It was the promise he made during construction: ‘Soon we will have to supply 24/7.’ Bart Hoefakker, CEO of Gemini and also responsible for Operations & Maintenance, was very busy at the time making careful preparations for the phase of management, operations and maintenance. After commissioning in the spring of 2017, that phase has now arrived. What is the current situation of the park?


‘We reached full operations in May 2017. And I am very satisfied with our performance since then. What we envisioned has come to life. We started – almost unnoticed – while the construction was still in full swing. And now we have completely taken over the park and we are continuously looking for opportunities to perform even better.’ Hoefakker mentions the systematic thinking in terms of ‘plan, do, check, act’ as an example: ‘It means continuing to look closely at your costs, but also at your performance.’
That’s a pleasurable challenge with the people surrounding him: ‘I have been able to put together a proper team. The different characters fit well together. They are unique people who, together, provide for sufficient diversity. They are calm, but in the meantime they are always looking for the finishing touch – how we can do things just a little better. Our team is also small, so people have a lot of responsibility and the opportunity to develop themselves. At Gemini, learning is allowed and is made possible.’

Always trying to do better

Making connections

Looking at the park’s performance – the 150 workhorses from Siemens, with the 4MW turbines – Hoefakker is just as satisfied. ‘The technical availability is excellent. We said: if there is wind, the windmills must operate. And we have done that.’ Even the maintenance teams in the park work well: ‘Technically and organisationally. We have said from the beginning that we want to make connections with our maintenance people and companies. Try to find the common interest and go for it. We are continuously working on it.’
Another of Bart’s tasks is to keep Gemini’s shareholders up to date of the park’s performance. ‘Here, too, we are very proactive. The Board receives an operations update every month. This works well. It’s also part of my personal motto: always one step ahead.’


‘Try to find the common interest together and then go for it. We are constantly working on that.’



Wind park Gemini is connected to the mainland via two large export cables. All sorts of information about the performance of the park is also received through these cables. The task now for Peter Huiberts, as a SCADA engineer, is to manage this well. ‘We have no less than 40,000 sensors in the park and they each measure something.’


It’s quite a mouthful, the meaning of SCADA – supervisor control and data acquisition. In other words: the managing, collecting, forwarding, processing and visualising of measurement and control signals of machinery in large systems. It is a profession in which Peter Huiberts previously gained experience at Vattenfall, until Gemini crossed his path in 2015. He started at Gemini in January 2016, in the last phase of the construction of the park. He immediately clarifies the importance of SCADA in a project like this one: ‘The park is much more than steel, cables and turbines. SCADA is, in fact, the backbone for the park’s performance. You could also call it technical automation.’ All sorts of information are received from the park on a 24/7 basis. ‘We have two control centres – one at energy provider EWE in Oldenburg, which is mainly used for the operation & maintenance for the electrical infrastructure, and one at OutSmart (energy asset advisers) in Emden, where the marine and air coordination takes place, among other things.’

Custom made

This structure was devised before and during the construction of the park, says Peter. ‘You have to know ahead of time how you want to set up SCADA. Then you provide these requirements to the builders in the requirements specification.’ He encountered all of this when he started working at Gemini. ‘Everything has been custom made for Gemini. Everything is redundant, so we can always switch over to a second system.’ Over the course of time new topics continually arise, such as cybersecurity – protection against external malicious figures.

Managing the dataflow

‘The park is much more than steel,

cables and turbines. SCADA is the

backbone for the functioning

of the park.’

 ‘But we are also already thinking about the replacement of the first systems, for example.’
Besides the two control centres, a massive amount of data is also received each day at Gemini’s data warehouse in Amsterdam. ‘There we extrapolate important information for our package employees and for our management team. Live displays of how the park is functioning appear on six screens in the office, which is very good for team building. We also use it as new product introduction (NPI) to advise our shareholders on how they can use SCADA in their new projects. And the data are also used by outside researchers, such as for monitoring the fauna in the area.’


Thousands of sensors

Because Peter Huiberts already had experience with other wind parks and joined Gemini in the construction phase, he can precisely explain the difference between “builders” and “managers”. ‘We are calmer, and not continuously busy with deadlines, contracts and other commotion. Our task is clear: keep the flow of electricity going. We use all sorts of sensors for that, which can be found on the park but also, for instance, in the export cables. We can continuously monitor the temperature in the cables, if the park is supplying 600 MW, for example. With some 40,000 points of measurement, we can monitor what is going on almost 100 km off the coast.’



