ESB Raheenleagh Wind Farm

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Upper Reservoir
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Lough Nahanagan

Water held in the Upper Reservoir is an example of stored potential energy (similar to how a battery is an example of stored electrical energy).

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Pumped Storage Physics

It is important to understand that energy can be neither created or destroyed. It can only be converted from one form of energy to another. The conservation of energy is one of the pillars around which physics is built.

Potential Energy
This is the energy an object (or body of fluid) has due to its position. In the case of Turlough Hill, the water resting in the Upper Reservoir is positioned high above the Turbine so there is the "potential" to transfer energy from this raised elevation down to the Turbine which is 549 metres further down the mountain.

Kinetic Energy
This is the energy that something has due to its motion. In this case as the water travels down the Pressure Shaft its potential energy is converted into kinetic energy as it accelerates whilst falling.

Mechanical Energy
The sum of energy due to an object's position (potential) plus the energy due to its motion (kinetic) is known collectively as mechanical energy. The sum must at all times be a constant for the conservation of energy to be maintained.
Energy Cycles

Generation Cycle (Daytime)
During periods of high daytime demand, water is released down through a Pressure Shaft which converts potential (height based) energy into kinetic (motion based) energy. The rushing water drives a Turbine providing mechanical energy to the rotor, which in turn is converted to electrical energy by the Stator. The electricity is then distributed to the National Grid.

Pumping Cycle (Night-time)
At night, there is spare low cost electricity in the system that is used to drive the motor in Turlough Hill. This rotating motor turns the blades on the Pump Turbine and pumps water from the lower Lough Nahanagan back to the Upper Reservoir in readiness for the next generation cycle.