As regulatory pressure continues to curb greenhouse emissions, there has been a lot of attention on solar and wind energy. However, a less-publicized renewable energy source could play a major role in preparing for a world that is less dependent on fossil fuel — tidal energy.
The potential energy that could be harvested from tidal movements on a global scale is enormous, with some experts citing about 1 terawatt of power is stored in the world’s oceans. This would be enough to power 10 billion 100-watt lightbulbs at once.
Industry experts describe tidal energy as one of the greatest untapped renewable energy sources on the planet. In the U.S., where there are thousands of miles of coastline, the Department of Energy estimates that developing just 5% of tidal energy’s identified technical resource potential would generate electricity in the amount of 12.5 terawatt-hours per year, which is enough to power slightly more than 1.1 million typical American homes.
Read part 2 of our white paper- 2021 Power Generation and Renewable Energy Trends, to explore renewable energy technology trends, both established and newer technologies including hydropower, wind, solar, and biogas.
Tidal energy is attractive for many reasons. It is environmentally friendly and represents a highly predictable energy source, especially when compared with wind energy or solar power. It also offers high energy density and provides an inexhaustible source of energy with comparatively low operational and maintenance costs.
There are several disadvantages, however, that need to be addressed before tidal energy can reach its full potential. The largest barrier to tidal energy is the high cost associated with building tidal power stations. Another major concern is the potentially negative environmental effects on marine life. Spinning blades can injure living organisms, as can water fouling resulting from various system components.
Other disadvantages of tidal energy include the variable intensity of sea waves. Plus, there are location limits. Tidal energy plants must be located where tides are the strongest, yet not too close to cities where aesthetic concerns prevail.
Recent technological developments have reduced economic and environmental costs to competitive levels, opening the door to a bright future for tidal energy.
There are two primary methods of generating electricity from tides:
Tidal range devices utilize the difference in water levels between high and low tides.
Tidal stream devices utilize the energy of flowing water in tidal currents to generate electricity directly.
A tidal barrage is one of the better-known tidal range devices. Tidal barrage technology utilizes dam-like structures that are often built across the entrance to a bay or estuary. Their tunnels contain turbines that generate energy created by the changing heights in tides.
Although tidal barrages have a long history, their future is less certain. High installation costs and concerns about the effects on local marine life have turned the interest from barrages to stream devices. These include a variety of turbine designs, as well as more innovative concepts, such as oscillating hydrofoils and tidal kites.
Many different technologies are currently in development in the tidal stream sector. Challenges remain, however, before they may prove commercially viable.
Durability is a primary concern, as any tidal stream device needs to withstand greater loading forces because of the high density of water. There are also concerns regarding the impact of tidal turbines on water quality since they disrupt upstream and downstream current velocities. In addition, local sea life is adversely affected by noise pollution, the generation of electromagnetic fields, and possible injury from rotor blades and other moving parts.
Tidal turbines are similar to wind turbines in that they have blades that turn a rotor to power a generator. They can be placed on the seafloor where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines must be much sturdier and heavier than wind turbines, which makes them more expensive to build. However, they can capture more energy and release greater amounts of power with the same size blades.
Given the increased water density, the harsh corrosive environment of the sea, and concerns about oil leaking from components and harming marine life, tidal energy systems require components that are highly durable, reliable, and proven safe.
Parker has led the market with several innovative products that have proven, over time, to withstand the harsh marine environment and provide safe, reliable operation.
Some of these products include:
A proprietary Global Shield™ Coating Technology for steel cylinder rods that offers significantly increased corrosion protection for longer component field life at a lower cost than stainless steel.
Parker F37 / Complete Piping Solutions (CPS) that eliminate welded pipe connections, increasing safety and decreasing installation time.
The Parker Tracking System (PTS), which reduces asset downtime as well as the efforts of the maintenance staff when replacing products such as ruptured hoses.
As tidal power engineers work to refine existing technologies, there has been a focus on improving turbines and how they are powered. Consider some of the more noteworthy innovations that have taken place in just the past few years:
Modified bulb turbines with an additional set of guide vanes are allowing better management and control of the flow through the turbine. Bulb turbines are attractive because they can deliver very high-power output.
A breakthrough announced in mid-2020 was a turbine that does not require a gearbox. With fewer moving parts in the turbine, there is greater reliability and longer intervals between maintenance checks.
Concentrators or shields are being placed around turbine blades to optimize tidal current flow toward the rotors. A remaining challenge is that high-tech equipment is required to deploy these devices in rough seas and anchor them to the seabed.
Direct-drive, hydraulic, and inertia systems continue to evolve. For example, considerable research is being done on dielectric elastomer generators, which utilize soft capacitors that do a better job of withstanding harsh ocean environments than traditional electromagnetic generators.
Artificially intelligent turbines promise to provide greater efficiency and the ability to adjust to changing conditions in real-time. A newer AI system has been designed to utilize data derived from wind energy. Data is captured at the surface and transmitted to the turbine system to maximize turbine performance and efficiency. Such a design is projected to reduce lifetime costs for this tidal energy system by nearly 20%.
A new 73-meter-long floating superstructure has been developed that supports two 1-MW turbines on each side to generate twice as much energy.
An innovative tidal kite known as Deep Green is creating several hundred times more electricity than a stationary turbine on the seafloor. The tidal kite can produce electricity from slower currents which makes it more versatile.
A wave energy team at Oregon State University is researching novel direct-drive generators which don’t require the use of hydraulic fluid or air. Instead, they leverage the velocity and force of a buoy to power the generator. The generators respond directly to ocean movement by employing magnetic fields for contactless mechanical energy transmission and power electronics for efficient electrical energy extraction.
Although much of the research on tidal turbines over the past decade has focused on design options that will produce greater energy efficiency, today there is greater awareness regarding the need to achieve a more reliable operation to ensure the consistent production of tidal energy. Types of damage that most often affect the drivetrain of a tidal turbine include:
broken gear teeth
lubrication variability resulting in dry contact of the rotating surfaces
This has opened the door to a new generation of condition-based monitoring and diagnostics equipment. Parker offers in-depth expertise in this area with products such as:
icountPD Online Particle Detector that features the most up-to-date technology in solid particle detection for independent, real-time monitoring of system contamination trends.
Parker On-Site Heated Viscometer, an on-site oil analysis that detects out-of-spec fuels or lubricants before equipment damage occurs.
Parker Acoustic Bearing Checker monitors high-frequency Acoustic Emissions (AE) signals naturally generated by deterioration in rotating machinery.
To learn more about tidal and other energy trends impacting our world, read our Power Generation and Renewable Energy Trends White Paper – Part 2.
Article contributed by the Filtration and Energy Teams.
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