Peak sun hours in Pennsylvania
Pennsylvania averages 3.9 peak sun hours a day across the year, 45th of the 50 states. At that figure a 400-watt panel produces about 1.20 kWh a day after real-world losses, and covering the 900 kWh average US bill takes about 25 panels. Philadelphia, the state's biggest city, runs slightly ahead of the statewide figure at 4 hours; treat 3.9 as the midpoint of a real spread rather than a local reading.
modest sun: 3.9 of a possible ~6.5 hours
Panel counts for Pennsylvania bills
Computed at Pennsylvania's 3.9 hours with 400W panels and the 0.77 derate; the US-average column shows what the same bill takes at 4.5 hours, so you can see what your state's sun is worth in hardware.
| Monthly usage | Pennsylvania | System size | US average |
|---|---|---|---|
| 500 kWh/mo | 14 panels | 5.6 kW | 12 panels |
| 750 kWh/mo | 21 panels | 8.4 kW | 18 panels |
| 900 kWh/mo | 25 panels | 10 kW | 22 panels |
| 1,000 kWh/mo | 28 panels | 11.2 kW | 24 panels |
| 1,500 kWh/mo | 42 panels | 16.8 kW | 36 panels |
| 2,000 kWh/mo | 55 panels | 22 kW | 48 panels |
What 3.9 hours means in practice
Pennsylvania runs 13% below the national solar average, 45th of 50 at 3.9 hours. That is workable sun, not bad sun: the 900 kWh bill takes 25 panels here versus 22 nationally, 3 more. Germany built the world's densest solar fleet on worse.
How a Pennsylvania year is shaped
The 3.9-hour figure is an annual average, and no month is average. These are the twelve monthly means for Pennsylvania from NASA's 2001-2020 solar climatology, each as a share of the state's own annual mean, with that share applied to the 3.9-hour planning figure. July and December are marked.
| Month | Share of the annual average | Peak sun hours (est.) |
|---|---|---|
| January | 44% | 1.7 |
| February | 66% | 2.6 |
| March | 93% | 3.6 |
| April | 124% | 4.8 |
| May | 142% | 5.5 |
| June | 157% | 6.1 |
| July | 158% | 6.2 |
| August | 139% | 5.4 |
| September | 112% | 4.4 |
| October | 75% | 2.9 |
| November | 52% | 2.0 |
| December | 36% | 1.4 |
Best to worst in Pennsylvania is 4.4 to one: July at 158% of the annual average, December at 36%, 6.2 hours a day against 1.4. Four months hold 50% of the year's light. A grid-tied array absorbs that on net metering; a battery bank has to be sized for the December end of it.
Half the Pennsylvania calendar sits above the annual average and half below: April through September are the six months that beat it, carrying 69% of the year's light. April is already worth about 4.8 hours a day, so the productive half of the year starts earlier than most people expect.
Pennsylvania's average home used 817 kWh a month in 2024 by EIA's count, within a few percent of the national 863, so the national panel counts on this page transfer here better than they do in most states. That average bill needs 23 panels across the year and 63 to be carried by December sun alone, a factor of 2.7.
Pennsylvania is more uniform than most. The 12 grid cells sampled across the state span 7%, sunniest in the southeast and dimmest in the north, which scales to about 4.0 hours against 3.8. Enough to notice on a production estimate, not enough to change which system you buy. Philadelphia sits inside that band, not at the edge of it.
What that sun is worth on a Pennsylvania bill
| EIA, 2024 residential averages | Pennsylvania | United States |
|---|---|---|
| Average home's monthly use | 817 kWh | 863 kWh |
| Price per kilowatt-hour | 17.77¢ | 16.48¢ |
| Average monthly bill | $145.17 | $142.26 |
| One 400W panel, a year's output | 438 kWh | 506 kWh |
| What that output displaces | $78 | $83 |
At 17.77¢ a kilowatt-hour Pennsylvania sits 8% above the national 16.48¢, 14th of the fifty states on price. One 400-watt panel offsets roughly $78 of Pennsylvania power a year. Mid-table on rates means the project lives or dies on the quote and the net-metering terms rather than on either the sun or the tariff.
Which is why the sun ranking undersells Pennsylvania. It places 45th of fifty for sunlight and 23rd for what a panel actually earns, a jump of 22 places, and the second number is the one that shows up on a bill. Compare it with a state that gets similar sun: Rhode Island gets more sun (4.1 hours to Pennsylvania's 3.9) and pays 28.65¢ against 17.77¢, so one panel is worth about $54 less a year in Pennsylvania than in Rhode Island.
Two warnings on those dollar figures. They are displaced electricity and nothing else: no install cost, no incentive, no financing, and no assumption about how your utility settles a surplus, which is the single biggest unknown in the sum. And a state average hides the utility you are actually on; 17.77¢ is every Pennsylvania residential customer averaged together, and neighbouring territories can differ by more than the gap between two states in the ranking.
Getting a number for your address
For a location-exact figure, run your address through NREL's free PVWatts; it uses measured weather for your grid cell and will also model roof tilt and direction, which statewide numbers cannot. Then compare its annual kWh against a quote's promise before you sign anything.
Questions people ask
How many solar panels do I need in Pennsylvania?
About 25 400-watt panels (10 kW) for the 900 kWh a month an average US home uses, at Pennsylvania's 3.9 peak sun hours. For the average Pennsylvania home specifically, which EIA measured at 817 kWh a month in 2024, it is 23. Your own bill is the variable that matters, and the calculator takes any figure.
Is 3.9 peak sun hours good for solar?
It is below the 4.5-hour national average but far from disqualifying. Panel counts run about 15% higher here for the same bill, and the December trough measured above deserves respect in any off-grid plan. Grid-tied systems ride through it on net metering.
How much is one solar panel worth a year in Pennsylvania?
About $78. One 400-watt panel at Pennsylvania's 3.9 peak sun hours makes roughly 438 kWh a year after the 0.77 derate, and Pennsylvania residential electricity averaged 17.77¢ a kilowatt-hour in 2024 (EIA), which puts Pennsylvania 23rd of the 50 states on this measure against 45th on sunlight alone. That figure is displaced electricity only. It says nothing about install cost, incentives, or how your utility settles a surplus.
Do peak sun hours change with the seasons in Pennsylvania?
Yes, by a factor of 4.4 here. NASA's 2001-2020 climatology puts Pennsylvania's July at 158% of the annual average and December at 36%, so the 3.9-hour figure on this page is the midpoint of a curve running from roughly 6.2 hours a day down to 1.4. Grid-tied homes bank the summer surplus as credit; off-grid designs have to size for the trough, and in Pennsylvania that means 63 panels for an average local bill instead of 23.