The Danish solution
- The total overview in the central control room of Energinet.dk in Fredericia.
In stormy months 41% of the power coursing through the Danish grid is wind-generated. Some hours there’s more of it than needed. So that it can become even more, consumers are to co-manage the grid.
Written and photographed by Marcus Franken
Dusk is slowly darkening Roskilde Fjord as Erik Bindner opens the door to an octagonal building. The house on the fringe of a former nuclear research centre looks like a Mongolian yurt that got too big. A breeze drives the rotors of four small wind converters nearby. “That one there,” says Binder, pointing to a plant with blue, turnable blade tips, “is the prototype of one of the first wind converters made by Bonus.” It’s a 55-kilowatt machine which was made decades ago for export to the US, was tested here at the Risø National Laboratory, and is now used for renewable energy experiments. Erik Bindner switches on the lights in the laboratory hall.
As neon lights flicker on, part of a test bed emerges that used to be for measuring rotor blades. For today’s blades the hall would be far too small. We’re standing beside beige-coloured switchgear cabinets and a small server. “We’re in the process of building a separate power grid at Risø with the wind converters and a building,” Bindner explains. More switch cabinets are to be added this year to control a photovoltaic module and a Redox Flow battery. Redox Flow batteries are the latest thing in power storage. When there’s surplus energy, the electrons attach to the element vanadium and when the power is needed again it’s retrievable. But of more interest than the new power storage technology that’s to stand in the old Risø reactor hall will be patient testers. “We want to connect up a few student offices next door as consumers.”
A laboratory for Europe
At Risø they’re sure big power stations won’t dominate the power grids of the future. The energy will be fed in by more and more small-scale producers, from wind turbines through to combined heat and power (CHP) from bio energy installations. And such small plants are no longer manageable from a master control room somewhere in the middle of the grid. “The network has to be managed locally,” says Poul Sørensen, head of the wind energy division at Risø. Large, transnational grids can no longer be controlled with the centralistic concepts of the 60s. To deal with outages, localised structures for 10,000 to 100,000 people have to be designed in a way that enables them to operate alone if they have to. Hence PV installations, wind converters and consumers from the toaster to spatial heating have to work together. And best would be if all installations were networked and able to be switched on and off independently.
This is the utopia Henrik Bindner and his colleagues want to try out. If the wind converters deliver too much power, the electric heaters will come on in the work rooms and use the surplus power to heat water. It hasn’t all been seriously tested yet. But even in a blackout the damage stays manageable. “There are no real people working here,” says Bindner, “but students.”
What the little Risø grid is to Denmark, Denmark is to the rest of Europe: a laboratory trialing the feeding in of renewable energies. With 15% to 25% wind share in their power supply on annual average, the Danes have a clear lead on other nations. In stormy January 2005 their wind proportion even shot up to 41%. That month contained all the ingredients needed to rob a grid operator of his sleep: substantial production surpluses, so that the only option left was to give power away. There was also a sudden outage of all wind converters because from 7 to 8 January a hurricane-like storm ripped through the Jutland Peninsula causing the machines to switch themselves off.
The Danish grid has extremely harsh conditions to contend with. Unlike in Germany, France and Spain, the power can’t be spread into a large hinterland. An added difficulty is that the power grids on the western peninsula of Jutland and the island of Fyn are completely separate from the cables of the island of Sjælland, where the capital Copenhagen, the biggest consumer, is located. The already small Danish grid is thus split into two even smaller ones.
Grid state-owned again
“There must just be a lot of wind,” comments Jens Pedersen, as he enters the control room from which the power stations in Denmark’s west are managed. Pedersen is a scientist with Energinet.dk in Fredericia, the state-owned grid operator. In the middle of the semicircular command centre sits Allan Sjøgern behind seven monitors incessantly blinking the operating data of all larger Jutland and Fyn power stations. Four metres in front of him an old-fashioned control wall displays all 400-kilovolt (kV) and 150-kV lines in red and black; the panel fi lls the entire face wall of the room. In two columns to the right green digital displays show the outputs of all the key stations. At this moment Block 1 of “FVO”, a coal-fired station near Århus, is producing 358 megawatts (MW), Block 2 136 MW. Some stations are showing zero. “They’re just undergoing inspection,” says Sjøgern. Other plants are delivering between 150 and 300 MW. Only the reading next to the initials “WMP” causes a double take: 1,271 MW. That’s the production of all wind farms in the west, whose data converge here.
37% at the border with Germany, 49% at Rinkøbing Fjord, 95% in the north, where the most Danish wind converters are. The current capacity utilisation ratio of the individual wind regions is lit up on a digital map. At this particular point in time Danish power stations are jointly delivering 4,330 MW, while consumers are using only 3,081 MW. At the same time Denmark is importing power from Norway. The surplus goes to Germany through 400-kV lines. The neighbouring Eon grid can absorb up to 1,800 MW. “The power follows the power price,” says Sjøgern, looking over to a colleague sitting to the side of the big picture with the power lines who is monitoring a few computer screens and busily talking on the telephone. This is where Denmark’s surplus or shortfall production is traded. Since August 2005 this is, in a sense, a state task because the Danish government decided to bring the grid back into the ownership of the citizens. And so the merger of Eltra and Elkraft brought forth Energinet.dk, now solely responsible for the entire grid operation. Every day Allan Sjøgern’s colleagues inform the producers how much power will be needed the next day. That’s not that hard because the consumption patterns are very regular in the daily and weekly progressions and fluctuate reliably between 1,700 MW on Sunday night and 3,500 MW in the early evening of every weekday. The power station operators put in their bids 24 hours in advance for every hour of the day and the best-priced make the sales. The biggest variable in the system is the wind.
