Calculator inputs
Example scenarios
| Scenario | Annual load (kWh) | Offset | Panel (W) | PSH/day | Losses | Panels (est.) | System (kW) |
|---|---|---|---|---|---|---|---|
| Small home | 6,000 | 80% | 450 | 5.0 | 15% | 8 | 3.60 |
| Average home | 10,800 | 100% | 550 | 5.3 | 14% | 12 | 6.60 |
| Large home | 18,000 | 100% | 600 | 5.5 | 16% | 17 | 10.20 |
| Small business | 36,000 | 70% | 550 | 5.2 | 18% | 27 | 14.85 |
| Warehouse | 120,000 | 60% | 600 | 5.8 | 20% | 86 | 51.60 |
Formula used
1) Convert usage to annual energy
AnnualLoad(kWh) = Usage(kWh) × 12 (if monthly), otherwise AnnualLoad = Usage
2) Target energy to offset
TargetOffset(kWh/yr) = AnnualLoad × (Offset% / 100)
3) Annual energy per panel
AnnualPerPanel = (PanelW × PSH × 365 / 1000) × (1 − Loss%/100) × (Performance%/100)
4) Panel count and system size
Panels = ceil(TargetOffset / AnnualPerPanel)
SystemkW = Panels × PanelW / 1000
How to use this calculator
- Enter your energy use as monthly or annual kWh.
- Set the target offset percentage you want to cover.
- Choose a realistic panel rating and peak sun hours.
- Adjust system losses and performance if conditions reduce output.
- Optionally add roof area and panel dimensions for a fit check.
- Click Calculate to view results above the form.
- Use Download CSV or Download PDF to export.
Load Normalization and Offset Targeting
The calculator first converts your consumption into annual kilowatt-hours. Monthly entries are multiplied by 12 to create a consistent baseline. Then the offset percentage sets the target energy solar should cover. Example: 900 kWh per month becomes 10,800 kWh per year; a 75% goal targets 8,100 kWh annually. This keeps planning comparable across billing cycles. It supports seasonal comparisons and upgrades.
Panel Production Modeling with Sun Hours
Production uses peak sun hours (PSH), an average measure of usable daily sunlight. Annual energy per panel equals panel watts × PSH × 365, converted to kWh, then adjusted for losses and performance. With a 550 W panel, 5.3 PSH, 14% losses, and 100% performance, one panel yields about 915 kWh yearly. Improving PSH or reducing losses lowers panel count. Small shading can reduce yields sharply.
System Size, Inverter Margin, and Practical Design
Once panel count is known, the tool reports DC system size in kilowatts. System size equals panels × panel watts / 1000, enabling consistent quote comparisons. It also suggests inverter size by adding a margin to the DC rating. A 12-panel array at 550 W is 6.60 kW DC; with a 15% margin, guidance is about 7.59 kW. Use electrical limits to finalize selection. This improves budgeting for equipment wiring.
Roof Area Footprint and Layout Considerations
Space constraints are checked using panel dimensions and roof area. Panel footprint equals length × width, multiplied by panel count to estimate roof area needed. Using 1.72 m × 1.13 m modules, each panel occupies about 1.94 m², so 12 panels need about 23.3 m² of clear space. If you enter usable roof area, the calculator flags likely fit before layout drawings. Allow walkways, setbacks, and tilt spacing.
Savings and Emissions Impact
Savings are estimated as offset kWh × your rate per kWh, capped at your annual load. At 55 PKR/kWh and a 10,800 kWh offset, the estimate is 594,000 PKR per year. Environmental impact uses an emission factor: with 0.70 kg/kWh, that offset avoids about 7,560 kg of CO₂ annually. Update rate and emissions inputs to reflect tariffs and local grid intensity. Treat outputs as ranges, not guarantees.
FAQs
1) What are peak sun hours, and where do I get them?
Peak sun hours summarize average daily solar energy for your location. Use a local solar map, installer proposal, or historical PV production data for your city to choose a realistic annual average.
2) Why does the calculator include both losses and performance?
Losses capture common efficiency reductions like inverter, wiring, temperature, and soiling. Performance factor lets you apply an additional adjustment for shading, tilt limits, or conservative planning without changing loss assumptions.
3) Can I target more than 100% offset?
Yes. Enter up to 200% to explore overproduction for future loads or battery charging. Real-world bill credits depend on net metering rules and export rates, so validate the economic impact locally.
4) What does the roof fit check actually mean?
It compares your usable roof area to total panel footprint. It does not include setbacks, walkways, or spacing for tilt. If it flags insufficient area, consider higher-watt panels or a lower offset target.
5) How accurate is the savings estimate?
Savings use your entered rate and the calculated offset energy, capped at your annual load. Taxes, fixed charges, time-of-use pricing, and export compensation can change results, so treat savings as an initial planning range.
6) Which inverter size should I pick if my result is between models?
Choose the nearest standard size that meets electrical limits and installer guidance. A slightly smaller inverter can be acceptable if occasional clipping is expected, while larger units may help with future expansion.