Calculator Inputs
Use the responsive input grid below. It shows three columns on large screens, two on smaller screens, and one on mobile.
Example Data Table
This example shows how a typical backup setup can be entered before you run the calculator.
| Device | Running Watts | Qty | Hours/Day | Surge Watts | Daily Energy (Wh) |
|---|---|---|---|---|---|
| Mini Fridge | 120 | 1 | 10 | 600 | 1200 |
| LED Lights | 12 | 6 | 5 | 12 | 360 |
| Laptop | 60 | 1 | 8 | 80 | 480 |
| Wi-Fi Router | 15 | 1 | 24 | 15 | 360 |
| Ceiling Fan | 75 | 2 | 6 | 150 | 900 |
| Total Daily Energy | 3300 Wh/day | ||||
Formula Used
The calculator sizes the battery bank from adjusted daily energy, backup days, usable battery depth, and inverter losses.
It sizes solar input from your energy target, average daily sun, and expected real-world derating losses.
It sizes the inverter from simultaneous load demand, then adds extra headroom so the system handles startup spikes more safely.
How to Use This Calculator
- Select your battery type and system voltage.
- Set backup autonomy, battery depth of discharge, inverter efficiency, and solar derate.
- Enter your expected peak sun hours for the location where the system will operate.
- Add every appliance you want the solar generator to support.
- For each appliance, enter running watts, quantity, daily runtime, and surge watts if known.
- Set simultaneous load if not all devices run together at once.
- Choose preferred panel wattage and battery unit size for an easier parts estimate.
- Click the calculate button to view the result above the form, then export the summary as CSV or PDF.
Frequently Asked Questions
1. What does this calculator size?
It estimates battery storage, inverter rating, solar array size, panel count, battery units, and expected runtime based on your loads and backup target.
2. Why do I need surge watts?
Some devices draw extra power at startup. Surge sizing helps your inverter and generator avoid trips when fridges, pumps, fans, or compressors first switch on.
3. Why does battery type matter?
Different batteries safely allow different usable depth of discharge. Lithium usually permits deeper cycling than lead-acid, so required total battery size can change a lot.
4. What is solar derate?
Solar derate accounts for real-world losses from heat, wiring, dust, angle, controller inefficiency, and non-ideal conditions. Lower derate means more panels are needed.
5. What is simultaneous load?
It is the share of your total running watts that may operate at the same time. This mainly affects inverter sizing and estimated runtime under active use.
6. Should I add a safety margin?
Yes. A safety margin helps cover unexpected usage, seasonal sunlight variation, battery aging, future device additions, and efficiency drift over time.
7. Can I use this for homes and cabins?
Yes. It works for cabins, RVs, small homes, emergency kits, field stations, and backup circuits. Just enter realistic loads and good local sun-hour assumptions.
8. Is this a final engineering design?
No. It is a planning calculator. Final equipment choice should still consider wiring limits, charging current, controller sizing, battery chemistry rules, and local installation requirements.