Renewable Energy Looks Offshore

Belgium’s Minister of Economy recently described the country’s offshore waters in the North Sea as the country’s eleventh province. Offshore has, in fact, become prime real estate for renewable energy entrepreneurs, and visions for the future are emerging that could indeed turn the sea into a new multipurpose extension of coastal infrastructure.

Belgium has plans to build an artificial island that will have a deepwater reservoir at its center. Turbines in the reservoir will pump water in and out as a way of storing and releasing excess wind energy, making it available during times of low wind conditions. It’s an ambitious plan with an undisclosed price tag, but the minister envisages combined wind and aquaculture projects that will “leave the North Sea better than before.”

Classification society Germanischer Lloyd (GL) has evaluated the feasibility of producing liquid hydrogen from the excess energy generated from offshore wind farms during times of peak production. Dr. Pierre C. Sames, GL’s head of Research and Rule Development, has set out a concept for a zero-emission container feeder vessel that uses liquid hydrogen in a combined fuel-cell-and-battery propulsion system.

A 500 MW wind farm could produce up to 10,000 tons of liquid hydrogen from surplus power it is unable to feed into the grid, and GL estimates that the concept could be commercially attractive between 2020 and 2030 provided the price of marine gas oil increases beyond $2,000 per ton. Two onshore plants have recently commenced operation in Germany that demonstrate the viability of using wind energy to generate hydrogen through electrolysis.

Wind Power

The offshore wind industry is only 20 years old, but output has already exceeded 5 GW. DONG Energy of Denmark has led the industry’s development. DONG has built 40 percent of Europe’s capacity and intends to have 6.5 GW of offshore wind capacity installed by 2020. Three new farms will become fully operational this year: Anholt in Denmark, and London Array 1 and Lincs in the UK. These farms will have a total capacity of 1.3 GW, equivalent to the annual electricity consumption of 1.1 million households.

Also to become operational this year is a demonstration project at Gunfleet Sands in the Thames Estuary using two Siemens 6 MW turbines, the largest yet to be deployed in the industry. “We will go through our entire logistical setup to see how we can keep developing sites with larger turbines, more standardized solutions, new foundations for deeper water deployment, and the use of new and more sophisticated vessels,” said DONG spokesman Rune Birk Nielsen. “The majority of the cost of a farm occurs during the construction phase, so it is crucial to reduce these costs while at the same time increasing productivity.”

In addition to technological innovation, DONG has been at the forefront of managing financial risk and securing framework agreements. About two-thirds of its wind revenue comes from government schemes that include fixed tariffs for the electricity generated, and DONG continues to enter into partnerships with industrial and financial players to secure co-funding for its projects and diversify risk.

“The next step will be to get volume into the sector,” Nielsen adds. “I think everybody in the industry is very keen, and for the next five to 10 years we will see the volume that is needed to bring the cost of wind energy down and make it competitive. Wind is definitely a key part of the energy mix in a large part of the world, and offshore wind will make up a substantial portion going forward once we prove we can build large-scale facilities.”

Wave Action

Other technologies are already vying for offshore real estate. The World Energy Council has estimated that approximately 2 million MW of electricity could be produced from wave power, double the current production. Pelamis Wave Power has been a leader in this technology. The Pelamis prototype was the world’s first commercial-scale wave energy converter to generate electricity for a national grid from offshore waves when a three-machine farm with a capacity of 2.25 MW was installed off the northwest coast of Portugal at Aguçadourain in 2004. The second-generation Pelamis machine (P2) includes a number of significant design improvements. At 180 meters long, four meters in diameter and approximately 1,350 tons in weight (mostly sand ballast), the P2 Pelamis is wider, longer and heavier than the P1 design. This allows it to capture more energy while substantially reducing the cost per MW. The P2 design has been sold to utility customers E.ON and ScottishPower Renewables, and P2 machines are currently being tested for a number of other commercial-scale projects across Europe.

The U.S. is beginning to take notice, and the State of Oregon has adopted a new Territorial Sea Plan that includes policies and maps governing how renewable energy will be allowed to develop in state waters, taking into account other users such as fisheries. Four sites have been designated for initial development, representing about two percent of territorial waters.

The Oregon Wave Energy Trust runs programs that accelerate the commercialization of ocean energy technologies developed by businesses that work in Oregon. Ocean Power Technologies (OPT) is one partner involved with the trust, and its utility-scale PowerBuoy is expected to be deployed off the coast of Reedsport, Oregon, this spring. The PowerBuoy, which incorporates a proprietary new direct-drive power takeoff system, will be the first of up to 10 proposed devices for the grid-connected Reedsport OPT Wave Park. The project will generate 1.5 MW of electricity, enough to power about 1,000 homes.

