Solar Calculator: Size Panels, Battery & Inverter
Add the appliances you plan to run off-grid and get the exact solar wattage, battery capacity, and inverter size you need. Calculations use NREL peak-sun-hour data for your ZIP code and match your requirements against 363 tracked kits with real build cost.
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RV / Van Life
Lights, phone, laptop, 12V fan, mini fridge — a mobile setup that runs overnight on battery and recharges while you drive or park in the sun.
~600–900Wh/day · 200–400W solar · 1–1.5kWh battery
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Weekend Cabin
Lights, Wi-Fi, fridge, coffee maker, fan, hair dryer — a fully off-grid weekend getaway with enough headroom to cover cloudy-day shortfalls.
~2–3kWh/day · 600–1,200W solar · 3–5kWh battery
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Homestead / Full Off-Grid
Lights, security, fridge, freezer, well pump, washer — a self-sufficient property that runs appliances, pumps water, and survives multi-day storms.
~5–8kWh/day · 2,000–4,000W solar · 10–15kWh battery
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How to Size Your Off-Grid Solar System
Step 1: Calculate Your Daily Energy Consumption
Start by listing every appliance you plan to run off-grid. For each device, multiply its wattage × quantity × hours per day × duty cycle to get daily watt-hours (Wh). A mini fridge rated at 60W that cycles its compressor 33% of the time uses about 475 Wh/day. A CPAP machine at 40W running 8 hours uses 320 Wh/day. Add up all your loads to get your total daily energy need.
Step 2: Size Your Solar Panels
Divide your daily Wh by your location's peak sun hours and system efficiency (~85% for MPPT controllers with wiring losses). Phoenix gets 6.5 peak sun hours; Seattle gets 3.5. A 2,000 Wh/day load in Phoenix needs about 360W of panels. The same load in Seattle needs about 670W. Our calculator uses NREL data mapped to your ZIP code for precise estimates.
Step 3: Size Your Battery Storage
Multiply your daily Wh by the number of days of autonomyyou want (days without sun), then divide by your battery's usable depth of discharge. LiFePO4 batteries can safely use 90% of capacity; AGM batteries should stay above 50%. A 2,000 Wh/day system with 1 day of autonomy needs about 2,222 Wh of LiFePO4 storage or 4,000 Wh of AGM.
Common Off-Grid Appliance Wattages
| Appliance | Watts | Typical Hours | ~Daily Wh |
|---|---|---|---|
| LED Light (×4) | 9W | 5h | 180 |
| Phone Charger | 10W | 2h | 20 |
| Laptop | 50W | 4h | 200 |
| Starlink | 75W | 24h | 1800 |
| Mini Fridge | 65W | 24h | 546 |
| CPAP Machine | 60W | 8h | 480 |
| Coffee Maker | 800W | 0.25h | 200 |
| Window AC | 500W | 8h | 2000 |