Peak Sun Hours by State: The Complete US Reference Guide
Alright, here’s something that surprises most people when they first look at solar numbers across the country: the same 10-panel solar system produces wildly different amounts of electricity depending on which state it’s installed in.
A 5kW system in Phoenix, Arizona generates approximately 33 kWh per day. That same 5kW system on a roof in Seattle, Washington generates just 14 kWh per day. Same panels. Same inverter. Same size system. But Arizona homeowner gets more than double the electricity — purely because of where they live.
The number that explains this entire difference is peak sun hours (PSH) — the single most location-specific variable in any solar sizing calculation. This guide gives you the complete state-by-state reference for all 50 US states, a clear ranking of solar potential, and a practical guide to using your state’s PSH number in a real system sizing calculation.
If you’ve been following this solar series, you already know how peak sun hours work. If you’re coming to this fresh — no worries, we cover the essentials right here.
What Are Peak Sun Hours?
One peak sun hour = one hour of sunlight at exactly 1,000 W/m² — the intensity threshold at which solar panels produce their rated output.
They are not daylight hours. A location might have 10 hours of daylight but only 4.5 peak sun hours — because early morning and late afternoon sunlight is weaker than the intense midday sun. Only the hours that are equivalent in energy to 1,000 W/m² count toward peak sun hours.
The practical use: a 400W panel at 5.0 PSH produces 400 × 5.0 = 2,000 Wh (2 kWh) per day. That’s your per-panel daily output — multiply by your panel count to get total daily system generation.
The values in this guide represent annual daily averages — the number that best represents year-round system performance for sizing purposes.
How to Read This Data
A few important notes before diving into the tables:
Annual average is what you use for sizing. Your system needs to perform year-round, not just in summer. The annual average captures the full seasonal reality — hot sunny summers and shorter, cloudier winters — in a single representative number.
There’s a range, not one exact figure. Every state has geographic variation — coastal vs. inland, north vs. south, elevation differences. The ranges provided reflect this internal variation. Use the lower end if you’re in a cooler, cloudier, or coastal part of your state. Use the higher end if you’re in a dry, inland, or high-elevation area.
For precise location data, use PVWatts (pvwatts.nrel.gov) or Global Solar Atlas (globalsolaratlas.info) with your exact address for the most accurate figure.
All 50 States — Complete PSH Reference Table
The Southwest — America’s Solar Powerhouse
| State | Annual Avg PSH/Day | Best City | Notes |
|---|---|---|---|
| Arizona | 6.5 – 7.5 | Phoenix 7.0–7.5 | #1 solar state; desert climate, clear skies |
| New Mexico | 6.5 – 7.0 | Albuquerque 6.5–7.0 | High elevation boosts irradiance |
| Nevada | 6.0 – 7.0 | Las Vegas 6.5–7.0 | Dry desert air, exceptional irradiance |
| Utah | 5.5 – 6.5 | Salt Lake City 5.5–6.0 | High plateau; excellent solar resource |
| Colorado | 5.0 – 6.0 | Denver 5.5–6.0 | High altitude compensates for cold winters |
The Southeast — Surprisingly Strong Solar
| State | Annual Avg PSH/Day | Best City | Notes |
|---|---|---|---|
| Florida | 5.0 – 5.7 | Miami 5.3–5.7 | Consistent year-round; humidity causes some diffuse loss |
| Texas | 4.5 – 6.5 | West Texas 6.0–6.5; Houston 4.5–5.0 | Massive variation; western TX is exceptional |
| Oklahoma | 5.0 – 5.5 | Oklahoma City 5.0–5.5 | Strong Southern Plains solar resource |
| Kansas | 5.2 – 6.0 | Wichita 5.5–6.0 | Underrated solar state; wide-open skies |
