What are peak sun hours?
Peak sun hours is a convenient way to express daily solar resource at a location. The metric represents the equivalent number of hours per day that the sun would need to shine at 1,000 watts per square metre (STC irradiance) to deliver the actual daily solar energy received. A site with 5 peak sun hours per day receives the same daily energy as 5 straight hours of full STC irradiance, even though the real day has variable irradiance from sunrise through sunset.
Mathematically: PSH = daily total irradiance (kWh/m²) ÷ 1 kW/m². A location receiving 5.4 kWh/m² of solar energy in a day has 5.4 peak sun hours. Annual PSH is the daily PSH averaged across 365 days. Indian annual PSH varies from about 3.5 (Northeast) to 6+ (Rajasthan and Gujarat).
PSH is widely used in solar sizing and quick yield estimates because it directly relates to expected energy generation. Annual kWh per kWp roughly equals annual PSH × 365 × Performance Ratio. A site with 5 daily PSH on average, at PR 0.79, yields about 1,440 kWh per kWp per year.
Why peak sun hours matter
For solar EPCs, PSH is the location-driven productivity factor that determines how much energy a kWp of solar will produce at a given site. Knowing the local PSH lets the EPC quote realistic annual generation and credible payback to the customer.
For utility-scale developers, PSH (and the underlying detailed irradiance data) is the foundation of every project finance model. Tariff bids assume specific PSH-driven yields. Underestimating PSH inflates the required tariff; overestimating it understates project cost.
For homeowners and businesses, PSH provides a first-order sanity check on solar economics. A 3 kWp system at 5 PSH yields about 4,300 to 4,800 kWh per year in Indian conditions; that translates to known savings against retail tariffs.
For state policy, PSH distribution explains why states differ in solar economics. Rajasthan's high PSH supports faster payback than Kerala's lower PSH for the same project cost.
How peak sun hours is used
- Site resource lookup. Reference solar resource maps from MNRE, NISE, NREL, or NASA for the location's annual average PSH.
- Tilt and orientation adjustment. Plain horizontal PSH is adjusted for the module tilt and orientation using standard formulas.
- Annual yield estimate. Annual kWh per kWp = annual PSH × 365 × Performance Ratio.
- Monthly modelling. Detailed forecasts use monthly PSH to capture seasonal variation.
- System sizing. Required kWp = target annual kWh ÷ (PSH × 365 × PR).
- Quotation and finance modelling. PSH-driven yield feeds into payback, IRR, and lender models.
- Field verification. Year-1 measured generation is compared against PSH-based forecast.
Real example: PSH-based sizing for an Indore residential rooftop
Customer. Family in Indore consuming 450 kWh per month, or 5,400 kWh per year.
Local PSH. Indore annual average PSH approximately 5.2.
Sizing. Target annual generation 5,400 kWh. Assume PR 0.79.
Required kWp. 5,400 ÷ (5.2 × 365 × 0.79) = 5,400 ÷ 1,499 = 3.6 kWp.
Recommendation. 3.5 kWp system (matching the recommended residential size for the PM Surya Ghar subsidy slab plus a margin).
Expected annual generation. 3.5 × 5.2 × 365 × 0.79 = 5,250 kWh per year, about 97 percent of consumption.
Benefits of using PSH
- Simple first-order metric. Easy to communicate to customers.
- Location-specific. Captures the dominant variable in solar economics.
- Foundation of sizing. Required kWp = target kWh ÷ (PSH × 365 × PR).
- Globally standardised. Same concept used in solar resource maps worldwide.
- Useful for sanity checks. Customer can verify forecasts against local PSH.
- Public data availability. MNRE, NISE, NASA, NREL all publish PSH data for Indian locations.
Limitations of PSH
Annual average smooths seasonal variation. Monthly modelling is more accurate.
Horizontal PSH does not equal tilt-adjusted. Tilt and orientation matter.
Spatial resolution. Maps are typically at km-level grid; local microclimate can differ.
Cloud cover and weather variability. Annual average masks variability that affects month-to-month yield.
PSH alone does not predict yield. Performance Ratio, degradation, soiling all affect realised generation.
Peak sun hours across India
| State / region | Typical annual PSH |
|---|---|
| Rajasthan | 5.8 to 6.5 |
| Gujarat | 5.5 to 6.0 |
| Madhya Pradesh | 5.2 to 5.7 |
| Karnataka | 5.0 to 5.5 |
| Tamil Nadu | 5.0 to 5.5 |
| Maharashtra | 5.0 to 5.5 |
| Andhra Pradesh / Telangana | 5.0 to 5.5 |
| Uttar Pradesh | 4.8 to 5.3 |
| Bihar / Jharkhand | 4.5 to 5.0 |
| West Bengal | 4.2 to 4.7 |
| Kerala | 4.5 to 5.0 |
| Northeast states | 3.5 to 4.5 |
| High-altitude hill states | 4.0 to 5.5 (variable) |
Quick facts
| Term | Peak Sun Hours (PSH) |
|---|---|
| Definition | Equivalent hours per day of 1,000 W/m² irradiance |
| Calculation | Daily kWh/m² ÷ 1 kW/m² |
| Indian range | 3.5 (Northeast) to 6+ (Rajasthan) |
| Use in solar sizing | kWh/year = kWp × PSH × 365 × PR |
| Typical Indian rooftop yield | 1,400 to 1,650 kWh/kWp/year |
| Data sources | MNRE, NISE, NASA, NREL, India Meteorological Department |
Common mistakes about peak sun hours
- Confusing PSH with daylight hours. They are different things.
