At first sight, the apartment complex in Bochum-Weitmar in Germany looks just like any other. But between the blocks built in the 1960s and 1970s is a modern low-rise building that really stands out. It has large windows that give a view of all the technology inside – and of the future. This building is an innovative energy center that will store solar energy generated on the roofs and distribute it to the different consumers.
The control center provides more intelligent solutions in many areas, such as charging electric cars. Normally all the car owners want to charge their cars as soon as they get home in the evening, but that leads to short-term load peaks and the use of additional electricity from the public grid. By contrast, the intelligent energy center would charge the cars overnight, one after another, with locally generated and stored electricity. The first solar cells have already been installed in Bochum-Weitmar and the owner of the complex, Vonovia, plans to bring the energy center into operation during this winter. It will enable the complex to generate 25 percent of its electricity and 60 percent of its heat in the future.
We will see self-sufficient islands of this kind in more and more cities in the future because they are good for the climate. Experts estimate that a housing complex can reduce its CO2 emissions by up to 20 percent with a control center of this kind. District energy management systems will also reduce the residents’ utility bills and bring the energy transition closer. If the supply and demand for electricity can be balanced out locally, fewer new power lines will be needed to bring wind power inland from the coast, and it will be possible to do without extra power plant capacity to cover peaks in consumption.
Optimizing the entire system
The positive feature of district energy management is that it improves the entire system, not just individual parts of it. “This opens up the possibility of using solutions that are not possible or not affordable for individual buildings,” says Clemens Felsmann, a professor at TU Dresden. The new houseboat complex Schoonschip in the north of Amsterdam is a good example of the benefits of an overall control system. All 30 floating buildings there are equipped with a photovoltaic system on the roof and a house battery. Each houseboat rarely manages to supply all its own energy, but the complex as a whole succeeds in doing so almost all the time, as a result of a control center with an overview of the entire system. For example, if the residents of house A go on vacation while the people in house B are hosting a party, the electricity generated by house A is transferred to its neighbor. This means that as little electricity as possible is taken from the grid operator. Because of the control center developed by the Fraunhofer Institute for Industrial Mathematics ITWM, the houseboat complex has only a 137-kilowatt mains supply. For a community of this size, 435 kilowatts is a more normal figure.
Preparing for the winter with hydrogen
For local energy management to function, the problem of storage first needs to be resolved. “The big challenge is that energy is often generated precisely when it’s not needed and vice versa,” explains Dr. Dirk Pietruschka, managing director of Enisyst in Pliezhausen in Germany, which develops district energy management systems or DEMS. These are central software solutions that manage all the energy flows in a residential complex. One typical problem is that solar cells on the roof produce most electricity in the middle of the day, but the power is mainly needed in the evenings when the cooker, the washing machine and the TV are switched on in many households. This means that the central management system has to “put electricity aside.”
In Bochum-Weitmar, hydrogen is one of the solutions to this problem. Behind the glass façade of the energy center is an electrolyzer that uses solar energy from the roofs to produce hydrogen. This happens mainly in summer when electricity generation exceeds consumption. The process runs in reverse in the winter with a fuel cell that turns the hydrogen stored in the energy center back into electricity to power heat pumps, for example. Batteries will also be used, together with a central heat storage facility that can supply all the homes via a local heating network. In theory, the buildings themselves can also be used for energy storage. For example, if a DEMS sees from the weather forecast that a particularly cold night is coming, it could pre-heat all the rooms slightly during the day. “The residents would not generally consider half a degree or one degree to be annoying,” says Pietruschka.
Electric cars for decentralized storage
In theory, the control center could also use the residents’ electric cars for storage purposes, because private cars generally spend around 95 percent of their time in the parking lot. This concept, which is known as vehicle-to-grid or V2G, is already being tried out on the works site of the Italian car manufacturer Fiat. In the future, up to 700 cars here will function as a buffer for the local electricity grid. The municipality of Wüstenrot near Heilbronn in Germany is also planning to use cars as storage facilities. But there are still some obstacles to be overcome, because only a few electric models are designed to return electricity to the grid and many owners fear that this will lead to excessive battery wear.
The magic word for local energy management is “predictive.” A DEMS not only balances supply and demand in the moment but is also constantly looking to the future. “The trick is to take the chance out of the system,” explains Karsten Schmidt, founder of the Munich-based company Ampeers Energy that developed the software for the energy control center in Bochum-Weitmar. Among other things, it follows the weather forecast and estimates how much electricity is likely to be generated and consumed over the next few hours and days. For example, if the sky is going to be overcast, the software puts more energy into the storage systems. In addition, the system analyses historical consumption figures, identifies patterns, and responds accordingly. For example, if a public holiday is approaching, the electricity storage facilities are charged up as a precaution, because more people generally spend time at home on a national holiday, which means using more electricity.
Conventional algorithms are not able to handle these complex forecasting tasks. This is why artificial intelligence (AI) is increasingly being used for energy management purposes. Ampeers Energy uses an AI system that produces uninterrupted forecasts for the next seven days, 24 hours and 15 minutes. The calculations are so complex that they have been outsourced to an external data center and even that takes almost 30 seconds to produce the 15-minute forecast. A normal PC would take 15 minutes!
The central intelligence of a housing complex can do its job best when it gets support from the residents. For example, in the Dutch houseboat community Schoonschip, the DEMS can see everyone’s appointment schedule, which allows for perfect advance planning. For example, if a resident is going on vacation, their heating is turned down early and the solar power generated on their roof is transferred to their neighbors. This brings the dream of self-sufficient districts a little closer. “Predictive management will enable the proportion of locally supplied energy to increase to as much as 70 percent,” explains Pietruschka.
Experts currently disagree about how heavily the residents should be involved in the energy management process. Some want systems that the people living there do not even notice, while others would prefer the residents to play an active role. For example, it would be possible for every resident to be connected to the central control system via an app. If excess electricity were generated, the DEMS could send out a message saying: “Electricity is cheap at the moment. Put your washing machine on.”
Legal acrobatics are needed
There are plenty of visions of decentralized energy supply systems, but the road is long and tough. “Among other things, we need some legal acrobatics,” says Volker Stockinger, professor of energy-efficient buildings and building automation at Nuremberg Tech university. The obstacles include the fact that the law in Germany does not currently allow electricity to be sold by one housing complex to another if there is a road in between. In addition, the wide variety of different ownership models make action on a district level difficult. “We need to lay two cables to each household as part of a pilot project,” explains Stockinger.
Another inhibiting factor is that district energy management can only be easily implemented in new buildings. For example, underfloor heating can be installed from scratch, which reduces energy consumption when combined with a heat pump. It is difficult to retrofit these systems in existing homes. “We don’t have the data connections we need to connect all the components,” says Pietruschka, highlighting another problem. The conclusion of the professionals is that district energy management is not affordable at the moment without subsidies unless the long-term consequences of climate change are included in the calculation. But the vision of a district without a connection to the public grid remains realistic, even in cold, cloudy Europe. “The technology is available,” stresses Felsmann from TU Dresden. “Self-sufficiency is just a question of space and money.”