The Mezen Tidal Power Project site is located in the Gulf of Mezen on the East shore of the White Sea at the entrance to the Barents Sea, opposite the Kola Peninsula, as shown in Figure 2.
Figure 2: Location of Mezenskaya TPP
The Gulf of Mezen takes its name from the nearby town of Mezen and the river of the same name, which discharges into the White Sea at the south of the Gulf.
Mezen lies in the administrative district of Arkhangelsk and is some 1200 km north of Moscow and 1000 km NNE of St Petersburg.
Mezen has a regional airport. There is road access to Arkhangelsk (a distance of some 300km) and to Moscow. Arkhangelsk is connected by train to Moscow (20 hours) and St. Petersburg (25 hours).
Although the White Sea and Barents Sea freeze over in winter, access to the port of Arkhangelsk is maintained through winter by icebreakers.
The history of the Mezenskaya Tidal Power Project dates back over 75 years. In 1938 a survey of potential tidal sites was carried out around the White Sea and Kola Peninsula, and the Gulf of Mezen was identified as the best site available. It has the highest tidal range in the White Sea (up to 10 metres) and the size of the bay provides huge energy generation potential.
The 1938 proposal was for a small tidal scheme in the mouth of the MezenRiver estuary, with around 112 MW installed capacity. Over the years around ten other configurations have been considered, leading to the current layout developed in 1983.
The potential for tidal range generation at the site of Mezenskaya TPP has been covered by international literature for more than 30 years, and it has long been recognised as one of the best sites for tidal power in the world.
The technology proposed for Mezenskaya TPP has been under development for more than two decades. In 2006 a prototype orthogonal turbine was installed at the Kislogubskaya TPP, west of Murmansk, on the north shore of the Kola Peninsula. This turbine has been tested for several years to confirm its suitability for operation in similar conditions to Mezenskaya.
The tidal range at the MezenRiver estuary is reported to be up to 10 metres, and is the highest range in the White Sea. This exceptionally high tidal range is caused by the geometry of the region, and in particular by the narrowing of the White Sea south of the Gulf of Mezen, which restrict the tidal flow into the main part of the White Sea.
The geometry of the Gulf of Mezen and the high tidal range mean that this site is ranked among the best tidal resources in the world.
The Mezen scheme is a “tidal range” project where the difference in water level inside and outside the barrage is used to drive hydraulic turbines to generate electricity. Generation on both the ebb tide and flood tide is possible. In simplistic terms the process is as follows:
Ebb Tide Generation
The water in Mezen basin is impounded at high tide by closing all the sluice gates and turbine control gates. When the sea level outside the basin has fallen sufficiently to create enough head to drive the turbines, the turbine control gates are opened and generation commences. Generation takes place, drawing down the water level in the basin, while the tide level outside the basin also continues to fall. Generation continues until there is insufficient head between the impounded water in the basin and the sea level outside to drive the turbines; at this point the remaining water in the basin is released through sluice gates and the turbine openings. The water level inside the basin falls to low tide level, ready for reverse flow generation (flood tide generation) to commence.
Flood Tide Generation
The water level in Mezen basin is kept at low tide level by closing all the sluice gates and turbine control gates as the tide level outside the basin starts to rise. When the sea level outside the basin has risen sufficiently to create enough head to drive the turbines, the turbine control gates are opened and generation commences. Generation takes place, filling the basin while the tide level outside the basin also continues to rise. Generation continues until there is insufficient head between the sea level outside and the basin to drive the turbines; at this point the seawater is allowed to flow in through the sluice gates and the turbine openings. The water level inside the basin rises to high tide level, ready for ebb tide generation to commence.
The physical environment in the project area is challenging, being subjected to extreme cold in winter. The climate is classified as sub-arctic, with the average temperature below freezing for five months of the year. Extreme winter temperatures can reach as low as 45oC, while in summer temperatures in excess of 30oC can occur.
Water temperatures remain low throughout the year, with thick sea ice forming from November to May. Ice thickness of six metres or more is reported in winter, although below the ice the water temperature remains above freezing.
The physical environment will prove challenging for the design, construction and operation of the powerhouse structures and transmission equipment. However there is good experience in Russia for such equipment, including at the test facility at the Kislogubskaya TPP.
The main feature of the Mezenskaya TPP is a 75 km long barrage across the Gulf of Mezen comprising of a 20 km long powerhouse section, shipping locks, and 55km embankment section.
The powerhouse section will comprise two hundred reinforced concrete pontoons, each housing ten 3-tiered orthogonal turbine units of 4 MW capacity each. The pontoons will be constructed under controlled conditions in dry docks, and will be floated into position and ballasted with sand to found them on the sea bed. The combined length of the powerhouse pontoons will be around 20 km.
Locks will be provided to enable ships to continue to pass through the barrage on their journey to and from the ports on the MezenRiver.
The remaining length 55 km of the barrage will be constructed from rockfill deposited by bottom dumping from barges and building out from the shore.
An innovative feature of the Mezenskaya TPP is the use of multi-tiered orthogonal turbines. Three orthogonal turbines with five metre diameter runners are located on a common vertical shaft, and drive a single asynchronous generator through a gearbox.
These turbines have been developed in Russia specifically for tidal range projects. A prototype of this turbine has been undergoing successful testing at Kislogubskaya TPP since 2006 under conditions very similar to those of Mezenskaya TPP.
