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Food & Health

Solar Roof Performance in Sri Lanka and Benefits to the Society


Authors of the Article

Sarath Wijesinghe is a senior power system engineer at RWE Renewables, one of the largest offshore wind development companies in UK. Over the past 12 years he has gained industrial expertise within the offshore wind sector and is currently designing a 1320 MW HVDC offshore windfarm in the UK. Prior to this, he worked as an electrical engineer in Ceylon Electricity Board from 1990 to 2005. Sarath graduated from the University of Moratuwa Sri Lanka in 1990 and obtained a postgraduate qualification in power systems from NTNU Norway in 1998. Further to this, he obtained an MSc and MBA from UK universities. (

I.M. Dharmadasa (IMD) is Senior Staff Grade Professor of Applied Physics and leads the Electronic Materials and Solar Energy Group at Sheffield Hallam University(SHU), UK. He is a graduate from Univ. of Peradeniya, and completed his PhD in 1980, from Univ. of Durham. After working in Dept. of Physics at Peradeniya as a lecturer, he returned to UK in 1984 because of his interest in solar energy conversion research. Since then, he has worked on this subject, in Univ. College Cardiff, British Petroleum Research in London and Sheffield Hallam University in the UK. During his 30 years of service at SHU, he has supervised 29 PhD students, 14 years of postdoctoral years, and published 6 GB patents, over 250 scientific articles and two books in solar energy field. Over the past 30 years, he was actively promoting renewables, and designed, piloted, monitored, and now replicating “Solar Village” projects in Sri Lanka. Two solar villages, one in Nochchiya sponsored by APSL-UK (Association of Professional Sri Lankans – UK) and Hela Sarana charity organisations and the other in Puthiya Nagar sponsored by APSL-UK. IMD is one of the founding members of APSL-UK, was the President of APSL-UK during 2009-2011 period and now serving as a senior Ex-Co member of this professional organisation. He is a dual citizen of Sri Lanka and UK and involved in several development projects through APSL-UK and Hela Sarana charities. (

In the era of solar revolution taking place, solar roofs are mushrooming round the globe. In Sri Lanka also, solar roofs are becoming popular and the aim of this article is to provide real data to help the Sri Lankan community to understand the value of these projects. This in turn will accelerate the take up of solar roofs in the country by more families learning the benefits of solar roofs. For this series of articles, we have selected rather a large solar roof of 20 kW. Our next article will be on a small-scale solar roof of 5 kW for average families in Sri Lanka.

The solar roof selected for this article is from Kandy area. The photograph of the system is shown below, and the technical details of the system is given in the following Table.

The 20 kW solar roof installed at Kumburegama village, Kandy in Sri Lanka.

Performance of the Solar Roof

This system is installed under the “Net Plus” scheme introduced by the Government of Sri Lanka. The performance of the solar roof during a day is given below. There are two charts to show the performance during a sunny day and a rainy/cloudy day. The system produces electricity from 7 am to 4 pm during the day and the total produced is fed to the national grid. A sunny day, the system produces 94.5 kWh (units), and a rainy/cloudy day produces 65.3 kWh.

The performance during a whole month is given by the following charts. Again, the data for a typical good month and a monsoon month are shown for comparison. A good month (March) produces 2,744 units and a monsoon month (November) produces 1,773 units.

The total production of electricity and exported to the national grid, during the year 2019 is given by the next chart. The average production per month is 1,965 units and the total for the whole year is 23,582 units.

Income and Simple Pay-back Period

The grid connection agreement according to the “Net Plus” scheme is for 20 years. The Ceylon Electricity Board (CEB) will pay Rs 22 per kWh for the first 7 years, and Rs 15 per kWh for the remaining 13 years. Solar panels can work up to 30 years, and after 20 years the system could be used according to the rules and regulations during that time.

There will be slight changes to these figures due to ageing of the system, but these figures show the financial benefits to the owner of this system. By the end of 20 years contract, by spending Rs 26 Lakhs, the owner will receive Rs 82.3 Lakhs as the total return. These solar panels have a lifetime of ~30 years and the owner will enjoy free electricity for another 10 years subject to the system continue after 20 years, to use at home plus export the surplus to the grid receiving continuous income, during retirement.

Other Benefits of the System

The above figures indicate the financial benefits to the owner of the solar roof. In addition to these personal benefits, the owner contributes to many other social benefits.

  • This system provides significant carbon offset showing approximately 62 Tons per annum. This reduces emission of carbon dioxide and other polluting gas & particles to the atmosphere.
  • The system itself acts as a promotional system to encourage people to produce clean energy to use in the country, instead of producing energy by burning imported, expensive, and polluting coal, liquid, and gaseous fossil fuels
  • In the future most of the cars will be electric, and the owner will benefit by having enough solar energy to charge the car free at home. Policies have already been announced in the UK, prohibiting manufacture of cars based on combustion engines, after 2030.

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