When it comes to solar irradiation in India, everyone would expect this to be better when compared to Spain, for example.
With respect to GHI (Global Horizontal Irradiation), which is relevant for Photovoltaic (PV) projects, this is truly the case. In regard to DNI (Direct Normal Irradiation), which is relevant for CSP projects, the annual sum of DNI is almost comparable, with values in the range of 1900-2100 kWh/m2a.
Suntrace, a company established in Germany in 2009 focusing on the development, investment, operation and ownership of Solar Thermal Power Plants, has compared the DNI values for 2 reference locations, located in regions favorable for CSP project locations:
1. Spain, Andalusia region
2. India, Rajasthan region.
Main assumptions for the comparison:
• Identical DNI of 1950 kWh/m2a for both locations: An individual year with an identical annual sum for DNI in both locations was used for the calculations.
• A standard performance simulation tool for CSP plants was applied.
• Technical configuration: 50MW parabolic trough CSP plant with 8 hours of storage, identical set-up for both locations (no# of loops, cooling method, etc.)
One would expect at first glance that the annual electricity yield of both plants would be approximately equal.
Regarding DNI frequency distribution for the locations in Spain and India, a location in India, compared to a location in Spain, accumulates more hours with moderately high DNI values. While in Spain, only during summer some high DNI values are reached.
A CSP-plant at the Indian location can deliver significantly more energy compared to a location in Spain with the same average DNI.
Specifically the low production during the cold seasons creates the disadvantage in Spain. The Indian production curve also shows the dip in energy production during the monsoon-summer month (Jun-Aug)
This comparison did not reflect a project-specific adjustment of the technology in order to focus on the one variable: DNI frequency distribution.
The performance of a parabolic trough plant is a function mainly of DNI, solar field size, and storage size. The plant configuration requires a project specific optimization to identify the feasible size of the plant (number of loops, capacity of thermal energy storage), which can only be optimized once the DNI is properly evaluated. Further optimization will then review the cost related to the technically optimized concepts.
As a conclusion, one can use as rule of thumb, that energy yield at a location in India could be >20% above a location in Spain with the same average DNI.