While industry consumes energy mostly in the form of electricity — thankfully so, because electricity is the easiest to green — factories and businesses also use a lot of heat. Most of this heat is low-grade, 120–150 degrees Celsius. According to one estimate, Indian industry annually consumes low-grade heat equivalent to 3,737 kilo tonnes of oil, valued at ₹18,400 crore. 

Many factories need heat, either in the form of hot water or steam. The usual way of obtaining it is to heat water using diesel, LPG or biomass — which is messy and greenhouse gas emitting.

A simpler method would be to use electricity to heat water. If the electricity is from renewable sources, it is green too. However, this method is expensive. 

It need not be, say scientists. Plenty of work is on in Indian laboratories on ways to switch over to green sources of heat and bring down costs. Here are two such technologies. 

Flowers of carbon

Capturing the sun’s heat (as opposed to grabbing its light for producing electricity) has been toyed with for a long time, but with limited success. Actually, it is a no-brainer. You just place two glass plates, say, an inch apart from each other, under the sun and the layer of air in the gap becomes heated. Paint the glass black and the air turns even hotter, because black absorbs more sun. Rooftop solar water heaters work pretty much like this.

Yet, they are not in a raging demand. Why? Because the heat you get is not much — about 80-85 degrees C, which is okay for drying mango or fish.

But for major industrial applications you’d need much higher temperatures, namely, capture a lot more radiation from the sun, including the invisible infra-red.

Prof Subramaniam Chandramouli, Associate Professor, Department of Chemistry, IIT-Bombay, has figured out a way to do this.

He brought in ‘carbon nano florets’ to the game. These are man-made structures where carbon exists as thousands of tiny funnels bunched up like ice-cream in a cone or like marigold flowers.

Chandramouli created the florets much like castings, using silica to make the ‘moulds’ (templates) and forcing vapours of carbon into it. Once dried, it was easy to dissolve the silica to get the carbon nano florets. The florets are formed of feather-like graphitic sheets that converge at the centre and are held in place through a solid, connected core — like a marigold flower. 

Now, when sunlight falls on this material, it is trapped well and good — it will not be reflected back. A series of internal reflections will cause the sunlight to be directed to the bottom of the funnels, rather than out of it. The system is designed for a high absorption rate, 98 per cent, of the radiation, Chandramouli told Quantum. 

Chandramouli made a sort of paint with the carbon nano florets and coated it on a porcelain or copper surface. Under the sun, the device instantly heated up to 160 degrees Celsius.

Chandramouli’s prototype has been proven in the lab (‘technological readiness level 3’); the next step is to make a prototype that can work in field conditions.

This opens up a range of exciting possibilities, such as tents coated with the material to keep soldiers warm in chilly heights.

Chandramouli says the material is amenable for industrial production.

Because of the floret structure, a large surface area occupies a tiny space, like a crumpled sheet of paper. A gram of the material has the same surface area as four tennis courts, he says. As such, it doesn’t take much material to paint a substrate (like porcelain, copper). As for cost, when produced at industrial scale, it would be less than a few rupees for a square metre of nano carbon florets. 

Can this system be tweaked to produce even higher temperatures? For instance, if you could get 500 degrees Celsius, you could try to produce hydrogen by the thermochemical splitting of water. 

“Theoretically, yes,” says Chandramouli. One could get to higher temperatures by adding concentrators, but the cost and complexity would need further analysis. 

Pumping heat from the atmosphere

Another technology is cooking at the Energy and Emissions Lab of Prof Satyanarayanan Seshadri, Associate Professor, Department of Applied Mechanics, IIT-Madras. He has developed a ‘high-temperature heat pump’ that can deliver 2 kWhr of heat for every kWhr of electricity put in.

This may sound a little off-the-rocker, but it works because the system is designed to pick up ambient heat.

The machine, a prototype of which will soon be deployed at a Chennai-based auto components company, is a closed loop. One can take as the starting point the situation where a refrigerant (R134A) is compressed in a compressor, for which electricity is taken from the grid (or a solar PV system). 

When compressed the refrigerant becomes hot and the heat is picked up by water in a heat exchanger. The refrigerant liquid is less hot but still at a high pressure. A throttle valve de-pressurises it and you have the refrigerant, cold, in a mixture of liquid and gas on the other side of the valve. This mixture, being cooler than outside air, absorbs heat from the atmosphere. Then it goes back into the compressor, to start the cycle all over again. 

Now, this is how all heat pumps work and it’s nothing new. But Seshadri has tweaked the design to deliver much higher heat — about 120 degrees Celsius. Water in at 25 degrees, water or steam out at 120 degrees. The regular heat pumps can do 90 degrees, at best. He says that with electricity  at, say, ₹7 a kWhr, the machine can deliver steam at ₹3 a kg, at 1.2-1.4 bar pressure. Bring in solar PV interface to lower the cost of electricity, you can get steam at ₹2 a kg. 

As for the cost of the machine, since at the moment it is entirely hand-crafted, no costing is realistic. However, a start-up called Aspiration Energy, mentored by Seshadri, has been producing smaller-sized, conventional heat pumps for some years. Even without mass production, the cost of these machines have come down from ₹17,000 a kW a few years ago, to ₹12,000 a kW.

Seshadri’s research was funded by the Ucchatar Aavishkar Yojana (UAY) scheme of the government of India and the prototype was funded by UNIDO. The user company, which receives the machine free of cost, would validate its functioning and provide operational data, based on which commercial manufacture would be taken up by Aspiration Energy.