of full‑sun hours. It lets you estimate annual yield using a single, practical site resource input.
Use detailed losses when you need transparent assumptions for reviews. Use a single performance ratio for quick screening or when project data is limited but you have a trusted PR benchmark.
PSH reflects horizontal resource, while roofs and arrays face specific directions. The tilt factor adjusts for orientation and tilt differences so energy estimates align with the actual installation geometry.
Start with 1–3% for regularly cleaned sites and 4–8% for dusty environments. Increase if cleaning access is limited or rainfall is low. Validate with local operations experience when possible.
Availability covers expected uptime, including routine maintenance and outages. Downtime loss is an extra adjustment for site‑specific interruptions beyond your availability assumption, such as curtailment or frequent breaker trips.
NPV shows discounted value of cashflows compared with the installed cost. LCOE expresses discounted cost per generated kWh, helping compare solar against utility rates or alternative generation options.
Yes for early estimates and option studies. For final submissions, replace assumed inputs with engineered layouts, verified shading studies, and locally sourced PSH. Attach the exported PDF plus input rationale for traceability.