Pumped hydro resurfaces when sun doesn’t shine and wind doesn’t blow

When the sun doesn’t shine and the wind doesn’t blow, grid-scale energy storage will be a big challenge as climate neutrality increasingly presses for a massive scale-up. Pumped hydro is back and can catapult India into the big league to make up for the lost opportunities. Not just that, as we are seeing during the current power challenge, excessive renewable generation during the day needs a storage medium to be used when it is needed later.

Signing a joint declaration of Intent on Indo-German Hydrogen Task Force virtually on May 2, Union Minister for Power and New and Renewable Energy R.K Singh called upon German Minister for Economic Affairs and Climate Change Dr. Robert Habeck to help develop storage for balancing RE such as Pumped Hydro and battery storage.

In India, PSH potential of about 120GW has been identified at about 120 sites. Yet, some of these sites could be taken up only after obtaining land, forest and environmental clearances. Only nine plants with an installed capacity of 4,785MW have been commissioned so far, and three with a capacity of 2.7GW are under construction. Out of the nine PSH plants commissioned, three of 1,480MW capacity are yet to be operated in pumping mode, for various reasons. About 17 PSH projects with a capacity of 16.5GW in different states are under various stages of implementation (which include pre-feasibility studies, detailed surveys, investigations and project reports, and clearances).

PHES is the world’s largest energy storage system, representing 96% of the installed storage capacity worldwide (176 GW).

Pumped Storage as a percentage of wind and solar capacity is high in countries like China (11%), United States (17%), Japan (55%), Spain (26%), Italy (24%) and France (27%). Pumped storage hydro plants serve the grid in wide range of applications and represent a valuable source of flexibility.

The advantages are:

– PHES can meet the highest demands in a short period of time with very high ramp rate, to the tune of 200 MW/min.

– PHES can play a crucial role in load balancing or load leveling, that is, storing power during period of light loading (off peak hours) in the power system, and utilizing the same when required during periods of high demand.

– PHES can provide excellent frequency regulation to maintain the frequency within the given band.

– PHES can also be used to provide back-up reserve, spinning reserve, with its high ramping rate and can be operated in case of sudden outage or failure of any load in the grid. It also provides quick start capability as it can be set up in just a few minutes, much less than other sources. In comparison to this, gas turbines take 30 min to 1 hour, and thermal steam generation few hours, for full ramping.

– PHES can provide black start capability, which means, if the upper reservoir of PHES is full and ready for generation, it can be used for energizing the grid in case of cascade tripping.

– PHES can also provide voltage control services by rendering reactive power balancing services.

Business Model: Assuming that a PHES with 75% overall efficiency pumps for 8 hours a day, it can generate for around a 6-hour period. In such a situation, the negative energy component is neutralized as long as the price for the 6 hours [peak hrs.] is more than 1.33 (8/6) times the pumping [off-peak] price. Hence, the entire operational financial viability of PHES depends on the differential between peak and off-peak period. Going forward, if we envisage a large difference between peak and off-peak period rates, then in addition to addressing the issue of negative energy factor, there may be some component from the differential in peak and off-peak rates towards the capacity charges as well.

Highly useful options for the integration of RE power with the power system, Pumped storage hydro (PSH) plants are storage systems based on hydropower operations between two or more reservoirs (upper and lower) with an elevation difference. At the time of demand, downward water flow generates electricity with a hydraulic turbine, and water is pumped back to the upper reservoir using power from grid or RE sources, with an overall efficiency of 75-80%.

Currently, some of the biggest PHES plans have been made by the Greenko Group, with a 6 GWh roadmap,  across Andhra Pradesh, Madhya Pradesh, Karnataka and Rajasthan by 2025.