The honest answer with real math — for home solar, RVs, portable setups, and off-grid systems. No engineering degree required.
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"How much solar do I need?" is the right first question to ask — and it's also the one most solar company websites answer vaguely, because the correct answer is: it depends on how much electricity you use.
This guide gives you the actual formula, a reference table of real appliance wattages, and realistic size estimates for the most common scenarios. By the end, you'll either know your answer or know exactly what to plug into our solar savings calculator to get it.
🎯 Quick Answer by System Type
Average US home: 6–10 kW system | Small home / apartment: 3–5 kW | Home + EV charging: 10–15 kW | RV / van: 200–600W | Portable / camping: 20–200W
Solar system sizing comes down to one core calculation — with three variables you need to know.
📋 Worked Example — Average American Home:
Monthly bill: 900 kWh → Daily use: 30 kWh
Location: Tennessee → Sun hours: 4.5 hrs/day
Formula: (30 kWh ÷ 4.5 hrs) ÷ 0.80 = 8,333W ≈ 8.3 kW system
At $2.80/W installed: ~$23,300 before any incentives
Use this to find the right sun hours value for your location. These are annual averages — summer is higher, winter lower.
| Region | Example States | Avg Peak Sun Hours | Note |
|---|---|---|---|
| Southwest Desert | AZ, NM, NV, S. CA | 6.0–7.0 hrs | Best solar resource in the US |
| Southeast | FL, TX, LA, GA | 5.0–6.0 hrs | Excellent, especially Florida |
| Mountain West | CO, UT, MT, WY | 5.0–6.0 hrs | High altitude boosts output |
| Midwest | OH, IN, IL, MN, KS | 4.0–5.0 hrs | Good solar economics due to high rates |
| Mid-Atlantic / Northeast | NY, PA, NJ, MA, CT | 3.5–4.5 hrs | Still viable; higher electricity rates offset lower output |
| Pacific Northwest | WA, OR, N. CA | 3.5–4.5 hrs | Lower sun hours but panels still pay off in many areas |
For exact sun hours at your address, use NREL's PVWatts calculator or enter your zip code in our savings calculator.
Use this to estimate your daily watt-hour consumption. Find your appliances, multiply watts × hours used per day, and add them up.
Formula: Watts × Hours/Day = Daily Wh. Then divide by 1,000 for kWh. Sum all appliances = your daily kWh usage.
| Appliance | Typical Watts | Avg Hours/Day | Daily Wh | Energy Impact |
|---|---|---|---|---|
| 🌡️ Heating & Cooling | ||||
| Central AC (3-ton) | 3,500W | 8 hrs | 28,000 Wh | Very High |
| Window AC Unit | 900–1,500W | 8 hrs | 7,200–12,000 Wh | High |
| Electric Furnace | 10,000–15,000W | 4 hrs | 40,000–60,000 Wh | Very High |
| Ceiling Fan | 15–75W | 8 hrs | 120–600 Wh | Low |
| 🍳 Kitchen Appliances | ||||
| Refrigerator (modern) | 100–200W avg | 24 hrs (cycling) | 1,500–2,000 Wh | Medium |
| Electric Oven / Range | 2,000–5,000W | 1 hr | 2,000–5,000 Wh | High |
| Microwave | 600–1,200W | 0.3 hrs | 180–360 Wh | Low |
| Dishwasher | 1,200–1,500W | 1 hr | 1,200–1,500 Wh | Medium |
| Coffee Maker | 800–1,200W | 0.2 hrs | 160–240 Wh | Low |
| 🧺 Laundry & Water | ||||
| Electric Clothes Dryer | 5,000–7,500W | 1 hr | 5,000–7,500 Wh | Very High |
| Washing Machine | 500–1,000W | 1 hr | 500–1,000 Wh | Medium |
| Electric Water Heater | 4,000–5,500W | 2–3 hrs | 8,000–16,500 Wh | Very High |
| 💡 Lighting & Electronics | ||||
| LED Light Bulb | 8–15W | 5 hrs | 40–75 Wh each | Very Low |
| LED TV (55") | 80–130W | 4 hrs | 320–520 Wh | Low |
| Desktop Computer | 150–300W | 6 hrs | 900–1,800 Wh | Medium |
| Laptop | 30–65W | 6 hrs | 180–390 Wh | Low |
| Phone Charging | 5–20W | 2 hrs | 10–40 Wh | Very Low |
| 🚗 EV Charging | ||||
| Level 1 EV Charger (120V) | 1,400W | 8 hrs | 11,200 Wh | High |
| Level 2 EV Charger (240V) | 7,200W | 3 hrs | 21,600 Wh | Very High |
Wattages are typical ranges — check the nameplate label on your specific appliances for exact figures. Cycling appliances (refrigerators, AC) use less than their peak wattage on average.
Here's what the math produces for the most common situations.
The US average home uses about 900 kWh/month (30 kWh/day). In a location with 5 peak sun hours, you need roughly (30 ÷ 5) ÷ 0.8 = 7.5 kW of panels. Round up to 8–10 kW to account for seasonal variation and any planned load growth (like adding an EV). At 2026 install prices of $2.80–$3.50/W, expect $22,000–$35,000 installed.
Energy-efficient 2-bedroom homes or apartments using 400–500 kWh/month. A 5 kW system covers the vast majority of your load in most US locations. Good candidate for pairing with a battery like the Enphase IQ Battery 5P or LG RESU for added value.
Adding an EV (average 15 kWh/day of charging) substantially increases your solar needs. A household charging 40 miles/day at home adds roughly 15 kWh to daily consumption. Size your system for your combined home + EV load. Smart EV chargers (like Tesla Wall Connector with solar integration) can prioritize charging during peak solar production to reduce grid draw.
Full-time van or RV living typically uses 3–6 kWh/day (12V fridge, lights, fans, devices, occasional laptop). A 400–600W rooftop panel array with a 200Ah lithium battery bank covers most needs. Add 200W more if you're running a CPAP or want to work remotely on power-intensive equipment. See our DIY Solar Kits guide for system component recommendations.
For weekend camping — phones, camera, lights, a small fan — 100W is usually plenty. Add a 500–1,000Wh portable power station and you have a self-contained system that handles most campsite needs. See our camping solar panel guide for specific product picks by use case.
Unless you have excellent net metering, oversizing creates stranded production you can't use or store. Size for your consumption during the day (when solar generates), and evaluate battery storage separately for night and peak loads.
Size to cover 85–95% of your annual consumption if your utility has good net metering. Size to 100%+ only if you're going off-grid or your utility has poor export rates.
Oversizing your solar array beyond what your inverter can handle wastes money. Every inverter has a maximum DC input — panels beyond that are clipped. Always size panels to your inverter capacity (within a 1.0–1.3 DC:AC ratio).
Your solar system size is determined by your energy consumption (kWh), not your instantaneous peak power draw (kW). Your utility's grid covers peak demand spikes. Solar is about reducing how much energy you pull from the grid over time.
A panel in shade produces dramatically less power — and in traditional string inverter systems, one shaded panel drags down the entire string. If your roof has shading from trees, chimneys, or neighboring buildings, add 10–20% more panels or spec microinverters (Enphase) or DC optimizers (SolarEdge) to mitigate losses.
Enter your monthly electric bill and zip code. Our calculator runs the sizing formula, pulls real sun hours data for your location, and gives you a personalized estimate of system size, cost, and payback period.
Calculate My Solar Needs →Now that you know how much solar you need, here's where to go next.