History was made when performance of the world’s first tidal underwater turbine of one megawatt capacity was successfully demonstrated recently in Orkney Isles, Scotland, which has established commercial viability of harnessing the tidal energy resources.
The machine HS1000, developed by Andritz Hydro Hammerfest, was installed at the European Marine Energy Centre’s tidal test site in December 2011, and since then the turbine has underwent extensive testing during its continuous operation, with focus on comparing measured load and performances with figures calculated during the project design phase. Results were very positive and the machine was found generating grid-compliant electricity of over 3 GWh annually, meeting its design parameters fully.
The turbine, developed on most advanced concept, has rotor diameter 21m, depth of 50m underwater, rotational speed 10.2 rpm, operating in a 4 m/s tidal current, and is capable of delivering power with 98 percent availability. The state-of-the-art machine is a horizontal axis turbine, similar to a wind turbine, mounted and locked onto a solid steel structure and positioned on the seabed. The rotor blades are driven by water currents and coupled to an electric generator through a step-up gearbox. A dedicated blade pitching system allows optimum adjustment of the rotor blade to the direction and speed of the tidal current. Electrical power is transmitted onshore by means of a subsea cable connected to the grid.
Scottish Power Renewables has already selected these turbines for its 10MW tidal turbine array in the Sound of Islay (Scotland), which would be the world’s first tidal turbine array, and subsequently, for use in Duncansby Head (the Pentland Firth) project of 95MW scheduled for completion by 2020. Scotland is the world leader in the commercial development of wave and tidal energy having commenced power generation in November 2000. Generating electricity using tidal currents in coastal waters is an enormous challenge. The related technology, though emerging, is well-proven as the first large-scale tidal powerhouse was established in France in 1966. Since then a number of tidal power stations have been constructed. These power stations have mostly installed bulb type turbines along generator, similar to that of hydroelectric power station.
Research and development continues in its design, installation and maintenance, with a view to mainstreaming these technologies so that it becomes cost effective. In recent years there have been major advancements in wave and tidal energy technologies. The recent tidal power stations are based on the concept of windmill---tidal energy unit functioning like an underwater windmill, without requiring construction of tidal barrages/dams. All leading companies in technologies for energy generation, namely Alstom Hydro, Andritz Hydro Hammerfest, Atlantis Resources Corporation, OpenHydro, Scotrenewables Tidal Power and Voith Hydro, have been actively engaged in developing tidal turbines for commercial-scale power generation.
OpenHydro and Alderney Renewable Energy will develop, in joint venture, a 300MW tidal energy array off the coast of Alderney in the English Channel, using 2MW tidal turbines. Swansea Bay Tidal Lagoon project in South Wales of 320MW will be the largest tidal turbine in Europe to be completed by 2018. UK electricity supplier Good Energy has already agreed to purchase electricity from the proposed project that would install Alstom’s most powerful single rotor AR 1000 tidal turbine weighing 1,500 tons, which is currently undergoing tests at the European Marine Energy Centre.
Atlantis Resources Corporation’s AK 1000 largest bladed tidal turbine and Voith Hydro’s HyTide 1000, both of one megawatt capacity, are also currently under tests and trials in Orkney Isles. Scotrenewables Tidal Power has developed unique floating tidal technology to minimise installation and operating costs. After successful modelling of 250 kW unit, the company is in the process of launching larger commercial scale 2MW turbine, more suited to tidal array development. China too has recently established 3.2MW tidal power station, and has signed an agreement with the Netherlands to develop the world’s largest tidal power project based on new tidal technology. Construction of 50MW power plant has been undertaken by India in the Gulf of Kutch.
Theoretical global ocean energy resources are estimated to be over 32,000GW. Interestingly, net potential of both wave and tidal power is greater than wind and solar, in global perspective. Tidal energy, a form of hydropower, is clean, environmentally friendly and more predictable compared to wind energy. Tidal power has the greatest energy density (watts/cum per second) compared to solar (medium) and wind (lowest). Tidal power belongs to most efficient renewable energy resources, with about 80 percent efficiency. It has high initial capital cost, whereas cost for establishing infrastructure is the same as for wind-based power, but it is inexpensive to maintain. Other benefits include lower project construction time as tidal turbine can be installed in 9-10 months. However, power generation cost, which is in the range of cents 10-12 per kWh, is considered higher compared to other sources.
There are many other new resources of energy that could benefit Pakistan in the long term, such as ocean energy including marine current power, osmotic power (from salinity gradients), ocean thermal energy, oceanogenic power (from surface waves), wave energy and tidal power. Pakistan has not yet done any work in this direction despite having various strategic locations with high tidal current velocities or strong ocean currents along its 990km coastline.
Tidal energy resources offer an inexhaustible supply of energy. Pursuant to the government policy for the development of alternate energy resources through private sector the government had allowed in February 2013 setting up tidal energy projects of cumulative capacity of 10MW at Sonmiani Bay (Balochistan), but so far there has been no physical progress achieved.
According to a study conducted by the National Institute of Oceanography, creeks network in the Indus deltaic region extending over 70km along the Arabian Sea can alone generate 900MW tidal power. Detailed study, testing, and assessment of tidal energy across the coastline could show a huge potential of marine energy resources that can be exploited for power generation on commercial scale. In future, tidal power could be a significant part of the renewable energy mix in Pakistan. Tidal power stations can be grid-based or off-grid installations, depending on site conditions.
In view of the emerging energy scenario the world over, a more focused approach by the government towards developing non-conventional and renewable energy resources is required. Optimal exploitation of tidal energy resources has potential to provide solution to the prevalent power crisis. A proper policy on tariff and commercial development of these resources, providing enabling environments to the investor, both domestic and foreign, will be helpful. There is therefore a need to give policy directive for encouraging promotion of these indigenous resources too, in line with the neighbouring countries like India and China where such resources are being rapidly harnessed economically.
The writer is the Chairman of the Institution of Engineers, Pakistan