Photo: DONG Energy

Easier to connect cables between wind turbines

Wednesday 10 Dec 14
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by Ivalo-Jensen

Prize winning MSc thesis

The master's thesis ‘Optimization of the Cable Collection Grid in Offshore Wind Farms’ received top marks. And in 2013, Michael Lindahl and Niels-Christian Fink Bagger received DONG Energy’s thesis award of DKK 25,000.

The thesis subsequently also received the Dansk Selskab for Organisationsanalyse (Danish Society for Organization Analysis) award for best Operations Research MSc thesis.

Connecting offshore wind turbines and submarine cables is a complex undertaking. A newly developed tool makes the calculations both easier and less expensive.

The Danish government's target is to be among the world's three most energy-efficient countries by 2020. And by 2050, 100 per cent of Denmark's energy consumption must come from renewable energy.

With its directive to promote the use of energy from renewable sources, the EU has also set ambitious targets, i.e. that 20 per cent of EU's total energy consumption by 2020 must come from renewable energy. One of the means to achieve these targets is to establish more and bigger offshore wind farms. Something which DONG Energy among others, is doing—currently setting up offshore wind farms in England, for example.

Offshore wind turbines
When an area has been earmarked for offshore wind farming, and the optimum location for the wind turbines in relation to the wind conditions has been identified, the turbines must be connected to each other by miles and miles of cables, and again be connected to a substation—an offshore platform that transmits the power to the shore via submarine cables. However, the cables can be connected in a myriad of ways using several different cable types. This involves calculations that DONG Energy's engineers have to make on the basis of a wide range of factors.

Saving both time and money
To optimize the planning process, Iván Arana Aristi, Cable Engineer in DONG Energy, in spring 2011 entered into a collaboration with DTU Management Engineering. In this connection Associate Professor Thomas Stidsen proposed that the task of simplifying the calculations be carried out as an MSc thesis, and two MSc students (today both industrial PhD students), Niels-Christian Fink Bagger and Michael Lindahl, took up the challenge. The result was a tool which functions as a add-on program to Excel which DONG Energy's engineers already use in their work. A result with which Iván Arana Aristi is extremely pleased.

“Niels-Christian and Michael have developed an amazing software tool. Their method optimizes the process and uses as little cable as possible,” he says.

Grid Analysis Engineer at DONG Energy REN Power, Georgios Rogdakis, is also very satisfied:

“The new tool saves us a lot of time. In a matter of just a few hours, we can identify ten layouts (ways in which you can place and connect the cables, ed.) and at the same time decide which of them is most suitable. Previously it took a whole day to create two-three layouts."  

Photo: DONG Energy
Connecting large offshore wind farms requires many miles of cables. Thus, finding the best way of doing this has extensive savings potential. However, it requires advanced mathematical calculations.

Complicated mathematics
The underlying mathematical model turned out to be extremely complicated, as it in its final form consisted of almost one billion equations and 50 million unknown variables. But by employing mathematical and engineering methodologies, Niels-Christian Fink Bagger and Michael Lindahl were able to program an algorithm that could solve the model in a computer program that could act as a plug-in program to Excel.

The tool makes it possible to calculate the impact of different decisions early in the process. This could be by changing the location of a platform or the type of cables used. This gives DONG Energy the opportunity to make much more informed decisions at an early stage in the process because it is possible to examine several possible combinations, before a final decision is made.

"Flexibility is one of the tool's most important contributions to the company. Previously, users did not know which locations or which layout were the best , but using this new tool they can be sure to always choose the most optimum combination," explains Iván Arana Aristi.

Article from DYNAMO no. 39, DTU's quarterly magazine in Danish.