| Georgia | 4.5 – 5.2 | Atlanta 4.5–5.0 | Good solar resource; growing market |
| South Carolina | 4.5 – 5.0 | Charleston 4.5–5.0 | Coastal humidity slightly reduces PSH |
| North Carolina | 4.5 – 5.0 | Raleigh 4.5–5.0 | Solid solar resource; strong state market |
| Tennessee | 4.2 – 4.7 | Nashville 4.3–4.6 | Moderate; good enough for strong ROI |
| Alabama | 4.2 – 4.7 | Birmingham 4.2–4.5 | Underutilized solar potential |
| Mississippi | 4.2 – 4.7 | Jackson 4.3–4.6 | Similar to Alabama |
| Louisiana | 4.5 – 5.0 | New Orleans 4.7–5.0 | Good despite humidity |
| Arkansas | 4.5 – 5.0 | Little Rock 4.5–4.8 | Decent Southern solar resource |
| Virginia | 3.8 – 4.5 | Richmond 4.0–4.5 | Moderate; varies north to south significantly |
| West Virginia | 3.5 – 4.0 | Charleston 3.5–4.0 | Terrain and cloud cover limit PSH |
The West Coast — High Variation by Location
| State | Annual Avg PSH/Day | Notes |
|---|---|---|
| California | 4.8 – 7.5 | Coastal 4.8–5.5; Inland 5.8–6.5; Desert 6.5–7.5 |
| Hawaii | 5.5 – 7.0 | Varies dramatically by island and elevation |
| Oregon | 3.5 – 5.0 | Eastern Oregon 4.5–5.0; Coastal/Portland 3.5–4.0 |
| Washington | 3.0 – 4.5 | Eastern WA 4.0–4.5; Seattle/Western WA 3.0–3.5 |
The Great Plains & Mountain States
| State | Annual Avg PSH/Day | Notes |
|---|---|---|
| Wyoming | 5.5 – 6.5 | High elevation, dry air — exceptional and underrated |
| Montana | 4.5 – 5.2 | Eastern plains better than west; high elevation helps |
| Idaho | 4.5 – 5.5 | Southern Idaho desert areas excellent |
| South Dakota | 4.7 – 5.5 | Strong plains solar resource |
| North Dakota | 4.5 – 5.0 | Better than most expect for northern state |
| Nebraska | 4.5 – 5.2 | Good Central Plains irradiance |
| Iowa | 4.2 – 4.8 | Moderate; worthwhile with federal ITC |
| Minnesota | 4.2 – 4.8 | Better than reputation; cold keeps panels efficient |
| Missouri | 4.3 – 5.0 | Reasonable Midwest solar resource |
The Midwest & Great Lakes
| State | Annual Avg PSH/Day | Notes |
|---|---|---|
| Illinois | 4.0 – 4.5 | Chicago 4.0–4.2; southern IL slightly higher |
| Indiana | 3.8 – 4.3 | Moderate cloud cover; viable with strong incentives |
| Ohio | 3.5 – 4.2 | Frequent overcast; workable with good system design |
| Michigan | 3.5 – 4.0 | Great Lakes cloud effect; lower PSH |
| Wisconsin | 3.8 – 4.3 | Similar to Michigan; cold keeps panel efficiency up |
| Kentucky | 4.0 – 4.5 | Moderate; viable market |
The Northeast
| State | Annual Avg PSH/Day | Notes |
|---|---|---|
| New York | 4.0 – 4.5 | NYC 4.1–4.3; Upstate 3.8–4.2 |
| Pennsylvania | 3.8 – 4.2 | Philadelphia better than Pittsburgh |
| New Jersey | 3.8 – 4.2 | Dense market; high electricity rates compensate |
| Connecticut | 3.8 – 4.2 | Similar to NJ; strong incentives |
| Massachusetts | 3.5 – 4.0 | Boston 3.7–4.0; one of the best state incentive programs |
| Rhode Island | 3.8 – 4.2 | Small but strong solar market |
| Vermont | 3.5 – 4.0 | Cold keeps panels efficient; good net metering |
| New Hampshire | 4.2 – 4.8 | Better than most New England states |
| Maine | 4.0 – 4.5 | Better than reputation; cold and clear days common |
| Maryland | 4.0 – 4.5 | Good Mid-Atlantic resource |
| Delaware | 4.0 – 4.5 | Strong incentives compensate for moderate PSH |
| District of Columbia | 4.0 – 4.4 | Viable urban solar market |
Special Cases
| State | Annual Avg PSH/Day | Notes |
|---|---|---|
| Alaska | 2.0 – 3.5 | Extreme seasonal variation; summer 3.5–5.0, winter 1.0–1.5 |
| Hawaii | 5.5 – 7.0 | Among the best in the nation; very high electricity rates |
States Ranked by Solar Potential
Here’s the complete state ranking from highest to lowest annual average peak sun hours — giving you the clearest picture of where solar energy is most productive across the country.
