☀ US Solar Resource Tool

Peak Sun Hours Calculator:
54 US Cities, Monthly PSH Data, Tilt & Azimuth Adjustment, kWh Output & Annual Savings

Select your US city to get accurate peak sun hours (PSH) data based on NREL solar insolation records. Adjust for panel tilt angle and roof orientation. Calculate daily and annual kWh output and electric bill savings for your solar system size.

☀ Your Solar Location & System

Step 1 — Select Your City
PSH data sourced from NREL National Solar Radiation Database (NSRDB). Values represent annual average peak sun hours — the equivalent hours per day of full 1,000 W/m2 irradiance. Range: 3.2 PSH (Anchorage) to 6.8 PSH (Albuquerque).
Step 2 — Panel Tilt & Orientation
Optimal tilt = your latitude degrees facing true south. A south-facing roof at optimal tilt gives 100% output. East or west facing reduces output by ~22%. North-facing reduces by ~45%. Flat roof = 88% of optimal.
Step 3 — System Size & Electric Rate
panels
$/kWh
US average electric rate: $0.13-0.17/kWh. Hawaii: ~$0.40/kWh. California: ~$0.25/kWh. Texas/Plains: ~$0.12/kWh. Check your electric bill for your exact rate. kWh output x your rate = annual savings.

📈 Your Solar Resource Data

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Select your US city, panel tilt angle, orientation, and system size. Get annual and monthly peak sun hours, daily and annual kWh output, annual savings, and a full month-by-month production chart.

What Are Peak Sun Hours and Why They Are the Most Important Number in Solar System Design

Peak sun hours (PSH) is the single most important input for sizing any solar energy system in the United States. The term is frequently misunderstood: a peak sun hour is not simply a sunny hour. It is a unit of solar irradiance that represents the equivalent number of hours per day during which the sun delivers exactly 1,000 watts per square meter (1 kW/m2) of energy. This is the standard test condition (STC) under which all solar panels are rated.

In practice, solar irradiance varies continuously throughout the day — rising from zero at sunrise, peaking around solar noon, and falling back to zero at sunset. The total energy delivered over a day (measured in watt-hours per square meter, or Wh/m2) is converted to an equivalent number of “peak” hours at 1,000 W/m2. So a day in Phoenix that delivers 6,580 Wh/m2 of total solar energy is expressed as 6.58 peak sun hours — as if the sun had shone at full intensity for exactly 6.58 hours. This allows simple math: a 400W panel in Phoenix at 6.58 PSH would theoretically produce 400W x 6.58h = 2,632 Wh (2.6 kWh) on that day. After applying a real-world derating factor of 80% (accounting for temperature losses, wiring losses, and inverter inefficiency), actual output is about 2.1 kWh per day per panel. This calculator performs exactly that math for 54 US cities across all regions and climate zones.

NREL Solar Data: The Official US Source

The PSH values used in this calculator are derived from the National Renewable Energy Laboratory (NREL) National Solar Radiation Database (NSRDB) — the most comprehensive solar resource dataset for the United States, covering 30+ years of satellite and ground-based measurements. NREL data is the official source used by solar installers, utility companies, and the US Department of Energy for solar energy assessment. For any specific location not in this calculator, the free NREL PVWatts tool at pvwatts.nrel.gov allows you to enter an exact address and receive detailed monthly production estimates.

How the Peak Sun Hours Calculator Works

Select your US city from the 54-location database covering all major regions from Anchorage (3.2 PSH) to Albuquerque (6.77 PSH). The calculator applies tilt and azimuth correction factors: panels tilted at your local latitude facing true south receive 100% of baseline PSH; flat panels receive 88%; east or west-facing panels receive 78%; north-facing receive only 55%. Monthly PSH data shows the seasonal variation for each location, which is critical for understanding winter production (particularly important in the Northeast and Northwest where December/January PSH can drop below 2.0). Daily and annual kWh output is calculated as: systemW / 1000 x PSH x 0.80 derating x days. Annual savings equals annual kWh x your electric rate.

Three Real Peak Sun Hours Examples Across the US

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10-Panel System — Phoenix, Arizona

10x 400W panels | Optimal tilt south | 6.58 PSH annual avg | $0.13/kWh

A Phoenix homeowner installs 10 standard 400W panels at optimal tilt facing south. Phoenix has the second-best solar resource of any major US city at 6.58 annual PSH, with July being the peak month.

