📖 Overview
This calculator translates appliance plans into battery and panel sizing numbers you can buy.
It accounts for system losses and local sun availability so off grid setups are less likely to fail in real use.
🧪 Example Scenarios
Use these default and higher-pressure example inputs to explore how sensitive this calculator is before using your real numbers.
| Input | Base Case | Higher Pressure Case |
|---|---|---|
| Daily Appliance Load (Wh) | 1,900 | 2,185 |
| System Loss Factor (%) | 20 | 24 |
| Battery Autonomy Days | 2 | 2.4 |
| Peak Sun Hours Per Day | 4.5 | 5.4 |
| Panel Wattage (W) | 100 | 115 |
⚙️ How It Works
Sizes off-grid systems by converting daily load into adjusted energy demand then mapping that demand to battery reserve and panel count.
The Formula
Adjusted Load = Daily Wh × (1 + Loss %) | Panels ≈ Adjusted Load ÷ (Sun Hours × 0.8 × Panel Wattage)
| Daily Load | Total planned appliance energy per day in Wh |
| Loss Factor | Percent inefficiency across inverter wiring and conditions |
| Autonomy Days | Days of battery backup required without charging |
| Peak Sun Hours | Usable daily solar generation window |
| Panel Wattage | Rated power of each panel module |
💡Designing for shoulder-season sun hours instead of summer peak hours usually avoids underbuilt systems.
Quick Reference
| Adjusted Daily Load | Sun Hours | Array Needed | 100W Panels |
|---|---|---|---|
| 1,200 Wh | 5.0 | ~300W | 3 |
| 2,100 Wh | 4.5 | ~583W | 6 |
| 3,000 Wh | 3.8 | ~987W | 10 |
When To Use This
- Use this tool when you need a fast decision during active planning or execution.
- Use this before committing money, time, or tradeoffs that are hard to reverse.
- Use this to compare options using the same assumptions across scenarios.
Edge Cases To Watch
- Results can be misleading if key inputs are missing, stale, or unrealistic.
- Very small or very large values may amplify rounding effects and interpretation risk.
- If assumptions change mid-decision, recalculate before acting.
Practical Tips
💡 Validate appliance duty cycles instead of nameplate-only estimates.
💡 Add margin for winter and cloudy-day variability.
💡 Keep battery depth-of-discharge limits in your final design.
Frequently Asked Questions
❓ Why include an 0.8 performance factor?
Real systems lose output to temperature, wiring, controller, and panel angle effects.
❓ Does this replace full electrical design?
No. It is a planning tool and should be followed by component-level design checks.