Solar Seasonal Production Calculator

Enter your system size and location — get a 12-month production table with daily kWh, monthly kWh, and seasonal variation for any US city.

System details

Location?

System size?

Panel tilt angle?

System losses?

Monthly production — Denver, CO

10423 kWh/year estimated

Month	PSH	Daily kWh	Monthly kWh
Jan	4.1	21.2	658
Feb	4.8	24.8	695
Mar	5.6	29.0	898
Apr	6.1	31.6	947
May	6.4	33.1	1026
Jun	7.0	36.2	1086
Jul ★	6.8	35.2	1091
Aug	6.5	33.6	1042
Sep	5.9	30.5	916
Oct	5.2	26.9	834
Nov	4.0	20.7	621
Dec ▼	3.8	19.7	609

Best monthJul (1091 kWh)

Worst monthDec (609 kWh)

Summer daily avg (Jun-Aug)35.0 kWh/day

Winter daily avg (Dec-Feb)21.9 kWh/day

Summer/winter ratio1.6x (consistent year-round)

Annual daily average28.6 kWh/day

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How to Use This Calculator

Select your city and system size

Choose the city closest to your solar installation from 20 US cities with pre-loaded monthly peak sun hour (PSH) data. Enter your system's nameplate DC capacity in kilowatts — a typical residential system is 5-10 kW. If you already have a system, use the size on your inverter nameplate or utility interconnection agreement.

Set tilt angle and system losses

Panel tilt angle affects seasonal production: a steeper tilt (closer to 90°) favors winter production; a shallower tilt (closer to 0°) favors summer. For most fixed-mount systems, set tilt to your latitude for maximum annual yield. System losses default to 14% — the NREL PVWatts standard that accounts for wiring, inverter efficiency, soiling, temperature, and mismatch losses.

Read the monthly table

The table shows each month's average PSH, estimated daily kWh output, and total monthly kWh. The best month (★) and worst month (▼) are highlighted. The summary below the table shows summer/winter ratio — a key number for battery sizing, backup planning, and understanding your bill credits over the year.

The Formula

Daily kWh = System kW × Monthly PSH × (1 − System Losses %) Monthly kWh = Daily kWh × Days in Month Annual kWh = Sum of all 12 Monthly kWh values Summer/Winter Ratio = Avg Daily kWh (Jun-Aug) ÷ Avg Daily kWh (Dec-Feb)

This calculator uses monthly average PSH data derived from NREL's National Solar Radiation Database. The tilt adjustment applies a small correction factor — for precise tilt optimization, use NREL PVWatts directly. System losses of 14% are the industry-standard default for a well-maintained residential system.

Example

Maria — 7 kW system in Chicago

Maria has a 7 kW south-facing rooftop system in Chicago, installed at a 42° tilt, with 14% system losses. She wants to understand the seasonal production swing before sizing a battery.

CityChicago, IL

System size7 kW

Tilt42°

System losses14%

Result

Best monthJun (~1,055 kWh)

Worst monthJan (~420 kWh)

Summer daily avg~34 kWh/day

Winter daily avg~14 kWh/day

Summer/winter ratio2.4x (moderate variation)

Annual total~8,200 kWh/year

Maria's Chicago system produces 2.4× more in summer than winter — a moderate seasonal swing. She'll have large utility bill credits in summer and may pull from the grid in January and February. This helps her decide whether to install a battery and how to size it for winter nights.

FAQ

Why does solar production vary so much by season? ▼

Solar production follows the sun's path. In summer, days are longer, the sun is higher in the sky (more direct radiation), and clear weather is more common. In winter, days are shorter, the sun is lower (more atmosphere to penetrate), and cloud cover is more frequent in most US regions. At extreme latitudes like Anchorage, AK, winter production is near zero while summer can exceed even Phoenix for a few weeks.

What is a good summer/winter production ratio? ▼

A ratio below 1.5x is excellent (Miami, Honolulu, San Diego) — your system produces consistently year-round, maximizing self-consumption. A ratio of 1.5-2.5x is typical for most US locations and is manageable with net metering. A ratio above 3x (Chicago, Seattle, Minneapolis) means you'll have large summer surpluses and winter deficits, making battery sizing and utility rate design especially important for your economics.

How accurate are these monthly production estimates? ▼

These estimates are within ±10-15% of actual production for most systems. Accuracy depends on: your exact location vs. the selected city, actual roof orientation and shading, real panel efficiency vs. nameplate, and local microclimate. For a precise estimate, use NREL PVWatts with your exact address and roof data. This calculator is ideal for planning, comparison, and understanding seasonal patterns before getting installer quotes.

Should I tilt panels steeper for winter production? ▼

If your utility does not offer annual net metering rollover, maximizing winter production makes sense — a steeper tilt (latitude + 15°) boosts December-February output by 10-20% while reducing summer output slightly. If you have annual net metering (credits roll over year-to-year), optimize for maximum annual yield (tilt = latitude). Dual-axis trackers can boost annual production 25-40% but cost 3-5× more than fixed systems.

Does snow affect winter solar production? ▼

Yes — snow covering panels stops production entirely until it melts or slides off. Tilted panels (30°+) self-clear faster than flat panels. NREL data shows snow losses average 1-5% of annual production in the Midwest and Northeast — modest because most snowfall occurs when PSH is already low. The bigger winter impact is simply fewer daylight hours and lower sun angle, not snow. This calculator's winter PSH data inherently includes typical cloud and weather losses.

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