Only half of the subsidy paid by the central government so far, laments the educational institute.  The system is not grid-interactive yet since there is no regulation on feeding electricity into the grid

The Radhasaomi Satsang in Dayalbagh is a spiritual center with a university campus (Dayalbagh Educational Institue), residential colonies, schools, hospitals etc. The residential colony and the Dayalbagh Educational Institute (DEI), now depend on solar energy besides conventional grid power for fulfilling their electricity needs.

Dayalbagh Educational Institute

The solar power plant at the DEI is a 520 kWp photovoltaic unit that is being largely used for the institute. The project was initiated in 2010 under the National Solar Mission for off-grid and solar photovoltaic applications. The project finished in February 2012. It costed about Rs 11 crores for the entire project and continues to depend on the institute's funding for maintenance. The MNRE was supposed to allocate 30% of the project cost. “However, only about 15% has been received so far,” says Prof. A.K. Saxena, Dept. of Electrical Engineering. He, along with Prof. D. Bhagwan Das, was instrumental in setting up the project. The turnkey project was contracted to Bharat Heavy Electricals Limited, a Bengaluru based public sector undertaking. “We were involved in every step of the project cycle and we decided the kind of technology we preferred for inverters, and batteries,” says Das.

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Solar power generation at the Dayalbagh Educational Institute

The power plant is not the sole supplier of electricity to the institution. The institution is connected to the grid, and therefore there is a mix of grid connected and solar based electricity being utilized. Usually, there is enough electricity being produced by the power plant to meet the load of the institution. However, in summer months when temperatures are high the output is reduced, as solar photovoltaic (PV) technology is not very efficient beyond 25 degrees Celsius. This is also when the demand for power is high and hence, more grid based electricity is needed. 

However, just after the rainy season, the temperature is ideal for the PV panel and the atmosphere is clear of dust particles. The output from the power plant is now at its peak. During winters, power demand also decreases as the fan and cooling requirements drop. “We are completely dependent on the solar power plant during this period,” says Das. The power plant electrifies the hostels in the evenings which houses about 300 students.

Sale of excess power

There is also excess supply from the power plant during this period. The surplus power is not exported to the distribution company (Torrent Power, in this case) because there is no Power Purchase Agreement (PPA) between the two parties. This is because there are no government regulations on small scale power producers. Instead, the surplus power is fed into the houses in Dayalbagh colony.

The DEI and the colony buy electricity in bulk from Torrent Power discom at 33kV. The voltage is stepped down at a transformer from where a line goes into the colony and another goes into the institute at 11 kV. “The excess that comes from the solar power plant is automatically fed into the colony because there is constant load demand from the households,” says B.S. Gupta, Renewable Energy Advisor at the Radhasaomi Satsang. “The households receive the electricity for free,” adds Gupta.

The switchgear prototype that was designed at the institute for grid interaction

Design

The technical arrangement is simple. There 520 kWp system is divided by 7 power plants of varying capacities depending on the size of the roofs they are on. In each power plant, the solar panels are directly connected to a Maximum Power Point Tracking (MPPT) charge controller.  They are in turn connected to low-maintenance lead acid batteries which can provide a back up of 4 hours. The batteries need to be refilled once every 8 months. “Just to be safer we have been refilling it every 6 months,” adds Das. The batteries are connected to a switch gear which helps in adjusting the incoming grid based electricity according to the load demand and the solar power available. The switch gear has been developed by the institution as part of their research.

Rooftop generation at the colonies

The households in the residential colony have also invested in solar power for reducing their energy bills. So far, 27 households have fitted rooftop solar power plants with a small capacity of 1-2 kWp according to their capabilities. “Sometimes, when they have surplus generation the electricity is fed into the other houses of the colony,” says Professor Das. The households are fitted with net meters. “The Renewable Energy Authorities at the Radhasaomi Satsang bill individual houses in the residential colonies for electricity. Torrent Power has no business beyond bulk purchase. We charge the households according to their meter,” says Gupta. If the houses have drawn power from the main grid beyond their solar power generation, they are charged for that. In case they have sold off power more than what they used from the main grid, the surplus is carried forward to the next month when it can be adjusted. “We don’t pay off in cash,” says Gupta.

There is no compensation for excess generation into the local grid. The credits are just rolled into the succeeding billing periods. “The advantage of roof-top grid interactive generation is that the batteries have longer lives compared to the islanded mini-grid system. This is because, the batteries are not discharging all the time as there is conventional power. The number of discharge cycles is lower as compared to the mini grid or individual home systems,” adds Gupta.

Problems

Cleaning the panels require ample labour. Currently about three to four people are engaged in this duty. Due to the size of the plant, it takes about 25 to 30 days to finish one cycle of cleaning. Therefore, by the time they restart the cycle, there is heavy accumulation of dust which has had negative effect on generation to about 30%.

For a micro-grid the use of a large battery bank does not seem like the best idea, according to Professor Bhagwan Das. The reason behind this is that there is a huge demand in the evenings which reduces through the night to the next morning. The entire demand cannot be met by the solar power plant alone because the battery bank can only store up to 4 hours back up. This, according to the professor, could be viewed as serious issue in rural villages when people would require water pumping early in the morning. However, the fact that there is a combination of grid and the solar power plant has helped the institution in withstanding power cuts in the area over the last year. “Even during the two-day power shut down earlier this year, we escaped it by shutting down some of the heavy loads without any interruption in the power supply,” says Das.