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Seawater pumped hydro storage

Inspiration from Okinawa, Japan


The pumped-storage hydro system on the northern coast of Okinawa Island, Japan, is the the world's first pumped-storage facility to use seawater for storing energy. The power station was a pure pumped-storage facility, using the Philippine sea as its lower reservoir, with an effective drop of 136 meters, and maximum flow of 26 m³/s (shown in figure 1). Its pipelines and pump turbine were installed underground. Its maximum output was approximately 2.1% of the maximum power demand in the Okinawa Island recorded on August 3, 2009. The upper reservoir, artificially excavated, was approximately 600 meters away from the shoreline and approximately 150 meters above sea level. It had an octagonal planar shape with a maximum width of 252 meters. Its maximum depth was 25 meters and its effective storage capacity was 564,000 cubic meters. The entire inner surface of the reservoir was covered with an impermeable liner to prevent seawater from leaking and damaging the surrounding vegetation[1].

How Pumped hydro works ?

Seawater pumped-storage hydro works similarly to traditional systems. The surplus electricity from fossil fuel, nuclear, or renewable energy power plants is used during periods of low energy demand to pump water uphill to be stored in reservoirs as potential energy. Then, when demand peaks the reservoirs are opened, allowing water to pass through hydroelectric turbines to generate the electricity needed to meet power demand. The main difference for seawater pumped-storage is that instead of having a lake, river, or some other source of fresh water serve as the lower reservoir, this systems pump salt water uphill from the sea to a land reservoir above. A typical layout is shown in figure2 [2]. This lowers the system’s freshwater footprint and greatly expands the potential for pumped-storage hydro worldwide because seawater pumped-storage is much less site-specific than traditional systems[3].


Pumped Hydro Storage at Cumbrae 


At Cumbrae, there is a reservoir near the golf course which we are recommending to use for the pumped hydro scheme (shown in figure 2). This reservoir is not a drinking water storage (the island has a water connection from the mainland), and hence, we consider this can be utilised as energy storage. It is currently using for fishing, and watering the adjacent golf area.

The features that we are identified for this storage are given below:
• Size of approximately 175x175 square meters (Measured by          google earth pro)
• Depth is roughly estimated around 5 - 10 meters. 
• The capacity of the reservoir is 153,125 cubic meters. 
• The altitude of the location is around 50 meters.
   Thus, the head drop is considered as 45 meters since the              depth of the reservoir in our models is assumed as 5 meters. 
• The distance from the reservoirs to the sea is approximately

Therefore, this location is considered for the suitable area for pumped hydro since it is an existed reservoir, and hence, we assume some of the constructional cost can be saved. Also, the location is far away from the community, and hence, the disturbance to the people during construction and its operation can be eliminated. So, we assume this reservoir can be converted for energy storage without major issues provided that there is no seawater contamination.

Some of the major advantages[4] with pumped hydro schemes are :
• Compared with other storage technologies like flow battery or lithium-ion battery the      pumped hydro has lower capital cost and higher storage capacity.
• Pumped hydro schemes have a longer lifetime as it has no cycle limitations.
• By implementing suitable approaches, a good chance for revenue from the tourism.
• Enhance energy security by reducing the dependency on the grid.                                       • It stores renewable electricity for a longer period at the Cumbrae.
• Reduced environmental Emissions to the atmosphere.


  1. Fujihara, T., Imano,H. and Oshima, K. (1998), Development of Pump Turbine for Seawater Pumped Storage Power Plant, Hitachi Review[online], 47(5), 199-202. Availabe from:[Accessed 03 Mar 2018]
  2. Tom Kenning. (2017), Energy Australia ponders world’s largest seawater pumped hydro energy storage plant, Energy Storage news[online]. Availabe from: [Accessed 10 Mar 2018].
  3. McLean, E. (2013), An Evaluation of Seawater Pumped Hydro Storage for Regulating the Export of Renewable Energy to the grid, Dublin Institute of Technology [online], Availabe from: [Accessed 08 Mar 2018]
  4. DNV GL. (2016), The Benefits of Pumped Storage Hydro to the UK [online], Availabe from: [Accessed 20 Mar 2018]


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