Solar power over water, an interesting bet at Tata

Imagine a small film floating on water. Now imagine the power of the sun flowing through the film.

Tata Power has imagined, and gone beyond, to build India’s first floating solar plant at Walvan lake near Lonavala, where the company has a hydel power station.

The beta — or trial — project, announced in March this year, is small, aiming to generate just 13.5 kilowatt of electricity. But the results of the experiment are to be evaluated by December this year, and if they meet expectations, a significant scale-up to 400 mw is on the cards.

For Tata Power, direct access to around 24,000 acres of water surface area is what makes it interesting. Current calculus is, it takes six acres of water body to generate 1 mw of solar power. So, potentially, the company can generate as much as 4,000 mw — equivalent to a ultra-mega power plant — harnessing the Sun.

The concept comes from an Australian solar power company, Sunengy Pty. Tata Power has entered into a partnership that will allow it to build a pilot plant for Sunengy’s patented low-cost, floating-on-water liquid solar array technology in India by the end of this year.

The project is being supported by the Australian government, and Tata Power has pumped in Rs3 crore as its portion of the investment.

“The logic of the technology is quite simple,” says Avinash N Patkar, chief sustainability officer, Tata Power.

The most expensive part of a solar power panel is the silicon chip or the photovoltaic (PV) film. So, was there a way to reduce this cost by reducing the size of the PV itself?

To achieve that, the inventors used a lens to concentrate the same amount of energy into one-hundredth of the area of the PV film — and ran into a problem.

While conventional solar panels heat up to around 30-400 degrees centigrade, the concentrated rays heated it to over a 1, 000 degrees.

Therefore, cooling was an imperative.

Using conventional cooling techniques was too expensive so what the inventors did was simplicity itself. They put the bit of solar film on a small vessel — almost like a Coke can — and let it float on water. And Voila! the solar film got concentrated sunlight, but did not overheat.

The next trick was to maximise the retention of the sun’s energy for as many hours as possible. The inventors therefore put in a mechanism that would track the sun’s rays during the day, thereby ensuring at least 12 hours of energy is captured.

What all of this meant was a reduction in solar energy cost by 30-50%.

“Conventionally, the price of solar power is around Rs15 per kilowatt hour (though some have already brought this down to Rs13). The new technology could help us bring the cost down to Rs8, if not less,” Patkar said.

Moreover, floating the solar array on water meant no need for expensive supporting structures to protect the panels from high winds. The lenses submerge in bad weather and the water also cools the cells, which increases their efficiency and lifespan.

What makes the project more interesting for Tata Power managers are three more added benefits.

First, most of the places where they have access to water surfaces already have power evacuation facilities — the cables and equipment to trasnsmit the power generated to the grid. So no additional infrastructure is required.

And since power can be evacuated as soon as it is generated, there’s no need for investment in storage systems.

Secondly, unlike conventional solar power panels (except the rooftop ones), no additional land will be required. All the film will be laid on water surfaces. So no issues of displacement of people, resettlement of local inhabitants etc.

The third benefit is that the film covering the water will prevent excessive evaporation, thereby conserving water as well.

Sounds too good? If large-scale viability is established, a solar revolution could be at hand.