| Rank | State | Annual Avg PSH/Day |
|---|---|---|
| 🥇 1 | New Mexico | 6.5 – 7.0 |
| 🥈 2 | Arizona | 6.5 – 7.5 |
| 🥉 3 | Nevada | 6.0 – 7.0 |
| 4 | Wyoming | 5.5 – 6.5 |
| 5 | Hawaii | 5.5 – 7.0 |
| 6 | Kansas | 5.2 – 6.0 |
| 7 | Florida | 5.0 – 5.7 |
| 8 | Oklahoma | 5.0 – 5.5 |
| 9 | California | 4.8 – 7.5 (widest range) |
| 10 | Utah | 5.5 – 6.5 |
| 11 | South Dakota | 4.7 – 5.5 |
| 12 | Colorado | 5.0 – 6.0 |
| 13 | Texas | 4.5 – 6.5 |
| 14 | Idaho | 4.5 – 5.5 |
| 15 | Montana | 4.5 – 5.2 |
| 16 | Nebraska | 4.5 – 5.2 |
| 17 | North Dakota | 4.5 – 5.0 |
| 18 | Georgia | 4.5 – 5.2 |
| 19 | Louisiana | 4.5 – 5.0 |
| 20 | South Carolina | 4.5 – 5.0 |
| 21 | North Carolina | 4.5 – 5.0 |
| 22 | Arkansas | 4.5 – 5.0 |
| 23 | New Hampshire | 4.2 – 4.8 |
| 24 | Iowa | 4.2 – 4.8 |
| 25 | Minnesota | 4.2 – 4.8 |
| 26 | Tennessee | 4.2 – 4.7 |
| 27 | Alabama | 4.2 – 4.7 |
| 28 | Mississippi | 4.2 – 4.7 |
| 29 | Missouri | 4.3 – 5.0 |
| 30 | Maine | 4.0 – 4.5 |
| 31 | Maryland | 4.0 – 4.5 |
| 32 | Kentucky | 4.0 – 4.5 |
| 33 | Illinois | 4.0 – 4.5 |
| 34 | New York | 4.0 – 4.5 |
| 35 | Wisconsin | 3.8 – 4.3 |
| 36 | Virginia | 3.8 – 4.5 |
| 37 | Pennsylvania | 3.8 – 4.2 |
| 38 | New Jersey | 3.8 – 4.2 |
| 39 | Connecticut | 3.8 – 4.2 |
| 40 | Indiana | 3.8 – 4.3 |
| 41 | Delaware | 4.0 – 4.5 |
| 42 | Rhode Island | 3.8 – 4.2 |
| 43 | Vermont | 3.5 – 4.0 |
| 44 | Massachusetts | 3.5 – 4.0 |
| 45 | Ohio | 3.5 – 4.2 |
| 46 | Michigan | 3.5 – 4.0 |
| 47 | Oregon | 3.5 – 5.0 |
| 48 | Washington | 3.0 – 4.5 |
| 49 | West Virginia | 3.5 – 4.0 |
| 50 | Alaska | 2.0 – 3.5 |
The Four Solar Zones of the USA
Rather than thinking state by state, it helps to visualize the US in four broad solar zones — each with its own characteristics, sizing implications, and financial dynamics.
