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Solar installation in the city as good as any others in the country

The performance of a solar plant installed at the Indian Institute of Science campus, Bengaluru has been found to be as good as other well-performing ones in the country, according to a team of researchers at the Divecha Centre for Climate Change. Armed with the data from a solar system they monitored in the IISc campus, the team shows that solar installations can perform reasonably well in the city. They also show that seasonal changes have significant impact on the performance of the system; with a reduced efficiency when the module is too hot. 

With the threat of climate change looming large, solar energy is being promoted in India in a big way with the current government targeting 1.75 GW of renewable power and an investment of $100 billion by 2022. It becomes essential, now more than ever, to look at the performance of solar panels under varying climatic conditions for realizing the potential of solar power. A solar system was installed on the roof of the JRD Tata Memorial Library to power the more-than-a-century-old Central office at IISc, thanks to a drive by the Ministry of New and Renewable Energy (MNRE) to power heritage buildings using solar power. A grid-interactive system of 20 kWp capacity was set up on the rooftop of the building and this study looked at the performance of this solar plant for about three years through different seasons and climatic conditions at Bengaluru.

The study monitored the surface temperature of one of the modules of the installed solar panels, recording the energy from both direct and diffused sunlight received at the site and power generated by the system. This system uses an efficient Transformer-less inverter and has the additional desirable qualities of reduced thermal losses and low maintenance. Using a data-logger connected to a remote monitoring system, real-time data was collected every five minutes and analyzed by the team.

Capacity Utilization Factor (CUF) and Performance Ratio (PR) are popular metrics to grade solar systems. CUF is the percentage of the total actual annual energy produced, given the maximum certified capacity in a year. PR is the percentage of energy measured in a module considering the theoretical energy that can be produced at the rated efficiency for a certain amount of sunlight received. The system was found to have a CUF of 16.5% and the average PR was 85%. This was comparable to other installed systems in the country, thus showing satisfactory performance. A total of 85 MWh has been produced by the system until May, 2016. “The money spent for this installation can be recovered in a period of four and a half years. More importantly, this plant has saved the emission of at least 60 tonnes of CO2 into the atmosphere through power savings from the grid”, quips Dr. Sheela with a quick back-of-the-envelope calculation.

The study also found that at times, power generation was handicapped by increase in module temperature beyond a certain limit. The average annual temperature at which efficiency was maximum was about 45°C. The highest yield was in the summers due to high amount of incident energy and long sunshine period but the module’s temperature was too hot and the efficiency started dropping after 45°C. This temperature, after which the efficiency of the module drops, is 35, 38 and 55°C for the monsoon, post-monsoon and winter seasons. PR of the system was inversely related to the module temperature. To gain the maximum benefit out of such systems, it would be advisable to devise strategies to cool the surface of the modules, such that efficiency remains constant.

A figure from the MNRE shows that all of India, except the Himalayan belt, receives high solar energy and has a huge potential for power generation. But more studies of this kind are required to study every potential site for a plant. The current study can be used to get a general idea of what one should expect in Bengaluru with solar installations. Apart from shades and bigger buildings, domestic users need to know about the right panels too.  “Picking the right panel is also a challenge. Performance of the panels is variable and there is no straightforward formula for this”, warns Dr. Sheela.To make the most of their plants, users need to be educated about the basics of solar plants, their monitoring and maintenance. Even dirt on the surface of the module can cause permanent shadows and damage the module. But this can be easily avoided by regular cleaning at least twice a month which also helps in increasing the longevity of the installation, the authors say.

“In remote areas where there is no accessibility to any electricity, solar power is an immediate solution. But, meeting urban domestic needs exclusively through solar power is certainly not feasible due to the variability of yield. Hybrid solutions like a combination of energy production from solar and wind and/or biofuel is the right solution,” she signs off.

About the authors:

Dr. Sheela K. Ramasesha, Mr. M. Shravanth Vasisht and Prof. J. Srinivasan are researchers at the Divecha Centre for Climate Change, Indian Institute of Science. Contact: sheela@caos.iisc.ernet.in | +91-80-2293-3427.

About the research:

The installation of the solar system worth 25 lakhs was funded equally by the Special Area Development Programmes under the MNRE and the Divecha Centre for Climate Change, IISc. The study has been published in the journal ‘Solar Energy’ under the title “Performance of solar photovoltaic installations: Effect of seasonal variations”. 

The article can be accessed here: http://dx.doi.org/10.1016/j.solener.2016.02.013