“Solar only makes sense if you live in a sunny state” — this is one of the most common and most expensive myths about going solar. Homeowners in Massachusetts, Michigan, and even the Pacific Northwest have systems that pay off within 7–9 years. The sun hours map doesn’t tell the whole story. Here’s how to actually calculate whether solar works for your specific home.
Thank you for reading this post, don’t forget to subscribe!What Are Peak Sun Hours?
“Peak sun hours” doesn’t mean the total number of hours the sun is up in a day. It’s a measure of solar intensity — specifically, the number of hours per day when sunlight is strong enough to deliver 1,000 watts of energy per square meter (1 kW/m²).
A location with 5 peak sun hours isn’t saying the sun shines for 5 hours. It’s saying the total daily solar energy is equivalent to 5 hours of full-intensity sunlight. That’s the number that matters for calculating system output.
Here’s a quick regional reference for the continental U.S.:
| Region | Avg. Peak Sun Hours/Day | Example Cities |
|---|---|---|
| Southwest | 5.5–7.0 | Phoenix, Las Vegas, Los Angeles |
| Southeast | 4.5–5.5 | Atlanta, Miami, Dallas |
| Midwest | 4.0–4.5 | Chicago, Detroit, Kansas City |
| Northeast | 3.5–4.5 | Boston, New York, Philadelphia |
| Pacific Northwest | 3.0–4.0 | Seattle, Portland, Eugene |
Notice that even Seattle — famous for rain — gets 3–4 peak sun hours per day on average. That’s genuinely enough to make solar worthwhile, especially with Washington’s high electricity rates.
Why Electricity Rate Matters More Than Sun Hours
Here’s the counterintuitive part: solar ROI depends more on your utility rate than on your sun hours. A homeowner in cloudy Massachusetts paying $0.24/kWh will often save more money from solar than a homeowner in sunny Arizona paying $0.12/kWh — even though Arizona gets nearly twice the peak sun hours.
Why? Because every kWh your solar system produces offsets a kWh you would have bought from the utility. The higher that utility rate, the more each kWh of solar is worth. When Massachusetts electricity costs twice as much as Arizona electricity, you need half as many peak sun hours to break even.
This is a critical input into your actual break-even calculation. We walk through the full math in our guide on solar panel ROI and when you actually break even.
How to Calculate How Much Sun Your Specific Roof Gets
Regional averages are a starting point, but your individual roof matters. Three things affect your actual solar resource:
1. Roof Orientation
South-facing roofs capture the most sun throughout the day in the Northern Hemisphere. East or west-facing roofs produce about 15–20% less than a south-facing roof. North-facing roofs are generally not viable for solar without unique circumstances.
2. Roof Pitch (Angle)
The optimal tilt for a solar panel is approximately equal to your latitude. If you’re at 35° north latitude, a 35° tilt is close to ideal. Most U.S. residential roofs are between 20–40°, which falls within the acceptable range. Very shallow or very steep roofs sacrifice some production.
3. Shading
Trees, chimneys, neighboring buildings, and dormers all create shade that reduces output. This is where the difference between string inverters and microinverters becomes critical — on a shaded roof, string inverters lose production from all panels when any one panel is shaded. Microinverters isolate each panel, so shading one doesn’t affect the others.
For a deeper look at how inverter type affects shaded-roof performance, see our guide on what a solar inverter is and why it matters.
The Simple Formula to Estimate Your System’s Output
Once you know your peak sun hours, you can estimate how much power a solar system would produce:
Daily output (kWh) = System size (kW) x Peak sun hours x 0.80
The 0.80 factor accounts for real-world losses: inverter inefficiency, temperature, wiring losses, and dust. It’s a conservative but realistic derating factor.
Example: A 8 kW system in Boston (4.2 peak sun hours) would produce approximately:
8 kW x 4.2 x 0.80 = 26.9 kWh per day, or roughly 9,830 kWh per year
The average U.S. home uses about 10,500 kWh per year. That same 8 kW system in Phoenix (6.5 peak sun hours) would produce about 15,200 kWh per year — well above average consumption. The difference is real, but Boston’s system still covers most of an average home’s usage.
The Minimum Threshold: When Is Solar Not Worth It?
Generally speaking, solar becomes financially questionable when your location falls below about 3 peak sun hours per day AND your electricity rate is below $0.12/kWh. Very few places in the continental U.S. hit both of those conditions simultaneously.
Alaska and parts of the far Pacific Northwest in winter can approach this threshold, but even then, battery storage, high utility rates, or state incentives often tip the balance positive. In the lower 48 states, it’s rare for solar to make zero financial sense — though the magnitude of savings varies significantly.
Seasonal Variation: What Happens in Winter?
Solar output drops in winter — not just because of weather but because the days are shorter and the sun is lower in the sky. A system in Chicago that produces 30 kWh per day in June might produce 10–12 kWh per day in December.
This matters for how you size your system. Installers typically size systems based on annual production targets, which means you’ll overproduce in summer (sending excess to the grid via net metering) and underproduce in winter (drawing from the grid). The net metering credits from summer offset winter grid usage — which is exactly how the billing is designed to work. Our guide on what net metering is and how it works covers the billing mechanics in detail.
How to Find Your Exact Peak Sun Hours
The most accurate free tool for U.S. homeowners is NREL’s PVWatts Calculator (pvwatts.nrel.gov). Enter your address, system size, and roof angle, and it models your expected annual production based on decades of historical weather data at your exact location. Any serious solar installer should be running this tool when designing your system — if they’re not, that’s a red flag.
The Bottom Line
The sun shines enough for solar to make financial sense in nearly every part of the continental U.S. The question isn’t whether you have enough sun — it’s whether the combination of your local sun hours, utility rate, and available incentives makes the math work for your specific situation. In most cases, it does. The key is knowing your numbers before you start talking to installers, so you can verify their production estimates against reality.
Want to understand how your location’s sun hours feed into the question of how many panels you need? See our guide on how many solar panels your home actually needs.