Get to Know Islay Limpet Wave Energy in the United Kingdom

Islay Wave Power Station

The Islay Limpet wave power station is the first to supply electricity generated by a device using wave energy to a commercial grid. The power station generates 500 kW and transmits the electricity to the United Kingdom’s power grid.

The location of Islay LIMPET is at Claddach Farm on the Scottish island of Islay. LIMPET means Land Installed Marine Power Energy Transmitter.

LIMPET was constructed in 1991 and the device was capable of generating 75 kW. In 2000, a 500kW unit was constructed. Development of LIMPET is attributed to Wavegen and Queen’s University Belfast.

Islay LIMPET is an oscillating water column wave energy converter located on the shoreline of Islay. It all began when Professor Trevor Whittaker of the Queen’s University Belfast constructed an OWC prototype that was capable of generating 75kW of electricity in 1991. The unit was decommissioned in 1999 after the project’s completion.

The project demonstrated that electricity could be produced by the power of waves pushing air in and out of a chamber thereby driving a Wells turbine.

Prior to the completion of the project, discussions were already underway as to whether or not shoreline devices were more beneficial than offshore wave energy converters. At that time, it had already been demonstrated that offshore devices provided more potential than shoreline devices in terms of generating electrical power. There was also a question if Islay was the right location for a shoreline device.

However, installation and mooring costs of offshore devices proved to be too costly. It was therefore decided that a shoreline device would be more cost-efficient.

The project development for a larger shoreline device using wave power technology formally commenced in 1998.

Half of the funding for the project came from Wavegen and QUB. The other half was funded by the EU Joule Programme.

It was decided that the primary objective of the project was for it to be able to generate 500 kW of electricity in order for it to make a meaningful contribution to the power grid. The other objectives of the project were to install instrumentation that would monitor the power station’s output and to try various settings to maximize the output during different sea wave conditions.

LIMPET was constructed about 400m north of the original prototype. While the prototype was constructed in a natural gully, the site where LIMPET was constructed had to be cut from cliff. However, the site was chosen because it was facing the ocean where it was open to stronger waves of the Atlantic.

Construction of the project started out as planned. A hole was dug in the cliff leaving a small wall protecting the construction site from the force of the waves. After the site was constructed, the wall was blasted so that the waves could enter the OWC chamber.

The project did not go as smoothly as planned. There were obstacles along the way. In fact, the initial output of LIMPET was below expectations. It was discovered that the blasting of the wall left debris that covered 75% of the water entrance to the chamber. After clearing the debris, output significantly improved.

LIMPET’s output did not reach the originally planned levels. However, its current output is enough to satisfy the requirements of the grid. The LIMPET wave energy collector is still considered to be a success even if it was not able to reach the projected maximum capacity.

How an OWC works

An OWC or oscillating wave column like the LIMPET design works by using the power of waves to generate pneumatic air pressure in a chamber. As the air pressure is released, it drives a Well’s turbine thereby generating electricity.

When the waves retreat from the chamber, air is then sucked back in. As air comes back into the chamber it will also drive the Wells turbine in the same direction, therefore continuous generation of electricity is achieved.

There are many factors that determine the pneumatic air pressure inside the chamber of an OWC. The slope of the wave entrance into the chamber and the slope of the back wall determine the amount of pressure that is achieved.

In the case of LIMPET, projected maximum output was not achieved due to several factors, but the main reason was that the actual construction was not in accordance with the initial survey. This affected performance of the power station due to its distance from the waves.

Despite the problems that prevented the LIMPET power station to perform at optimal levels, the project was deemed to be a success because it proved that shoreline power stations like the LIMPET OWC were a viable source of energy in the United Kingdom.

In addition to providing sufficient electricity to the grid, the plant proved to be extremely reliable.

There have been no major problems with its operation since its commissioning. This doesn’t mean to say that the plant hasn’t encountered shut-downs.

There have been times when the plant was shut down due to several reasons. Most of these reasons have been due to faulty instrumentation reports or inadequate conditions of the power grid. The plant itself has been very reliable.

In fact, the plant has been operating automatically since its commissioning. Monitoring and control of the plant has been done at Wavegen’s offices in Inverness.

There are only a few places in the United Kingdom that are ideal for shoreline wave power generation plants. One of the biggest hurdles that prevent the development of these devices is the lack of suitable power grids at those locations.

The situation is similar to the LIMPET plant at Islay. Most of the power outages have been due to local grid faults and not of the power station itself. More reliable power grids need to be constructed at ideal locations for a shoreline OWC before development of these devices can begin.

The Islay LIMPET wave energy converter proved not only to the United Kingdom but to the world in general that the ocean’s waves are a viable source of clean and renewable energy. It also proved that a shoreline OWC is also a viable alternative to offshore wave farms.

Maintenance costs of offshore wave farms are a concern since these are open to extreme weather conditions. These weather conditions may also affect the reliability of offshore wave farms. In the case of the LIMPET OWC, maintenance costs have been low due to the device having not experienced any major problems. The OWC has proven to be extremely reliable even during severe weather conditions and in conditions where the sea waves have been unusually calm.

The Islay LIMPET is a statement to the world that the power of waves can be harnessed efficiently and reliably by using a shoreline OWC. The generation output of an OWC is sufficient to supply the requirements of a local power grid thus making it a viable source for clean an renewable energy.

In 1994, Finland announced that they had installed the Waveroller. Energy was produced by installing a plate that was anchored at the sea bottom. Waves moved the upper portion of the plate back and forth and the kinetic energy was collected by a piston pump.

In 1997, Ocean Power Technologies in the United States developed the Powerbouy. The up and down movements of a wave caused hydraulic fluid within a bouy to spin a generator thereby producing energy.

More companies around the world started to develop different technologies to produce energy from ocean waves. Looking into the history of wave farms, we’ll see that these only began sprouting in the last decade. To date, only a handful of wave farms can be seen around the world.

The first wave farm was in Portugal and was called the Agucadoara Wave Farm. The farm was commissioned in 2008 and produced 2.25 MW of energy. Unfortunately, it was shortlived as it was also decommissioned the same year.

In 2009, Spain announced Mutriku Breakwater Wave Plant and it was capable of producing 0.3 MW of energy. The same year Israel commissioned SDE Sea Waves Power Plant that produced 0.04 MW.

In 2011 two wave farms were commissioned in the United Kingdom. The Orkney Wave Power Station produced 2.4 MW and the Siadar Wave Power Station was capable of producing 4 MW of power.

The world’s wave energy technology has much more room for improvement. Technologies to harness wave power have been around for centuries, but the lack of conviction to develop these technologies and turn them into a main resource for energy has prevented this happening at a much faster pace.

How is wave energy used around the world? Sad to say, wave energy has not been a priority, mainly because of the initial setup costs.

Maintenance costs of wave power plants are not as expensive when compared to other power generation plants, but initial setup costs have prevented this type of technology being used around the world.

As the world starts to move away from the reliance on fossil fuels, more power generation plants that use clean sources of energy will be developed. The move from fossil fuel is already evident in many parts of the world, and this could mean that wave energy will soon become more popular.