- Using national average PSH for state-specific quotes. Variation across India is significant.
- Ignoring tilt and orientation. PSH from horizontal data should be adjusted.
- Quoting yield = PSH × 365 without Performance Ratio. Real yield is lower.
- Treating PSH as constant year-round. Monthly variation matters for accurate modelling.
- Skipping shading analysis. Site-specific shading can reduce effective PSH significantly.
- Mixing PSH from different data sources without verification. NASA vs MNRE vs NISE can differ slightly.
Key takeaways
- Peak sun hours expresses daily solar resource as equivalent hours of full STC irradiance.
- Indian annual PSH ranges from 3.5 (Northeast) to over 6 (Rajasthan).
- Annual kWh per kWp ≈ PSH × 365 × Performance Ratio.
- Most Indian rooftops yield 1,400 to 1,650 kWh per kWp per year.
- Tilt and orientation matter; horizontal PSH must be adjusted.
- Public data sources include MNRE, NISE, NASA, NREL.
- PSH is a useful first-order metric, but full modelling needs PR, degradation, and shading factors.
Frequently Asked Questions
What are peak sun hours?
Peak sun hours (PSH) is the number of equivalent hours per day that the sun delivers 1,000 watts per square metre of irradiance. It is a convenient way to express daily solar resource at a location. A site with 5 peak sun hours per day receives the same daily energy as if the sun shone at 1,000 W/m² for 5 hours straight.
How is peak sun hours calculated?
PSH = daily total solar energy (kWh/m²) divided by 1 kW/m². For example, a site receiving 5.4 kWh/m² of solar energy in a day has 5.4 peak sun hours.
What is the peak sun hours range in India?
Most of India averages 4 to 6 peak sun hours per day annually. Rajasthan and Gujarat have the highest values (5.5 to 6+). Northeast and hill states are lower (3 to 4.5). Annual yield per kWp roughly tracks the PSH distribution.
How does peak sun hours relate to kWh generation?
Annual kWh per kWp roughly equals annual PSH × 365 × Performance Ratio. A site with 5 daily PSH on average yields about 5 × 365 = 1,825 kWh/kWp/year at PR 1.0, or about 1,440 kWh/kWp/year at PR 0.79.
Are peak sun hours the same as daylight hours?
No. Daylight hours include all sunlight time, including low-irradiance morning and evening. PSH is the equivalent at full STC irradiance. A 12-hour day with peak noon irradiance of 950 W/m² might have 5 to 6 PSH.
Why does Rajasthan have higher PSH than Kerala?
Rajasthan has clearer skies, less monsoon-driven cloud cover, and higher annual solar resource. Kerala has more cloud cover and rainfall, especially during monsoon. The annual irradiance integral is significantly different.
Does tilt and orientation affect PSH?
The plain PSH value assumes horizontal surface. Tilted surfaces facing the sun receive more irradiance, increasing effective PSH. Solar design uses 'plane-of-array' PSH, which accounts for the module tilt and orientation.
How is PSH measured in practice?
Pyranometers at meteorological stations measure ground-level irradiance. Satellite-derived datasets (NASA, NSRDB equivalents) provide modelled estimates. India has solar resource maps published by MNRE and the National Institute of Solar Energy.
Does peak sun hours change seasonally?
Yes. Indian summer months typically have higher PSH than monsoon and winter. The annual average smooths out seasonal variation, but monthly modelling is needed for accurate energy forecasting.
Can PSH predict my system's exact generation?
PSH is a useful first-order estimate. Accurate forecasting also requires Performance Ratio, system losses, tilt and orientation factors, and degradation. PVsyst, NREL SAM, and similar tools integrate all of these.
How does cloud cover affect PSH?
Cloud cover reduces irradiance and therefore PSH. Annual PSH integrates clear-sky and cloudy days. Sites with consistent clear skies (Rajasthan, parts of Gujarat) have higher PSH; monsoon-heavy sites are lower.
What is the typical Indian residential rooftop PSH?
Most Indian residential rooftops experience effective PSH of 4 to 5.5 after accounting for tilt, orientation, and shading. Annual yield typically lands in 1,400 to 1,650 kWh per kWp per year.
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- MNRE / NISE Solar Resource Maps. India-specific irradiance data. mnre.gov.in
- NASA Surface Meteorology and Solar Energy. Global satellite-derived irradiance.
- NREL National Solar Radiation Database. Reference datasets and methodology. nrel.gov
- India Meteorological Department. Surface measurement data.
- PVsyst and NREL SAM. Solar resource analysis tools.
- Indian solar plant operational data. Site-specific yield correlation with PSH.
- National Institute of Solar Energy (NISE). Indian site resource characterisation.
Written by QuickEstimate Editorial, QuickEstimate Editorial (Surat).
Last updated: 4 June 2026.