Zone 1 — The Sun Belt (PSH 5.5 – 7.5+)
States: Arizona, New Mexico, Nevada, Southern California, Utah, West Texas, Southern Colorado, Hawaii, Florida (parts)
This is America’s solar gold mine. Dry air, clear skies, high elevation in many areas, and intense sunshine create the most productive solar environment on the planet outside of the Sahara and Middle East. A well-designed system here pays back in 5–7 years and generates maximum lifetime savings.
The catch: Extreme summer heat in Arizona, Nevada, and the Inland West reduces panel efficiency during the hours of peak irradiance. High temperatures push panels to 60–75°C, causing temperature coefficient losses of 10–15% during summer afternoons. A 25% buffer (×1.25) in the sizing formula is recommended for the hottest inland locations to account for this.
Zone 2 — The South & Southern Plains (PSH 4.5 – 5.5)
States: Georgia, South Carolina, North Carolina, Tennessee, Alabama, Mississippi, Louisiana, Arkansas, Oklahoma, Kansas, most of Texas, Florida, Virginia
Strong solar resource with good year-round consistency. Humidity in the Gulf States causes some diffuse light losses but still produces excellent economics given the high electricity consumption for air conditioning in summer months. Systems here typically pay back in 7–10 years.
Zone 3 — The Midwest & Northeast (PSH 3.8 – 4.5)
States: Illinois, Indiana, Ohio, Michigan, Wisconsin, Minnesota, Iowa, Missouri, New York, Pennsylvania, New Jersey, Maryland, Connecticut, Massachusetts, and most other Northeast states
Moderate solar resource — good enough for financially viable solar in most cases, particularly given high electricity rates in the Northeast that increase per-kWh savings. The cold climate actually helps panel efficiency — panels perform closer to their rated output in cold clear air than in hot summer heat. Many Midwest and Northeast states also offer strong incentive programs that improve economics despite lower irradiance. Systems here typically pay back in 9–13 years.
Zone 4 — The Pacific Northwest & Alaska (PSH 2.0 – 4.0)
States: Washington, Oregon (west), Alaska
The most challenging zone for solar economics. High rainfall, persistent cloud cover, and in Alaska’s case — extreme seasonal variation in daylight — reduce both PSH and system output significantly. Western Washington and Oregon average just 3.0–4.0 PSH annually. That said, electricity rates in Washington are very low (hydro power), which reduces the financial incentive anyway. Eastern Oregon and Washington are dramatically better — clearing 4.0–5.0 PSH in the drier inland regions.
Summer vs. Winter PSH — Why the Gap Matters
Every state experiences seasonal variation — and for some states, this variation is dramatic enough to significantly affect system design.
| State | Annual Avg | Summer PSH | Winter PSH | Seasonal Gap |
|---|---|---|---|---|
| Arizona | 6.57 | 7.42 | 6.01 | Small — excellent winter performance |
| Florida | 5.67 | 6.16 | 5.26 | Small — consistent year-round |
| Kansas | 5.79 | 6.14 | 5.28 | Small — surprisingly consistent |
| California | 5.38 | 6.19 | 3.42 | Large — coastal fog reduces winter |
| Colorado | 4.87 | 5.72 | 4.44 | Moderate — cold but clear winters |
| Kentucky | 4.94 | 5.97 | 3.60 | Large — cloudy winter months |
| Louisiana | 4.92 | 5.71 | 3.63 | Large — winter cloud cover |
| Montana | 4.93 | 5.70 | 3.66 | Large — shorter winter days |
| Nebraska | 4.79 | 5.40 | 4.38 | Moderate |
| Alaska | 2.99 | 3.87 | 1.78 | Extreme — 2:1 summer-to-winter ratio |
What this means for sizing:
- Grid-connected systems: Use annual average — the grid covers seasonal shortfalls automatically
- Battery backup systems: Check that battery is large enough for the worst winter month
- Off-grid systems: Size based on the lowest winter PSH — not annual average — to ensure self-sufficiency year-round
States like Florida, Arizona, and Kansas with small seasonal gaps are ideal for off-grid solar because winter performance is nearly as strong as summer. States with large seasonal gaps like Kentucky, Louisiana, and coastal California require much more conservative sizing for off-grid applications.
