• Market integration of decentralised energies

    Integrated solution for virtual power plants

Virtual power plants (VPP) play a decisive role in the required market integration of decentralised energy generation systems. PSI presents an integrated solution that maps a VPP in its entirety. As well as taking account of the required communications infrastructure, it also represents a solution that meets the increased requirements for next-generation intelligent portfolio management.

The concept of a “virtual” power plant appears inappropriate in light of the very real systems that are interconnected into a controllable network. Fundamentally, a virtual power plant refers to the creation of a portfolio of decentralised generators, energy storage providers and sliding-load consumers. Interesting marketing options can be derived from the different characteristics and options of these stakeholders— provided that a suitable marketing model is in place.

In contrast to the virtual contract world, which dominates the usual portfolio of an energy trader, the preferred term to be used here is a real portfolio. As you would expect, this includes conventional generation systems and consumers. In pre-liberalised times, conventional energy management had the entire range of instrumentation for generation control and load influencing at its disposal.

However, as services were unbundled, energy suppliers, traders and distributors no longer had access to the required communications infrastructure, as this remained with the network operator. At the same time, there was no longer any need for influencing consumption, as the economic stimuli were no longer present. However, the increasing expansion of generation from renewable energy sources and the resulting price volatility has changed this scenario. The effect of this has been the construction of an efficient, affordable and secure communications infrastructure that is available to the energy trade and distribution sector, and has enabled the connection and integration of the systems under their control to the control concept.

Next-generation portfolio management

Setting up an independent communications infrastructure has resulted not only in increased opportunities for exerting influence on the portfolio with the aim of advancing various accounting objectives and marketing options, but also in more time and room for manoeuvre in the intra-day field, right up to real-time control of the systems.

As a result, portfolio management in its current form is gaining a new dimension, and we can confidently refer to a next generation and new quality of required portfolio management and optimisation systems.

A new system solution is presented below that has been designed with these requirements in mind and that meets these requirements. 

Optimum use of market flexibility and thereby optimum use of the VPP in the overall portfolio is determined on the basis of stochastic optimisation. In this regard, the optimisation procedure takes into account the stochastic nature of the energy market, fluctuating generation, uncertain inflow forecasts on storage reservoirs and other imponderables in the market that are reflected in highly volatile pricing. This procedure brings significant performance and results benefits under uncertain framework conditions for many use cases.

Other optimisation algorithms and procedures that have been adapted to the task at hand can also be implemented. This can be advantageous in the very short term, as stochastics no longer play a significant role. After determining the optimum power plant deployment, control signals or timetables can be transmitted to the systems.

Similarly, there is an opportunity to influence demand among price-sensitive consumers by sending price signals. All control specifications for the optimisation are implemented via an integrated SCADA system.

PSI<em>vpp</em> system overview in the monitoring and control system


Dr. Benno Zielonka
PSI Energy Markets GmbH, Aschaffenburg
Phone: +49 6021 366-351

Klaus Becker
PSI Nentec GmbH, Karslsruhe
Phone: +49 721 94249-20

PSIvpp—a comprehensive turnkey solution for VPP

The proposed solution maps all the required aspects of a VPP in an integrated solution comprising individual modules. This starts with the connection of the systems to intelligent controllers that also enable decentralised control, and continues with a high-performance communications chain for transmitting control commands and capturing consumption and generation data online, right through to integration of the real portfolio into an overarching energy portfolio and optimum marketing of this portfolio.

The solution is based on three main components:

  1. A central portfolio management system with a stochastic procedure for portfolio evaluation and optimisation
  2. A streamlined, efficient SCADA system for data capture, control and monitoring of systems
  3.  A Smart Telecontrol Unit—a hardware unit for decentralised coupling and control of the systems

All the components are seamlessly connected with one another in an integrated overall approach, but can also be implemented as “stand-alone” solutions.

Construction concept for a virtual power station

Central portfolio management system

Weather data and feed-in forecasts for wind power and photovoltaic systems

Portfolio management is used for mapping and evaluating all systems in a VPP, for determining the optimum marketing strategy and, optionally, for integrating the VPP in an overarching overall portfolio. Contract management maps all physical and commercial contractual relationships of the (market) roles involved, and models all components of the VPP.

A calculation of costs, revenue and results is derived from this process. This calculation forms the basis of a similarly integrated accounting. Based on a flexible time series system and a programmable formula system with more than 100 functions that relate to the energy sector, even complex compensation and invoicing models can be mapped and calculated.

