Calculator Inputs
Example Data Table
| Scenario | Load (W) | Backup (hrs) | System Voltage | Battery Size | Recommended Inverter |
|---|---|---|---|---|---|
| Cabin lights and router | 350 | 6 | 12 V | 12 V 250 Ah | 900 W |
| Home essentials | 1500 | 4 | 24 V | 24 V 400 Ah | 4200 W |
| Small office backup | 2400 | 5 | 48 V | 48 V 400 Ah | 7300 W |
| Off-grid workshop | 3200 | 8 | 48 V | 48 V 800 Ah | 9800 W |
These are planning examples, not final procurement values.
Formula Used
1) Design Load
Design Load (W) = Running Load × (1 + Growth Margin)
2) Required AC Energy
AC Energy (Wh) = Design Load × Backup Hours
3) Required Battery Energy
Battery Energy (Wh) = AC Energy ÷ (Inverter Efficiency × Battery Efficiency × Depth of Discharge × Temperature Derating) × (1 + Safety Margin)
4) Battery Capacity
Battery Capacity (Ah) = Required Battery Energy ÷ System Voltage
5) Inverter Size
Recommended Inverter (W) = Design Load × Surge Factor × (1 + Safety Margin)
6) Inverter VA Rating
Inverter Rating (VA) = Recommended Inverter Watts ÷ Power Factor
7) Battery Count
Series Batteries = Ceiling(System Voltage ÷ Single Battery Voltage), Parallel Strings = Ceiling(Required Ah ÷ Single Battery Ah)
8) Recharge Array Estimate
Suggested Solar Array (W) = Required Battery Energy ÷ (Sun Hours × Charge Controller Efficiency)
How to Use This Calculator
- Enter the total running wattage of all appliances.
- Set the surge factor for startup-heavy loads.
- Enter the number of backup hours required.
- Choose your battery bank voltage and battery unit values.
- Adjust efficiency, discharge depth, and temperature derating.
- Add safety and growth margins for practical design.
- Click calculate to see inverter size and battery layout.
- Use CSV or PDF download buttons to save results.
FAQs
1. Why does inverter efficiency matter?
Batteries supply DC energy, but many loads consume AC energy. Inverter efficiency captures conversion losses, so the battery bank is sized using realistic delivered power.
2. What is depth of discharge?
Depth of discharge is the usable share of total battery capacity. Lower allowable discharge usually improves battery life, but it requires a larger bank.
3. Why include a surge factor?
Some appliances draw extra power during startup. Pumps, refrigerators, and compressors commonly do this. Surge factor helps avoid choosing an inverter that trips on startup.
4. Should I match the exact result?
Usually you should round up to available equipment sizes. That gives extra reliability, leaves room for future loads, and reduces stress on the system.
5. Why is temperature derating included?
Battery performance changes with temperature. Cold conditions can lower available capacity, while hot environments may shorten life. Derating makes the estimate more practical.
6. What does suggested solar array mean?
It estimates the panel wattage needed to recharge the required battery energy within the entered sun hours, after considering controller losses. Final design still needs detailed review.
7. Can I use this for lithium batteries?
Yes. The battery type selector preloads common assumptions, and custom mode lets you set your own values. Manufacturer data should guide final settings.
8. Is this a full engineering design?
No. It is a planning calculator. Final system design should also check cable size, protection, charging limits, ventilation, environment, and installation standards.