Enter your inputs
Example data table
| Scenario | Inputs | Outputs |
|---|---|---|
| Typical home, with backup |
12 kWh/day, PSH 5.5, derate 80%, growth 10%
Panel 550 W, 48 V, peak 2500 W, surge 1.25 Battery yes, 1 day, DoD 80%, eff 90/92 |
Required array: 3.00 kW
Panels: 6 (3.30 kW) Expected: 14.52 kWh/day Inverter: 3.13 kW Battery: 15.94 kWh, 415 Ah |
Formulas used
target_kWh = daily_kWh × coverage% × (1 + growth%)
required_array_W = target_Wh / (peak_sun_hours × derate)
expected_kWh = (panels × panel_W × peak_sun_hours × derate) / 1000
controller_A ≈ array_current_A × 1.25
inverter_W ≈ peak_load_W × surge_factor
bank_Ah = battery_Wh / (system_V × DoD)
How to use this calculator
- Pick daily or monthly energy, then enter your kWh value.
- Set coverage and growth to match your goals.
- Enter peak sun hours for your location.
- Choose derate to reflect real-world losses.
- Enter panel wattage and system voltage.
- Add peak load and surge factor for inverter sizing.
- Enable backup to estimate battery needs and autonomy.
- Press Submit, then download CSV or PDF.
Aligning energy targets with coverage
Start with measured consumption, then choose daily or monthly entry. Monthly values are converted to daily using a 30.4 day average. Set the coverage percentage to reflect how much of that demand you want solar to supply. Add a growth margin if you expect new appliances, EV charging, or occupancy changes. The calculator converts your target into watt-hours, creating a consistent baseline for sizing the array across locations and seasons with confidence.
Peak sun hours and seasonal variability
Peak sun hours represent equivalent full-sun hours per day and are the strongest driver of array size. Use a location-specific annual average, then consider rerunning with winter or monsoon values to stress-test your design. Roof tilt, azimuth, shading, and nearby obstructions reduce effective sun hours even on clear days. When uncertain, choose a conservative number to avoid underproduction and frequent grid or generator reliance. Document your source and date.
Derate factor and real-world losses
Derate captures losses from temperature, inverter conversion, wiring resistance, soiling, mismatch, and aging, plus component tolerances too. A typical planning range is 0.75 to 0.85, depending on equipment quality and maintenance. Higher temperatures lower module output, while dust can be significant in dry climates. By dividing target watt-hours by peak sun hours times derate, the calculator estimates required array watts. Improving wiring, cleaning schedules, and ventilation can reduce needed panels.
Hardware checks: panels, controller, inverter
Panel wattage determines how many modules are needed to reach the required array power. The calculator rounds up to whole panels, then recomputes expected daily production using the installed capacity. For controller sizing, it estimates array current as array watts divided by system voltage and adds a 1.25 safety factor. Inverter sizing uses your peak load multiplied by surge factor, supporting motor starts and transient loads. Roof area estimates help validate placement feasibility.
Battery autonomy and capacity planning
Enable backup to estimate storage for a chosen number of autonomy days. The battery calculation accounts for inverter efficiency, battery efficiency, and depth of discharge, producing a usable energy target and an amp-hour bank size at your system voltage. Lithium systems can operate at higher discharge percentages than lead-acid, reducing required capacity for the same autonomy. Use the results as a planning guide, then match them to specific battery modules, protection hardware, and allowable charge currents.
FAQs
1. What peak sun hours should I enter?
Use a local average for your site, not a national estimate. If you are unsure, run three scenarios: conservative, typical, and optimistic. Designing around the conservative case usually reduces the risk of shortfall.
2. What is a good derate value?
Derate bundles common losses from heat, wiring, inverter conversion, dirt, and mismatch. For many residential systems, 75–85% is a practical planning range. Cleaner modules and better airflow can justify a higher value.
3. Why does the panel count round up?
Panels are discrete units, so the calculator rounds up to ensure the installed array meets or exceeds the required power. That extra capacity also provides a small buffer for aging, weather variability, and measurement error.
4. How should I set the surge factor?
Start with 1.25 for mixed household loads. Increase it if you have motors, pumps, or compressors that draw high starting current. Confirm surge requirements in appliance datasheets and match them to inverter surge ratings.
5. Is this suitable for grid-tied and off-grid setups?
Yes. For grid-tied designs, focus on array sizing and inverter capacity. For off-grid or hybrid systems, enable battery backup, set autonomy days, and use conservative sun hours to cover low-production periods.
6. How accurate are the CSV and PDF downloads?
Exports reflect the same inputs and formulas used on-screen, so they are consistent for documentation and quoting. Accuracy depends on your assumptions for sun hours, derate, and loads. Validate final designs with equipment specifications.