ParameterValueNotes
System size4,000W (4 kW)10 x 400W panels
Annual avg PSH (optimal tilt)6.58 PSH/dayTilt at 33.4 degrees, south
Daily kWh output21.1 kWh/day4kW x 6.58 x 0.80 derating
Annual kWh output7,695 kWh/yr21.1 x 365
Best month (July)6.8 PSH — 879 kWhHigh sun, slightly clouded by monsoon
Worst month (December)4.8 PSH — 620 kWhShort winter days, still good output
Annual savings$1,000/yr7,695 kWh x $0.13/kWh
Phoenix is exceptional because even its worst month (December at 4.8 PSH) delivers more solar energy than Seattle’s best month. The summer/winter ratio is only about 1.4 — unlike Seattle where July produces 5x more solar than January. This consistency makes Phoenix solar economics extremely reliable, with no dramatic seasonal production swings to plan around.
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10-Panel System — New York City

10x 400W panels | Low tilt (15 deg) south | 4.31 PSH annual avg | $0.22/kWh

A Brooklyn homeowner with a low-pitch flat roof installs 10 panels at 15-degree tilt on a south-facing roof. New York’s higher electric rate ($0.22/kWh) partially compensates for the lower solar resource versus Phoenix.

ParameterCalculationResult
Base annual PSH (horizontal)4.31 PSH/dayNREL New York data
Tilt adjustment (15 deg)4.31 x 0.954.09 PSH adjusted
Daily kWh output4kW x 4.09 x 0.8013.1 kWh/day
Annual kWh13.1 x 3654,782 kWh/yr
Best month (June)6.0 PSHNearly as good as Phoenix year-round
Worst month (December)2.7 PSHShort winter days, significant drop
Annual savings4,782 x $0.22$1,052/yr
New York’s high electric rate ($0.22/kWh) delivers comparable annual savings to the Phoenix system despite 30% less solar resource. This is the often-overlooked economics of northeast solar: lower PSH is partially offset by higher electricity costs. The NYC system produces 62% of the Phoenix system output but saves about the same dollars annually. The seasonal swing is dramatic — June produces 2.2x more kWh than December — which is why battery storage or net metering matters more in the Northeast than in the Sun Belt.
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Off-Grid System Comparison — Denver vs Seattle

5.21 vs 3.73 PSH | System sizing difference for same daily demand

Two off-grid cabins with the same 5 kWh/day demand. Denver has 5.21 PSH; Seattle has 3.73 PSH. Same demand, different panel requirements.

ParameterDenverSeattle
Annual avg PSH5.21 PSH3.73 PSH
Required daily kWh5 kWh/day5 kWh/day
Required system W5 / (5.21 x 0.80) = 1,199W5 / (3.73 x 0.80) = 1,676W
Panels needed (400W)3 panels (1,200W)5 panels (2,000W)
January PSH (worst month)4.0 PSH1.5 PSH
Winter system output3.8 kWh/day2.4 kWh/day — SHORT 2.6 kWh
Winter panel needSame 3 panels adequate11 panels for winter sizing!
This comparison reveals the critical off-grid system sizing challenge in low-sun climates: Seattle’s January at 1.5 PSH is catastrophically low for off-grid sizing. If you size for annual average (3.73 PSH), you will run out of power every January. Off-grid designers in Seattle must size for worst-month PSH (1.5) — requiring 3x more panels than if sizing for annual average. Denver’s worst month (4.0 PSH) is still reasonably close to its annual average, making off-grid sizing far more practical in the Mountain West.

Expert Tips for Using Peak Sun Hours Data in Solar Design

1

Always Apply the 80% Derating Factor to Theoretical Output

Solar panels are rated at Standard Test Conditions (STC): 1,000 W/m2 irradiance, 25 degrees Celsius cell temperature, and specific air mass. Real-world conditions differ from these lab conditions in several critical ways. Panel temperature in summer can reach 50-70 degrees Celsius, reducing output by 15-25% versus STC. Wiring and connection losses add another 2-3%. Inverter efficiency averages 95-97% but degrades with temperature. Soiling (dust, bird droppings, pollen) can reduce output 1-5%. Module mismatch in a string reduces output to the weakest panel. Adding these up, the standard industry derating factor (also called the “performance ratio” or “system efficiency”) is 75-85%, with 80% being the conservative industry standard used by professional solar designers and the NREL PVWatts tool. This calculator uses 80% throughout. Never calculate solar production from raw PSH x panel wattage without this derating — you will overestimate production by 20-25%.

