Ocean Waves as a Source of Electrical Energy: Cost-efficient or Uneconomical?
The energy production industry has been heavily reliant on coal, oil, and other fossil fuels for hundreds of years to power everything from light bulbs to automobiles to factories. Furthermore, we constantly use fossil fuels, which has led to historically high levels of greenhouse gases emitted when those fuels are burned (1). Thus, the growing energy sector creates jobs, makes the electric grids more resilient, and expands energy access in developing countries, helping lower energy bills. All of those factors have contributed to a renewable energy renaissance in recent years, with wind and solar setting new records for electricity generation (1).
So how does another environmental-friendly, hydroelectric-generating source help ease the growing demand for better and cleaner energy? Built around 2007 at Strangford Lough in Northern Ireland, the first tidal solar power generating plant was introduced in the race to transcend to low-carbon emitting electrical energy production (2).
Economic Impact
In regions where there is a substantial tidal range—the difference in area between high tide and low tide—engineers innovated ways to use tidal movement to generate power. Each technique converts tidal energy into electricity using specialized generators (2).
What are Ocean waves and how does it help produce Tidal energy?
Waves are ocean movements generated by wind, tides and meteorological events. These movements help generate electrical energy via the installation of tidal turbines. These turbines generate electricity as the current alternates between high tide and low tide. Tidal energy can take the form of kinetic energy or potential energy (3). The difference in the water level is considered potential, or stored energy, while the movement of the current is considered kinetic energy. In places with appropriate tidal ranges, tidal power is a viable contender for electricity generation since high and low tides occur naturally at predictable times of the day (3).
What are the existing methods used to harvest tide energy?
With today’s technology, tide energy is harvested in two methods: mechanical and electrical methods. Mechanical techniques turn a turbine to produce electricity by utilizing the kinetic energy of the waves. The motion of the wave is used in Electrical technologies to produce an electromagnetic field, which then produces electricity (3).
By utilizing mechanical and electrical methods, tidal power plants use three different mechanical operations: tidal streams, barrages, and tidal lagoons.
In a tidal stream, energy comes from horizontal water currents that are created by the vertical variation of water levels caused by tides. These currents affect areas where tides act in opposite ways (high tide on one side, low on the other) and the flow changes direction with tide level changes (5). The force of the current on the blades spins/rotates the rotor shaft of a generator. The generator, in turn, converts the mechanical (kinetic) energy of the rotor to electrical energy (4).
In a Barrage generator, the barrage gates are open as the tide rises. At high tide, the barrage gates close, creating a pool, or tidal lagoon. The water is then released through the barrage's turbines, creating energy at a rate that can be controlled by engineers. The environmental impact of a barrage system can be quite significant. Among the tide energy generators, the barrage is one of the most non-marine-life-friendly mechanical operations as it is disrupting the salinity in the tidal lagoon, affecting the marine life and the environment on its operational range. It is also more expensive than turbine generators, and although there is no fuel cost, the downside is its extensive construction and its effect on the environment (2).
Tidal Lagoon
In a tidal lagoon, a body of ocean water is partly enclosed by a natural or manmade barrier. Tidal lagoons might also be estuaries and have freshwater emptying into them. Similar to barrages it is constructed along natural coastlines which could help generate continuous power. Their difference is tidal lagoons have minimal impact on the environment as it is constructed with natural materials like rocks. They appear to be low breakwater seawalls and submerge with the ocean at high tide (6).
Why Isn’t Tidal Power Used More Often?
So why isn't tidal energy used more frequently as a renewable energy source if it is such a reliable method of generating electricity? According to Brian Polagye, Associate Professor of Mechanical Engineering and Director of the Pacific Marine Energy Center at the University of Washington, “The fundamental question is one of economics,” Because of the early stage of the technology, tidal power is an expensive source of energy: according to a 2019 study, commercial-scale tidal energy is estimated to cost $130-$280 per megawatt-hour, compared to $20 per megawatt-hour for wind (5).2 High upfront costs of building plants, expenses associated with maintaining machinery that can survive corrosive seawater, and the pricey engineering work that goes into them make up a significant portion of that cost discrepancy (5). Polagye adds that the supply chain for tidal power also isn't yet capable of providing the necessary components and technologies at scale to make this energy source and, as of now, "everything’s pretty custom.” In fact, the market discrepancy between tidal and other, more mature, renewable energy systems is actually growing because the cost of generation from wind and solar generation continues to drop (5).