How to Use Your State’s PSH to Size a Solar System
Now that you have your state’s PSH figure, here’s the complete sizing formula — the same one we’ve used throughout this series:
Required System Size (kW) = (Daily Energy Usage ÷ Peak Sun Hours) × 1.2
Quick sizing examples by state:
A home consuming 900 kWh/month (30 kWh/day) — here’s what system size it needs in different states:
| State | PSH | Formula | System Size | 400W Panels Needed |
|---|---|---|---|---|
| Arizona | 7.0 | (30 ÷ 7.0) × 1.2 | 5.1 kW | 13 panels |
| Nevada | 6.5 | (30 ÷ 6.5) × 1.2 | 5.5 kW | 14 panels |
| Florida | 5.5 | (30 ÷ 5.5) × 1.2 | 6.5 kW | 17 panels |
| California (inland) | 6.0 | (30 ÷ 6.0) × 1.2 | 6.0 kW | 15 panels |
| California (coastal) | 5.0 | (30 ÷ 5.0) × 1.2 | 7.2 kW | 18 panels |
| Texas (west) | 6.0 | (30 ÷ 6.0) × 1.2 | 6.0 kW | 15 panels |
| Texas (east) | 4.7 | (30 ÷ 4.7) × 1.2 | 7.7 kW | 20 panels |
| Georgia | 4.8 | (30 ÷ 4.8) × 1.2 | 7.5 kW | 19 panels |
| New York | 4.2 | (30 ÷ 4.2) × 1.2 | 8.6 kW | 22 panels |
| Massachusetts | 3.8 | (30 ÷ 3.8) × 1.2 | 9.5 kW | 24 panels |
| Washington (Seattle) | 3.2 | (30 ÷ 3.2) × 1.2 | 11.3 kW | 29 panels |
The same 900 kWh/month home needs 13 panels in Arizona but 29 panels in Seattle — that’s a 2.2× difference in system size purely from peak sun hours.
Best and Worst States for Solar ROI
Here’s the thing — high PSH doesn’t automatically mean best ROI. Financial return depends on the combination of solar production (PSH) and electricity savings (local utility rates). A state with moderate PSH but very high electricity rates can deliver better ROI than a sunnier state with cheap electricity.
Best ROI States
Arizona — Highest PSH in the country (6.5–7.5) combined with APS/SRP rates that have risen significantly. Payback periods of 5–7 years are common. One of the best solar investments nationally.
California — Sky-high electricity rates ($0.28–$0.35/kWh average) combined with strong PSH (especially inland) create exceptional ROI despite NEM 3.0 changes. A solar + battery system here is one of the strongest financial investments a homeowner can make.
Hawaii — The highest electricity rates in the nation ($0.35–$0.45/kWh) combined with excellent PSH (5.5–7.0) create the fastest payback periods in the country — often 4–6 years. Hawaii homeowners save more per kWh than anywhere else in the US.
Massachusetts — Lower PSH (3.5–4.0) but compensated by high electricity rates ($0.25–$0.30/kWh), the nation’s strongest state solar incentive program (SMART program), and generous net metering. Excellent ROI despite being a northeastern state.
New Jersey — High electricity rates, strong state incentives (SREC market), and PSH of 3.8–4.2 combine for solid economics. One of the top solar markets in the northeast.
