Solar geometry is the foundational concept behind solar PV system design. It determines how much solar radiation a module receives, which directly affects energy generation, system efficiency, and return on investment. The key parameters of solar geometry include solar altitude, solar azimuth, module tilt, and module azimuth. These factors define the position of the sun relative to the PV module and are crucial for maximizing annual energy yield.
1. Solar Altitude and Solar Azimuth
Solar altitude angle (α) represents the height of the sun above the horizon. At solar noon, the altitude is at its maximum for the day. In the morning and evening, the sun is lower in the sky, which means the solar altitude angle is smaller. The solar altitude changes throughout the year depending on the earth’s tilt and the latitude of the location.
Solar azimuth angle (βs) represents the direction of the sun relative to true south. In the morning, the sun is in the east, and in the evening, it is in the west. The azimuth angle is important for determining the optimal orientation of PV modules to capture maximum sunlight throughout the day.
Understanding these angles helps in predicting how sunlight strikes the module surface and enables accurate estimation of energy yield using PV simulation tools such as PVSyst and RETScreen.
2. Module Tilt (β)
Tilt is the angle between the PV module plane and the horizontal ground. It is one of the most important design parameters for rooftop solar systems. The optimal tilt is generally equal to the latitude of the location, plus or minus seasonal adjustment. A higher tilt angle improves winter energy generation because the sun is lower in the sky. Conversely, a lower tilt reduces wind load and structural requirements but may reduce energy yield.
In India, typical rooftop tilt ranges from 10° to 28°, depending on latitude and rooftop constraints. In dense urban areas, tilt is often limited by roof space, structural limitations, and wind load considerations. The higher the tilt, the better the winter generation, but it may increase wind loading and structural complexity.
Benefits of correct tilt:
- Higher annual energy yield
- Better winter output
- Improved self-cleaning due to rain runoff
Constraints:
- Wind load on tilted modules
- Roof height and structural capacity
- Shading from nearby structures
3. Module Azimuth (φ)
Module azimuth is the orientation of the PV module relative to true south (in the northern hemisphere). A module facing true south (0°) receives the highest annual solar radiation and maximum yearly energy output. However, east–west oriented modules are often used due to rooftop constraints or to widen the generation profile.
East–west orientation reduces peak power output but spreads energy generation across morning and evening hours. This can be beneficial for reducing peak demand charges and aligning solar output with load profiles.
Azimuth orientation options:
- 0° (South-facing): Highest annual yield
- +90° (West-facing): Peak in the evening
- –90° (East-facing): Peak in the morning
- Mixed orientations: Requires separate MPPTs (Multiple Power Point Trackers)
When multiple azimuth planes exist, each plane should be connected to a separate MPPT input of the inverter to optimize power generation and avoid mismatch losses.
4. Practical Implications for Rooftop Solar
In rooftop installations, ideal solar geometry is often compromised due to structural constraints, shading, and roof shape. Roofs may have multiple slopes, parapets, and HVAC equipment that obstruct optimal orientation. Therefore, designers must balance ideal geometry with practical constraints.
Key practical considerations:
- Wind load: Higher tilt increases wind uplift and requires stronger mounting structures.
- Roof layout: East-west roofs reduce peak power but improve generation profile.
- Shading: Even small shading can significantly reduce output, so orientation must consider shadows.
- MPPT strategy: For mixed azimuths, separate MPPTs reduce mismatch losses.
Seasonal Tilt Adjustment:
Some systems allow seasonal tilt adjustment, which can provide a 3–6% gain in annual energy. This is useful for regions with high seasonal variation but may increase installation complexity.
5. Conclusion
Solar geometry is not just a theoretical concept—it is a practical design tool that determines the efficiency and output of a solar PV system. By understanding solar altitude, azimuth, tilt, and module orientation, designers can optimize energy yield, reduce losses, and improve system performance.
Whether the system is a residential rooftop installation or a large commercial plant, the same principles apply: align modules for maximum sunlight exposure, minimize shading, and design mounting structures that can withstand wind and weather conditions.
Ultimately, a well-designed PV system based on solar geometry can deliver higher annual yield, better performance ratio, and stronger financial returns.
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