02 Aug 2018 19:51 IST

Hot or cold: compress, and store

The energy storage space is hotting up — rather, cooling down — thanks to an IIT-M professor’s design

Under Pressure

When you spot him walking down the tree-lined avenues of IIT-Madras you might take him to be a serious student trying to tap his cerebrum for more marks. Actually he is a professor, though you’d never guess unless you are told.

If things go well for Dr Satyanarayanan Seshadri, he could turn into a celebrity in the energy space. The scientist has a few patents under his belt and his design for a new machine could well earn him one more — and perhaps fatten his bank balance too.

Dr Seshadri — Satya to friends — has designed a system that can store energy. By the looks of it, his method is path-breaking. But, first, a little background.

Energy storage

There are many ways of storing electrical energy; the most common being the battery, or electro-chemical battery, to be precise. Here, as you all know, electrical energy is converted into, and stored as, chemical energy which can be de-stored and re-converted into electricity when needed. The problem is, a lot of energy is lost in the process, and storing large parcels of electricity in batteries is still quite expensive.

You can also store electrical energy by converting it into potential energy — by using electricity to pump water to a height and store it there. When needed, the water can be made to fall through pipes and turn turbines. When the turbines turn, a shaft that runs through them turns and, at the other end, a system of magnets and coils generates electricity.

As I have mentioned often in these columns, energy storage is ‘the next big thing’ in the industry; it is the stuff of a chunk of doctoral and industrial research.

Old, but new

One method of energy storage, which has been known for over half a century but discarded, perhaps because of its unwieldy nature and attendant problems, is a techniquecalled ‘compressed storage’.

In this, electricity is used to compress air and store it in containers. Then, when the electricity is needed, the compressed air is allowed to hit an array of turbines – and you are in business.

The problem is a simple law in physics — when the pressure goes up, so does the temperature. The same vice-versa is also true. This, as some of you may remember, is called Boyle’s law.

So, when you compress air, the high pressure causes it to become hot; very hot. As much as nearly 700° C. It would be great if one could use the heat right there, but if there was a use for energy at that point, you wouldn’t need ‘storage’ in the first place.

Also, when you let out the air, the pressure drop causes the temperature to fall so drastically that the outlet air is extremely cold — around minus 20° C; which is, again, pretty good if you can use the cold right then, but if you can’t then it is a headache to handle.

There is also the matter that you need ultra-large containers to store the compressed air.

Now, let us come back to Dr Seshadri.

Path-breaking design

This gentleman’s design has solved the problem of rising temperatures by using the ‘cold’ from the outlet to chill the inlet air. The air being compressed is thus very cold right from the start; so, when compressed, it merely heats up to room temperature. The beauty of this system is that it can be compact — the energy just keeps looping around.

This method can well open up a new area in energy storage. There are very, very few compressed air energy storage plants in the world. In fact, if you Google it, you will find just two — one in Alabama, in the US, and the other in Huntsdorf, in Germany. They are medium-sized power projects — 100-200 MW — but there is no system recorded that is compact enough to fit into the lawn or backyard of a factory. Dr Seshadri’s design can provide one.

This, therefore, has the potential to unlock a whole new area in storage science — compressed air energy storage. And, since all you basically need is a compressor, a container, and a turbine, the cost of the system is potentially very low, that is, when such systems are sold in large numbers the costs can be kept down.

Are we close to cracking the problem of energy storage with our own desi solution? Only time will tell; but there is a pretty good chance of it becoming a reality. If it does, it will be a booster shot to India’s renewable energy story because you can put up large capacities of wind and solar projects without having to worry about what to do with the energy if the electricity cannot be transmitted to consumption points.

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