Peak Sun Hours in Philadelphia, Pennsylvania, United States
- Solar zone
- Zone 3 (good)
- Best month
- June (6.2)
- Worst month
- December (1.8)
- Climate
- Temperate · 12.0°C
Monthly solar breakdown
| Month | GHI | Clear-sky | DNI | DHI | Temp °C | Humid % |
|---|---|---|---|---|---|---|
| Jan | 2.02 | 2.97 | 3.14 | 0.91 | -1.0 | 84 |
| Feb | 2.90 | 4.10 | 3.75 | 1.23 | 0.1 | 83 |
| Mar | 3.83 | 5.54 | 4.08 | 1.59 | 4.5 | 80 |
| Apr | 4.99 | 6.89 | 4.66 | 1.98 | 10.8 | 78 |
| May | 5.57 | 7.70 | 4.56 | 2.34 | 16.5 | 79 |
| Jun | 6.17 | 7.92 | 4.97 | 2.54 | 21.6 | 79 |
| Jul | 6.17 | 7.57 | 5.00 | 2.49 | 24.6 | 75 |
| Aug | 5.40 | 6.79 | 4.59 | 2.22 | 24.0 | 74 |
| Sep | 4.42 | 5.74 | 4.59 | 1.70 | 20.4 | 74 |
| Oct | 3.18 | 4.38 | 4.10 | 1.21 | 13.5 | 78 |
| Nov | 2.33 | 3.17 | 3.67 | 0.92 | 7.1 | 81 |
| Dec | 1.75 | 2.59 | 2.89 | 0.80 | 2.0 | 85 |
GHI, Clear-sky, DNI, DHI in kWh/m²/day. Data: NASA POWER climatology (long-term monthly averages).
Off-grid calculator
Add appliances
- Add an appliance to size a system.
Sizing
- Daily load
- 0.00 kWh
- Panel wattage
- 0 W
- Panel count (400W modules)
- 0
- Battery bank
- 0.0 kWh
Sizing against worst-month PSH of 1.75 kWh/m²/day, 0.77 system efficiency.
About solar in Philadelphia
Philadelphia, United States has a temperate climate with meaningful seasonal variation in solar resource. Its annual peak sun hours average 4.06 kWh/m²/day, a good solar resource by global standards.
The strongest month in Philadelphia is June (summer) at 6.17 kWh/m²/day, and the weakest is December (winter) at 1.75 kWh/m²/day. When sizing a year-round off-grid system, it's standard practice to design against the December value rather than the annual average — otherwise the battery bank runs low during the darkest weeks.
Philadelphia's solar conditions are well within the range where off-grid PV is a straightforward engineering exercise with standard-sized arrays and lithium batteries.
FAQ
- What are the peak sun hours in Philadelphia?
- Philadelphia averages 4.06 peak sun hours per day annually, ranging from 1.75 in December to 6.17 in June.
- How many solar panels do I need in Philadelphia?
- Panel count depends on your daily load. At Philadelphia's annual average of 4.06 kWh/m²/day, a 5 kWh/day load needs roughly 4 × 400 W panels. Use the calculator above for your actual load.
- What size battery do I need in Philadelphia?
- Sizing against Philadelphia's worst month (December, 1.75 kWh/m²/day) with 2 days of autonomy at 80% depth of discharge, a 5 kWh/day load needs about a 12.5 kWh battery bank.
- How does Philadelphia's solar resource compare globally?
- Philadelphia sits in solar zone 3 out of 5 (where 5 is strongest) at 4.06 kWh/m²/day — good by global standards. For reference, top-tier desert sites average ~6.5 and high-latitude cities around 2.5 kWh/m²/day.
- How much does winter reduce solar output in Philadelphia?
- Philadelphia's worst month (December) delivers 1.75 kWh/m²/day — about 28% of the summer peak of 6.17. Off-grid systems here typically oversize 1.5–2× or pair with a backup source.
- Do cloudy days significantly affect Philadelphia's solar?
- Partly. Diffuse light still produces 10–25% of clear-sky output. Philadelphia's 4.06 kWh/m²/day already reflects average cloudiness, so no further derating is needed for sizing.
- What panel tilt works best in Philadelphia?
- At Philadelphia's latitude (40°), a fixed tilt near 40° balances year-round yield. Winter-heavy loads favor latitude + 15°; summer-heavy, latitude − 15°.