Tom Obdam has only been with the team for a short while but he has already found his place at Gemini. He graduated from Eindhoven University of Technology in wind energy and subsequently worked at ECN Offshore Wind and in the Offshore Operations department at Eneco. And now one of his responsibilities is the “electricity supply contract” at this wind park. ‘Fundamentally, it’s about satisfying our obligation to provide electricity.’


In his profession, Tom Obdam is always focused on tomorrow: “Each day we try to make the most accurate prediction we can of the next day’s capacity of the wind park, and that specified for each hour. The energy we produce is delivered to PZEM in Zeeland. They issue green certificates for the production and then the electricity is sold.” For Tom Obdam and his colleagues, the trick is to estimate the capacity of the park based on expected wind speeds. “How many turbines will be operating, what will be the wind direction and the wind force?. We are continually evaluating and based on that we learn how to explain the deviations that occur. We use data analysis to try to discern which factors influence the actual capacity of the park. This is certainly an art. In the perfect curve, the forecast yield is exactly equal to the actual generated capacity.” Tom maintains close contact with two offshore representatives who are located in the park on a ‘two weeks on, two weeks off’ basis. “They provide me with the most current information, such as which turbines will be disengaged. And we also have to take into account, for example, the campaigns that are necessary for maintenance.”

Predicting the Gemini-power curve


Tom Obdam, as the asset manager, is also concerned with maintenance contracts. “We conclude these contracts for a longer period of time, but naturally do look at opportunities for improvement and any cost reductions in the intermediate term. Optimisation is the keyword here.” All aspects relating to maintenance are monitored, even, for example, the performance of the maintenance ship Windea la Cour: “The ship has been in operation for a year now, so we can see how it has fared with, for instance, different wave heights. These are all data, which are becoming available in this – still quickly developing – industry. Eventually, the objective is to pass on the experiences from the management phase to the builders of new parks, so that they will ask themselves at the start: Can we properly maintain it later?”


‘Ultimately, the goal is to bring the experiences from the management phase back to the builders of new parks.’



We are speaking with Guido de Groot for the second time. The first time, he was still living a very varied life as a client representative: he was monitoring the construction of the wind park, both on land as well as on location. Now the title on his business card has changed to Balance of Plant Engineer. That means he is responsible for the maintenance of all the hardware in the park, except for the turbines and the High Voltage Stations. How does he feel about this new job?
All foundations, cables and jackets that are located in the wind park – up to and including the deposit of stone – form the working grounds for Guido de Groot. His job: the annual check and the subsequent maintenance. ‘I have seen how it has been built, and the trick is to keep it in good condition throughout its entire operation.’ In doing so, the key concept in his vocabulary is “control”: ‘We work with all sorts of teams who are responsible for both the planned and the unplanned maintenance. They must be sent on their way with the proper assignments. And vice versa: the teams must ensure that they do the right work and report back to us properly about it.’ The accent here is increasingly on the first category, says Guido: ‘The growing pains are over and with them the remedying of the problems we have experienced in the first year of operation.’

Maintaining the valuable assets

‘The trick is always to come up with the right measures - in this sense we are really a learning organization.’

Cyclical process

De Groot sketches an average maintenance year at Gemini: ‘It is divided into three phases – preparation, implementation and analysis. Preparation in the spring, implementation during the months of nice weather from May to the end of August. This occurs in all sorts of ways: under water with remotely-operated underwater vehicles (ROVs) but also with specialists who hang in ropes alongside the construction of the OHVS. The rest of the year, we look at how it functions and we all learn from that.’ All sorts of issues come up in this phase: ‘We see that a component is wearing. Is that in line with the expectation given by the manufacturer? Or is something else going on? But we also look at the quantity of sand on top of the export cables, for example. The entire length of cable is measured with a survey and then we can see if any action is required. Certainly in the Wadden area, where we are in a living system with high and low tides, we see all sorts of dynamics at work.’ Guido is enthusiastic about the varied work: ‘Is this work boring? Absolutely not! If we do it well, we are securing the value of the park. The trick is to keep thinking of the proper measures – in that sense, we really are a learning organisation.’
2x75 Wind Turbine Generators
Offshore        Onshore
Land High Voltage Station
Horizontal Directional Drilling
Offshore High Voltage Station (Zee-energie)
Offshore High Voltage Station (Buitengaats)