Weather monitoring is critical at all stages of the life cycle of a solar power plant: from assessing financial viability of a project, to analyzing plant performance, to predicting power generation.
Local environmental conditions have a profound influence on plant performance. We know only too well the effect of dust on power production of solar plants in Rajasthan and the unanticipated costs associated with cleaning of panels. Likewise, high ambient temperatures are not always predictive of high performance and module performance starts to decrease with high temperature depending upon the panel technology as we see in plants in Northern India. We’ve recently looked at how relative humidity affects plant performance in Gujarat. Wind also impacts the performance of solar power plants and their impact will come to light with time as data from plants in coastal regions of Tamil Nadu become available.
Thus, a weather monitoring station helps in monitoring the efficiency and performance of solar power plants and will provide intelligence on plant operation and possible avenues to increase the plant output.
A Typical Solar Weather Monitoring Station should include:
Generally speaking, comprehensive weather monitoring stations are not considered for small power generation systems. However, there are two parameters that are essential monitoring even for small projects: measuring incoming solar irradiance and back of the panel temperature. Kipp & Zonen has recently launched a new product called RT1 which can measure this. Especially for rooftop and small plants, the RT1 is a small, fully weatherproof duo-sensor that independently measures the incoming solar irradiance and the back panel temperature. It is extremely simple to mount on a corner of PV panel and has a soiling resistance design for low maintenance.
As a rule of thumb, for each 5MW sized plant, at least one Weather Monitoring Station should be considered, and for every additional 5MW another Weather Monitoring Station should be used. The quantity of monitoring stations is also dependent on the plant terrain and layout of installed PV plant.
Wind flow certainly has an impact on performance of solar power plants. While there are ample studies demonstrating the impact of ambient temperature on plant performance, studies from India delineating the impact of wind on panel performance have been limited. The impact of wind flow will come to light with time as data from plants in coastal regions of Tamil Nadu become available.
There is no substitute for a pyranometer, period. Pyranometers are preferred by plants. Although reference cells have properties similar to the to PV panels, but even when properly calibrated, they will have shortcomings in temperature, spectrum and degradation. Therefore they will not be able to give an accurate measurement of the available solar radiation under all conditions. Depending on the application and the type of energy calculation several differences can be noted.
Advantages of Pyranometers:
In summary, for all the reasons above, Performance Ratio or Performance Index calculations are more accurate using a pyranometer.
Accuracy of all measuring devices degrades over time. Therefore regular calibration of all measurement equipment is essential. Calibration is a comparison between a known measurement (the standard) and the measurement using your instrument. The accuracy of the standard should be higher than or equal to the measuring device being tested. The calibration standards for solar radiation sensors are traceable to World Radiometric Reference (WRR) in Davos, Switzerland and of meteorological instruments to the National Institute of Standards and Technology (NIST).
Solar radiation sensors should be re- calibrated every two years and meteorological sensors, every year.
We recommend calibration of pyranometers after completion of two years from the date of first use. Meteorological sensors like anemometer, temperature sensor, rain gauges, and wind sensors should be recalibrated after completion of one year from date of first use. This is mandatory to maintain the accuracy validity and performance of instrument for long periods. We provide calibration services. The time normally involved in carry out the calibration is approximately 3-4 weeks as all devices are sent back to the OEM. At the OEM, the accuracy of the instruments is checked, as well as the traceability of the measurement. In practice, re-calibration also includes repair of the device if it is out of calibration. A report is provided by the calibration expert, which shows new sensitivity/uncertainty/error in measurements with the measuring device after the calibration.
Our sensors are designed for a long operation period and most instruments, other than consumables used in regular maintenance, do not have a specific life-time. However, components do degrade or require servicing to maintain optimal performance depending upon age, the operating conditions and maintenance.
It sometimes happens that products become damaged by accident or by extreme conditions (such as lightning strikes). In this case repair and the replacement of parts will be necessary for smooth operation of sensors. We do provide a servicing and repair facility in our office in India.
Absolutely. High quality weather monitoring equipment will last for the entire 25 years of the solar power plant. Like any other equipment, automated weather stations require regular maintenance for better performance and longer life expectancy. Each and every sensor needs maintenance on a regular basis. Also, one of the main and crucial points to extend the life of the sensors is to re-calibrate them to maintain their accuracy.
Agriculture and solar power generation may have a symbiotic relationship provided the ratio of land used for power generation versus agriculture is not skewed. Weather monitoring is critical to both aspects so there is a natural synergy to pooling resources for an Agro PV developer.
Please find following a brief profile of the interviewed person:
Dr. Jaya Singh, Head - Strategy and R&D, BKC WeatherSys Pvt. Ltd., India