Calculator Inputs
The page is stacked in one column, while the input area uses a responsive 3-column, 2-column, and 1-column grid.
Example Data Table
Illustrative planning scenario| Load | Watts | Hours/Day | Qty | Duty % | Daily Wh |
|---|---|---|---|---|---|
| Refrigerator | 180 | 10 | 1 | 40 | 720 |
| LED Lights | 12 | 6 | 8 | 100 | 576 |
| Fans | 70 | 8 | 3 | 100 | 1680 |
| Router | 15 | 24 | 1 | 100 | 360 |
| Total Daily Energy | 3336 Wh/day | ||||
A real design should also consider local weather, battery chemistry, temperature, cable sizing, and acceptable discharge depth.
Formula Used
1) Daily Energy Per Load
Daily Wh = Watts × Hours/Day × Quantity × Duty Cycle
Duty cycle is expressed as a decimal fraction. A refrigerator with 40% duty uses only 40% of its connected running time.
2) Adjusted Daily Energy
Adjusted Daily Wh = Total Daily Wh × (1 + Reserve Margin)
This creates design headroom for estimation error, future devices, battery aging, and weather-related uncertainty.
3) Battery Bank Energy
Required Battery Wh = (Adjusted Daily Wh × Autonomy Days) ÷ (DoD × Inverter Efficiency × Battery Efficiency)
This converts the AC energy requirement into required DC storage after considering losses and usable discharge range.
4) Battery Bank Capacity In Amp-Hours
Required Battery Ah = Required Battery Wh ÷ System Voltage
5) Inverter Sizing
Recommended Inverter W = Estimated Running W × (1 + Inverter Margin)
Recommended Surge W = Total Surge W × Simultaneous Factor × 1.05
Surge allowance helps cover startup demand from motors, compressors, and pumps.
6) Solar Array Sizing
Solar Energy Needed/Day = Adjusted Daily Wh + (Battery Recharge Wh ÷ Recharge Days)
Recommended Solar W = Solar Energy Needed/Day ÷ (Peak Sun Hours × Controller Efficiency × Solar Derate)
This estimates the solar capacity needed to supply daily use and restore stored energy within the selected recovery period.
How to Use This Calculator
- Add each appliance or critical load in the load table.
- Enter running watts, hours per day, quantity, duty cycle, and surge multiplier.
- Set the required autonomy period, reserve margin, and simultaneous load factor.
- Enter battery bank details including system voltage, unit voltage, unit capacity, and maximum discharge depth.
- Provide inverter, battery, controller, and solar derating efficiencies.
- Enter local peak sun hours and the number of days allowed for recharging.
- Press the calculate button to show results above the form.
- Use the CSV or PDF buttons to export the current planning summary.
Frequently Asked Questions
1) What does autonomy mean?
Autonomy is how long the battery bank should power your loads without meaningful solar input. It is usually expressed in days or fractions of a day.
2) Why is duty cycle important?
Many devices do not draw rated power continuously. Duty cycle prevents oversizing by reflecting actual average operation, especially for refrigerators, compressors, and thermostatically controlled appliances.
3) Why are there so many efficiency inputs?
Every stage loses energy. Batteries, inverters, controllers, wiring, temperature, and panel conditions all reduce usable output. Including them gives more realistic system sizing.
4) Is the inverter size based on all connected loads?
The calculator uses total running load and applies the simultaneous load factor. This helps estimate what actually runs together, then adds an inverter safety margin.
5) Why is surge power separate from running power?
Motors and compressors may need a short startup burst much higher than normal running demand. Inverter surge capability must handle that temporary peak safely.
6) Can I use this for lithium and lead-acid batteries?
Yes. Adjust depth of discharge, efficiency, and battery unit ratings to reflect the chemistry you plan to use. Conservative settings are recommended for lead-acid systems.
7) Does this replace a professional design review?
No. It is a strong planning tool, but final design should also verify protection devices, cable sizing, charging limits, ventilation, mounting, compliance, and site conditions.
8) What should I do if results look too high?
Check running watts, daily hours, duty cycle, autonomy days, and sun hours first. Oversized results usually come from optimistic assumptions being replaced by realistic loss factors.