My city is not listed — what should I use?

Pick the listed city closest to you in latitude and climate zone. Seattle represents the Pacific Northwest, Chicago covers the Midwest, Phoenix covers the Southwest desert. For precise data, use NREL's PVWatts calculator.

Solar Production Calculator

Month-by-month solar production estimates for your system size, city, and tilt angle.

System & location

System size?

Location / city?

Panel tilt angle?

System efficiency?

Annual production

14,859 kWh/year

Month	Avg PSH	Production
Jan	5.63	1,201 kWh
Feb	6.10	1,176 kWh
Mar	6.36	1,356 kWh
Apr	6.26	1,292 kWh
May	5.92	1,263 kWh
Jun	5.99	1,236 kWh
Jul	5.69	1,213 kWh
Aug	5.85	1,248 kWh
Sep	6.15	1,269 kWh
Oct	6.12	1,304 kWh
Nov	5.51	1,137 kWh
Dec	5.45	1,163 kWh
Total		14,859 kWh

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How to Use This Calculator

Enter your system size

Input your total system size in kW. If you know your panel count and wattage, multiply them: 20 panels × 400W = 8,000W = 8 kW. This calculator uses nameplate capacity — what the panels are rated at under ideal conditions.

Select your city

Choose the city closest to your installation. Each city uses real monthly average peak sun hours from NREL solar radiation data. This is the biggest variable in month-to-month production — Denver gets nearly 7× more effective sunlight in July than Seattle gets in December. The monthly breakdown table shows exactly how your location's seasonal variation affects production.

Set the tilt angle

Tilt angle significantly affects how much sun your panels capture in different seasons. A 30° south-facing tilt is standard for residential US installations. Steeper tilts (40-45°) capture more winter sun but less summer sun — better if you have time-of-use rates that peak in winter. A flat (0°) roof loses 10-15% annually vs. optimal tilt in most US locations.

Read the month-by-month table

The production table shows each month's adjusted peak sun hours and total kWh output. The bar chart helps visualize seasonal variation. Most US locations produce 2-3× more in their best month vs. their worst month — an important factor for battery storage sizing and grid interaction planning.

The Formula

Monthly kWh = System kW × Adjusted daily PSH × Days in month × System efficiency Adjusted PSH = Base city PSH × Tilt angle factor Annual total = Sum of all 12 monthly values

The tilt angle factor adjusts each month's production based on how the panel angle interacts with the sun's varying elevation throughout the year. In summer, the sun is high in the sky — flat panels capture it well. In winter, the sun is low — tilted panels face it more directly. A 30° tilt in Denver increases January production by ~14% over flat but reduces June production by ~6%.

City data uses monthly average peak sun hours from NREL's National Solar Radiation Database (NSRDB), which aggregates decades of measured solar irradiance.

Example

8 kW system in Chicago, IL — 30° tilt

Chicago has significant seasonal variation — one of the most dramatic in the US. Understanding the monthly profile helps with battery sizing and energy planning.

System size8 kW

LocationChicago, IL

Tilt30°

System efficiency86%

Monthly Highlights

Best month (June)~1,280 kWh

Worst month (Dec)~445 kWh

Annual total~9,950 kWh

Summer average~1,200 kWh/mo

Winter average~560 kWh/mo

This Chicago system produces about 2.9× more in June than December. If the homeowner uses 1,000 kWh/month, they're fully solar-powered from April through September but rely heavily on the grid in winter months. This seasonal mismatch is why net metering (banking summer credits for winter use) is so valuable in northern climates.

FAQ

Why does solar production vary so much by month? ▼

Monthly variation is driven by two factors: day length and sun angle. In summer, days are longer and the sun is higher in the sky, delivering more intense radiation for more hours. In winter, shorter days and a lower sun angle mean less energy hits your panels. Locations further from the equator (like Seattle or Chicago) experience more dramatic seasonal swings than southern cities like Miami or Phoenix.

What tilt angle maximizes annual solar production? ▼

For maximum annual production, the optimal fixed tilt equals your latitude minus 2-3°. In Denver (latitude 39.7°), optimal tilt is about 37°. However, most residential roofs are installed at the roof's existing pitch, typically 18-35°. Forced to choose between a 25° and 35° roof, the 35° pitch is usually better in the northern US and 25° is better in the southern US. Use our Solar Panel Tilt Calculator for seasonal optimization.

My city isn't listed — what should I use? ▼

Pick the listed city closest to you in latitude and climate zone. For precise data, use NREL's PVWatts calculator which has data for thousands of locations worldwide. The cities in this calculator cover the major climate zones in the US — Seattle represents the Pacific Northwest, Chicago represents the Midwest, Phoenix covers the Southwest desert, etc.

Does cloud cover affect the monthly production numbers? ▼

Yes — the peak sun hours data already accounts for average cloud cover. The NREL data used here represents multi-decade averages that include cloudy days. Seattle's 1.76 PSH in January, for example, already reflects the notoriously cloudy Pacific Northwest winter. Individual months will vary from the average, but over a full year, the estimates are typically accurate within ±10%.

How do I use this data for battery storage sizing? ▼

Look at your worst production month and compare it to your monthly electricity consumption. If December produces 600 kWh but you use 1,000 kWh, you need 400 kWh from the grid (or stored earlier). For daily sizing, divide the worst monthly production by days in that month to get average daily output, then size your battery for 1-3 days of autonomy. Use our Solar Battery Calculator for complete storage sizing.