Free calculator
Size your off-grid solar system: panels, batteries, charge controller and inverter, from your own appliance list.
List the appliances you want to run, choose your sunshine and battery type, and this calculator sizes your whole off-grid solar system: daily energy use, solar array, battery bank, charge controller and inverter. Results update as you type, and the method is explained below.
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Estimates for planning only. Always check equipment specifications, local codes and, for electrical work, a licensed professional.
Sizing an off-grid solar system is not complicated, but it does require working through the numbers honestly. Use this guide to calculate your actual system requirements before buying any equipment. The four-step process below is the same one professional solar installers use — you will have accurate numbers in about 30 minutes.
List every appliance and multiply its wattage by the hours per day you use it. The result is watt-hours (Wh) per day. Add them all up for your daily total.
How to find wattage: Check the label on the appliance, look it up in its manual, or use a Kill-A-Watt meter ($25) to measure actual consumption — manufacturers’ ratings are often higher than real-world use.
| Appliance | Typical Watts | Notes |
|---|---|---|
| LED bulb | 8–12W | Per bulb; multiply by number in use |
| DC compressor refrigerator | 30–50W | Average over 24 hours |
| Standard AC refrigerator | 100–200W | Average; high surge on startup |
| Laptop computer | 45–90W | Varies by model and usage |
| Desktop computer + monitor | 150–300W | Avoid if possible on small systems |
| Phone charging | 5–20W | Per phone |
| WiFi router | 5–15W | Continuous when on |
| Starlink dish | 50–100W | Varies by generation and conditions |
| Television (LED, 40″) | 50–80W | |
| Well pump (1/2 HP) | 750–1,000W | High surge; short duration |
| Washing machine | 400–1,200W | Front-loader uses less |
| Electric kettle | 1,000–1,500W | Replace with propane for off-grid |
| Toaster | 800–1,500W | Replace with toaster oven or propane |
| Hair dryer | 1,500–2,000W | Replace with air-dry for off-grid |
| Power drill | 300–700W | Intermittent use |
| Table saw | 1,500–3,000W | High startup surge; size system accordingly |
| Appliance | Watts | Hours/Day | Wh/Day |
|---|---|---|---|
| LED lighting (8 bulbs × 10W) | 80 | 5 | 400 |
| DC refrigerator | 40 | 24 | 960 |
| Laptop | 65 | 6 | 390 |
| Starlink | 75 | 12 | 900 |
| Phone charging (2) | 20 | 3 | 60 |
| TV (evenings) | 60 | 2 | 120 |
| Well pump | 900 | 0.3 | 270 |
| Washing machine (3×/week avg) | 600 | 0.3 | 180 |
| Daily Total | 3,280 Wh |
This example home uses approximately 3.3 kWh per day — a reasonable off-grid consumption level for a working couple or small family.
Your battery bank must store enough energy to power your home for 2–3 days without any solar input (cloudy days, heavy storms). The formula:
Battery bank (Wh) = Daily consumption × Days of autonomy ÷ Usable depth of discharge
For LiFePO4 batteries (recommended): 80–90% usable. For AGM/flooded lead-acid: 50% usable.
Example: 3,280 Wh × 3 days ÷ 0.85 = 11,576 Wh ≈ 12 kWh battery bank
In LiFePO4, 12 kWh of usable capacity costs approximately $4,800–$6,000 in 2026. Consider this your most important cost.
You need panels to recharge your batteries daily and meet your real-time consumption. The formula:
Panel array (W) = Daily consumption ÷ Peak sun hours × 1.25 (losses factor)
| Region | Average Peak Sun Hours/Day |
|---|---|
| Southwest (AZ, NM, NV, CA desert) | 5.5–7.0 |
| Southeast (TX, FL, GA) | 4.5–5.5 |
| Pacific Northwest (WA, OR) | 3.5–4.5 |
| Mountain West (CO, UT, ID) | 4.5–5.5 |
| Midwest (IA, MO, KS) | 4.0–5.0 |
| Northeast (NY, VT, ME) | 3.5–4.5 |
| Alaska (Anchorage) | 2.5–4.0 |
Example (Northeast homestead, 4.0 peak hours):
3,280 Wh ÷ 4.0 × 1.25 = 1,025W of solar panels
Round up to 1,200W (three 400W panels) as a practical minimum. In a northern climate, I would go to 1,600W (four panels) to handle reduced winter sun and cloud cover.
Charge controller amperage: Panel array watts ÷ Battery voltage = Amps. Example: 1,600W ÷ 24V = 66.7A. Choose a 60A or 80A MPPT controller.
Inverter sizing: Your inverter must handle your peak simultaneous load. Add up the wattage of everything that might run at once. In our example, the well pump (900W surge ~1,800W) + refrigerator (200W surge) + lighting (80W) + laptop (65W) = peak ~2,145W. Choose a 3,000W inverter minimum.
Important: Size the inverter for peak surge demand, not average consumption. A washing machine starting while other loads run can demand 2,000W+ for a fraction of a second — your inverter must handle this without shutting down.
| Component | Specification | Estimated 2026 Cost |
|---|---|---|
| Solar panels | 4 × 400W monocrystalline | $1,100 |
| MPPT charge controller | 80A (Victron 150/85) | $450 |
| Battery bank (LiFePO4) | 12 kWh usable (e.g., 6× 200Ah 12V in series-parallel) | $5,500 |
| Inverter/charger | 3,000W pure sine wave (Victron Multiplus) | $1,200 |
| Wiring, disconnects, fuses | Complete system | $500 |
| Mounting hardware | Ground-mount rack | $350 |
| Total (DIY) | $9,100 |
Any off-grid system in a climate with significant cloudy season (Pacific Northwest, Northeast, Upper Midwest) needs a backup generator. Rule: if you have 5+ consecutive days of less than 2 peak sun hours in winter, add a generator. A 3,500–5,500W propane generator ($600–$1,200) connected through your inverter/charger provides recharge during extended overcast periods.
Once you have your numbers, use our Complete Solar System Guide for specific product recommendations by system size, our Battery Review for the latest LiFePO4 options, and our Resources page for the complete list of tools and references used by OffGridSage.