Formula Used
Design daily load = Daily load × (1 + System loss %) × (1 + Reserve %)
Required solar array = Design daily load ÷ Peak sun hours
Number of panels = Required array watts ÷ Panel watts
Battery size = Daily load × Autonomy days ÷ Depth of discharge ÷ Inverter efficiency
Battery amp hours = Battery kWh × 1000 ÷ Battery voltage
Inverter size = Peak load × Surge factor ÷ Inverter efficiency
Roof area needed = Number of panels × Area per panel
Total cost = Panel cost + Battery cost + Inverter cost
Solar Panel Needs Planning Guide
Why Solar Sizing Matters
A solar system works best when every part matches the real load. Guessing the panel count can create weak charging, wasted roof space, or a costly system. This calculator uses daily energy, sunlight, losses, reserve margin, battery storage, and inverter demand. It gives a practical starting size for homes, cabins, shops, pumps, and small offices.
Daily Load Comes First
The daily load is the main input. It should include lights, fans, appliances, computers, pumps, and other devices. Use actual meter data when possible. If meter data is not available, list each appliance. Multiply watts by hours used. Then convert watt hours to kilowatt hours.
Sunlight Changes the Result
Peak sun hours are not the same as daylight hours. They represent the useful solar energy received during a day. A site with fewer peak sun hours needs more panels. Roof direction, shade, dust, heat, and cable losses also reduce output. The loss field helps include these real conditions.
Panels, Batteries, and Inverters
The panel result shows how many modules are needed to produce the design energy. The battery result shows stored energy for backup days. Depth of discharge protects battery life. The inverter result checks peak load and surge demand. Motors, refrigerators, and pumps often need extra starting power.
Roof and Cost Review
Roof area is another limit. Large panels need enough open space with low shade. The calculator compares required panel area with available area. It also estimates system cost from panel, battery, and inverter prices. The estimate is useful for early planning, quotes, and comparison.
Use Results Carefully
The result is a planning estimate. Final designs should check wire size, mounting, local codes, safety devices, battery chemistry, charge controller limits, and inverter surge rating. Weather patterns should also be reviewed. For critical power, use a larger reserve margin and more autonomy days.
FAQs
1. What is daily energy load?
Daily energy load is the total electricity used in one day. It is measured in kilowatt hours. You can get it from a power bill, meter reading, or appliance-by-appliance estimate.
2. What are peak sun hours?
Peak sun hours show usable solar energy at your location. They are not simple daylight hours. More peak sun hours usually means fewer panels are needed.
3. Why add system loss?
Solar systems lose energy through wiring, heat, inverter conversion, dust, and panel mismatch. A loss percentage makes the estimate more realistic and prevents undersizing.
4. What reserve margin should I use?
A reserve margin covers load growth, cloudy days, aging panels, and measurement errors. Many users start with 15% to 25%, then adjust for reliability needs.
5. Why is battery depth of discharge important?
Depth of discharge shows how much battery capacity should be used. Lower discharge can improve battery life. Higher discharge reduces the required battery size but may increase wear.
6. How is inverter size selected?
The calculator uses peak load, surge factor, and inverter efficiency. This helps cover heavy starting loads from motors, pumps, refrigerators, and compressors.
7. Can this calculator size an off grid system?
Yes, it can estimate off grid panel and battery needs. For critical systems, use conservative losses, more autonomy days, and professional electrical review.
8. Is the cost result final?
No. It is an early estimate. Final price depends on mounting, wiring, protection devices, labor, permits, taxes, batteries, inverter type, and site conditions.