In the future, automated demand-side management through e.g. the deployment in-home energy management systems (EMS) and the implementation of highly dynamic tariffs that are being processed by the energy management systems can become a means for active distribution network management. Next to offering consumers greater price flexibility and transparency, the demand response benefits' options for active distribution grid management lies in the fact that the status of the network can be represented by the ever-changing prices of flexible tariff or other contractually based agreements, thus, adapting the consumption to the current situation in the grid. Complex real time pricing tariffs that take into account intraday developments and translate them into the prices for electricity within just a few hours can help avoid critical states of the distribution grid or help to consume locally generated excess feed-in from DER units at their origin to decrease tension on the network. The automated in-house control equipment plays a decisive role as the adaption of the intraday price signals needs to be implemented reliably without a loss of comfort for the customers.
In a “green, market-driven zone”, the MeRegio price signal is utilized by suppliers and aggregators to access the flexibility of residential and commercial customers for market options, e.g. to optimize their buying processes and forward the better prices to customers. The green zone was tested in field with a day-ahead price signal that was sent to the customers in order for their automated energy management system (EMS), called “control box”, to schedule household applications in the most cost efficient way.
A successful distribution network management, however, requires mechanisms that relate to the traffic light system’s yellow or even red, grid-oriented phases and exert influence on loads or load shifting capacity on short notice on behalf of the grid operator in exactly those distribution grid feeders that are the origin of the stress situation or bottleneck.
Based on load and generation prognoses from all monitored nodes, the „MeRegio Hybrid Model“ enables the distribution network operator to calculate a permanent prognosis of potential grid bottlenecks and thereby initiates timely, market actions based on tender invitations to prevent the bottleneck from taking place. Thus, the MeRegio hybrid model’s goal is avoid the red-phase by trying to maintain the network in the yellow phase or even enabling a situation, in which the network can be actively led back to the green phase via demand response. The field test experience could prove that under certain conditions the hybrid model can be successful in decreasing or even avoiding traditional grid reinforcement by means of resources such as cable, transformers etc.
A data hub platform, in case of MeRegio the so called a-core platform (provided by IBM), enabled the unbundling compliant approach. The network operator receives load prognoses based on the settings of the local energy management systems in the households and businesses in form of aggregated data from the a-core platform. Together with other input variables, such as weather forecasts determining the generation from DER units in the region, the network operator can then calculate a very fine grained prognosis for the load on its network and can isolate certain nodal points within that might come under stress due to excess generation or consumption. In order to communicate a potential distress situation to the market actors that can help to avoid a costly bottleneck or even blackout situation, the network manager simply has to send a signal to the a-core platform, which in in turn initiates a tender based bidding process on an independent marketplace to find and select offers for the mitigation of the distress situation in the network.
MeRegio Priority Signal processing from Network Management System to Households, source: MeRegio 2014
Utilities, other suppliers, aggregators or virtual power plant (VPP) operators can react to the bidding process by scanning the load and generation units they control for intraday flexibility and calculating how expensive an intraday modification of the load (and/or generation) curves of their facilities would become.
The MeRegio hybrid model operated with a so-called Demand Side Manager, an aggregator function within the supplier, in its trial to verify whether the principle could technically work in practice. So tenders were only submitted by this particular actor. In order to determine the price for the intraday flexibility, the Demand Side Manager sent an intraday price signal to the “control boxes” in the households received an intraday price signal, the so called priority signal, in order to reschedule the applications and thus their load curve based on the goal to avoid the stress situation in the grid. The control boxes sent their flexibility offer back to the Demand Side Manager, who can determine, whether sufficient flexibility at the specific distressed nodal point in the grid is present and in case it is, how many different applications at how many customers’ premises have to be included at what price. The price is sent back to the marketplace. In a real market scenario, the network operator could now choose from different offers. The entire process of detecting a potential grid bottleneck to initiating the bidding process, calculating and submitting offers, of which one is chosen and implemented by a demand side manager or aggregator could be realized within a few hours. The technology and method have proven to be manageable and reliable.
However, the flexibility potential at the actual grid bottleneck areas was too low to actually practice this approach right now. The loadshifting potential of flexible residential customers is not sufficient to prevent a stressful situation from occurring. In fact, in order to test the approach, the MeRegio consortium had to simulate the actual priority signal events, by mapping extra households into the stressed network feeders and thereby artificially enhancing the demand flexibility potential.
A breakthrough in the integration of Evs for instance or a funding scheme for heatpumps and other highly flexible household applications could however significantly increase the flexibility potential thereby rendering the MeRegio Hybrid Model highly important for the future market modelling of IT-based energy systems. It has shown the possibility for Smart Grids to counter the stress that networks encounter with the mass integration of DER units and has shown that ICT can help tackle the challenge while at the time maintain a transparency between the actors in the energy system and securing an unbundling-compliant, non-discriminatory approach.
MeRegio (Model Region Baden-Württemberg)
Hellmuth Frey, EnBWEnergie Baden-Württemberg AG
Durlacher Allee 93, 76131 Karlsruhe