Quick Facts
What Peak Sun Hours is
Peak Sun Hours (PSH) is the equivalent number of hours per day at standard “peak sun” intensity (1,000 W per sq m) that would deliver the same daily solar energy as the actual variable sun.
The concept simplifies solar resource description. Instead of saying “today received 5.2 kWh per sq m of total irradiation over 12 hours of daylight with varying intensity,” you can say “today had 5.2 Peak Sun Hours.” The two statements are equivalent.
Numerically, PSH is identical to daily GHI (Global Horizontal Irradiance) in kWh per sq m per day. The unit conversion makes them the same number:
5 PSH = 5 kWh per sq m per day.
The metric is intuitive and widely used in solar sizing, especially for residential and small commercial installations where simple estimates suffice.
How PSH simplifies solar calculations
For a quick estimate of solar plant output:
Daily Energy (kWh) approximately = Plant kWp x PSHThis gives the DC energy before losses. Applying Performance Ratio (PR) of 0.80 to 0.85 gives the actual AC energy.
For a 5 kWp solar plant in Mumbai (4.9 PSH):
DC daily energy: 5 x 4.9 = 24.5 kWh.
AC daily energy at PR 0.82: 24.5 x 0.82 = 20 kWh.
Annual generation: 20 x 365 = 7,300 kWh.
This matches typical actual generation for the location and configuration.
For comparison, a 5 kWp plant in Jaisalmer (6 PSH):
DC daily energy: 5 x 6 = 30 kWh.
AC daily energy at PR 0.82: 30 x 0.82 = 24.6 kWh.
Annual generation: 24.6 x 365 = 8,979 kWh.
The 23% higher PSH in Jaisalmer produces 23% more annual energy from the same installed capacity.
PSH values across India
| City | Annual Average Daily PSH | Solar Resource |
|---|---|---|
| Jaisalmer | 6.0 to 6.2 | Excellent |
| Bikaner | 5.9 to 6.0 | Excellent |
| Ahmedabad | 5.5 to 5.7 | Very good |
| Jaipur | 5.5 to 5.7 | Very good |
| Bhopal | 5.3 to 5.5 | Very good |
| Bengaluru | 5.0 to 5.2 | Very good |
| Hyderabad | 5.2 to 5.4 | Very good |
| Chennai | 5.0 to 5.2 | Good |
| Mumbai | 4.8 to 5.0 | Good |
| Delhi | 4.7 to 4.9 | Good |
| Kolkata | 4.4 to 4.6 | Moderate |
| Patna | 4.4 to 4.6 | Moderate |
| Guwahati | 4.2 to 4.4 | Moderate |
These are long-term annual averages. Year-to-year variation is 3% to 6%; seasonal variation is larger.
PSH seasonal variation
PSH varies through the year:
Summer (March to May): Highest PSH. Clear sky in most of India. Long days. Sun close to overhead.
Monsoon (June to September): Reduced PSH due to cloud cover. South Indian sites can drop 30% from peak.
Post-monsoon (October to November): Recovery toward annual average.
Winter (December to February): Lower PSH due to shorter days and lower sun angle. Northern Indian sites drop most.
For solar plant performance analysis, monthly PSH data is more useful than annual averages.
PSH versus other solar metrics
PSH is one of several solar resource metrics:
GHI (Global Horizontal Irradiance): Numerically same as PSH but in kWh per sq m per day rather than hours.
DNI (Direct Normal Irradiance): Direct component only. Used for concentrating solar.
DHI (Diffuse Horizontal Irradiance): Diffuse component only.
POA (Plane of Array): Irradiance on the tilted module surface, slightly higher than GHI for typical tilts.
For solar PV plant design and performance analysis, POA irradiance is the relevant metric. PSH (or GHI) is a simpler proxy used for quick estimates and resource assessment.
Using PSH for solar sizing
For a homeowner estimating solar savings:
Look up PSH for the city (use averaged annual value).
Multiply PSH by typical PR (0.80 to 0.85) to estimate kWh per kWp per day.
Multiply by 365 days to get annual kWh per kWp.
Multiply by desired plant kWp.
Multiply by electricity tariff to get annual savings.
For Bengaluru (5.1 PSH):
5.1 x 0.83 = 4.23 kWh per kWp per day.
4.23 x 365 = 1,544 kWh per kWp per year.
5 kWp plant: 7,720 kWh per year.
At Rs 8 per kWh: Rs 61,760 annual savings.
This first-order estimate is sufficient for residential decisions. For precise sizing, use PVsyst or similar tools with location-specific data.
PSH data sources
NIWE Solar Atlas: Free, India-specific. Provides annual and monthly PSH for any Indian location.
NREL SAM: Free software with global PSH data.
NASA SSE: Free satellite-derived data.
PVGIS: European Commission’s database including India coverage.
Solargis: Premium paid dataset with high accuracy.
Meteonorm: Premium paid dataset.
For project decisions, satellite-derived multi-year datasets (Solargis, Meteonorm) are typically used. For residential and educational purposes, NIWE and PVGIS provide adequate data.
Common PSH mistakes
Using a single annual PSH for projects with strong seasonal variation. Monsoon-heavy regions need monthly analysis.
Treating PSH (horizontal) as POA (tilted). POA is slightly higher for tilted modules; use the correct metric for sizing.
Ignoring shading and obstruction. PSH measures available resource, not what reaches the panels after shading.
Using outdated data. Solar resource varies year-to-year, so multi-year averages from current datasets are needed.
Confusing PSH with daylight hours. PSH is the equivalent at full sun intensity, not total daylight.
Best practices
For residential sizing, use city-level PSH from NIWE Solar Atlas.
For commercial sizing, request site-specific irradiance data from satellite datasets.
For utility-scale projects, install met station with pyranometer for site-specific data.
For seasonal analysis, use monthly PSH rather than annual average.
For project finance, use lender’s preferred dataset (typically Solargis or Meteonorm).
For lender-grade economics, use P90 (90% probability) PSH, not P50 (median).
Standards and references
PSH calculations follow WMO and ISO standards for meteorological measurements. NIWE (National Institute of Wind Energy) publishes the India Solar Atlas with PSH data. International datasets (NREL, Solargis, Meteonorm) follow industry-standard processing methodologies.
Related glossary terms
- Solar Irradiance
- Global Horizontal Irradiance
- Pyranometer
- Met Station
- Performance Ratio
- Capacity Utilisation Factor
- What is kWp
- Tilt Angle
Key takeaways
Peak Sun Hours (PSH) is the equivalent number of hours per day at 1,000 W per sq m irradiance that would deliver the same daily solar energy as the actual variable sun. Numerically equal to daily Global Horizontal Irradiance in kWh per sq m. India’s PSH ranges from 3.8 (Northeast) to 6.2 (Jaisalmer), with Rajasthan and Gujarat at the higher end. PSH provides an intuitive metric for solar resource comparison and quick first-order sizing estimates. For precise solar plant design, use POA irradiance with detailed modelling tools rather than PSH alone.