2

Size Off-Grid Systems for Worst-Month PSH, Not Annual Average

For grid-tied solar systems, annual average PSH is the right sizing metric — excess summer production offsets low winter production through net metering. For off-grid systems, you must size for your worst month’s PSH, not the annual average. In Seattle, annual average PSH is 3.73 but January averages only 1.5 PSH — a 60% reduction. An off-grid system sized for 3.73 PSH will run out of power every January without supplemental generation or very large battery storage. In the Pacific Northwest and New England, many off-grid designers use a hybrid approach: solar sized for autumn through spring, with a propane or diesel generator for the 2-3 worst winter months. This is more cost-effective than sizing the solar array large enough to cover December at 1.5 PSH. In contrast, Denver’s worst month is still 4.0 PSH — much easier to design around. The monthly PSH chart in this calculator makes worst-month design straightforward.

3

Roof Azimuth Matters More Than Tilt in Most US Climates

Homeowners often focus on roof pitch (tilt angle) but are surprised to learn that roof orientation (azimuth) has a larger impact on production. A south-facing roof at 15-degree tilt produces about 95% of optimal output — nearly identical to 45-degree tilt (also 95%). But the same roof turned to face east or west drops to only 78% of optimal. A north-facing roof drops to 55%. The practical implication: if you have a choice between a lower-pitch south roof and a steeper east or west roof, always choose the south roof regardless of tilt. For east-west facing houses, split arrays — half on the east slope, half on the west — can capture morning and afternoon sun separately and actually reduce inverter oversaturation on summer afternoons, potentially improving net annual output versus a pure west-facing array. Modern string inverters and microinverters handle split-orientation arrays well. This calculator provides azimuth correction factors for all four major orientations.

