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24 October 2019

India preps Indira Sagar Dam for 1 GW floating solar

You may have seen the odd story this week involving floating solar – it is like a giant that has woken up, and it is rubbing its eyes, sitting up and making itself noticed.

The one we are thinking about is on the Indira Sagar Dam in India, where a dam that initially only gave 1 GW of peak energy capacity will now have 1 GW of solar placed on the surface of its reservoir – doubling the amount of energy that can go on the grid.

Of course this is not what will happen, it is all so much less predictable than that – dams sometimes dry out, or lower and produce less than 50% of their peak capacity, and solar does the same, producing intermittent energy when the clouds come out. However being that this dam is at 22 degrees North, so inside the tropics, there is a very good chance that it would outproduce the dam – but whether it does or not, it not the entire benefit.

Most dams are expected to offer baseload capacity at key times of the day and year, and solar is rarely associated with baseload, unless it has a storage element. Obviously if the dam is thought of as hydro generation AND a way of storing solar power, the combination of these two sources can be highly complementary. Use up the solar during the day, supported with as little hydro capacity as required to keep the output flat, and keeping your water levels high, and then switch the entire output to hydro during the evening and night. And repeat.

This is effectively one of the best ways of making solar a baseload supply, and actually the level of the baseload on each dam can be lifted by the solar considerably. Over the coming weeks Rethink Energy will give its take on a forecast for floating solar and once again it is no good looking at the pipeline out there. These projects have a way of springing to life rapidly, going through a trial phase and coming online in short order.

Most floating solar to date, the 1.1 GW that is already out there, have been created separately from any energy coming from the dam. This is not what will happen in the future. In China at the Longyangxia Dam built in 1992, has a further 850 MW of solar added to it in 2013. They key to making them work together was that the dam’s turbines could be turned up or down rapidly in a response time of a few seconds. That way, when you add local weather forecasting to tell you what is about to happen to the 850 MW of solar, you can increase the hydro output to compensate. This is the first of this type of installation anywhere in the world.

Given that China is desperately hungry for electricity, and is has 22,000 dams, the great majority of which were built in the last 25 years, this becomes one of the easiest and cheapest ways to add generation capacity. However this Chinese solar installation did not go on the reservoir, because around it were just mountains and rock, and so the land was incredibly cheap. This will not be true everywhere.

The first effect is around a 10% decrease in evaporation on the reservoir is eliminated, immediately creating a surplus of hydro-electricity, moving its turbine output closer to its real capacity for longer. Secondly, and this is especially true inside the tropics, the solar has another 7% or 8% output added to it by the cooling effect of the water. Thirdly they can both share the same transmission line, which already comes from the dam and send electricity to a part of the grid nearer to civilization. So no transmission costs.

There are other side benefits, like the shade preventing as much algae growing the water, fouling up the turbines. All of which makes this a very low risk approach to augmenting dams.

So it comes as no surprise that India is trying the same trick. We note that India has 50 GW of hydro, and that the Indira Sagar Dam is one of the larger dams in India, and relatively new (2005), so is likely to have sufficiently responsive turbines.

The Times of India came across the story and quoted the state’s renewable energy minister. It cites the World bank as being at the heart of the matter, currently preparing feasibility reports. The world bank recently sponsored a report into floating solar, and this is where that 1.1 GW of existing installations comes from. But given that in many cases across Africa and the South East Asia this is the bank that has set up finance for these dams, it makes perfect sense that it bundles a second, far smaller amount into supporting their extension into double their current size.

Currently the largest floating solar plant in the world is one in China of 150MW in Anhui, built on a collapsed mining site which has been flooded. There are multiple similar projects, especially those led by Sungrow, which plans to overtake this 1 GW marker in one of its next projects, on dam reservoir surfaces there. Meanwhile in South Korea there is a plan for 2.1 GW of floating solar in two phases on the Saemangeum Seawall, inside a 33 km long man-made dyke, between two headlands, separating the Yellow Sea and an estuary.

Surprisingly the development of the India 1 GW of solar would cost only $700 million, far less than the dam itself, and that’s after 20 years of inflation and so far, it says that it only has one offtaker, the Madhya Pradesh state in India which wants just 200 MW.

Like so much solar in India, whether this comes to fruition in short order is up for grabs. More likely it will happen, but in India things always seem to take longer than planned. But now the World Bank has this template, it could spend multiple tens of $ billions in this way, highly effectively over the coming decade.