What are Peak Sun Hours
Peak Sun Hours (PSH) is a simplified measure of solar resource expressed as the number of hours per day during which solar irradiance averages 1,000 W/m² (1 kW/m²). It is the time integral of daily GHI normalised by STC reference irradiance.
PSH (hours/day) = Daily GHI (kWh/m²/day) / 1 kW/m²
For Indian sites, PSH ranges from 4.0 to 6.5 hours/day on annual average. PSH is widely used in residential and off-grid sizing because it gives an intuitive single number for daily solar resource. See Solar Irradiance Data India, State-Wise Peak Sun Hours for the full state and city breakdown behind the regional table below.
Why PSH matters
Simplified sizing. PSH × capacity × PR = daily energy. Direct sizing formula.
Customer communication. Customers grasp “5 hours of sun per day” easily.
Off-grid design. PSH drives PV-to-load sizing for off-grid inverter systems.
Yield estimation. Quick annual solar yield: capacity × PSH × 365 × PR.
Regional comparison. Single number to compare solar potential across locations.
How PSH is calculated
Where G_STC = 1 kW/m² = 1000 W/m².
For daily PSH, integrate hourly GHI over the day and divide by 1 kW/m².
Indian PSH by region (annual average)
| Region | PSH (hours/day) |
|---|---|
| Western Rajasthan, Ladakh | 6.0 to 6.5 |
| Andhra Pradesh, Telangana | 5.5 to 5.7 |
| Gujarat (non-Kutch) | 5.5 to 6.0 |
| Karnataka, Tamil Nadu | 5.0 to 5.5 |
| Maharashtra, MP | 5.0 to 5.5 |
| Delhi, Haryana, Punjab | 4.7 to 5.0 |
| Mumbai | 5.0 |
| Bengaluru | 5.3 |
| Chennai | 5.3 |
| Kolkata | 4.5 |
| Hyderabad | 5.5 |
| Uttar Pradesh, Bihar | 4.5 to 4.8 |
| West Bengal, Odisha | 4.3 to 4.7 |
| Kerala, Goa | 4.5 to 5.0 |
| North-east states | 4.0 to 4.5 |
Technical deep dive
PSH vs GHI
| Metric | Definition | Use |
|---|---|---|
| GHI (kWh/m²) | Total irradiation | Scientific resource measure |
| PSH (hours) | Equivalent hours at 1 kW/m² | Simple sizing |
Numerically equal in daily averages: 5.5 kWh/m²/day = 5.5 PSH.
Yield from PSH
Daily yield (kWh) = Capacity (kW) × PSH × PR
Off-grid sizing using PSH
PV size = (Daily load × autonomy factor) / (PSH × PR × battery efficiency)
For 5 kWh daily load, 1.3 oversize, 5 PSH, 0.85 PR, 0.92 battery: PV size = (5 × 1.3) / (5 × 0.85 × 0.92) = 6.5 / 3.91 = 1.66 kWp
See Off-Grid Solar Battery Bank Sizing, India Complete Guide for a full worked methodology covering autonomy days and depth of discharge.
Seasonal variation (Delhi example)
| Month | Approximate PSH |
|---|---|
| January | 4.0 |
| February | 4.8 |
| March | 5.8 |
| April | 6.5 |
| May | 6.8 |
| June | 5.5 |
| July | 4.5 |
| August | 4.0 |
| September | 4.8 |
| October | 5.2 |
| November | 4.3 |
| December | 3.8 |
| Average | 5.0 |
Real-world applications
Residential and small commercial solar sizing.
Off-grid system design.
Solar pumping capacity calculation, for example sizing solar inverters for water pumps against site PSH.
Customer-facing quick-estimate tools, such as PSH-driven solar savings calculators.
State-wise solar potential comparison.
Limitations of PSH
Ignores temperature, soiling, shading separately (PR captures these).
GHI-based PSH not optimal for tilted arrays without plane of array correction.
Does not capture intra-day variability.
Less precise than full hourly simulation.
Best practices
Use multi-year average PSH for sizing.
Apply realistic PR for the application.
For tilted arrays, use POA-based PSH.
Validate against ground irradiance data gathered during site survey when available.
Communicate PSH alongside expected yield.
Indian market context
NIWE Solar Atlas provides Indian PSH and GHI data.
PM Surya Ghar customer education materials use PSH to explain expected generation.
Residential rooftop sizing typically uses 4.5 to 5.5 PSH depending on city.
Utility solar developers use full hourly simulation with GHI, DNI and DHI rather than PSH alone, typically inside bankable solar simulation software.
Off-grid solar under PM-KUSUM and rural electrification programmes use PSH-based sizing.
Standards and certifications
| Standard | Scope |
|---|---|
| Industry convention | PSH definition |
| IEC 61724 | Performance monitoring (uses irradiance) |
| WMO CIMO Guide | Underlying meteorology |
Key takeaways
PSH is a simplified single-number measure of daily solar resource, equal to daily GHI divided by 1 kW/m². Indian PSH ranges from 4.0 to 6.5 hours/day. PSH provides intuitive sizing for residential and off-grid systems through the relationship: daily yield = capacity × PSH × PR. Multi-year averages and realistic PR assumptions are essential for accurate use.
Further reading
For how Peak Sun Hours plays out in real projects, these guides go deeper:
Sources
- NIWE Solar Resource Atlas.
- Solargis Solar Resource Database.
- NSRDB National Solar Radiation Database, NREL.
- Meteonorm Global Solar Radiation Database.
- IEC 61724, Performance monitoring.
- Duffie J. A., Beckman W. A., Solar Engineering of Thermal Processes, Wiley.
- IEA PVPS Trends in Photovoltaic Applications 2024.
- MNRE Solar PV Design Guidelines.
- Mertens K., Photovoltaics: Fundamentals, Technology, and Practice, Wiley.
Frequently Asked Questions
What is PSH in simple words?
What is the typical Indian PSH?
How is PSH calculated?
PSH vs sunshine hours?
How does PSH relate to solar yield?
Does PSH change with season?
Does location latitude affect PSH?
Is PSH a formal standard?
What is the highest PSH in India?
Does PSH count cloudy hours?
How is PSH used in off-grid design?
Does tilt affect PSH calculation?
What is PSH for Delhi?
What is PSH for Mumbai?
Where do I find Indian PSH data?
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