Nevada — Exceptional PSH (6.0–7.0) combined with NV Energy rates that have risen steadily. Strong market with good installer competition keeping installation costs reasonable.
States Where ROI Is Challenging
Washington (Western) — Low PSH (3.0–3.5) combined with very cheap electricity from hydropower (rates as low as $0.08–$0.10/kWh) creates a very long payback period. The solar savings per kWh are minimal when grid electricity is already cheap.
Louisiana — Moderate PSH (4.5–5.0) but historically low electricity rates and less aggressive state incentive programs make economics tighter than many comparable states.
West Virginia — Low PSH (3.5–4.0) and some of the lowest electricity rates in the country create challenging economics without significant federal incentives.
Alaska — Extreme seasonal variation, very low winter PSH (1.0–1.5), and the high installation costs associated with remote locations make solar economically marginal except in specific off-grid situations where it competes with diesel generation.
Frequently Asked Questions
Which US state has the most peak sun hours?
Arizona and New Mexico consistently top the rankings, with Arizona reaching 6.5–7.5 PSH annually in cities like Phoenix and Tucson, and New Mexico averaging 6.5–7.0 PSH. The desert Southwest’s combination of low humidity, minimal cloud cover, and high elevation makes it the most solar-productive region in the continental United States.
Which US state has the least peak sun hours?
Alaska has the lowest annual average PSH at 2.0–3.5 hours per day, with dramatic seasonal variation — summer can reach 4–5 hours while winter drops to 1.0–1.5 hours in many regions. Among the contiguous 48 states, Washington (western) and Oregon (coastal) have the lowest PSH at 3.0–3.5 hours due to persistent cloud cover and rain from the Pacific.
Does high peak sun hours always mean better solar investment?
Not necessarily. ROI depends on the combination of PSH and local electricity rates. Hawaii has excellent PSH (5.5–7.0) and the nation’s highest electricity rates — delivering the best solar ROI nationally. Massachusetts has moderate PSH (3.5–4.0) but high rates and strong incentives — delivering better ROI than many sunnier but low-rate states. Always consider both factors together.
How does altitude affect peak sun hours?
Higher altitude locations generally receive more PSH because the atmosphere is thinner — absorbing and scattering less sunlight. This is why Colorado (5.0–6.0 PSH), Wyoming (5.5–6.5 PSH), and New Mexico (6.5–7.0 PSH) have surprisingly strong solar resources despite their northern latitudes. Denver’s altitude of 5,280 feet boosts its solar resource meaningfully compared to a lower-elevation city at the same latitude.
Is solar worth it in low-PSH states like Michigan or Ohio?
Yes — with the right expectations and incentives. Ohio’s PSH of 3.5–4.2 is workable, particularly when factoring in the federal 30% Investment Tax Credit, rising utility rates, and net metering policies that credit solar generation. The payback period is longer (10–14 years) than in Arizona, but with a 25-year panel lifespan, the net lifetime savings are still substantial. Cold climates also keep panels running at higher efficiency than hot desert states — partially compensating for fewer sun hours.
Why does California show such a wide PSH range?
California is geographically enormous with dramatically different climates within the same state. Coastal San Francisco experiences marine layer fog that reduces effective PSH to 4.8–5.2 annually. Inland Sacramento and Fresno reach 5.8–6.5 PSH. Palm Springs and the Imperial Valley hit 6.5–7.5+ PSH in the desert. No single number represents “California” — always use your specific city’s figure from PVWatts or the Global Solar Atlas.
Should I use summer or winter PSH for system sizing?
For grid-connected systems, use the annual average — the grid covers seasonal shortfalls. For off-grid systems, use the lowest month’s PSH (typically December or January for most US states) to ensure self-sufficiency during the hardest period. For battery-backed systems, use annual average for panel sizing but check that battery capacity is adequate for the worst winter week’s consumption
