The electricity system has been operated to date using stored energy from fossil fuels. These were burned in central power plants whenever electricity was required, obviating the need to control the consumers.
With photovoltaics and wind power, cost-effective alternatives are available today which make it possible to turn our back to the fossile energy system and to protect the climate and the environment by avoiding CO2 and pollution. The fluctuating sources of sun and wind power can only be integrated efficiently into the energy system, however, if large consumers receive incentive signals or control signals in order to follow the current supply of electricity to a large extent. If these methods are not used, there will be a high demand for expensive standby energy.
The term “smart grid” is used to describe the intelligent configuration and control of the grids in order to orchestrate the central and local generators and the consumers. Storage facilities and converters are needed between the electricity, heat and fuel sectors in order to even out the fluctuations. The intelligent control of these elements and of the consumers enables efficient use of the existing distribution grids, even with the increasing demand for power coming from electromobility and heat pumps. New business models are becoming possible which will bring rewards for grid-friendly operation of systems and allow storage facilities to be paid for.
The ZSW has the means to support grid operators, with modern methods of digitisation, forecasts and the use of artificial intelligence all available to display the status in distribution grids at the present time and for the next 36 hours, to identify future bottlenecks and to run automated processes charting recommended courses of action. Consumers are given rules and offered incentives to avoid bottlenecks. The selective control of battery charging points designed to exploit the long downtimes of electric cars will greatly reduce the network load, for example, while ensuring that the electric cars are ready to drive and still offer high levels of availability.
Connection networks are increasingly distributing electricity from decentralised feed-in to the nearest consumer and feeding the regional surplus of electricity from photovoltaic systems, wind power or combined heat and power plants back into the transmission grids. Depending on the weather, high peak loads can arise from decentralised feed-in, or there can be high demand peaks from additional consumers like heat pumps and electric charging stations.
The ZSW has developed the “GridSage” forecasting system to help distribution network operators and energy traders by predicting the generation profiles of systems which are dependent on the weather, mapping the various aggregation levels and sending automated reports to the network control room. The forecasts can include the many small roof-mounted solar power systems which, when added together, often generate significantly more than the large systems on industrial roofs in the vicinity of a municipal utility company and therefore make up a significant proportion of the decentralised feed-in. This is supplemented by the forecast of consumption over a wider area, on the basis of which the network control room can then calculate the future capacity load depending on the grid operating status.
Other ZSW projects involve working on controlling loads, such as battery charging points, storage facilities and district systems, in order to avoid bottlenecks in the grid through the appropriate exploitation of flexibility or in order to be able to maximise the proportion of renewable energies in use at local level.
If electric cars replace all of the 50 million or so private motor vehicles currently on the road in Germany, the demand for electricity in Germany will increase by only 10%. The cars are driven just under 40 km a day on average. This corresponds to daily electricity consumption of around 7 kWh with a downtime of about 22 hours a day[1], i.e. a low average level of demand for charging power. The majority of commuters will come home in the evening between 18:00 and 20:00 hours, however, resulting in a high demand for electricity for a short time if charging is allowed “without constraints” for short daily journeys.
Then again, there are customers who want to cover longer distances and have no access to a socket at home. Or they charge far less frequently and therefore need to use the charging infrastructure, with AC stations offering a capacity of 11 or 22 kW and DC points with an output of at least 50 kW and in some cases significantly more.
The ZSW is analysing the statistics of charging requirements in various projects and is developing solutions for the management of the charging infrastructure. The methods used include forecasting the required amounts of energy and demand profiles, as well as integration in the grid infrastructure of a distribution network operator or systematic control with a view to avoiding bottlenecks in the grid.
[1] 2018: 13,700 km per year and per car; a total of 47 million cars (cf. page 135 in https://www.bmvi.de/SharedDocs/DE/Publikationen/G/verkehr-in-zahlen-2019-pdf.pdf?__blob=publicationFile (17 kWh/100 km assumed on average)
The total storage capacity of all the electric cars in Germany is a resource that must not be underestimated. Even if only 25% of the cars in Germany are electrified and 50% of them are connected to the power grid (the cars are not driven for an average of 22 hours!) and make 25% of their battery power available for utility services, this will result in a storage capacity of 73 GWh. This could cover the electricity demand in Germany for one hour, even in winter[1]. In other words, one car with 50 kWh of energy in its battery can provide the electricity consumed by an average household for five days.
It soon becomes very clear that there is a legitimate interest in the use of the “car battery” as a resource, either for the individual household, in order to increase its internal consumption from local solar power generation, for example, or for the power grid as a whole. Various manufacturers are working on the necessary infrastructure and interfaces for the use of the car battery for the grid (vehicle-to-grid technology) in the form of bidirectional charging stations and power electronics in the car.
The ZSW has explored the potential of vehicle-to-grid technology in various projects in relation to the grid and for the customer, also investigating the influence on battery life, and offers advice on this subject. As soon as the technology is commercially available, there will be business models aimed at customers, grid operators and vehicle manufacturers which will allow them to benefit from variable electricity charges or to use the vehicle battery for utility services. The ZSW can help its customers to navigate their way through the propositions with its know-how on power grids, batteries and the optimisation of operation when given a set of specifications.
