How to use the solar yield estimator

By Emily CarterPublished October 27, 2026Data as of 2026-10-27: PVWatts® v8, typical-year weather

Choose a city, type the system size in kW, pick one of six panel layouts and, if you like, a second city. The estimator multiplies the modelled output of 1 kW in that city by your size and shows yearly and monthly kWh, the city's rank for that layout and the gap to the second city. For example, 6 kW facing south at 20° in Denver makes about 9,610 kWh a year.

Step by step

1. Choose the city. The list holds the 100 cities on the site, sorted by name. If yours is missing, choose the closest listed city, or one with similar weather from the list of cities.
2. Type the system size. Use the rated power of the panels in kW: add up the wattage of the modules and divide by 1,000. Twenty 400-watt panels are 8 kW. Any value from 0.5 to 100 kW works, including decimals.
3. Choose the layout. Pick the one closest to your roof. The six options are the six that were modelled for every city: south at 20°, south at the city's latitude, flat, east at 20°, west at 20° and a 1-axis tracker. The tracker is a ground mount, included for comparison.
4. Add a second city if you want. The same size and layout are placed there, so the difference is down to location alone.

Results update as you change any field, and the address bar keeps your choices, so you can bookmark or share the exact estimate. Without JavaScript, the page still shows a full worked example.

Comparing layouts for one city is a matter of switching the layout and watching the total. In Denver, 6 kW facing south at 20° makes 9,610 kWh a year; the same panels tilted to the city's latitude (40°) make 9,990, and facing west 7,980. The monthly bars show where the difference comes from: the steeper roof gains in winter and gives a little back in summer.

Three worked examples

A small west-facing roof in Phoenix. Phoenix panels facing west at 20° make 1,497.5 kWh per kW a year. Four kW gives about 5,990 kWh a year. That is 9th of 100 cities for a west-facing roof. Mesa, next door, makes almost the same.

A larger, steeper roof in Boston. Tilted to Boston's latitude (42°), each kW makes 1,314.0 kWh. An 8.5 kW array gives 11,170 kWh a year. The best month is March and the weakest December.

Flat panels in Minneapolis against Denver. Flat, 6 kW in Minneapolis makes 6,750 kWh a year, against 8,000 for the same panels at 20° south. Denver makes more with the same flat panels, and the monthly table shows the gap is widest in winter.

How the numbers are made

For every city and layout the site stores the modelled output of 1 kW of panels for each month of a typical year. The estimator multiplies those figures by your size. Output in this model scales in proportion to system size, which is also how the 6 kW figures on city pages are made.

Rounding. The yearly total is rounded to the nearest 10 kWh and each month to the nearest 1 kWh, so the months may differ from the year by a few kWh. Per-kW figures keep one decimal, as in the data.

Rank places the city among all 100 for the chosen layout, 1 being the most output. A city can move a few places between layouts, because each layout changes output by a different amount in each city. Phoenix, for example, is 6th at 20° south and 9th facing west.

The comparison is the second city's yearly output against the first, as a percentage, with the same per-month comparison in the table. With latitude tilt, each city is tilted to its own latitude, and the result says so.

What the estimator cannot tell you

It cannot see your roof. There is no shading in the model, and the six layouts are the only ones in the data: a roof facing south-east, or pitched at 35°, falls between the options and is not interpolated. The weather is a typical year, so a real year will differ, and snow, dirt and the equipment chosen all change the result. The methodology lists every setting.

The estimator answers one narrow question well: how much electricity a given size and layout makes in a typical year in each city, and how that compares with somewhere else. For the meaning of the units, read what kWh per kW means.

Sources

• PVWatts® Calculator API v8, National Laboratory of the Rockies (NLR, formerly NREL): developer.nlr.gov. 600 model runs (100 cities × 6 layouts), retrieved 2026-10-27.
• Weather: NSRDB typical-meteorological-year data returned by PVWatts® (NSRDB PSM V3 GOES tmy-2020 3.2.0, NSRDB PSM V4 Polar tmy-2023 1.0.0).
• City list and locations: U.S. Census Bureau, Vintage 2024 Population Estimates for incorporated places (SUB-EST2024) and U.S. Census Bureau, 2024 Gazetteer Files - Places (census.gov).
• Every figure in this guide is computed by SunYieldMap from those model runs. Settings and limits are in the methodology.