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Hydro accumulation power plant

The question of how to store energy has been challenging power engineering specialists for a long time and there have been different solutions to this problem. One of the most effective of these solutions is to use water in a method where at times when there is lots of electricity available water is being pumped somewhere high and then, if there is a shortage of electricity, that water will be streamed down again through a turbine where it generates electricity.

The most popular method in hydropower engineering is to create an obstacle for the flowing water and then to release the accumulated water from behind the dam when there is a need for electricity. Bu this method requires very large areas of land to be flooded, which is extremely detrimental to the environment. It is better to use a lake or large reservoir at the top of a mountain where water will be pumped to and where the same pumps can then later act as turbines. As there are no mountains in Estonia, it is not possible to use such a solution.

That is why we are planning to build a hydro accumulation power plant in Estonia, where an underground mine will be used to create a difference in height. The sea will act as the upper reservoir and the lower reservoir will be built at a depth of 500 m. This solution means that only a substation will be built above ground, the water intake and all the technical equipment—the turbine hall, water channels, shafts and the water reservoir itself—will be built under ground.

A short overview of the hydro accumulation power plant project:

• A hydro accumulation power plant—the most effective solution for power balancing and energy security

• Planned power output 500 MW

• Estimated investment 304 MEUR: 608,000 EUR per MW

• Planned operating time at max power output 12 hours

Operating principle

In the underground reservoir of the hydro accumulation power plant, seawater will be moved up and down—when there is a lot of electricity available, water will be pumped into the upper reservoir and when there is a shortage of electricity the water will flow down from the upper reservoir. Such a solution has many advantages—the plant is not visible and there is no need for a water reservoir where there is a danger of drowning accidents or that would interfere with the environment—as the whole mechanism is under ground. This also makes the whole reservoir pollution proof because accidental pollution or terrorism-related activities simply do not reach under the ground. The third advantage of such a power plant is that it does not use valuable freshwater as only seawater will be pumped up and down. From a power engineering standpoint a hydro accumulation power plant is unique because it can operate as a regulating power plant, as a peaking power plant or as an emergency power plant simultaneously.

A hydro accumulation power plant guarantees the reliability of the electricity system with the help of the following functions:

• Emergency reserve. An unavoidable necessity from the standpoint of the electricity system.

• Upwards and downwards regulation: production and consumption of balancing energy. Balancing for wind parks. Covering consumption peaks and filling consumption valleys of the electricity system.

The effects of the hydro accumulation power plant on the economy:

• Lower electricity prices. Peaks are smaller and cheaper. Balancing energy is cheaper.

• Improving the balance in foreign trading. No need to buy emergency reserves or balancing energy from Latvia. Granite export instead if import.

• Resource tax and other taxes for the state.

• Allows Estonia to meet its renewable energy commitments.

• Balancing function for wind turbines.