16 Frequently Asked Questions About Peak Sun Hours

What is the difference between peak sun hours and sunlight hours?+
Sunlight hours (also called daylight hours) is simply the number of hours between sunrise and sunset — in Los Angeles, this ranges from about 10 hours in December to 14 hours in June. Peak sun hours is a completely different and more useful metric. It represents the equivalent number of hours per day that the sun delivers exactly 1,000 W/m2 of solar irradiance. In reality, irradiance varies from zero at dawn, rises to a peak around noon, and falls back to zero at dusk. The total energy delivered in a day (watt-hours per square meter) is divided by 1,000 to get peak sun hours. A location might have 13 hours of daylight but only 6 peak sun hours, because the morning and evening sun deliver much less than 1,000 W/m2. Peak sun hours is the correct metric to use for solar panel output calculations because panels are rated at 1,000 W/m2 in standard tests.
Which US city has the most peak sun hours?+
Among major US cities, Albuquerque, New Mexico leads with 6.77 annual peak sun hours per day — more than Phoenix (6.58) or Las Vegas (6.41). Albuquerque’s high altitude (5,312 feet above sea level), low humidity, and location in the Chihuahuan Desert combine to create exceptionally clear skies and intense solar radiation. The broader Southwest region consistently leads the US in solar resource, with Phoenix, Tucson, Las Vegas, and parts of California’s inland valleys all exceeding 6.0 PSH annually. Hawaii falls in the middle at 5.91 PSH (Honolulu) despite its tropical location, because trade wind clouds moderate peak irradiance. Alaska is the lowest, with Anchorage averaging only 3.20 PSH annually and January averaging a mere 0.6 PSH — a 10:1 ratio between summer and winter that makes off-grid solar very challenging there.
How do I calculate how many kWh my solar panels will produce?+
The formula for daily solar panel output is: kWh/day = (system watts / 1000) x peak sun hours x derating factor. For example, a 6,000W (6 kW) system in Dallas at 5.38 PSH with 80% derating: (6000/1000) x 5.38 x 0.80 = 25.8 kWh/day. Annual production: 25.8 x 365 = 9,423 kWh/yr. Annual savings at $0.14/kWh: 9,423 x $0.14 = $1,319/yr. This calculator performs all three steps automatically for your selected city, tilt, orientation, and system size. The 80% derating factor is the industry standard accounting for temperature losses (typically the largest factor at 10-15%), wiring losses (2-3%), inverter inefficiency (3-5%), soiling (1-5%), and module mismatch (1-2%). NREL’s PVWatts tool uses a similar approach and is the authoritative US calculator for professional solar design.
What is the ideal solar panel tilt angle in the US?+
The optimal fixed tilt angle for a solar panel to maximize annual energy production in the US is approximately equal to your local latitude, facing true south (not magnetic south). For Phoenix at latitude 33.4 degrees, the optimal tilt is about 33 degrees. For Minneapolis at latitude 44.9 degrees, optimal tilt is about 45 degrees. Tilting steeper (greater angle) increases winter production at the expense of summer production; tilting flatter increases summer production at the expense of winter. For grid-tied systems with net metering, optimal tilt maximizes annual kWh production. For off-grid systems or time-of-use rate optimization, the optimal angle may differ. Most residential roofs are pitched at 20-35 degrees, which is within 5-10 degrees of optimal for most US latitudes and has minimal impact on annual production. This calculator applies NREL-derived correction factors for flat (0 deg), low tilt (15 deg), optimal (latitude deg), steep (45 deg), and vertical (90 deg) configurations.
Why does solar output vary so much by season?+
Solar output varies seasonally for two main reasons: day length and sun angle. In summer, days are longer — up to 15 hours at 45 degrees latitude versus 9 hours in winter. More importantly, the sun is higher in the sky in summer, meaning sunlight travels through less atmosphere and strikes solar panels at a more direct angle (closer to 90 degrees). Both factors dramatically increase summer irradiance versus winter. In Seattle, this creates extreme seasonal variation: July averages 7.0 PSH while January averages only 1.5 PSH — a 4.7:1 ratio. In Miami, the ratio is much smaller (6.3 PSH in May vs 4.7 PSH in December) because Miami’s latitude (25.8N) keeps the sun higher even in winter. This seasonal variation is why net metering (banking excess summer production as credits against winter bills) is so valuable for grid-tied systems in northern US states, and why off-grid designers must carefully plan winter energy budgets.
How accurate is this peak sun hours data?+
The PSH values in this calculator are derived from NREL NSRDB data, which combines satellite measurements with ground-based validation across 30+ years of solar radiation records. They represent typical meteorological year (TMY) values — long-term averages that are the standard reference for solar energy system design in the US. Actual annual production at a specific site can vary from these values by 5-15% due to local microclimate effects (urban heat islands, coastal fog, elevation, terrain shading), year-to-year weather variation, and localized cloud patterns. For precise system design at a specific address, use the NREL PVWatts tool at pvwatts.nrel.gov, which accepts exact addresses and uses higher-resolution spatial data. This calculator provides excellent accuracy for preliminary planning, system comparison, and education about the US solar resource map.