100% wind power is possible
The difference between calm and consistently strong wind in the west Danish grid is around 2,200 MW – the sum of the wind capacity installed. In stormy nights Denmark’s wind turbines regularly produce more than the Danes use. Every six hours the meteorologists give the grid operators a forecast for the next 72 hours. The 24-hour prognosis used by the state-owned grid operator to set the energy needed the next day also contains wind power. The Danish grid operators now have more than a decade’s experience with the prognoses. But the forecasts are not 100% reliable so Energinet.dk buys and sells the lacking or excess amounts short-term as balancing power. 100 MW deviation from the prognosis is nothing special. The grid operator adds the expenses to the charges Danish consumers pay for operating their power network. Despite these costs, Poul Erik Morthorst of the Risø research facility has calculated that in 2005 wind power brought down Danish power costs by about 10%. This was because wind could often replace expensive power from peak load stations.
The 23% wind power share in west Denmark is higher than the national average. “Technically that’s no problem,” says Hans Abildgaard, who’s developing scenarios at Energinet.dk for increasing wind power absorption. In a model calculation he worked out what would happen if with the present grid concept Denmark were to slowly raise its wind power share from 20% to 100%. Technically possible, was the outcome, if Denmark kept at the ready a capacity of some 5,500 MW from gas and coal to deal with wind calms or hurricanes. By comparison, Denmark currently has a good 10,000 MW of conventional power production on the grid. However, the proportion of peak load stations would have to rise from now a third to two thirds. Power costs would only increase from a wind power share of about 30%.
The fact that the Danes can now absorb so much wind power without problems is also due to their being able to balance out their production fluctuations by exporting to and importing from Norway, Sweden and Germany, all countries with much greater power turnovers. Especially the Scandinavian neighbour countries produce power in hydro stations and can easily drop their output if a lot of Danish and German wind power is being produced.
But Denmark also wants to be able to operate its grid independently of neighbours while increasing the wind share. The already announced expansions of the Horns Rev and Nysted offshore farms by 200 MW each will be followed by more projects. The Danish energy authority ENS has not given details of how exactly the expansion is to proceed. “Next year the minister will present a strategy paper,” says Anders Kristensen, who looks after the licensing of high-voltage lines and the connection of offshore parks in the relevant section of the ministry for transport and energy.
New links, new lines and power for heating
One can already get a rough idea of what the Danish solution will look like. To take in more wind power, a direct current link will first be built between the east and west Danish grids. It’s to buffer the fluctuations and regularise the intake. If everything goes according to plan, the cable will be laid across the Store Bælt in 2009 and Denmark will gain scope for another 600 MW of wind energy. New high-voltage lines are also to make the grid less prone to outages.
But that’s not going to be enough. Denmark is also one of the countries producing the most electricity from CHP. “For decades effi ciency was the central philosophy of Danish energy policy,” says Kristensen. The CHP units have capacities from 2 MW - 15 MW and are connected to the local heating grids. On cold winter nights they not only produce the most heat but also the most power. Their peak production happens at precisely the same time of year when the wind turbines are also delivering their highest output. At the same time, in those nights power consumption drops to a minimum. So what to do with the surplus?
The Danish government is in the process of softening up its efficiency paradigm. Just like the Redox Flow battery and the electric heating in the student offices at the Risø National Laboratory, it wants to use the combined heat and power plants to use the power at peak times. Instead of oil or gas burners, in future big immersion heaters could switch on in the boilers to turn wind energy into heating.
The heating rods are to tap electricity when power gets cheaper than heating with gas. “The licensing procedures for the first two or three installations are underway,” Kristensen indicates. On the other hand, nothing changes in the way wind parks are operated. They’re to keep running as much as possible. Their good manageability will remain a silent reserve for emergencies. “We can drop production here by 50 MW in a second,” says Carsten Nielsen in the control room of Horns Rev, the biggest wind farm off Denmark’s west coast. The 80 2-MW turbines are some 40 kilometres from the Vattenfall offices in Esbjerg. On this day they can’t be seen over the coal heaps and ferries in the port. Only on the monitor screen can you see live video imges of the high sea. Should a big consumer drop out anywhere, the wind turbines could cut output in seconds and so stabilise the grid. But also in a large-scale grid failure the wind machines could deliver the power that coal-fired and CHP stations need to restart.
Even now Horns Rev often performs below its peak. When at three or four in the morning a good wind is blowing, the Vattenfall power stations control in Stockholm has the rotors of the machines turned out of the wind. “Probably,” say the experts at Energinet.dk, “Vattenfall can then operate its coal and gas power stations more evenly.” Only when Denmark’s consumers need power around 6 in the morning, Horns Rev ups its output.
Numbers on Denmark’s grid
The state-owned Danish grid operator Energinet. dk was formed on 24 August 2005 from the enterprises Eltra, Elkraft System, Elkraft Transmission and Gastra, who regulated and secured the grid until then. But the official hour of birth of Energinet.dk is 1 January 2005, because the merger was backdated to the start of the year. Rather than leave the electricity infrastructure to private enterprises, by nationalising the infrastructure the Danes wanted to ensure that all power suppliers have the same opportunities to sell. Energinet.dk passes its costs on to consumers. Its turnover in 2005 was just over a billion euros.
With this money the enterprise operates, expands and maintains the gas grid as well as 1,180 kilometres of 400-kV power lines throughout the country. When it needs to, Energinet.dk can also access the 150-kV grid in the west and the 132.kV grid in the east, although these lines continue in local ownership. The entire high-voltage grid in east and west Denmark remains completely separate. In 2009 the grids are to be connected through the Store Bælt with a direct current line. That is also why after 2009 the west Danish grid will pulse to the beat of the west European system while the east Danish one will remain synchronous with the Scandinavian grid.