☀️ Off-Grid Solar Sizing Worksheet
A step-by-step printable checklist for calculating your off-grid solar panel, battery bank, and inverter requirements.
📄 Free Printable · Complete in 15–20 minutes📋 How to Use This Worksheet
This worksheet guides you through every calculation needed to size an off-grid solar system. Work through each section in order — each builds on the previous one.
For a faster, automated experience, use our interactive Solar Sizing Calculator — just enter your appliances and location, and we'll do the math instantly. This worksheet is perfect for planning offline, field work, or as a teaching tool.
Tip: Fill in the worksheet first, then check your numbers against our calculator to validate your design.
Appliance Inventory & Energy Audit
List every appliance, light, and device you plan to power. Include each item's wattage, estimated hours of use per day, and quantity. Multiply to find daily watt-hours.
- ☐ Make a list of every AC appliance, DC device, and lighting load you want to run off-grid.
- ☐ Find the wattage for each item. Check the nameplate (usually on the back or bottom), the manual, or use our appliance presets for common values.
- ☐ Estimate daily run time in hours. Be honest — overestimating is better than underestimating.
- ☐ Account for surge loads — refrigerators, pumps, and motors have startup surges 3–7× their running wattage (we'll handle this in Section 4).
| # | Appliance / Device | Watts (W) | Hours/Day | Qty | Daily Wh |
|---|---|---|---|---|---|
| 1 | ________________________ | ________ | ________ | ________ | ________ |
| 2 | ________________________ | ________ | ________ | ________ | ________ |
| 3 | ________________________ | ________ | ________ | ________ | ________ |
| 4 | ________________________ | ________ | ________ | ________ | ________ |
| 5 | ________________________ | ________ | ________ | ________ | ________ |
| 6 | ________________________ | ________ | ________ | ________ | ________ |
| 7 | ________________________ | ________ | ________ | ________ | ________ |
| 8 | ________________________ | ________ | ________ | ________ | ________ |
| 9 | ________________________ | ________ | ________ | ________ | ________ |
| 10 | ________________________ | ________ | ________ | ________ | ________ |
| 11 | ________________________ | ________ | ________ | ________ | ________ |
| 12 | ________________________ | ________ | ________ | ________ | ________ |
| TOTAL Daily Energy (Wh/day): | ______________ | ||||
Pro Tip: Don't forget "phantom loads" — devices that draw power even when off (coffee makers with clocks, modem/routers, standby electronics). These can add 50–100 Wh/day each.
Solar Panel Array Sizing
Use your total daily energy from Section 1 to calculate how many solar watts you need. You'll need Peak Sun Hours (PSH) for your location.
- ☐ Find your location's Peak Sun Hours (PSH) — Use our calculator with your city, or check the NREL solar maps. Most US locations get 3.5–6.0 PSH (annual average).
- ☐ Choose your derating factor — Account for system losses: inverter (96%), wiring (98%), temperature (92%), dust/soiling (95%), battery round-trip (85% for LiFePO₄, 80% for lead-acid). Typical combined factor: 0.70–0.80.
- ☐ Decide on panel type — Monocrystalline (21–23% efficiency, most common), Polycrystalline (16–18%, budget), or Thin-film (10–13%, flexible but less efficient).
Winter Adjustment: If you plan to use the system year-round, use the lowest monthly PSH (typically December). In northern US, winter PSH can be 40–60% lower than the annual average. Consider adding 25–50% more panels for winter resilience.
Battery Bank Sizing
Your battery bank stores energy for nighttime use and cloudy days. Lithium batteries can be discharged deeper than lead-acid, so you need less capacity.
- ☐ Choose battery chemistry — LiFePO₄ (Lithium): 80–100% DoD, 5,000+ cycles, best value long-term. Lead-Acid (AGM/Gel): 50% DoD, 500–1,000 cycles, lower upfront cost.
- ☐ Select system voltage — 12V (small systems <1,500 Wh/day), 24V (medium 1,500–3,000 Wh/day), or 48V (large >3,000 Wh/day). Higher voltage = lower current = thinner wires.
- ☐ Choose days of autonomy — How many days of cloudy weather should your system cover without sun? 2–3 days for most setups, 5+ days for critical off-grid or northern climates.
Temperature Note: Battery capacity decreases in cold weather. Lead-acid batteries lose 30–50% of capacity below freezing. LiFePO₄ performs better in cold but cannot be charged below 0°C (32°F) unless equipped with a heating pad. If your batteries will be in an unheated space, add a 20–30% capacity buffer.
Inverter Sizing & Surge Loads
Your inverter must handle both your continuous loads (running watts) and surge loads (starting watts). Surge loads from motors, compressors, and pumps can be 3–7× the running wattage.
- ☐ Identify all continuous loads — List everything that could run simultaneously. This determines your inverter's continuous rating.
- ☐ Identify the largest surge loads — Refrigerator (startup ~1,200W), well pump (2,000–4,000W surge), freezer, microwave, power tools.
- ☐ Decide on inverter type — Pure Sine Wave (required for electronics, motors, and modern appliances) or Modified Sine Wave (budget option for resistive loads only — not recommended for most off-grid systems).
| Appliance(s) Running Simultaneously | Running Watts | Surge Watts |
|---|---|---|
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| ___________________________ | ________ W | ________ W |
| Total Running Watts: | ______________ W | |
| Largest Single Surge: | ______________ W |
Safety First: Always oversize your inverter by 25–50%. A 3,000W inverter is the most popular size for off-grid homes. If you plan to add more appliances later, size up now — replacing an inverter is expensive. And always use pure sine wave inverters for sensitive electronics.
System Summary — Final Checklist
- ☐ Total Daily Energy: ___________ Wh/day (from Section 1)
- ☐ Solar Array Size: ___________ W (from Section 2)
- ☐ Number of Panels: ___________ panels at ___________ W each (from Section 2)
- ☐ Battery Bank: ___________ Ah at ___________ V (___________ kWh) (from Section 3)
- ☐ Inverter: ___________ W continuous / ___________ W surge (from Section 4)
- ☐ Charge Controller: ___________ A MPPT (from Section 4)
- ☐ Wiring & Safety: Have I accounted for proper wire gauge, fuses/breakers, and disconnect switches? (Consult a licensed electrician for final installation.)
✅ Done with your worksheet?
Validate your numbers in seconds with our free interactive calculator. It uses real NREL solar data for your exact location and provides a complete system design report.
☀️ Use the Solar Sizing Calculator →No signup required. Just enter your appliances and location.