Solar Calculator: Monumental role played by SAC-ISRO remote sensing scientists

Tapan Misra

Our scientists had all the data and science, one leading business group had resources and ideas of building renewable energy business but had a gap in requisite science, and the country had an urgent requirement of leap frogging in utilisation of renewable energy as a responsible nation, in preventing looming climate disaster. Together came Solar Calculator. It was an honour for ISRO, when our Honourable Prime Minister dedicated our Solar Calculator to the common good of mankind in the recent COP 26 meeting, held in Glasgow.

In SAC-ISRO, remote sensing scientists are like Kuber Bhagavan – the God and Protector of Wealth in the Hindu pantheon of gods and godesses. They sit over piles of data, collected by our array of satellites and jealously guard them.

In 2016, Adani Green approached SAC. They were planning to establish solar power plants, following commitment by our Honourable PM in COP 20 meeting in Paris in 2015 and his personal initiation of establishment of International Solar Alliance.

For maximum energy output, solar panels need to be oriented perpendicular to sunlight. But sun light directions change over day, over seasons, over the earth latitude. Over the day Sun moves from East to West and somewhere near middle of the day, the Sun is overhead. During winter in northern hemisphere, sun is tilted southwards and in summer, northwards. In southern hemisphere, the phenomenon is reverse- in summer sun is tilted southwards, in winter northwards.
Sunrays’ incidence angle changes with latitude also. Maximum solar illumination occurs on equator. As you move towards South and North Pole, solar energy density reduces rapidly, becoming almost nil at polar regions.

Sunlight is available during day only. But the length of the day varies with season. Maximum during summer and minimum during winter.

Atmosphere plays truant too. All of us know that cloud and rain block sunlight substantially. But do you know that water vapour present in the atmosphere attenuates sunlight? Similarly dust, smog also block sunlight to some extent. Surface topography plays a significant role. All of us know that depending on slopes and their direction, sunlight appear brighter or softer in hilly regions. Based on directions of shadows of hills and mountains, day duration also shortens differently.

The local temperature plays a role. Solar cells operate with maximum efficiency at 35 deg C. At temperatures above and below this temperature, their efficiency goes down.

Adanis wanted following basic information:

  • Average sunlight power or solar insolation at a particular location
  • Average diurnal and seasonal variation of the same
  • Optimum angle of orientation of solar panels in terms of azimuth and elevation angles over a day and over a year.
  • Additionally they wanted prediction of the loss in solar energy on daily basis due to variability of atmospheric conditions.

All of these inputs are necessary to select optimum site for establishment of Solar farms, prediction of average outputs and controlling power feed to national power grid.

I discussed with our scientists. We have decades of archives of weather data from our weather satellites to predict Average behaviour of atmosphere over Indian subcontinent. Our weather satellites update our weather information on half hourly basis. We have detailed map of topography over Indian subcontinent. But all of them are available in different places and different minds.

I always felt that the greatest weakness of ISRO’s remote sensing programme was collation of science and data with practicable information. That is why in 2016, I triggered a small team to establish VEDAS- Visualisation of Earth Observation Data and Archival Sustem. Key word was Visualisation of Information in terms of colour maps and plots. We gave power to laymen to bring out information from time series of our remote sensing data by carrying out necessary science computation with in-built algorithm on the fly. In essence, the idea was to make science easy.

I gave the task of building the Solar Calculator to VEDAS team. We delivered the necessary software and data interface to Adanis in 2017. VEDAS team also made this Calculator as freely available mobile app on their portal. I understand that till today, there have been 71000 downloads, a staggering number for a scientific App. By 2017 time frame, this idea was truly novel and ISRO was pioneer. VEDAS team even augmented their information system by adding our scatterometer data and global altimeter data to predict coastal wind and wave energy too. In essence, we built a complete suit of renewable energy assessment tools for anybody, that too at free of cost. In 2018, we have made a special version, applicable for whole of African continent and demonstrated it in the International Solar Alliance meeting in New Delhi.

Our scientists had all the data and science, one leading business group had resources and ideas of building renewable energy business but had a gap in requisite science, and the country had an urgent requirement of leap frogging in utilisation of renewable energy as a responsible nation, in preventing looming climate disaster. Together came Solar Calculator. It was an honour for ISRO, when our Honourable Prime Minister dedicated our Solar Calculator to the common good of mankind in the recent COP 26 meeting, held in Glasgow.

I have a personal satisfaction in playing a miniscule role in mobilising my fantastic colleagues from SAC to achieve this feat. Together we win.

Further ref:
https://vedas.sac.gov.in/en/

https://vedas.sac.gov.in/renewable-energy/index.html

Tapan Misra is a globally acclaimed distinguished scientist. He has headed the Space Application Centre and also served as Advisor in Department of Space. His contribution to India’s Space Programme is immense.

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