Hybrid renewable energy systems have a future

Hybrid renewable energy systems, drawing energy from different sources, are more economical than those running on a single source, a study finds. 

A team of researchers from the University of Agder, Norway, which studied the sizing of a mini-grid for electrifying a rural community left out of the national grid, reports that the most economical configuration is a combination of solar, wind and diesel generators. 

The report to be published in the September issue of Sustainable Energy Technologies and Assessments also says that hybrid systems are economically viable whether operated off-grid or connected to the grid. 

The researchers based their study on Siyambalanduwa, a remote Sri Lankan village with about 150 households, drawing about 270 kilowatt hours of energy daily with a night time peak of about 25 kilowatts.

They hypothetically divided the village population into three income categories with different consumption levels and also considered power usage by a community centre. 

The monthly average solar irradiation and wind speed data were obtained from the NASA Surface Meteorology and Solar Energy Database.

Calculations based on these numbers showed that, the most economical configuration would be 40 kilowatts from wind turbines, 30 kilowatts from solar panels, 25 kilowatts from a diesel generator with the system supplemented by a battery bank with a capacity of 222 kilowatt hours.   

Many villages in Sri Lanka are too remotely located to be connected to the national grid. Recently, the Ceylon Electricity Board released a list of more than a thousand villages that cannot be connected to the national grid in the near future. 

There are no off-grid hybrid renewable energy systems in Sri Lanka, says Iromi Ranaweera, fellow at the Norwegian University of Science and Technology, Trondheim and one of the authors of the report.  

“There are several examples in India, Nepal and China. They are reliable and economical when compared to grid expansion,” Ranaweera tells SciDev.Net.  

Debajit Palit, associate director and senior fellow at The Energy and Resources Institute, New Delhi, says that “unlike other South Asian countries, Sri Lanka doesn’t have proactive policies to promote off-grid energy projects.” 

The Siyambalanduwa study has the drawback that it is not based on actual electrical loads.

“Without a detailed survey, one can’t categorise the village into rich, medium income, and poor,” says Binayak Bhandari, assistant professor of mechanical engineering at Woosong University, Daejeon, South Korea.

“Also, the electricity consumption of these families and the community centre should be supported by at least one month of ground data to validate the assumptions,” Bhandari said. 

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