A one-page cheat sheet for sizing off-grid solar: appliance wattages, what an array actually produces, how big a battery bank you need, and realistic example systems.
1. Common Appliance Wattage & Daily Use
| Appliance | Running Watts | Typical Hours/Day | Daily Wh |
|---|---|---|---|
| LED bulb | 8–12 W | 5 | 40–60 |
| Wi-Fi router | 10–15 W | 24 | 240–360 |
| Laptop | 45–90 W | 4 | 180–360 |
| TV (LED 40–50") | 60–100 W | 4 | 240–400 |
| Refrigerator (Energy Star) | 100–200 W (cycles) | ~8 equiv. | 1,000–1,500 |
| Chest freezer | 80–150 W (cycles) | ~7 equiv. | 700–1,000 |
| Well pump (1/2 HP) | 900–1,000 W (start 2–3×) | 1–2 | 1,000–2,000 |
| Microwave | 1,000–1,500 W | 0.25 | 250–375 |
| Coffee maker | 800–1,200 W | 0.25 | 200–300 |
| Space heater | 1,500 W | 4 | 6,000 ⚠️ avoid on solar |
Add up daily Wh for everything you run = your daily energy budget. Motors (pumps, fridges) need 2–3× running watts at startup — size your inverter for the surge.
2. Panel Output by Peak Sun Hours
| Array Size | 3 Sun-hrs/day (winter/north) | 4 Sun-hrs | 5 Sun-hrs (most of US) | 6 Sun-hrs (southwest) |
|---|---|---|---|---|
| 200 W | 0.5 kWh | 0.6 kWh | 0.8 kWh | 1.0 kWh |
| 400 W | 1.0 kWh | 1.3 kWh | 1.6 kWh | 1.9 kWh |
| 800 W | 1.9 kWh | 2.6 kWh | 3.2 kWh | 3.8 kWh |
| 1,200 W | 2.9 kWh | 3.8 kWh | 4.8 kWh | 5.8 kWh |
| 2,000 W | 4.8 kWh | 6.4 kWh | 8.0 kWh | 9.6 kWh |
| 4,000 W | 9.6 kWh | 12.8 kWh | 16.0 kWh | 19.2 kWh |
Output = watts × sun-hours × 0.8 (system losses: wiring, controller, temperature, dust). Size the array for your worst season, not the average.
3. Battery Bank Sizing
| Daily Load | Days of Autonomy | LiFePO4 Needed (90% usable) | Lead-Acid Needed (50% usable) | @ 12V That's |
|---|---|---|---|---|
| 1 kWh | 2 | 2.2 kWh | 4.0 kWh | 185 Ah Li / 335 Ah PbA |
| 2 kWh | 2 | 4.4 kWh | 8.0 kWh | 370 Ah Li / 670 Ah PbA |
| 3 kWh | 2 | 6.7 kWh | 12.0 kWh | 560 Ah Li / 1,000 Ah PbA |
| 5 kWh | 2 | 11.1 kWh | 20.0 kWh | 925 Ah Li / 1,670 Ah PbA |
Battery kWh = daily load × autonomy days ÷ usable depth of discharge. LiFePO4 costs more upfront but delivers 3–5× the cycle life of lead-acid.
4. Example System Sizes
| Setup | Daily Use | Solar Array | Battery (LiFePO4) | Inverter | Ballpark Cost (DIY) |
|---|---|---|---|---|---|
| Weekend cabin / shed | 0.5–1 kWh | 200–400 W | 1.2–2.5 kWh | 1,000 W | $800–$1,800 |
| RV / van build | 1–2 kWh | 400–800 W | 2.5–5 kWh | 2,000 W | $1,500–$4,000 |
| Off-grid tiny home | 3–5 kWh | 1.2–2 kW | 7–12 kWh | 3,000 W | $5,000–$12,000 |
| Full off-grid homestead | 8–15 kWh | 4–8 kW | 15–30 kWh | 6,000–12,000 W (split-phase) | $15,000–$40,000 |
⚡ MPPT > PWM
An MPPT charge controller harvests up to 30% more energy than PWM, especially in cold weather and with higher-voltage arrays.
🧮 The 20% Rule
After calculating your loads, add 20–30% headroom for cloudy stretches, battery aging, and the loads you haven't thought of yet.
🔥 Heat ≠ Solar
Resistance heating (space heaters, electric water heaters) devours batteries. Use propane, wood, or diesel for heat off-grid.
📐 Tilt & Direction
Face true south (northern hemisphere); tilt ≈ your latitude. Winter: latitude +15°. Even flat-mounted panels lose only ~10–15% annually.