Example Data Table
| Use Case |
Daily Load |
Sun Hours |
Panel Size |
Losses |
Estimated Panels |
| Small cabin |
6 kWh |
5.5 |
450 W |
18% |
3 panels |
| Family home |
25 kWh |
5 |
550 W |
18% |
12 panels |
| Large home |
45 kWh |
4.7 |
580 W |
20% |
21 panels |
Formula Used
Adjusted daily load: Daily load ÷ (1 − system loss rate)
Solar array size: Adjusted daily load ÷ peak sun hours
Panel count: Required array watts ÷ panel wattage
Battery storage: Daily load × 1000 × autonomy days ÷ depth of discharge
Battery amp-hours: Battery watt-hours ÷ battery bank voltage
Inverter size: Peak load × surge factor ÷ inverter efficiency
Charge controller current: Installed array watts ÷ battery voltage × 1.25
How to Use This Calculator
Start with your total daily energy use in kilowatt-hours. You can get this from utility bills, appliance labels, or a load worksheet. Enter the average peak sun hours for your location. Use conservative sun hours when planning backup power.
Add system losses for heat, wiring, dust, inverter loss, and controller loss. A value between 15% and 25% is common for early planning. Enter the wattage of one solar panel. The calculator rounds the panel count upward.
Next, enter backup days, battery voltage, and usable discharge limit. These values estimate storage size. Finally, enter peak load, surge factor, and inverter efficiency. The result helps compare panel, battery, inverter, and controller needs.
Plan Solar Power Needs With Better Detail
Why Solar Sizing Matters
A solar system should match real energy demand. Oversized systems cost more. Undersized systems cause outages. Good planning starts with daily use. This calculator uses daily kilowatt-hours as the main load value. It then adjusts that value for expected losses. Those losses can come from wiring, heat, dust, charge control, and inverter conversion. The result is a better estimate of required solar production.
Panel Planning
Solar panels are rated in watts. Yet daily output depends on sunlight. Peak sun hours convert panel size into daily energy. For example, a larger array may still produce less energy in a cloudy region. That is why location matters. Use realistic peak sun hours. Avoid using perfect summer numbers only. A safer design uses average or low-season values.
Battery Storage
Batteries support night use and cloudy days. The calculator estimates battery storage from daily load, backup days, and depth of discharge. Depth of discharge means the usable share of stored energy. Lithium batteries often allow deeper discharge than lead-acid batteries. Still, keeping a reserve can improve reliability. Battery voltage also changes the amp-hour result. Higher voltage systems usually reduce current.
Inverter and Surge Load
The inverter must handle running load and startup surge. Motors, pumps, refrigerators, and compressors can draw extra power at startup. The surge factor adds this margin. Inverter efficiency also matters. No inverter converts power perfectly. This tool includes that loss when suggesting inverter size.
Using the Results
Use the output as a planning guide. Compare the panel count, battery size, and inverter rating with available equipment. Round up when safety matters. Check local electrical rules before installation. Roof space, shading, wire size, and mounting angle can change the final design. A qualified installer can confirm the final system. This calculator gives a strong starting point for better solar decisions.
FAQs
1. What does daily energy use mean?
Daily energy use is the total electricity consumed in one day. It is usually measured in kilowatt-hours. You can estimate it from bills, appliance ratings, or a load list.
2. What are peak sun hours?
Peak sun hours describe useful solar energy available per day. They are not the same as daylight hours. A location with strong sunlight has more peak sun hours.
3. Why are system losses included?
Solar systems lose energy through heat, cables, dust, controllers, batteries, and inverters. Adding losses gives a safer and more realistic panel estimate.
4. How many panels do I need?
The calculator divides required array watts by panel wattage. It then rounds upward. This gives the minimum panel count for the entered assumptions.
5. What is battery autonomy?
Battery autonomy is the number of days your system should run without strong solar charging. More autonomy needs more battery storage.
6. What depth of discharge should I use?
Use the safe usable percentage for your battery type. Many lithium batteries allow higher discharge. Lead-acid batteries often need a lower discharge setting.
7. Why does inverter surge matter?
Some appliances need extra power during startup. Pumps, refrigerators, and motors can surge above normal running watts. The surge factor adds that margin.
8. Is this calculator enough for final installation?
It is useful for planning and comparison. Final installation should also check wiring, codes, shading, mounting, protection devices, and local safety rules.