Hydel power is simple: build a dam across a river, store the water in a reservoir, run it through a turbine-generator and produce electricity.
How about another hydel?
No river, no dam, pump-cum-generator, and two connected reservoirs – one up, the other down. Feed in 100 units of electricity, get back 70.
‘How stupid! What a waste!’ you may be thinking.
Wasteful – maybe.
But stupid? No.
Since this is about electricity, let us take a quick look at the power scene in India.
India has an installed generation capacity of 416GW (gigawatts), consisting mainly of thermal - 237GW (57%), hydroelectric - 47GW (11%), and renewables (solar & wind) – 110GW (26%).
These power plants feed electricity into the national grid which distributes it throughout the country.
The government, and indeed all of us, would like to see the power generation pattern shift from thermal to renewables for two reasons:
- Renewables eliminate carbon emissions, without hydel’s environmental issues arising from big dams, and huge reservoirs.
- Renewables are cheaper. Solar or wind costs around Rs2.30 per unit, while thermal costs almost Rs4 a unit.
There is a problem, though.
Renewables don’t provide a steady supply of power. The sun does not shine at night and, though the wind blows 24x7, it is not always steady.
Power from renewables does not match power demand. Around noon, solar power generation is at its peak but demand is low;, after dusk, electricity demand shoots up, but there is no solar power.
To an extent, this imbalance can be managed by tweaking the output of the other plants in the system. Thermal plants can run on high output in the evening and reduced output around mid-day.
But, if the proportion of renewables in the total mix of power plants exceeds about 25%, problems start arising. A lot of backup thermal power capacity is needed to meet evening demand and it remains partly idle in the daytime. Thermal plants become less efficient and more costly if they are run like this.
India has crossed 25%, power demand is rising and we would like to have a higher ratio of ‘clean’ renewables to ‘dirty’ thermal.
To make this workable, we need a device that will store electricity when it is not needed and release it when required.
It will take a monster-sized battery, or a forest of batteries, to store electricity in GW quantities. Besides, batteries require expensive material such as lithium which has its own environmental baggage.
Enter the ‘wasteful and stupid’ other hydel—pumped storage hydro (PSH)—which is actually a gigantic battery.
This picture shows how it works.
When renewables are running at full blast on a sunny and windy day, the turbine in the middle works as a pump, taking in surplus electricity to pump water from the lower (right-hand) reservoir and lift it to the upper (left-hand) reservoir. Later, when renewable output slackens off while power demand rises, water flows down the pipe through the turbine, which becomes a generator, producing electricity.
The water simply goes up the hill and comes down again, like the 10,000 men of the grand old duke of York.
Of course, some energy (20%-30%) is lost in the process because of friction in the pipes and losses in the machinery.
Nevertheless, even after this wastage, the power generated by the system carries a direct cost of around Rs3.3 per unit (2.3/0.7). The fixed cost component will vary greatly over different locations, but let us add 33% more towards fixed cost recovery. This brings the total cost to Rs4.4 a unit, comparable to the cost of thermal power.
There are other pluses, too;
- Low environmental impact because:
a.) no big dam, only an embankment or a small dam;
b.) no huge reservoir, only two small ones—measured in hectares, not sqkm (square km); and
c.) no water loss, except through evaporation.
- Quick response (within one minute) to increase/ decrease in power demand.
- Long life, negligible running cost and low maintenance cost.
The key benefit—having a sizeable PSH capacity permits the usage of a higher proportion of renewables, because the PSH balances out the fluctuations in renewable energy production.
A study of global PSH potential, published by Australian National University, states that there are enough potential sites worldwide for building 100 times the PSH storage capacity needed to power the entire world on renewable energy alone.
In India, there are lots of potential sites—north-east region, Himalayan foothills and the Western ghats – to build many times the PSH storage that we will need for 100% renewable power.
Is this all a dream? And, what are we doing about it?
No, PSH is not a dream. It has been around since 1909. Right now, there is over 110GW of PSH storage capacity worldwide. China leads with 46GW, followed by Japan (22GW) and US (19GW).
Where is India? A poor 5th place with 4.8GW.
But we are moving forward.
Some 109 PSH sites, with a total potential of 119GW, have been identified for development. The target for 2030 is 39 sites totaling 47GW of PSH, in tandem with the target of 500GW for renewables.
Work has started on several projects, such as the one being built at Pinnapuram in Andhra Pradesh, a combo system with 1GW solar + 550MW wind + 1.2GW PSH, total cost being US$3bn (billion). This site will eventually expand to 3GW solar, 2GW wind and 2.4GW PSH.
Mind—there are hurdles to be crossed, too.
One such is the power transmission system. Ours is a huge country, stretching about 3,000km north to south and east to west. If solar power is generated in the Thar desert, stored in PSH sites in the north-east, and used to power Maharashtra in the evening, lots of electricity will have to be moved over very large distances.
The regional transmission capacity of the Indian power grid is about 112GW. Renewable power plants and PSH sites cannot just be built wherever it is most convenient, without paying heed to the distance factor. The power grid has to balance supply and demand country-wide, over different seasons and varying weather, and move electricity all over the country, in an environment of ever-increasing demand... whew —that is some job!
Obviously, we have a long way to go, but there are enablers. We have the technology, engineering capability, available sites, money and above all—the will to do it. The eventual goal of ‘Net Zero’ carbon emissions is reachable.
Unfortunately, though, not in my lifetime!
(Deserting engineering after a year in a factory, Amitabha Banerjee did an MBA in the US and returned to India. Choosing work-to-live over live-to-work, he joined banking and worked for various banks in India and the Middle East. Post-retirement, he returned to his hometown Kolkata and is now spending his golden years travelling the world, playing bridge, befriending Netflix & Prime Video and writing in his wife’s travel blog.)