Will solar radiation measure up to expectations?

The mega plan for solar power generation in India envisaged under the Jawaharlal Nehru National Solar Mission (JNNSM) and various State Solar Policies, calls for reliable and bankable solar radiation data in order to establish plant performance and project economics. The large-scale solar parks coming up in Gujarat and Rajasthan in association with the Clinton Climate Initiative further intensify the pressing need of bankable solar data.
The overall power generation and the Capacity Utilization Factor (CUF) of Solar PV plants and Solar Thermal plants depend on Global Horizontal Irradiance[1] (GHI) and Direct Normal Irradiance[2] (DNI) respectively. Thus, it is critical to have reliable data around solar radiation while conceptualizing a solar power project. The reliability of solar resource data also impacts the lender’s assessment of these projects and affects their overall bankability.

In order support and accelerate the development & planning upcoming projects, EVI has established a state-of-the-art Solar Radiation and Meteorological Parameters monitoring station in the upcoming Rajasthan Solar Park in Jodhpur. This station will support the solar power projects by being source of an independent, third party data set. The station has following features:

ü  Installed equipments are in accordance with the guidelines from World Meteorological Organization (WMO) for a reference grade station.
ü  Station is manned to ensure regular cleaning & maintenance thereby ensuring accurate data measurement.
ü  24X7 security by ex-army personnel to ensure station safety and security
ü  Following parameters are being measured at the station:
·       Global Horizontal Irradiance (GHI)
·       Direct Normal Irradiance (DNI)
·       Diffuse Horizontal Irradiance[3] (DHI)
·       Ambient Temperature
·       Atmospheric Pressure
·       Relative Humidity
·       Rainfall
·       Wind Speed & Direction

We understand that in Wind Industry at least one year site specific studies are required for generating bankable data-sets. Therefore for Solar it is quite plausible that banks might not accept weather model generated data-sets only and may want ground measured data as well.

Therefore, in addition to undertaking ground measurements, EVI has partnered with US based global weather resouce assessment firm 3TIER to provide the industry with long-term hourly time series data based on combined approach of ground-based and satellite data.

At present , there are various sources of satellite based observation data - some of which are being used without comparision to ground observations to develop solar projects. Recent evidence from ground observations and production from commissioned projects in Rajasthan suggest that GHI estimates from satellite are good but DNI is over-stated. We strongly suggest project developers and financial institutions NOT to get misleaded by satellite data alone for designing solar projects and rather use combination of ground observations along with satellite data for the purpose.

Subscription to the ground measured data from EVI’s monitoring station and the Solar Resource Assessment report produced in partnership with 3TIER are available for project developers. Please contact Rahul Gaba (
rahul.gaba@emergent-ventures.com) at EVI for further information in this regard.

[1] GHI is the total amount of solar radiation per unit area that is intercepted by a flat, horizontal surface. It includes both direct beam radiation (radiation that comes from the direction of the sun) and diffuse radiation (radiation that has been scattered by the atmosphere and which comes from all directions of the sky).
[2] DNI is the amount of direct beam solar radiation per unit area that is intercepted by a flat surface that is at all times pointed in the direction of the sun.
[3] DHI is the amount of radiation received per unit area by a surface (not subject to any shade or shadow) that does not arrive on a direct path from the sun, but has been scattered by molecules and particles in the atmosphere and comes equally from all directions.

Key words: DHI, DNI, GHI, Jodhpur Solar Park, Phalodi Solar, Radiation Data India, Rajasthan Solar Park, Solar Radiation India


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