There are currently very few tidal power plants, despite a few projects for tidal energy being developed. Thus, one of the reasons is that it is highly expensive to use ocean waves as a source of electrical energy (4). The infrastructure requires a substantial initial outlay, and ongoing maintenance is also quite expensive (3). Due to the equipment's ongoing need for maintenance, maintenance expenditures are likewise fairly significant. To rationalize, the factors to consider that is considered “clean energy” is outweighed by the potential damage it causes to the environment as well as its economically challenging to depend on for a source of electrical supply. Though tidal energy production is still in its infancy there is always room for improvement and development (3).
Existing Tidal Power Plants
SIHWA TIDAL POWER STATION, SOUTH KOREA
The Sihwa tidal power station is the world's largest and most expensive tidal installation, with an installed capacity of 254MW, and according to IRENA cost $298m to build in 2011.
The cost per kilowatt hour (kwh) of the plant is worked out by multiplying the construction cost and the capacity. As such, it has been estimated that Sihwa cost $117 per kWh, while it produces electricity at $0.02 per kWh. It is formed of 10 generators, which produce a total energy capacity of over 550GWh annually (7).
ANNAPOLIS ROYAL GENERATING STATION, CANADA
The Annapolis Royal Generating Station on the Bay of Fundy, Nova Scotia, is the third largest tidal farm in the world but has a much smaller capacity than the previous tidal stations producing just 20MW.
Construction began in 1980 and it began producing energy in 1984. It currently produces 50GWh annually, enough to power 4,500 homes. Similar to the Sihwa farm, Annapolis is built on a pre-existing causeway from the 1960s, allowing the local community to benefit from previously wasted structures (7).
LA RANCE TIDAL POWER STATION, FRANCE
La Rance tidal power station is the oldest tidal power station and the first producer of renewable energy in Europe, built in 1966. La Rance is an important example as it is the oldest tidal power station in the world, and at 53 this year it is still a reliable source of power with no end date in sight. As such it proves that tidal have a very long life expectancy, while wind turbines for example currently only last for around 20 years.
La Rance cost $115m and the time of construction, which adjusted for inflation is $918m in 2019 and has a capacity of 240MW. The farm cost $382 per kWh and produces electricity at a range from $0.04 to $0.12 per kWh (7).
Jiangxia tidal power station, China
Jiangxia tidal power station was the first tidal power station in Asia. Located in the East China Sea outside the city of Wenling, Jiangxia first produced energy in 1980.
Initially it had a capacity of 3.2MW formed of five generators. A sixth 700kW generator was added in 2007 and an older generator was upgraded by 200kW in 2014, taking total capacity to 4.1MW. The project highlights the ease with which tidal power stations can be retrofitted, further adding to the longevity of the technology.
The station produces about 6.5GWh of electricity each year. While this is much smaller than the previous stations it has been able to constantly produce energy for nearly 40 years, as such providing great value (7).
Kislaya Guba tidal power, Russia
The fifth-largest tidal power station is Kislaya Guba tidal power station in the Barents Sea, northern Russia. Built during the Soviet Union era in 1968, the station has a total capacity of 1.7MW.
The plant was originally built with Frech technology and had a capacity of 0.4MW, but after being closed for a decade it was re-opened in 2004 with new equipment which increased it to its current capacity (7).
It is clear therefore that there have already been huge developments in technology, although this has, as yet, happened relatively slowly. This is generally thought to be because of a lack of investment, but it is predicted to become commercially profitable within 2020. This is thanks to the larger scale of projects along with technological advancements.
The Russian government has looked to establish further tidal projects totaling over 100GW, including the possibility of a huge 87GW project at Penzhin Bay in the sea of Okhotsk (7).
References :
Enel Green Power S.p.A. is an Italian multinational renewable energy corporation, headquartered in Rome. The company was formed as a subsidiary of the power generation firm Enel in December 2008. https://www.enelgreenpower.com/learning-hub/renewable-energies/marine-energy/tidal-stream%20
tidallagoonpower.com was first indexed by Google more than 2013.
http://www.tidallagoonpower.com/tidal-technology/what-is-a-tidal-lagoon/National Geographic tidal energy 2020
https://www.nationalgeographic.org/encyclopedia/tidal-energy/International Hydropower Association 2019.
https://www.hydropower.org/blog/technology-case-study-sihwa-lake-tidal-power-stationclimate.mit.edu was first indexed by Google in November 2014
https://climate.mit.edu/ask-mit/why-dont-we-use-tidal-power-morePowerTechnology March 31, 2019
https://www.power-technology.com/features/tidal-energy-cost/National Geographic 2021.
https://www.nationalgeographic.org/article/renewable-energy-explained/National Geographic society
https://education.nationalgeographic.org/resource/tidal-energy/Just Energy Group Inc. ”
https://justenergy.com/blog/tidal-energy-electricity/” 2021Energy Information Administration
https://www.eia.gov/energyexplained/electricity/how-electricity-is-generated.php 2021.
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