Does my roof pitch affect solar output significantly?+
For most US residential roofs, pitch has a surprisingly small effect on annual solar production. A roof tilted at 15 degrees (common shallow pitch) facing south produces about 95% of optimal output. A roof tilted at 45 degrees (steep pitch) also produces about 95% — nearly identical. Flat roofs produce about 88%. The differences in output are generally not significant enough to justify mounting structures that tilt panels away from the roof pitch, except in special circumstances (very flat roofs in northern states where winter optimization is important, or commercial ground-mount systems where optimal tilt is easily achieved). Where tilt matters most is at the extremes — very flat roofs in the Pacific Northwest or Northeast lose about 12% of output versus optimal, which is meaningful over a 25-year system life but typically not worth the added cost and complexity of tilt frames on a residential roof.
What is a good peak sun hours value for solar to make sense?+
Solar installations are financially viable across a wide range of PSH values in the US today, because panel prices have fallen 90% since 2010. Generally: above 5.0 PSH (Southwest, South, much of California) solar economics are excellent — 6-12 year paybacks at average US electric rates. 4.0-5.0 PSH (Mid-Atlantic, Southeast, Mountain West, Midwest) — good economics, typically 8-14 year payback. 3.5-4.0 PSH (Pacific Northwest, Northern New England) — workable economics, especially where electric rates are high (Pacific Northwest is the exception with very low hydro power rates that weaken solar economics despite decent PSH). Below 3.5 PSH (Alaska) — grid-tied solar is marginal; off-grid applications need careful engineering. The key variable is not PSH alone but PSH x local electric rate. Seattle at 3.73 PSH with $0.10/kWh (cheap hydro) has poor economics. Boston at 4.22 PSH with $0.22/kWh has excellent economics despite lower PSH than Seattle because the higher electric rate more than compensates.
How do I find my exact peak sun hours by zip code?+
The most accurate free tool for zip code-level PSH data is the NREL PVWatts Calculator at pvwatts.nrel.gov. Enter your exact address and it returns month-by-month solar resource data and production estimates for your specific location at 4km spatial resolution. The NREL National Solar Radiation Database (NSRDB) viewer at nsrdb.nrel.gov provides even more granular data and allows you to download historical solar radiation time-series data for any US location. For a simple annual average PSH for any US location, the Solar Energy Industries Association (SEIA) US Solar Map and the EnergySage Solar Calculator (energysage.com/solar-calculator) provide good visual references. This calculator covers 54 major US cities representing all regions; for intermediate locations, use the nearest city with similar latitude and climate characteristics as an approximation.
Do solar panels produce power on cloudy days?+
Yes, but at significantly reduced output. On a fully overcast day, solar panels typically produce 10-25% of their clear-sky rated output. On a partly cloudy day, output varies continuously as clouds pass over, averaging perhaps 30-70% of clear-sky output. Interestingly, scattered cloud cover can occasionally produce brief “edge-of-cloud” effects where diffuse light focuses above 1,000 W/m2, causing brief output spikes above rated panel wattage — a phenomenon that inverter manufacturers design for. The PSH values in this calculator already account for average cloud cover in each city’s historical record. Seattle’s 3.73 annual PSH already reflects the city’s famously overcast winters. A given Seattle day might have 9 hours of daylight but only 0.5-1.0 PSH on a heavy overcast winter day, and 5.0+ PSH on a clear summer day. The month-by-month breakdown in this calculator gives you the realistic seasonal pattern rather than hiding it in an annual average.
What is NREL and why is their data authoritative?+
The National Renewable Energy Laboratory (NREL) is the US Department of Energy’s primary national laboratory for renewable energy and energy efficiency research. Located in Golden, Colorado, NREL has been collecting, validating, and modeling solar radiation data since 1977. Their National Solar Radiation Database (NSRDB) combines data from NOAA weather satellites with surface-based measurement stations to produce hourly solar irradiance estimates at 4km resolution across the continental US, Alaska, and Hawaii — going back to 1998. This multi-decade record allows computation of typical meteorological year (TMY) values that are statistically representative of long-term average solar conditions. NREL’s PVWatts calculator is the standard tool used by the US solar industry, government agencies, utilities, and researchers for solar energy production estimation. The NSRDB data underlying this calculator is freely available to the public at nsrdb.nrel.gov.
How does peak sun hours relate to solar panel kWh output?+
