The future of energy generation is localized and renewable. But that also changes the demands placed on the power grids. They will increasingly have to cope with larger, fluctuating amounts of energy from wind farms and solar arrays without allowing the grid voltage or frequency to drop out. To do so, they need flexible energy sources that the grid operators can call upon at short notice. The energy supplier ÜWAG in Fulda operates such an energy source. In recent years it has upgraded its power plant with custom-built diesel generators from MTU Onsite Energy and now supplies flexible emergency, control and peak-load power on the dot.
What does Hans Müller in Germany do at 7 in the morning? He makes a cup of coffee. Luigi Motta in Italy uses a fan heater to warm up the kitchen. Michelle Potier in France cooks breakfast. They all enjoy the last few moments of calm before the sun rises. Silence reigns but the grid is starting to hum. Because right on the dot of 7 a.m., not only Hans Müller, Luigi Motta and Michelle Portier use electricity – millions of other people do too. The electricity being generated just at this moment by power plants both big and small is not enough to cover the demand. The grid is overloaded.
Combined European grid delivers
This is the moment for flexible power plants. Überlandwerk Fulda Aktiengesellschaft (ÜWAG for short) is one of them. It was built 100 years ago – originally to supply electricity to the citizens of Fulda. But nowadays there is a combined European power grid into which not only largescale power stations but an increasing number of smaller, localized energy plants feed their electricity. That power is distributed to the individual households and industrial facilities via a network of transformer stations and substations. ÜWAG in Fulda had to find itself a new place in that system – and succeeded in doing so.
Power for demand peaks
The plant supplies peak-load power when demand is so high that there is not sufficient capacity available in the combined grid. Just about the time when Hans Müller, Luigi Motta, Michelle Portier and millions of others switch on the lights or put on the kettle. “Between 7 and 8 in the morning and at about 8 in the evening demand for power rockets,” explained Frank Weinmann, head of the Energy Generation and Procurement department at ÜWAG. In the past, the demand peak occurred around midday, whereas now people use most electricity in the morning when they get up and when they get home in the evening. “The demand pattern gives you a good idea of how people’s lifestyles have changed,” he smiled.
To be able to balance out the demand peaks more effectively in future, ÜWAG in Fulda has spent €10 million modernizing its power plant in recent years. Two old diesel engines were retired and replaced by six smaller generator sets supplied by MTU Onsite Energy. The key component of each genset is a 20-cylinder MTU Series 4000 engine. “I don’t know of any diesel power station in the world that is more modern than ours right now,” said Frank Weinmann looking down proudly from the control room onto the blue MTU Onsite Energy power modules. “Those engines are real Ferraris,” he enthused. They can start up and synchronize with the European power grid within a matter of a few seconds. The old engines would have needed several minutes to do so.
Control power balances out grid fluctuations
“In today’s power generation world you have to be fast,” he explained and he went on to point out that it is not just because demand peaks occur much more frequently nowadays. The constantly growing proportion of electricity from renewable sources is also a factor because, in contrast with conventional large-scale power plants, it is not possible to precisely predict how reliably they will supply energy to the grid. Put simply, if the sun is shining or if it is windy, there is a power aplenty. But what happens on windless days or if the solar panels are covered in snow? That is when the supply frequency of 50Hz is at risk and the possibility of a power outage looms. So that it does not happen, the transmission grid operators fall back on sources of control power. These are mostly provided by the energy suppliers themselves. But local authority power plant operators like ÜWAG in Fulda are becoming increasingly important. The ÜWAG staff do not know when the engines will start up. The grid operators pay for the privilege of being able to call on the generators in an emergency. But when that point is reached is up to them. When they do draw on the supply, they have to pay the going rate. And what that is depends on how quickly the power plants can supply the electricity. Up to now, ÜWAG has mainly supplied what is called tertiary or short-term operating reserve energy. That has to be available within 15 minutes of being called upon. However, with the new MTU Onsite Energy gensets, ÜWAG will be also be able to supply the substantially more lucrative secondary reserve power. To do so, a provider has to be capable of supplying 100% of the registered capacity within 5 minutes. Generating and delivering electricity that quickly is a major challenge because not only do the generators have to start up from standstill, they also have to synchronize their frequency, voltage and phases with the combined grid system within a matter of seconds. “Our modules can only do that because they are highly sophisticated and perfectly integrated systems made up of engine, generator and engine controller,” explained Dietmar Witzigmann, who was in charge of the project at MTU Onsite Energy.