This turbine arrangement has a number of specific advantages which make it particularly suitable for use in tidal range projects;
- The turbine is able to operate at very low heads. Traditional tidal energy turbines require a minimum head of around two metres. This requires a delay until the tide has fallen at least two metres before the turbines can start generating, and generation must stop when the basin water level is two metres above low tide. Hence there is only a short period available for generation, and a high installed capacity is required to command the available water in this short time. Also large gates are required to discharge the final two metres of water which cannot be used for generation, so that the basin reaches low tide level before flood-tide generation can start. As a consequence a much higher load factor can be achieved (55% or more), and generation takes place some 65%-70% of the time, compared with 40% to 45% of the time achieved by traditional turbines.
- The slow speed of rotation and the large clearances between the turbine and the casing mean there is much less harm caused to fish and other marine life compared with traditional tidal turbines.
- Because generation takes place over a much longer period than with traditional turbines, the tidal pattern more closely replicates natural tidal conditions, with less disturbance to the shoreline ecology.
The orthogonal turbines have a lower peak efficiency than traditional propeller turbines (Bulb and Kaplan units), but efficiencies of up to 70% have been achieved at the Kislogubskaya TPP test facility.
Simulation of the energy yield undertaken by the scientist working under RUSCOLD indicates that annual energy production from Mezenskaya TPP will be around 38.9 TWh per annum. The timing of this energy production will vary each day, depending on the time of the tides, but on average generation will take place for around 16 hours per day.
Although the orthogonal turbines tend to operate at lower average head than traditional turbines, the fact that they can generate at lower minimum heads means that energy can be produced at times when it would not be possible with traditional turbines. Hence greater energy yields are possible, especially when the tidal range is small (at neap tides).
The energy from tidal projects is available with a very high degree of reliability and predictability, since the timing of the tide is known with great accuracy, and tidal levels are predictable.
It is likely that the changing nature of the European Grid, with Smart Grid control and the ability to vary the timing of charging electric vehicles, means that the variable timing of tidal generation can easily be absorbed into the power system. However, if continuous generation is required, pumped storage including sites near St. Petersburg and near Murmansk can be used to regulate the daily generation variation.
The cost estimation for the Mezenskaya TPP will need to be confirmed at the feasibility study stage.
Tidal power schemes using traditional technology typically cost in the range €3 to €4 million per MW of capacity. However the cost of tidal schemes with orthogonal turbines is much lower than for traditional turbines due to the following factors:
- There is only one simple asynchronous generator per three turbines (traditional turbines have one generator per turbine);
- The rotor design is very simple and enables cheap manufacture;
- The water passage is very simple, reducing the cost of fabrication;
- The turbine runner does not require tight tolerances, hence reducing fabrication costs.
- There is considerable saving in the sluice gates which with traditional turbines are required to augment the discharge capacity to equalise the basin and sea levels at low and high tide.
- Since energy can be generated over a longer period, the same energy production can be achieved with a lower installed capacity.
In addition at Mezenskaya TPP the use of prefabricated pontoons has been determined to reduce the cost substantially when compared with in-situ construction. There are also great economies of scale to be achieved on a project of this size, with replicability of all the main scheme components.
The preliminary construction cost estimate for Mezenskaya TPP is € 20 billion. This would make the scheme one of the lowest cost producers of all renewable energy technologies.
A detailed construction programme will be produced in the feasibility study. There will be particular focus on development of construction methodologies to minimise the construction period of the barrage, in order that generation can start early.
According to current plans it is estimated that construction would take place over a period of 16 years, and impoundment and full tidal range operation would not take place until towards the end of this period. It is intended that, through optimisation of the construction process and innovation in the construction methodology, the construction period can be reduced. However, it is recognised that the extreme winter climate will restrict construction activities during the winter months, although pre-fabrication of the power pontoons should take place throughout the year.
Construction of the wind projects can take place earlier, possibly starting within three years. Initial generation from wind projects can be interconnected with the existing Russian and Ukrainian power grids and wheeled through the existing power grids of north and north-east Europe, until the dedicated HVDC transmission is available.
ENVIRONMENTAL AND SOCIAL IMPACTS
In developing the design of Mezenskaya TPP account has been taken of environmental and social impacts, although further studies will be required at the feasibility stage.
The experience gained from 45 years of operation of Kislogubskaya TPP together with that on other international tidal projects such as the scheme at La Rance in France provide a good understanding of the potential environmental impacts.
Measures to mitigate adverse environmental impacts include the following:
The proposed orthogonal turbines are more “fish friendly” than traditional propeller type turbines used for tidal power. They have low rotational velocity resulting in lower pressure transients, have large runner clearance and do not slice the water. Hence fish and zooplankton can pass the turbines with reduced likelihood of injury.
- With the ability of orthogonal turbines to generate at low heads, the impounded basin is able to follow the natural tidal levels more closely, minimising the shore-line impact.
- Ecologically safe bio-fouling protection systems are proposed to prevent the build up of biomass on the waterways and runners. This non-lethal system discourages the growth of biomass, and has been tested successfully at Kislogubskaya TPP.
GREENHOUSE GAS ABATEMENT
The huge energy production of Mezenskaya TPP estimated at some 39 million MWh (39 TWh), even allowing for transmission losses (around 10%), will make a very substantial contribution to greenhouse gas (GHG) abatement in the EU.
In Germany, in the absence of nuclear generation, the only alternative technology for providing reliable and predictable electricity on this scale is coal / lignite generation. Unless fitted with carbon capture and storage (CCS) systems, such stations produce around one tonne of CO2 equivalent per MWh of generation.
If it is assumed that some 35 TWh of energy is delivered to the EU to displace coal / lignite generation, Mezenskaya TPP will abate some 35 million tonnes of CO2 equivalent per annum.