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Intelligent operations management based on flexible tariffs in initial trial on test installation in the SmartEnergyLab of Fraunhofer ISE.
© Fraunhofer ISE
Storage systems for the energy transition

Smart Grid at favourable cost

The same technology for decades keeping street lights illuminated has the potential to motivate power consumers and decentralised generators to adopt system-friendly behaviours. The Fraunhofer Institute for Solar Energy Systems (ISE) has investigated how dynamic power tariffs can be transmitted based on ripple control technology together with project partners. Investigations involved sending electricity market prices across the regional power grid using tariff switching times.

Variable power tariffs offer incentives around grid-friendly operation of controllable loads and generators. They therefore have the potential to relieve the power grid. For small systems, the Smart Grid concept, however, is less appealing as things stand due to the costs of communication-capable electronic measuring instruments (smart metering). The innovative use of ripple control technology, as a tried-and-tested component of current grid control technology, offers the opportunity to implement the core functionality of the Smart Grid idea affordably and without delay.

Researchers are pursuing this idea in the “CheapFlex” research project. Instead of rigid switching times for high and low tariffs and blocking times determined by the distribution grid operator, currently the norm, ripple control technology allows for non-discriminatory dynamic tariffing based on tariff switching timetables. The system, however, is intended not only to offer tariff-related incentives for system-friendly behaviours in normal operation. In emergency and extreme situations, facilitating intervention is an aim, to include even direct control actions.

With ripple control technology, the grid operator sends control data across the distribution grid in an audio range of 110 to approx. 2,000 Hz in order to remotely control electrical consumers such as heat pumps or renewable energy systems. An affordable ripple control receiver upstream of the consumer supplies the control commands on location. A traditional application is the switching of multi-tariff electricity meters (low tariff LT and high tariff HT), or the interrupting of heat pump operation for grid congestion management.

“For over 100 years, the ripple control technology we use has been a tried-and-tested, robust and secure core technology for regulating distribution grids, today produced based on inexpensive microprocessor receivers,” states Prof. Christof Wittwer, department manager of Intersectoral Energy Systems and Grid Integration at the Fraunhofer Institute for Solar Energy Systems.

The concept envisages two-stage tariff schedules for dynamic tariffing, the LT and HT times of which are calculated for the following day. The basis for this is the “day ahead” electricity market price and the expected consumer behaviour. The grid control system sends ripple control telegrams with the tariff program the previous evening. Ripple control receivers store the switching times of the tariff locally and supply these to the energy management system via the standardised control system protocol.

Based on the tariff schedule and local forecast of load and PV yield, the operations management of electrical consumers and decentralised generators can be optimised. A simulation study has shown the market price for electricity to be a favourable reference parameter for compiling tariff switching times. It correlates greatly with the local loads and cross-regional loads of other distribution grids. The targeted shifting of loads and supplies not only reduces load peaks on the grid, it also cuts energy bills for end customers.

Field testing in Münster region

Following initial laboratory-based tests, functional prototypes were tested in the field. Generators and loads, both with and without control facility, were included in the grid area of Stadtwerke Ahaus. These included a CHP, heat pump, night storage system and photovoltaic storage systems and electric vehicles. Customers are notified of tariff switching times via a messaging app to enable them to flexibly adjust their consumption behaviours. Feedback from end customers has been very positive. They showed significant interest in flexible power tariffs and responsiveness to switching times was observed.

Grid state estimates for direct control

To facilitate decision-making around direct intervention for controllable loads and generators, the grid operator requires additional information on grid state values such as voltage, current, phase angle and values based on these. Measuring instruments for these are currently rarely found in distributions grids. Owing to the increasing supply of renewable energies and the change sweeping the heating and transport sector, these operating values are no longer readily predictable.

In the “CheapFlex” project, researchers therefore also hope to demonstrate grid state estimation with sufficient accuracy based on less measurement data. Project partner the Technical University of Kaiserslautern has developed a corresponding procedure for generating replacement values for household loads. The researchers assume in this regard the favourable predictability of the distribution of these loads for individual points in time. They expound a three-phase grid state estimation using input data with a large volume of replacement values compared against reference measurements in field operation. Deviations from the measured reference value of estimated voltage and current values were regarded as entirely satisfactory for the grid management of distribution grids.

Future-proof power grids

The project was funded as part of the “Future-proof Power Grids” funding initiative of the German Federal Ministry for Economic Affairs and Energy (BMWi). A project business card can be found on the website of the funding initiative.



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Project management, energy management system
Fraunhofer ISE

Grid control technology and operations management
TU Kaiserslautern, ESEM

Ripple control technology
Swistec GmbH

Field testing
Stadtwerke Ahaus GmbH


Cheap Smart grids with ripple control technology
Project business card ot the "Future-proof Power Grids" funding initiative

Future-proof Power Grids
Website of the research initiative with news from research and development