The distribution network as an active protagonist
Running a power grid is a real juggling act: production and demand have to be balanced at all times. Even minor deviations can alter the frequency and voltage in the power grid, causing damage to electrical devices. In the age of large, centrally controlled power plants, regulation was already a fairly complex task. In a world in which power is produced on a renewable, decentralised basis to supply electricity and heat, as well as being used for transportation, it becomes even more difficult still. For this reason, distribution networks have to change from being a passive recipient of electrical energy to become an active element of grid control. For this purpose they have to become smart and controllable – right down to the millions of power meters installed in households and office buildings: distribution networks have to become smart grids. In order to find out how this might work in practice, LEONI subsidiary Adaptricity has been collaborating for the last four years with utility provider Industrielle Werke Basel (IWB), the power grid operator for the third-largest city in Switzerland.
There are a wide range of factors that make controlling a distribution network more complex. One of these is how the power is generated. The City of Basel already produces a low two-digit percentage of its energy locally using solar power systems. How much power is produced depends on the weather, so it is bound to fluctuate. What is more, on very sunny days the distribution networks have to take the solar power generated that is not used locally and feed it in the reverse direction, i.e. from the low-voltage network into the medium-voltage network. Another factor is the effort to use more and more electric power to supply heat so as to replace fossil fuels such as natural gas and mineral oil. The heat pumps used for this purpose increase demand, but they also increase seasonal fluctuations in consumption. And: anyone serious about the energy turnaround has to include the transportation sector in their considerations. However, if there are large numbers of electrically powered vehicles being hooked up to the grid after working hours, for example, this might overload the networks in residential areas, for example.
One solution is the much-debated expansion of distribution networks: this involves reinforcing the cables or re-laying them completely. However, digging up roads and paths in densely populated conurbations is not just a lot of hard work, it simply may not be possible. In Basel, for example, freshly built or modernised roads must not be dug up in the first five years.
Another solution lies in intelligent distribution networks or "smart grids". These are based on power meters that digitally record current consumption and send their results to a central energy data management system via a communication module. Since 2012, IWB Basel has replaced a large number of power meters in the city area with smart meters. Today, Basel has 60,000 such devices installed out of a total of 140,000 power meters – the highest rate among Switzerland's major cities. "In this way we're laying the groundwork for a transparent distribution network so as to be able to integrate future loads and generation plants into the grid intelligently in the future," says planning engineer Dirk Schmidt of IWB, who is responsible for the smart meter project in Basel.
The next stage is to analyse the data. For this purpose, the numerous individual load profile measurements are imported to the grid analysis and simulation platform Adaptricity.sim. The software is now not only capable of running plausibility checks, it can also supplement any missing data. Drawing on certain other sources such as known levels of annual consumption, data from the surrounding smart meters and from the relevant transformer stations where available, the software calculates so-called synthetic load profiles and incorporates these in the model as a whole. In the form of area maps, the simulation platform then visualises production and consumption for the various grid regions, as well as the showing the current loads of individual power line sections and the voltage quality. "This tells us at a glance where the hotspots are in the distribution network, allowing us to forecast precisely where shortages might occur," says Schmidt. Over the course of the project it has turned out that integrating data from transformer stations relating to current flow and voltage can significantly enhance the validity of the forecasts. In the next five years, IWB will now be fitting all 600 transformer stations in the city area with permanently installed measuring devices.
This offers enormous opportunities: in this way, the distribution network will be transformed from a black box into an active element in overall load management. It will enable operators to offer time-based electricity rates in quarter-hour cycles, for example, encouraging consumers to adapt their demand to the given load situation. In this way, customers using heat pumps can benefit from lower power costs if these can be briefly switched off and on again during peak loads periods. One day, transparent insights into grid operation based on smart meter data analysis will also enable selective grid control. In combination with the further expansion of renewable energies, these are important steps towards a carbon-neutral energy supply, with the power grid as the central energy platform.
Dr. Andreas Ulbig