Clean Tech

Turn up the temp!

M. Ramesh | Updated on: Mar 12, 2019

It’s time to tap the potential of ‘solar drying’ — using the sun’s heat instead of light

Smartness lies in grabbing the low hanging fruits. In the context of solar energy, the low hanging fruit is all about using the sun’s heat for drying. Ask Chidambaram Palaniappan, who has been in the field for over three decades and whose company, Sun Best, has about 275 installations to its credit.

It is well acknowledged that using the sun’s heat, rather than light, gives more bang for the buck, because ‘solar heat’ converts more of what the sun bestows into useful energy. Solar PV, which produces electricity, scoops about 17 per cent of solar energy for human use but solar thermal systems can grab more than 60 per cent. Yet, solar heat has been a laggard because of the relative challenges in dispatching heat over long distances, according to experts.

Dry it in a jiffy

Large solar heating installations involve big parabolic dishes and mirrors to produce tonnes of steam — and they are good. However, the lower hanging fruits are situations where solar heating systems can be used to just produce a blast of hot air that you can pipe into your factory, to dry anything — wet paint, fish, pulses, tea, spices. These systems can be as ‘dumb’ as a black-painted metal plate placed between two layers of glass sheets or relatively more sophisticated glass vacuum tubes coated on the insides by a special paint.

With the upper versions, it is possible to get to temperatures as high as 150 degrees Celsius, says Dr Palaniappan, an academic-turned-small scale industrialist, whose doctoral work was in solar drying.

While 150 degrees could be the achievable peaks, steady-state temperatures of 120 degrees are easily possible. Until recently, solar could give air temperatures of around 85 degrees, and the hot air would be used to pre-heat with solar, before heated further with fossil fuels. But with higher temperatures possible today, solar air heaters could completely elbow out diesel-fired systems.

It is not that solar drying is entirely new. Large companies such as Hatsun Agro, Tube Investments, TTK Prestige and KLF Nirmal figure among Sun Best’s customers. But the adoption is still low although there are hundreds of thousands of situations where solar air heating systems can be used. Just look at one industry segment — mills that process paddy and lentils to make them ready for kitchen use. “There are thousands of them,” says Palaniappan.

The saving potential is big. He cites the case of the Theni-based pulses processor, AMR Kumar Mill, which set up a drying system at a cost of ₹22 lakh — the annual saving in terms of diesel avoidance works out to ₹14 lakh.

The message is simple: take up ‘solar drying’, a subset of solar heating, for special focus.

A few years back, some officials in the Ministry of New and Renewable Energy mooted the idea of setting up a ‘Centre for Solar Drying’ but it never took off. It is time to resurrect the idea.

Published on March 12, 2019

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