Backup supply for emergencies
That ability to supply energy within a few seconds also benefits the local population. Because ÜWAG not only provides peak-demand and control power for the big power grids, it also supplies electricity to the city of Fulda. If the national grid suffered a failure, the generators at ÜWAG would make sure all the lights do not go out. In that case, a “blackout startup” genset that requires no external electric pumps or auxiliary equipment to fire up automatically starts up and supplies the energy for the other five gensets to be started. Together, they can supply 24.8MW of electricity to power the street lights, traffic lights, hospitals, care homes, refuge hostels and community buildings. “Fulda is one of the few towns in Germany that can do this,” recounted Frank Weinmann confidently. So far, such an emergency has not happened, but the energy expert is certain that the Germany can expect to see more power bottlenecks in the future.
Project Leader Sven Kunkel was in charge of converting and updating the power plant. It was a considerable challenge for the electrical engineer because diesel engines had not been his specialist area before then. “I know all about power grids. But electricity generators were not part of my world before,” he smiled. There is little evidence of that now. Full of enthusiasm, he told of the many challenges he faced. It started even before the conversion because the power plant was actually too small for his plans. He wanted to be able to generate nearly 25MW of electrical power – as cleanly, economically and reliably as possible. “I did consider whether we should extend the plant, but that would have involved a vast amount of approval work,” he recalled. North Sea He was also impressed by the open and positive approach adopted by the team from MTU Onsite Energy. "We always regarded each other as equals in our discussions and developed our ideas jointly. That was how the suggestion came about to replace the two large gensets with six smaller ones and build a gallery floor to accommodate the SCR systems for exhaust gas aftertreatment.”
Cleaner, faster, more economical
He reported proudly how cleanly and efficiently the units run. “With the new engines we have reduced the particulate emissions to a sixth of what they were, nitrogen oxides to a quarter and carbon monoxide to half the previous level per kilowatt-hour generated, and even lowered fuel consumption by 10% at the same time,” he recounted. The reason for those impressive figures are the modern engines with commonrail fuel injection and controlled SCR catalytic converters. The latter clean the exhaust by injecting urea into it. In the catalytic converter, the urea reacts with the nitrogen oxides to form the hamrless substances water and nitrogen. “These generator sets are inside the air pollution limits by a long way,” he stated with conviction. And with the power plant being right in the town of Fulda, it goes without saying that the emission levels have to be as low as possible. Because of that inner city location, ÜWAG also paid particular attention to reducing noise emission. Special soundproof walls allow almost no sound at all to escape to the outside when the engines are starting up and running.
That is something that will be happening more frequently in the coming weeks. It is in the winter when the weather is cold that the demand for electricity increases. “In the run-up to Christmas, everyone is baking,” said Sven Kunkel. “And apart from that, it’s cold outside, the days are short, and businesses are working at full tilt to get the jobs finished before the end of the financial year,” he added. As at any other time of year, reliable generators are a must in this period. For that reason ÜWAG has had a special remote diagnosis system installed. It allows the specialists at MTU Onsite Energy in Friedrichshafen to access the gensets and other components of the plant remotely and give advice on how to prevent or rectify faults.
The first three of six gensets went into operation in the power plant on December 23, 2011. Sven Kunkel remembers the period just before then very well. He and the whole team were under extreme pressure. Especially because at that time the plant had to be kept running constantly at 75%. “We were contractually obliged to supply electricity, we couldn’t shut down.” It was not until September 2012, when the local authorities in Fulda celebrated the inauguration of the power plant that Kunkel was finally able to relax. "The flexibility of this power plant meets the demands of the current market perfectly. It really is something special for a local authority supplier to have something like this," recalls the electrical engineer who is now also a diesel engine specialist.