To improve the integration of decentralised energies in the energy market, the forecasting quality of the expected feed-in must be improved. To this end, new forecast models have been developed. This provides planning security when integrating VPP generation volumes into the overall portfolio and allows for optimisation while simultaneously taking account of the load transfer potential on the sales side. Forecast models have also been developed for this purpose; these need to take into account both the characteristics of different production processes as well as consumption price sensitivity.

Monitoring and control system in real time

A streamlined, efficient and high-availability SCADA system ensures secure data communication, technical control and system monitoring. This system is also based on many years of experience on the part of PSI with regard to largescale, high-end control systems, and guarantees secure capture and transmission of generation and consumption data, while also serving as a monitoring and control system in real time.

Detailed modelling of objects provides visualisation and control of generation units, storage and (large) loads/consumers. The graphical preparation supports simple process monitoring and provides an overview of the current status of the entire system. The hierarchical display concept enables both an easy overview as well as a detailed view right up to the level of the individual systems.

High availability is achieved in that distributed, redundant system architecture is supported. Implementation in Java ensures a high degree of user-friendliness and the seamless integration of the VPP components with the central portfolio management system, together with maximum platform independence.

The solution is rounded off by protocols as well as alarm management functions that support prioritisation of alarm messages and filtering according to criticality and time.

In addition to the display, storage and archiving of process information, the SCADA system also allows for control and monitoring of almost any number of connected intelligent end devices, otherwise known as Smart Telecontrol Units (STU). The control and regulation specifications are transmitted to these devices in real time.

Display of system overview in the monitoring and control system
Detailed display of an individual system in the monitoring and control system

Smart Telecontrol Unit (STU)

Developed by PSI, the Smart Telecontrol Unit (STU) is an intelligent device that can be connected to VPP components. Measurement data and messages for various generators and consumers are collected on the STU, stored and forwarded to the overarching VPS control system.

In addition to the usual telecontrol protocols, such as IEC 60870- 5-101/-103/-104, IEC 61850 and DNP3, the STU also supports proprietary telecontrol protocols (Modbus, CANopen) and numerous counter protocols (SML, SYM2, DLMS, IEC 62056-21).

Smart Telecontrol Unit (STU)

STU handles telegram forwarding as well as the required protocol conversion. An integrated Soft PLC, which can be programmed using industry standard IEC 61131, enables additional control and monitoring of systems where required. Intelligent applications (also referred to as smart apps) allow for local optimisation of the process as early as the system or micro-grid stage.

This includes short-term optimisations as well as autonomous fault handling. This optimisation is individually adapted to the requirements of the VPP, taking into consideration the special characteristics of the connected resources. The VPP can be flexibly adapted to future requirements by reloading applications.

The STU enables secure connection of decentralised generators and consumers in accordance with the BDEW (German Association of Energy and Water Industries) white paper. A robust STU system also meets the demand for secure communication. All data traffic between the central system, the transmission network operator and the decentralised resources is encrypted through a VPN tunnel. Central user authentication is possible using LDAP and RADIUS. 

A configuration server ensures secure configuration and updating of the STU.

The STU also assumes the task of redundant communication with the transmission network operator (ÜNB) for the provision of secondary balancing power. Communication with the ÜNB is via a serial interface that meets the requirements of IEC-60870-5-101.

The protocol in the network-capable IEC-60870-5-104 variant is converted and secured via an IPSec VPN for data exchange with the central system. Support for a wide range of communications interfaces, together with the integrated IP routing functions, provides support for flexible, redundant network structures. The integrated firewall function ensures additional communications security.

Virtual power plant—real benefits

The business models permitted by the current market model are limited in their appeal at present. However, there are some interesting and lucrative marketing options in the balancing power market, in particular with regard to the provision of negative balancing power.

Alongside the additional value creation resulting from the marketing of the real portfolio, other opportunities also arise for making the described infrastructure available to the relevant network operator as a service, provided, for example, that the shutdown of systems is required for safety reasons.

In general, few useful alternatives to a future market model will exist that ensure stronger market inclusion of energy generation from renewable sources and the corresponding financial incentives.

The flexibility of the presented solution provides solid preparation for the future market, as it offers scalability that supports economic marketing of smaller systems and also fulfils the performance requirements of larger volume structures, while also guaranteeing the required data security.