The idea of embedding turbines in breakwaters to convert wave energy into electricity is not new. However, Norwegian company WAVEenergy is developing a variation on the theme that demonstrates considerable innovative flare.
The so-called SSG is an energy converter based on the wave overtopping principle utilising a total of three reservoirs placed on top of each other in which the potential energy of incoming waves can be stored and exploited by embedded multi-stage turbines.
It was Norwegian Egil Andersen who came up with the idea. However, in autumn 2003, he sold the patented concept to entrepreneurs Stig Bakke and Leif Inge Slethei, both of whom have previous experience in developing successful oil&gas sector businesses.
They formed a company around the idea and, today, WAVEenergy is preparing a pilot project where a full-scale technical prototype of the SSG breakwater structure will be installed on the west side of the island of Kvitsoy, near Stavanger, subject to winning through on planning.
In preparation of the pilot project, which is part-funded by the European Commission FP6-2004-Energy fund, WAVEenergy carried out wave data recordings over the period November 3, 2004, to April 30, 2005, in order to determine the wave climate on the test site and to inform the design process for the SSG prototype, including turbine.
Two rounds of model tests have been performed in the deepwater 3D wave tank at the Hydraulics and Coastal Engineering Laboratory, University of Aalborg.
The tests were carried out using 1:15 and 1:25 scale models. The firm says the overtopping discharges results are promising.
Testing of a 3D model of the structure in oblique and 3D wave condition was performed in the autumn of 2005. These tests included measurements of local and global forces on the structure in order to enable a reliable structural design when the first full-scale prototype is built.
Much of the progress is down to the determination of Monika Bakke, WAVEenergy’s general manager and daughter of co-owner Stig Bakke. Monika started with the company in 2006, having spent a number of years in a variety of offshore oil&gas industry roles, and she appears happy with the decision.
“I don’t consider it a risk, but a challenge,” Bakke told Energy during a briefing trip hosted by the Offshore Northern Seas Foundation.
“I appreciate the opportunity to do something new. It’s not just about working in a new industry but also being with a company where one can be involved with the full range of activity.”
Bakke said WAVEenergy had attracted not just EC funding, but also more than 2million NKr (£200,000) from Norway’s Innova fund, plus a private placement in November raised a further 22.5million NKr (about £2.25million).
“As a result, we secured the capital required to prove the technology and build a full-scale pilot plant. That was the milestone of 2006,” she said.
“The stage we’re at now is to select the best location for the plant while also taking into account longer-term issues to do with commercialisation. Most likely, it will take us 12-18 months to construct the plant and get it started up.”
The initial emphasis is on integration of key elements of the structure and its turbine, also sorting out a grid connection, and so forth.
While the objective is to build commercial structures capable of generating six to 10 megawatts of power, the prototype will generate in the range 200-300 kilowatts.
“The main thing for us will be to show that our principle will work.
“It’s very simple, with few moving parts. It’s about taking existing knowledge and putting it together in a new way.”
Explaining the overtopping principle, Bakke said the SSG breakwater shared something in common with conventional hydropower.
“But our patent is based on having multiple reservoirs placed one above the other.
“The challenge all along has been to effectively use different wave heights.
“There are such large variations. Many wave technologies have to optimise for a single average wave height. In our case, the greater the head the more we should get out of the reservoir system. A head of three metres should give very good production.
“We have proved in lab tests that hydraulic efficiency above 50% can be achieved. This is the sort of thing we want to confirm through the prototype testing, as well as getting operational experience in terms of controlling turbine output.
“Another of the things that we have to prove is whether we can, in fact, build the structure that can take the forces that it will be exposed to.
“The first winter storm will, of course, be a big test.
“We have also started thinking in terms of commercial projects … they’re big and need a lot of planning and involve a lot of materials. They could be integrated into port infrastructure.”
But Bakke admitted that WAVEenergy faces the same basic challenge as all other wave-based energy converters – that of getting the cost down to an acceptable level.
“That is why we’re looking at potential projects where it may be possible to share costs … get double value out of one structure. So, instead of just a conventional breakwater, there could be a breakwater based on our over-topping design that could generate power for at least the next 50 years.
Recommended for you
