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Energy of a wave

Valery BORODIN
Sevmash Production Association

The world is becoming more and more «electric.» Automakers produce electric cars, public transport is converted to electric traction in major cities, electrically-powered drones patrol nature reserves and water areas, participate in rescue operations and deliver parcels. Battery-powered ships and even passenger airliners are under development. 

Нowever, looking for a future without greenhouse gas emissions, many high-tech adherents forget: electricity in the outlets does not arise just by the wave of a magic wand. And the farther the consumption grows, the heavier smoke the coal and peat heat power plants (HPP) will emit, remaining the main energy suppliers to this day. That’s just it turns out to be far from green. There is need to look for an alternative – in addition to the usual nuclear and hydroelectric power plants or relatively new wind generators and solar panels, which have already entered our lives, there’s another way to generate electricity using the gravitational forces of the Moon and the Sun through the mediation of the World Ocean. It’s about tidal power plants.

ROMAN MILLS AND KOREAN GIANTS

Mills operating on tidal energy were known even in the Roman Empire. The first tidal power station was built in 1913 in Dee Bay near Liverpool. Its capacity was just 0.635 MW.

The tidal energy industry was not taken seriously until 1966, when France launched the largest La Rance tidal power plant (TPP) at that time with a capacity of 240 MW. It has 24 turbines installed. The operation of such a power plant turned out to be profitable. If we compare, for example, with nuclear power plants, then the cost of generating a kilowatt-hour at La Rance TPP is one and a half times cheaper.

The Kislaya Guba TPP, launched in 1968 in the Murmansk Region on the cost of the Barents Sea, at Kislaya Guba Bay, became the first and only tidal power plant in the USSR. Two places were provided at this power plant for hydraulic units. A French-made 0.4MW hydroelectric unit was installed on one of them, the second one was reserved for the installation of a Soviet hydraulic unit, but, unfortunately, the project was never implemented in those years. In 1994, due to problems in the economy, the Kislaya Guba TPP was mothballed. 

Meanwhile, the world’s tidal energy reserves are estimated at 3 TW and are comparable in power to river energy resources (4 TW). The energy potential of marine wind waves, equal to approximately 2.5 TW, is only slightly inferior in this indicator to tides, which can provide up to 15% of the current energy consumption level. 

At the same time, TPPs do not have many shortcomings inherent in other types of power plants. Firstly, they operate steadily in power systems both in the basic mode and during peak load periods, with guaranteed sustainable monthly power generation. Secondly, they do not affect the environment. Unlike nuclear power plants, they do not pose a potential danger, there is no need for flooding the land, and harmful emissions into the atmosphere are excluded. In addition, it has been proven over 50 years of operation of the French La Rance: electric power generated by TPP is the cheapest in the power system. 

ECONOMY OF TIDES

It is for these reasons that tidal energy has long been used since the late 1960s for commercial purposes in Canada, China and France, and most recently in South Korea. As for economic efficiency, the initial installation costs high, but they retain good payback characteristics over a longer period. Many of the installations commissioned in the 1960s and 1970s still operate without any particular problems.

There’s not much economic data to analyze. This is partly because the cost is very dependent on the project. The two primary cost factors are the length and height of the barrage, which determine capital costs, and the difference in height between the tides, which determines electricity generation. Some estimates for the oldest and once the largest tidal installation in La Rance, taken from Internet sources, show that costs vary from $0.045 to $0.09–0.13/kWh. The Sihwa Lake Tidal Power Station, the largest tidal facility in the world, is estimated at $400 million and produces electricity for $0.024/kWh.

However, the construction costs need not be attributed to electricity generation. In the case of La Rance, this installation also functions as a motorway, reducing the travel distance by 30 km for 60,000 vehicles per day. Similarly, the tidal power station in Sihwa was built around an existing dam.

In addition to the initial costs, control, monitoring and environmental status management within the facility may be other significant costs. As noted in a study by the Norwegian Ministry of Road Administration, the cost of tidal flow technology may fall by up to 40% when construction is combined with and integrated into the design and implementation of new infrastructure (for example, bank protection, water quality improvement measures or road construction). In addition, such an integrated approach, which combines the planning and implementation of coastal protection structures and bridges with the implementation of tidal power plants, can significantly reduce the plant maintenance and operating costs.

In addition, technology developers are making every effort to increase the TPP utilization rate to approximately 40% and the availability factor to 90% by 2020–2021. The levelized cost of electricity at a tidal power plant with a capacity of 200 MW and higher will be $0.24–0.28/kWh by then. These estimates are similar to a study conducted by Carbon Trust, which estimated that the cost of tidal flow installations in 2020 would be about $0.19–0.26/kWh. An increase in capacity through advances in technology to 2–4 GW suggests that the levelized cost of electricity may drop to $0.22/kWh by 2030. All this suggests the high economic efficiency of tidal power plants in the long-term.

Given the relative novelty of tidal energy, most projects and works are mainly focused on the technology of the installation itself and its related infrastructure. However, for larger projects, communication with other sectors, such as shipping, recreation, and environmental protection, may not only reduce installation costs (by building dual- and even triple-use infrastructure), but also ensure public recognition.

RUSSIAN PROSPECTS

Tidal power development in Russia resumed ten years later after the Kislaya Guba Tidal Power Plant was shut down. In 2004, the plant was re-opened and a domestic 0.2MW generating unit was installed. In 2007, a new 1.5MW power unit was launched. The Sevmash Production Association contributed heavily to the rehabilitation of the domestic tidal power sector. It was there, in 2004, that a hydraulic unit with an orthogonal horizontal turbine with a runner diameter of 2.5 meters was manufactured. The hydraulic unit successfully passed full-scale tests at the power plant. 

