Denmark's clean energy future from waves
by G Lund, NOVA PRO, Denmark, et al

The Danish Wave Energy Programme is a result of a political agreement in the Danish Parliament in 1996 to develop and promote new renewable sources of energy and storage options. The programme has up to DKK 40 million at its disposal over four years. The aim is to develop relevant expertise and technologies, ultimately enabling future installation of MW- and GW-scale wave energy plants supplying 15% of the Danish electricity consumption.

An energy producing WavePlane model, scale 1:5, is survival tested during the summer of 1999

Wave Energy Programme

The Danish Wave Energy Programme has a budget of DKK 20 million (where DKK is the Danish krone) for the first two years (1998-1999).  It is administered by the Danish Energy Agency, in co-operation with an advisory panel of experts and the Danish Wave Energy Association (DWEA). The Association, formed in the spring of 1997, has about 120 members. It arranges meetings and disseminates information for its members and other parties interested in wave energy. Based on an evaluation of the results obtained, a second two-year programme may be funded by an additional DKK 20 million.

The Wave Energy Programme will adopt the "bottom up" approach that was successful in the early development of Denmark's wind energy industry by appealing to a broad popular base and seeking new ideas from inventors.  This approach is combined with a step-by-step technical evaluation programme to test the ideas.

Status Report 1999

A report published by the Danish Energy Agency in July 1999 shows that the Wave Energy Programme is making rapid progress, with the first DKK 8 million granted for development and testing of more than 20 ideas and concepts. These projects are either completely new or a further development of former Danish and foreign initiatives.

The advisory panel will follow the individual projects and try to identify those that have the potential for further development. It can be likened to an elimination race where two or three "winners" - projects with good potential - will emerge at the end of the programme in 2001. The situation is, in many ways, similar to the Danish development of wind turbines, which was also characterised by expensive and less effective plants at the beginning. To exploit wave energy commercially, substantial technical development is needed to develop devices strong enough to withstand large waves, which can produce a stable, regular electricity supply.

Step by step

Projects accepted by the programme develop in a step-by-step fashion. After each step, the project can be evaluated technically by the DWEA or the advisory panel before the next stage of development is undertaken. In the first two years of the programme (1998-1999), priority is being given to projects in early development (pre-prototype).  Several projects have now reached the final optimisation step prior to prototype development, such as the four devices which are described briefly in the shaded panels.

The programme provides economic support for appropriate initial testing of new ideas. This testing can take place either in indoor test facilities or in the open sea. An open site is located at Nissum Bredning, Jutland, near the Folkecenter for Renewable Energy. The centre provides facilities for model construction and improvements, assistance with measurements and dissemination of results.

Future options

For many years few resources have been available for wave power development and it is still very much an experimental technology. Yet its potential is particularly attractive for the colder regions of the world, as the amount of wave energy in the sea increases further from the equator. In addition, the energy content of the waves varies through the year and reaches a maximum in the winter period when energy demand is highest.

The low costs of both conventional energy and wind power make it difficult for wave energy systems to reach a commercial breakthrough without significant support in the R&D phase. Under the Danish Wave Energy Programme, a number of projects are presently being developed and tested. One of these concepts might be the one resulting in a technically and economically sustainable wave energy machine which can compete with other renewable energy sources such as wind power and solar energy.

Wave Dragon

The Wave Dragon operates almost like a floating water power plant in deep water. The waves are captured by a large platform between two floating concrete reflectors 227 m apart which focus the waves into a 2,600 m3 floating reservoir. From the reservoir the water flows back into the sea through energy-producing water turbines at a speed of 100 m3/s.  A 1:50 model has been tested at the University of Aalborg. The final platform is expected to be 100 m x 50 m x 15 m in size, with a reflector length of 100 m. The device is expected to generate 6-10 GWh/year of electricity. The next step is probably to test a 1:3 scale model within the next two years or a full-scale test in 2002. The Wave Dragon is the only Danish project participating in the EU Wave Power Energy Programme.

SWAN DK3

This project builds on a concept called the "Backward Bend Duct Buoy" which originated in Japan but has been further developed in China and now in Denmark too. The device consists of a float carrying an L-shaped pipe. The horizontal part of the pipe is situated beneath the float and is open at the rear. The vertical part is closed at the top and connected to an air turbine which is activated when the device is moved by the waves. Tests at the Danish Hydraulic Institute were completed last year. An offshore model will probably be tested in the North Sea in the year 2000. The full-scale device will be 20 m long.

Point Absorber

A float on the surface of the sea is connected to a suction cup anchor with a flexible polyester rope. Between the rope and the float is a hydraulic actuator pumping fluid into a high-pressure hydraulic accumulator. The return stroke is provided by hydraulic fluid from a low-pressure accumulator. As waves activate the float, a pressure difference between the high and low-pressure accumulators builds up. This pressure difference drives a hydraulic motor and generator. A 1:10-scale model with a float diameter of 1 m has been tested at the Danish Maritime Institute. If this is successful, a prototype with a diameter of 5-6 m and a rated output of 20-30 kW will be developed in the year 2000. The ultimate aim is a Point Absorber with a diameter of 10 m and an output of about 120 kW.

WavePlane

The WavePlane is a wedge-shaped (triangular) floating device, which is moored to an anchor at the central point. Mounted on the device is a series of funnel-like pockets, which always face the waves. Water passes through the funnels into a horizontal pipe in a spiral-shaped flow, creating torque which is converted into mechanical energy by a special turbine. The energy can be used to generate electricity or to oxygenate the bottom layers of polluted fjords and lakes. Since May 1999, a 1:5 scale model has been placed in the Mariager Fjord in Jutland. In this model, the water intake is 5 m wide and the water stream is conducted through two tubes towards the bottom instead of driving a turbine. The WavePlane has been tested at the Danish Maritime Institute. With 20 cm high waves, the flow was measured at 500 m3/hour.

For more information contact the CADDET Danish National Team in Tollose

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.