Calculator Inputs
Example Data Table
| Case | Size (kW) | PSH | Days | PR Used | Energy (kWh) |
|---|---|---|---|---|---|
| Small site, light losses | 5.0 | 5.2 | 30 | 0.80 | 624.0 |
| Mid site, warmer climate | 20.0 | 5.5 | 30 | 0.74 | 2,442.0 |
| Large site, high shading risk | 200.0 | 4.8 | 365 | 0.63 | 220,752.0 |
Formula Used
The calculator estimates energy using: Energy (kWh) = Size (kW) × Peak Sun Hours (h/day) × Days × PR
If you do not provide a PR override, PR is computed as the product of loss and performance multipliers:
- Loss Multiplier = (1 − shading) × (1 − soiling) × (1 − wiring) × (1 − other)
- Performance Multipliers = tilt/orientation × temperature × inverter efficiency × degradation factor
- Computed PR = Loss Multiplier × Performance Multipliers
How to Use This Calculator
- Enter system size, peak sun hours, and the days in your estimate period.
- Set realistic losses for shading, soiling, wiring, and other site constraints.
- Adjust tilt/orientation and temperature factors to match the installation.
- Enter inverter efficiency and optional age/degradation values as needed.
- Optionally enter a PR override if you already have a confirmed PR.
- Press Calculate to view results above the form, then export CSV or PDF.
- Use Save Scenario to compare alternatives and export scenario reports.
System Size and Peak Sun Hours Inputs
Construction planning often starts with DC nameplate capacity and an average peak sun hours (PSH) value. For quick estimates, PSH typically ranges from 3.0–7.0 h/day depending on season and location. Using a 50 kW array with 5.0 PSH over 30 days yields 7,500 kWh before applying performance ratio. Treat PSH as a period average, not a single-day maximum.
Performance Ratio Benchmarks
Performance ratio (PR) compresses real-world losses into one factor. Many grid-tied systems land around 0.70–0.85 when measured over months, while challenging sites may fall near 0.60–0.70. Use the PR override when you have verified monitoring data or a lender-grade model. Otherwise, compute PR from itemized losses to keep assumptions transparent.
Loss Allocation and Field Measurements
Shading losses can jump from 2% to 15% with nearby obstructions, especially in winter sun angles. Soiling often sits between 1% and 8% and varies with rainfall and cleaning intervals. Wiring and connection losses are commonly 1%–3% when cable sizing is adequate. Track these inputs during commissioning so later estimates can be tightened.
Temperature and Orientation Impacts
High module temperatures reduce output; a practical temperature factor of 0.90–0.98 is common in hot, low-wind roofs. Orientation and tilt can also move production by 5%–15% versus an optimal layout. If you anticipate significant deviation, adjust the tilt/orientation factor instead of inflating generic “other” losses. This keeps design decisions tied to measurable effects.
Scenario Comparison for Construction Planning
Use saved scenarios to compare layouts, equipment, and maintenance plans. For example, a 100 kW system with PR 0.78 produces about 11% more energy than the same system at PR 0.70 over the same PSH window. Add an electricity rate to translate kWh into budget impact and validate payback expectations across bid options. When estimating annual output, multiply the monthly average by 12 only if seasonal PSH is similar; otherwise run separate scenarios for dry and monsoon months. Document the chosen PR so subcontractors understand risk allowances during scheduling and handover reporting.
FAQs
1) What are peak sun hours and how do I choose them?
Peak sun hours convert local sunlight into equivalent full-sun hours per day. Use a monthly or annual average from a trusted solar resource, and match it to the same period length you are estimating.
2) What performance ratio should I use if I am unsure?
For early estimates, many projects start around 0.75 and adjust after reviewing shading, cleaning plans, and equipment. If losses are uncertain, lower PR slightly and document the reason in project notes.
3) Does this include panel efficiency or module brand differences?
Module efficiency affects how many panels fit into a given kW size, but energy here is driven by total installed kW, PSH, and PR. Differences are best represented by changing PR and temperature factors.
4) How should I estimate shading loss on a construction site?
Start with a site walk to identify obstructions, then apply a conservative percentage. Temporary cranes, stockpiles, and scaffolding can add seasonal shade. Update the input after commissioning measurements or monitoring trends.
5) Why does inverter efficiency matter if I size DC higher than AC?
Inverter efficiency captures conversion losses from DC to usable AC energy. If DC/AC ratio is high, clipping may also occur; represent that with “other loss” or a lower PR so estimates stay realistic.
6) Can I use this calculator for monthly and annual reporting?
Yes. Set days to 30 or 365 and use PSH for that same month or year. For better accuracy, run separate scenarios for different seasons and sum the results rather than averaging everything.