The direct relationship: daily kWh = (system watts / 1000) x PSH x derating factor. For a single 400W panel in Dallas (5.38 PSH): (400/1000) x 5.38 x 0.80 = 1.72 kWh/day. Annual: 1.72 x 365 = 628 kWh/yr. Same panel in Seattle (3.73 PSH): (400/1000) x 3.73 x 0.80 = 1.19 kWh/day, 435 kWh/yr — 31% less than Dallas. The relationship is linear: double the PSH, double the kWh output. Double the panel wattage, double the kWh output. This linearity makes PSH an ideal planning tool. If you know your monthly electric consumption from your utility bill (in kWh), you can divide by 30 to get daily kWh needed, then back-calculate system size: system watts = (daily kWh x 1000) / (PSH x 0.80). This calculator does this math in reverse — starting from system size to get kWh output. To find the system size needed to offset a specific electricity consumption, divide daily consumption by (PSH x 0.80 / 1000).
Will solar panel output degrade over time?+
Yes, solar panels degrade slightly each year due to UV exposure, thermal cycling, and encapsulant discoloration. The industry standard degradation rate for quality crystalline silicon panels is 0.5% per year — meaning a panel rated at 400W today will produce about 392W after 5 years and 380W after 10 years. Most major manufacturers (LG, SunPower, Panasonic, Q Cells, Canadian Solar) warrant output at 80-90% of rated watts after 25 years, implying total degradation of 10-20% over the system lifetime. For financial projections, NREL recommends using a 0.5% annual degradation rate for crystalline silicon (the industry average across field studies). Some premium panels from LG and SunPower achieve 0.2-0.3% annual degradation. This calculator uses current panel wattage without degradation factoring, which is appropriate for first-year production estimates. For 25-year financial models, the standard approach is to reduce annual kWh output by 0.5% per year.
What is the difference between PSH and GHI?+
Global Horizontal Irradiance (GHI) is the total solar radiation measured on a horizontal flat surface, expressed in watt-hours per square meter (Wh/m2) or kilowatt-hours per square meter (kWh/m2). GHI includes direct normal irradiance (DNI — the direct beam from the sun) plus diffuse horizontal irradiance (DHI — light scattered by the atmosphere and clouds). GHI is the primary measurement in solar radiation databases like NSRDB. Peak sun hours are derived directly from GHI: PSH = GHI (Wh/m2) / 1000 (W/m2). So if Dallas has a daily GHI of 5,380 Wh/m2 on a typical day, that is 5.38 PSH. For tilted panels facing south, a correction from horizontal GHI to tilted plane irradiance (POA — Plane of Array) applies — which is what this calculator’s tilt adjustment factor approximates. The difference between GHI and POA irradiance is the reason why south-facing tilted panels typically produce more energy than flat horizontal surfaces, particularly in winter when the sun is low in the sky.
How do solar panel costs compare to kWh production by location?+
The cost per installed watt for residential solar in the US is approximately $2.50-3.50/W across most markets, with an average of about $3.00/W before the 30% IRS 25D federal tax credit — making net cost about $2.10/W. A 4kW system costs roughly $8,400 before incentives, $5,880 after the federal credit. In Phoenix (6.58 PSH), that 4kW system produces about 7,700 kWh/yr. The cost per kWh over a 25-year system life at zero degradation: $5,880 / (7,700 x 25) = $0.031/kWh — far below the US average retail electricity rate of $0.14/kWh. In Seattle (3.73 PSH), the same system produces 5,500 kWh/yr, giving a lifetime cost of $0.043/kWh — still well below even Seattle’s relatively low retail electric rates of $0.10/kWh. This exercise illustrates why solar is economically attractive across virtually all US locations despite the wide PSH variation — the cost of the equipment (kW installed) is location-independent, while the value of the output depends on both local PSH and local electric rates.
Where can I find official US solar resource data?+
The authoritative US solar resource data sources are: NREL PVWatts Calculator for address-specific production estimates; NREL NSRDB for raw solar radiation data by location; DOE Solar Maps for visual US solar resource maps; and the Solar Energy Industries Association (SEIA) for market data and installation statistics. For state-level incentives that affect the economics of solar at different PSH locations, the DSIRE database lists current state, utility, and federal incentive programs. The PSH values in this calculator are derived from NREL NSRDB TMY (Typical Meteorological Year) data and are suitable for residential solar system planning.

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Legal Disclaimer and Editorial Transparency

Peak sun hours data in this calculator is derived from the NREL National Solar Radiation Database (NSRDB) Typical Meteorological Year (TMY) records. Values represent long-term annual and monthly averages and will vary from any specific year’s actual weather. Tilt and azimuth correction factors are approximate multipliers based on NREL modeling data; exact values depend on specific panel type, local sky conditions, and array geometry.

Energy output calculations use an 80% real-world derating factor (performance ratio), which is the industry standard per NREL PVWatts. Actual system performance depends on inverter efficiency, wiring losses, soiling, shading, and panel temperature. For site-specific production modeling, use the free NREL PVWatts tool at pvwatts.nrel.gov.

Editorial policy: USCalculators.com is an independent educational resource. PSH data is sourced from publicly available NREL/NSRDB records. No commercial relationship exists with NREL, solar panel manufacturers, or installers.