Calculator
Example Data Table
| Scenario | Daily Load | Sun Hours | Panel Size | Derating | Margin | Expected Panels |
|---|---|---|---|---|---|---|
| Small cabin | 4 kWh | 5 | 450 W | 80% | 20% | 3 panels |
| Efficient home backup | 8 kWh | 5 | 450 W | 80% | 20% | 6 panels |
| Large off grid use | 16 kWh | 4.5 | 550 W | 78% | 25% | 11 panels |
Formula Used
Daily Wh = Direct kWh × 1000 + sum of Watts × Hours × Quantity.
Daily Wh With Margin = Daily Wh × (1 + Safety Margin ÷ 100).
Required Array W = Daily Wh With Margin ÷ (Peak Sun Hours × Derating).
Panel Count = Ceiling of Required Array W ÷ Panel Rating.
Battery Wh = Daily Wh With Margin × Backup Days ÷ (DoD × Battery Efficiency).
Battery Ah = Battery Wh ÷ System Voltage.
Controller A = Array Rating W ÷ System Voltage × Controller Margin Factor.
Inverter W = Peak AC Load × Inverter Margin Factor ÷ Inverter Efficiency.
How To Use This Calculator
Enter your known daily energy use if you already have it.
Add appliance watts, running hours, and quantity for detailed load planning.
Enter local peak sun hours for your area.
Choose panel wattage, system voltage, battery size, and backup days.
Adjust derating, margins, efficiency, and depth of discharge.
Press the calculate button to view panel, battery, inverter, controller, space, and cost results.
Use CSV or PDF download buttons after the result appears.
Solar Panel Planning Basics
A solar panel plan starts with daily energy demand. Every light, fan, pump, charger, and appliance uses power for a set number of hours. The calculator converts those values into watt hours. It also accepts a direct daily load, so you can use data from a bill or energy meter.
Why Sun Hours Matter
Peak sun hours describe the useful sunlight available each day. A location with five peak sun hours can collect more energy than a shaded site with three hours. Real systems also lose power through heat, wiring, dust, controller limits, and inverter conversion. That is why derating is included.
Panel And Battery Sizing
The panel array must replace daily energy and cover planned safety margin. The battery bank must support the load during night or cloudy weather. Depth of discharge protects battery life. A lithium bank may allow deeper discharge than many lead acid banks. Battery efficiency also changes the required storage size.
Inverter And Controller Checks
The inverter should handle the largest expected AC load. Motors and pumps may need extra surge capacity at startup. The charge controller must pass the current produced by the array at the selected system voltage. Adding a controller margin helps avoid undersizing on bright, cool days.
Cost And Space Review
A useful design is not only electrical. It must also fit the roof, rack, or ground mount area. The panel count and panel dimensions estimate the needed space. Optional cost fields help create a quick budget for panels, batteries, inverter, controller, and installation.
Using Results Wisely
This tool gives planning estimates. Final designs should consider local codes, panel orientation, wire length, breaker sizing, battery chemistry, and weather patterns. A licensed installer can confirm safe wiring and protection devices. Still, the calculator is helpful for comparing system options before buying equipment.
Common Design Mistakes
Many systems fail because the load estimate is too low. Seasonal fans, routers, security devices, and standby loads are often missed. Shading is another problem. A small shadow can reduce production across a string. Battery banks are also sometimes sized without enough autonomy. Include realistic margins, then compare several cases before choosing final equipment. This also lowers risk and improves long term performance.
FAQs
1. What is a solar panel needs calculator?
It estimates how many solar panels, batteries, inverter capacity, and controller amps you may need for a planned electrical load.
2. What are peak sun hours?
Peak sun hours show the effective strong sunlight available each day. They are different from total daylight hours.
3. Should I use direct load or appliance rows?
You can use either method. If you use both, the calculator adds them together for total daily demand.
4. Why is system derating important?
Derating covers real losses from heat, dust, wiring, charge control, inverter conversion, and panel mismatch.
5. How much battery backup should I enter?
Enter the number of days you want the system to run without useful solar charging.
6. What inverter size should I choose?
Choose an inverter above the calculated continuous load. Also check surge needs for pumps, motors, and compressors.
7. Is the cost estimate exact?
No. It is a planning estimate. Local prices, mounting, labor, permits, wiring, and protection devices can change final cost.
8. Can this replace a professional design?
No. It helps with early sizing. A qualified installer should confirm code compliance, protection, wiring, and final layout.