This article describes in detail , the need and types of resource assessment for solar technology.
The name might sound unfamiliar to some, but if one plans on investing in a solar plant either for a rooftop or for a farm, this is one of the pre-requisites to be considered. It is as important as assessing how much fuel is in one's car before travelling out.
A simple definition of resource assessment would be, the systematic collection of site-specific meteorological data for the purpose of accurately estimating a prospective solar farm’s annual energy production.
Like the weather, solar radiation varies with location and time so it is important to measure factors such as solar radiation, wind speed, air temperature, etc. to ensure that your site receives enough solar radiation. This in turn would help you to choose the most optimum configuration of solar plant for your site resulting in maximum electricity production.
How is Resource Assessment Done?
There are various tools / models to assess solar resource, for simplicity they can be classified into into 2 broad categories:
- Ground mounted measuring instruments
- Satellite derived data
Ground Mounted Measuring Instruments
In the first method, i.e., Ground mounted measurements, instruments such as pyranometers or pyrheiometers are used for measurement of solar irradiation and other meteorological data. In India the Ministry of New and Renewable Energy has setup 115 automatic solar and meteorological measuring stations known as SRRA stations all over the country in Phase I and II. While without any doubt the data from such ground mounted instruments can be highly accurate, there are some limitations such as limited time of measurements, unknown accuracy, regular maintenance of the instruments, high cost of operation, etc.
Satellite Derived Data
One of the source for satellite derived data is SolarGIS, which uses statistically aggregated solar and temperature data stored in the database with a time step of 15/30 minutes.Solar radiation is calculated from IODC satellite data covering a period from 1999 to 2011. Derived solar parameters are calculated for any fixed-mounted or sun-tracking PV. Air temperature is derived from atmospheric models from ECMWF and NCEP. SolarGIS database has been independently identified as the most reliable irradiation database on multiple occasions.
To summarize, both the above methods have their pros and cons. However the importance of either cannot be discounted as both are complementary to each other. While the Satellite derived data method provides global coverage with a reasonable quality, the ground mounted systems provide high-quality ground measurements for local conditions.
While resource assessment is just the initial step, there are a list of other factors such as direction of solar PV panels, angle of mounting, losses which occur due to shading, wiring, soling, DC/AC conversion, etc. which play a key role in optimizing electricity yield of a solar plant. However as these are mainly system specific factors, they are rated after resource assessment.
- ↑ Renewable NRG Systems
- ↑ SolarGIS