Another partner, Columbia Power Technologies, aims to accelerate development by using software from Ansys and other companies to evaluate the performance design prototypes. The latest version of the company’s SeaRay wave device aims to have optimal shape and minimal complexity to minimize maintenance costs. The system is scalable and can be sized to suit low-energy generation and storage applications, such as powering oceanographic sensors, or to produce utility-scale electricity generation.

Harnessing the Currents

Hydro Alternative Energy (HAE) in Florida has developed a system that harnesses the energy from currents rather than waves or tides. The company is setting up a demonstration plant in the Agulhas Current off South Africa about 25 miles from shore. Eventually, up to 100 MW of capacity will be installed, consisting of around 25 of HAE’s Oceanus units. “Our technology works within ocean currents, which in most areas are consistent and stable,” says HAE President Enrique Pallares. “Such currents have been flowing through the same places for millions of years.”

The Centre for Renewable and Sustainable Energy Studies at the University of Stellenbosch in South Africa has studied the Agulhas Current and found that, if all the exchangeable kinetic energy from the current was able to be used for power production, it would total about 50 GW. While areas of extreme water velocity are very high in kinetic energy, they only exist in a small percentage of the world’s waters. HAE’s system is intended to provide electric power using typical water conditions.

Pallares says this makes Oceanus more attractive than solar or wind power. “It is just a matter of the mass of water being approximately 800 times denser than air, which means we need less speed than a wind turbine because we have a denser fluid hitting our turbine. The energy being extracted from solar requires sunlight to produce electricity; and in the best-case scenario there are 12 hours of sunlight a day, making it useless more than 50 percent of the time.”

There are many places in the world where the power of the currents can be tapped into, Pallares adds. “Our basic system is designed to produce 1 MW of power at speeds of one meter per second. If water flows faster, the output of the system increases considerably. The depth that we can go has no major limitations since we use the very same technologies and companies that have been mooring oil platforms for decades.”

Thermal Energy

Another predictable energy source is being developed in Japan by Yokogawa Electric Corporation, IHI Plant Construction and Xenesys on Kumejima Island. Ocean Thermal Energy Conversion (OTEC) uses the temperature difference between warm surface water and cold deep water to generate electricity. A low-boiling-point fluid such as ammonia is pumped into an evaporator where the transfer of heat from the warm water causes it to vaporize. This vapor drives a turbine to generate electricity and is then condensed by the cold of the deep water. The technology is most suitable for tropical and sub-tropical regions.

The first plant is an onshore facility since smaller than 1 MW units are more suited to onshore locations where they can be combined with other applications, such as air conditioning and agriculture. A 10 MW offshore facility is in the planning stages.

“The Japanese government’s restart of research and development into offshore renewable energy was not ‘after’ 3.11 (the date of the Fukushima nuclear accident), but approximately one year before,” says Shin Okamura, spokesman for power generation system manufacturer and designer Xenesys. “Then, after 3.11, public opinion has been pushing renewable energies, including offshore renewable energies, forward very strongly. So I think it is Japanese renewable energy engineers’ obligation to develop and promote OTEC to contribute to the power supply in Japan and South Asia for the next generation.”

Sun Power

DNV is also targeting the Asian region with its SUNdy concept – a large-scale offshore solar energy field that features an hexagonal array floating on the sea surface. A collection of these arrays, totalling 4,200 panels, forms a solar island the size of a large football stadium and capable of generating 2 MW of power. Multiple islands connected together make up a solar field of 50 MW or more, producing enough electricity for 30,000 people.

The SUNdy concept is made possible by the use of thin-film 560W solar panels which are flexible enough to allow them to undulate with the ocean’s surface, explains Dr. Sanjay Kuttan, Managing Director of the DNV Clean Technology Centre in Singapore. “The key to creating an ocean-based structure of this size is the use of a tension-only design. Rather like a spider’s web, this dynamic, compliant structure yields to the waves, yet is capable of withstanding considerable external loads.”

Kuttan says that separating the solar arrays into prefabricated sections allows for large-scale manufacturing and streamlined assembly offshore. The cable grid provides for maintenance access in the form of floating gangways. Below the surface, the shape of the island is maintained by the tensile forces from the lengthy spread mooring.

Many countries in Asia are turning to solar technology and renewable energy, particularly highly populated countries which need more and more energy to supply their booming economies. In the large cities of Asia there’s limited opportunity for rooftop solar power, and urban areas would command premium prices for large-scale mounted solar production.