The proposal of Moscow hydropower engineers to implement a joint project at Sevmash to build an experimental floating power unit with an orthogonal vertical water turbine with a runner diameter of 5 meters in order to test key solutions relevant to the further development of tidal energy in Russia contributed to the continued use of tidal energy. 

In a short time, the Sevmash design bureau completed the preliminary and detailed design of the floating power unit, which accommodated changes based on operating experience with the OGA-2.5 to increase the efficiency of the hydraulic unit through improved hydrodynamic characteristics of the turbine. 

In January 2007, a 2115-ton block was floated out to Sevmash’s water area to prepare it for towage. On February 5, 2007, the block was installed on a hydraulic foundation. 

The successful implementation of the project to integrate a 1.5MW floating power unit into the Kislaya Guba TPP makes it possible today to begin designing the Severnaya (Dolgaya Guba) and Mezen TPPs. The design capacity of the Severnaya TPP is 12 MW. 

 Its main generating element – a floating reinforced concrete power unit – is equipped with three orthogonal hydraulic units with a three-tier arrangement of runners and is installed at the same foundation levels that exist in the Mezen and Tugur TPP sites. 

UNIQUE TURBINE

The orthogonal hydraulic unit developed by Sevmash is of a Darreus rotor type with rectilinear wing-shaped blades that are rigidly mounted parallel to the shaft. This is a double-acting high-speed jet turbine, the axis of rotation of which is positioned vertically or horizontally across the flow, which is most effective for low heads typical of TPP. It is ideally suited for two-sided turbine operation at a tidal power station, since it does not change the direction of rotation of the shaft and its characteristics when the direction of water flow in the water conduit is reversed. Reduction in the cost of hydraulic units is achieved because orthogonal turbines are simpler in design than axial ones, less metal-intensive and easy to manufacture. In addition, two or more turbines can be installed on a common shaft in one hydraulic unit.

The weight, and therefore the cost of orthogonal turbines, is half that of the axial ones with the identical runner diameter. Compared with the axial scheme, the orthogonal one has twice the capacity in idle mode, which can significantly reduce the spillway front of the waterworks. In addition, the use of orthogonal machines leads to a a reduction of around a third in the volume of the plant building.

The efficiency of orthogonal machines (0.75–0.80) is still lower than that of axial machines, but the overall efficiency of the entire cycle is higher for orthogonal machines. In addition, owing to these advantages, the cost to equip tidal hydropower plants with orthogonal machines is halved, and the total capital expenditures are up 18% lower at equal capacities and power generation.

Experience in manufacturing the OGA-2.5 and OGA-5 orthogonal hydraulic units allows Sevmash to successfully apply its intellectual and production capacity in making a new three-tier orthogonal hydraulic unit for the Severnaya TPP, which, in turn, is a necessary stage in the design and manufacture of large tidal power plants, such as Mezen and Tugur.

Russia has considerable tidal energy resources. According to years of design studies, economically viable electricity generation at the planned Mezen TPP alone in the Gulf of Mezen of the White Sea is about 40 billion kWh per year, which is equal to the average annual electricity generation at the Volga-Kama cascade of hydropower plants. Electricity from the Mezen TPP can be transferred not only to the northwestern regions of the European part of Russia, but also to the central region, and in particular to Moscow. As regards the unused hydropower resources of the Russian rivers for power supply to these areas, they have almost been exhausted.

Another promising tidal plant is the Tugur TPP in Tugur Bay of the Sea of Okhotsk with a projected electricity generation of about 15 billion kWh per year. There are compelling arguments in favor of its construction in the coming years, despite the fact that there are many unused rivers and hydropower resources in the Asian part of Russia. The construction of the Penzhin TPP in Penzhin Bay of the Sea of Okhotsk with an enormous projected electricity generation of 190 billion kWh per year can be carried out in the longer term. 


THE WORLD’S BIGGEST TIDAL POWER PLANTS

LA RANCE

The barrage is 750 meters long and extends between Brebis point in the west to Briantais point in the east. It is located on the estuary of the Rance River and connects the cities of Dinard and Saint-Malo in Brittany, forming a tidal basin of 22 km2. The annual generation is about 500 GWh (491 GWh in 2009, 523 GWh in 2010 and 449 GWh in 2013), such amount of electricity can meet the needs of a city with about 225,000 inhabitants, such as Rennes. With the electricity generation cost estimated at €0.018/kWh, tidal electricity produced by La-Rance TPP is more economically competitive than nuclear energy (€0.0598/kWh).

SIHWA

A power plant on the northwest coast of South Korea in Gyeonggi Province, west of Ansan City, about 40 km southwest of Seoul, uses the power of the Yellow Sea located between the Korean Peninsula and China. Strong tides occur due to a large bay area and relatively shallow depths. In Asan Bay, from which Sikhwa Bay is separated, the tide height is about 8 m. The dam length reaches 12.7 km. The volume of the reservoir is 324 million m3. Its surface area is 56.5 km2. Eight culvert-type sluice gates measuring 15.3 x 12 m are used for the water outflow from the barrage. The seawater flow rate is approximately 160 million m3/day, which corresponds to approximately half the reservoir capacity.The tide height is 7.5 m. The rated head is 5.82 m. The annual electricity generation of the power plant – 550 GWh – roughly corresponds to the needs of a city of half a million people. According to experts, capital expenditures for building the TPP were less than $2,500/kW.


Energy of a wave
Energy of a wave
Energy of a wave
Energy of a wave
Energy of a wave
Energy of a wave