\u2600\ufe0f Off-Grid Solar Sizing Worksheet
A step-by-step printable checklist for calculating your off-grid solar panel, battery bank, and inverter requirements.
\U0001f4c4 Free Printable \u00b7 Complete in 15\u201320 minutes\U0001f4cb 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 \u2014 each builds on the previous one.
For a faster, automated experience, use our interactive Solar Sizing Calculator \u2014 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.
- \u2610 Make a list of every AC appliance, DC device, and lighting load you want to run off-grid.
- \u2610 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.
- \u2610 Estimate daily run time in hours. Be honest \u2014 overestimating is better than underestimating.
- \u2610 Account for surge loads \u2014 refrigerators, pumps, and motors have startup surges 3\u20137\u00d7 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" \u2014 devices that draw power even when off (coffee makers with clocks, modem/routers, standby electronics). These can add 50\u2013100 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.
- \u2610 Find your location\'s Peak Sun Hours (PSH) \u2014 Use our calculator with your city, or check the NREL solar maps. Most US locations get 3.5\u20136.0 PSH (annual average).
- \u2610 Choose your derating factor \u2014 Account for system losses: inverter (96%), wiring (98%), temperature (92%), dust/soiling (95%), battery round-trip (85% for LiFePO\u2084, 80% for lead-acid). Typical combined factor: 0.70\u20130.80.
- \u2610 Decide on panel type \u2014 Monocrystalline (21\u201323% efficiency, most common), Polycrystalline (16\u201318%, budget), or Thin-film (10\u201313%, 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\u201360% lower than the annual average. Consider adding 25\u201350% 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.
- \u2610 Choose battery chemistry \u2014 LiFePO\u2084 (Lithium): 80\u2013100% DoD, 5,000+ cycles, best value long-term. Lead-Acid (AGM/Gel): 50% DoD, 500\u20131,000 cycles, lower upfront cost.
- \u2610 Select system voltage \u2014 12V (small systems <1,500 Wh/day), 24V (medium 1,500\u20133,000 Wh/day), or 48V (large >3,000 Wh/day). Higher voltage = lower current = thinner wires.
- \u2610 Choose days of autonomy \u2014 How many days of cloudy weather should your system cover without sun? 2\u20133 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\u201350% of capacity below freezing. LiFePO\u2084 performs better in cold but cannot be charged below 0\u00b0C (32\u00b0F) unless equipped with a heating pad. If your batteries will be in an unheated space, add a 20\u201330% 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\u20137\u00d7 the running wattage.
- \u2610 Identify all continuous loads \u2014 List everything that could run simultaneously. This determines your inverter\'s continuous rating.
- \u2610 Identify the largest surge loads \u2014 Refrigerator (startup ~1,200W), well pump (2,000\u20134,000W surge), freezer, microwave, power tools.
- \u2610 Decide on inverter type \u2014 Pure Sine Wave (required for electronics, motors, and modern appliances) or Modified Sine Wave (budget option for resistive loads only \u2014 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\u201350%. A 3,000W inverter is the most popular size for off-grid homes. If you plan to add more appliances later, size up now \u2014 replacing an inverter is expensive. And always use pure sine wave inverters for sensitive electronics.
System Summary \u2014 Final Checklist
- \u2610 Total Daily Energy: ___________ Wh/day (from Section 1)
- \u2610 Solar Array Size: ___________ W (from Section 2)
- \u2610 Number of Panels: ___________ panels at ___________ W each (from Section 2)
- \u2610 Battery Bank: ___________ Ah at ___________ V (___________ kWh) (from Section 3)
- \u2610 Inverter: ___________ W continuous / ___________ W surge (from Section 4)
- \u2610 Charge Controller: ___________ A MPPT (from Section 4)
- \u2610 Wiring & Safety: Have I accounted for proper wire gauge, fuses/breakers, and disconnect switches? (Consult a licensed electrician for final installation.)
\u2705 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.
\u2600\ufe0f Use the Solar Sizing Calculator \u2192No signup required. Just enter your appliances and location.