How do we leverage the revolution in solar for India, for farmers, for households and even in cities?

I think it's important to acknowledge that India started with the Green Revolution in the mid 1960s, becoming food secure, which took several things. It took seeds. It took fertiliser, water, markets, minimum support price and public distribution system. But it also took power.

We extended grids, not just to the homes, but to each farm. When I work today in many countries in Sub Saharan Africa, farmers are desperate to have that. We accomplished that 30-40, years ago.

Now how do we steer this amazing achievement towards solar for lower cost power?

India is acknowledging that individual solar pumps for farmers may not always be the best for small-holders, but the good news is we have electricity distribution networks. So if you have a substation and a line running from there serving a few 100 farmers, called a feeder, if we put a much larger solar power system, not a few kilowatts, but 1000 kilowatts, at that feeder, then we can continue to utilise that solar and deliver it to the farm without the farmer having to maintain it.

There are many advantages to this. In May, when we discourage use of irrigation because evapotranspiration can be very high, air conditioning load for homes is high—solar power from these feeders can relieve the grid load at that time.

Give us an example of how this can work.

I've worked in both East and West Africa, but I want to give you an example from Senegal. Senegal was importing onions from Mauritania, and yet Senegal had perfect conditions to grow onions, but they needed irrigation and they did not have any grids like we did.

They had to leapfrog from hand-and-bucket lifted water straight to something new. If individual farmers size a solar system for the depth of the water they had, they would use that solar power maybe one hour a day and throw away four hours of sunshine. If they sized it for the energy that they needed, the solar energy panels would be so small it would not have enough power to lift the water. We worked with the farmers. They were completely willing to create a cooperative. They already were buying fertiliser or seed as a group. Banks in Senegal liked that too—organised farmers are seen as a lower risk. So the bank was willing to give them a loan.

Smart Metering is expensive, so they said we'll allocate by hours. So if this farmer gets two hours, they pay so much. No battery storage was needed at all, and it had a high level of solar power utilisation. They used it to eventually get three crops of onion in a year. This work was done by Columbia University and my laboratory, the Quadracci Sustainable Engineering Lab.

Are most innovations in cooling technology geared towards urban spaces only? What changes in this field do you foresee?

India, in the tropics, will need cooling. We are already seeing temperatures in the high 40 degrees Celsius that are lasting not just a day or two, but could be two weeks in a row. Everybody, not just those in commercial buildings or high-end residential buildings, but everybody will need cooling.

One thing is, it has to be we have to ensure that our distribution networks of our discoms can actually handle that load. Secondly, we want to do it in a way that we leverage the low cost of solar. And thirdly, we need to do it in a way that the consumer is able to make that transition.

Not just India, but in other places too, most rural households were primarily using electricity for either lighting, television, radio, entertainment, cell phone charging and so on. These are what I call small electronics loads, not high loads.

But a bucket of new loads is emerging, which are not low loads. Cooling is one. So if all these other loads need a tenth of a kilowatt, cooling needs kilowatts.

So we need to go from a 10th of a kilowatt economy to a kilowatt level system for every home, rural or not.

We need to worry about how to think of maintaining, upgrading transformers and creating the right system for discoms to be financially whole so that they can make the investments that are needed in capital to upgrade the system. The good news is that all these loads will also produce the demand for electricity which can pay for that. So we need to square that circle. There is going to be higher demand.

What is a cooling technology innovation that you are excited about?

We have worked on this technology – if you have a cluster of homes or a small, a three-storey building with 10 or 15 flats, which are beginning to appear in peri urban and second tier towns, even in some villages, you could use the daytime solar power to produce ice in the overhead tanks called Sintex tanks.

They are about a couple of meters in diameter, and two or three meters in height. It's a plastic tank which can be adapted to produce ice in the daytime.

That tank stores ice in the daytime using the sun as the source of power, and then that ice can distribute an air conditioning system using cold water, called a hydronic system.

You don't have to block your window with an AC unit; it can be used in small living spaces where you may not have enough window space; you may not have access to an individual compressor for a split unit; and you can provide cooling as a service. Those not using air conditioning can dial it back, somebody else may use more of it.

And we have the ecosystem in India to manufacture the valves and plumbing systems for it, so it's very much possible to make locally.