When I was growing up, Renewable Energy was developing at a steady pace. Conventional sources of energy were not a huge problem. But my young mind was already thinking ahead: “What happens when you run out of fuel?” My mother said, “There is the sun and the wind.” That was the spark. I made it my objective to figure out the best way to provide renewable energy.

On one front, wind energy is making rapid progress. Wind turbines have been set-up all around the world in on and off-shore wind farms. They are a useful source of energy, one that has helped reduce the use of conventional coal fired energy. But the question does persist: what to do when there is no wind?

On the other front, Solar energy is moving at a steady pace. Cost per KWh of electricity was reducing rapidly. I believe, as of today, the cost is equivalent or cheaper than producing electricity using coal. As we start to increase our reliance on solar energy, a major fault in harvesting solar energy shows up: What to do at night?

These problems have sparked research into one of the most important aspect of using renewable energy. One solution is to rely on the conventional sources for power supply on non-windy days, or at night. Is that a permanent solution though? I don’t think so.

Another solution is use an array of batteries to store energy when it is not being utilized. This solution seems to be going in the right direction. Tesla’s Powerwall has met with great success. Their flagship deployment in Australia epitomizes the fact.

While Tesla is doing wonders with the Powerwall, a small problem still persists: the batteries can’t be used to a great extent. As Engineering.com pointed out, even if the battery is used in an ideal manner, capacity degradation becomes a big factor.

Completely draining the battery every day shortens its life. A battery under those conditions would lose about 30% of its initial capacity after 500 charge-discharge cycles - not even two years of daily use. (Good thing there’s a ten-year warranty!) At a friendlier 80% depth of discharge, a Li-ion battery will survive about 1900 cycles (about five years) before losing a significant amount of its capacity.

This makes batteries a less attractive option to potential buyers.

The solution needed should have the following characteristics:

  • Large storage capacity:

By large storage capacity, I mean that the storage device should be able to power homes for at least a couple of days. This is important during winters when sunlight is limited.

  • Economically viable:

Far too often the idea of solar energy is disregarded for the simple reason that it is not investor friendly. The payback period for setting up solar energy systems is currently at 15 years. Investors who want to invest in solar are spooked by this number. The ideal storage system should be economically viable, i.e. it should start repaying it’s investor in 1-3 years.

  • Size and Lifetime:

The lifetime of a storage system needs to be enough for it to be useful in a long run. Tesla’s Powerwall, for example, has a warranty of 10-years. The ideal system has to match these numbers or better yet, outperform them.

Size is another important factor when it comes to installing these units in residential properties. Storage units that too large and too bulky are not well-received by residential buyers. So the ideal system has to be compact and yet perform as expected.

While in the short run batteries are the way to go ahead, for the long run, a new energy storage system is required.

I personally believe that the Thermal Energy Storage (TES) System is solution for the future. Thermal Energy Storage (TES) systems store energy by absorbing heat in the form of sensible heat or latent heat, and releases it when required. These systems are currently in development phase for residential applications. Large scale designs are currently used in countries like Sweden, United States of America, Japan, etc.

TES systems have the ability to store a large amount of energy. For example, for every kilogram of water that evaporates at 100°C (212°F), it absorbs 2.23MJ of energy. This property is not limited to water. Many materials exhibit this property, and can be used as an absorbing medium in a TES system. Thus, the system can be compact, while having a very large capacity.

Economic viability has remained a concern for TES, as small systems, suitable for residential use are very expensive. Research is being conducted to reduce the cost of these systems and make them commercially viable.

While the TES has its shortcomings, it seems to be the solution of the future, one which will make residential houses independent from the national grid. I hope to see a day when every household has a TES system installed to meet their energy needs.