Detailed information on energy research

Projektinfo 16/2011

New operating system for stand-alone gridsPhotovoltaic hybrid systems supply off-grid locations reliably and cost-effectively with energy

Even in a remote village far from the public electricity grid there is modern everyday life with radios, washing machines and electrical appliances. In energy terms this is a “stand-alone” system. The electricity is supplied by a hybrid system that combines various renewable energy sources and an additional diesel generator, and is buffered with a battery system. An information and control network with a new operating system keeps the stand-alone grid (mini-grid) stable.

The Universal Energy Supply Protocol (UESP) communication protocol, which has been developed by the Fraunhofer Institute for Solar Energy Systems ISE together with its industrial partner Steca, enables optimised interaction between the gen-erators and loads in decentralised power supplies. If a superordinate energy man-agement system (EMS) is available for the operational management, it calculates an optimised schedule and controls the individual loads and generators. Without the EMS, the batteries distribute their charging state in the network so that the generators and storage systems can accordingly switch themselves on or off.The results of the UESP project are incorporated into the new CiA 454 CANopen application profile for energy management systems. KACO new energy is using this as part of a new research project in which it is designing larger stand-alone grids that can also supply commercial machines and, if required, can also be linked to the public grid.The market for autonomous electricity supplies is potentially enormous: around 1.4 billion people in rural regions still do not have any electricity connections. This research project

is funded by the:

Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)

Another application area is provided by measurement and transport control systems as well as telecommuni-cations systems. According to Fraunhofer ISE, there are around 300,000 homes, hotel and catering businesses in Europe that are not connected to the public electricity grid. These could make excellent use of renewable ener-gies, since it is often more economic to generate electric-ity with a solar power system than to develop a supply network or use diesel generators.

Controlling smaller stand-alone grids with the UESP systemTo set up a stand-alone grid, the UESP protocol com-bines – as an open source platform – all components together such as the generators, inverters, storage sys-tems and loads. These are equipped with an intelligent interface that enables them to communicate with one another, whereby part of the system intelligence is out-sourced to them. The system offers device interfaces as well as communication and data software for operating stand-alone hybrid systems. Everything functions accord-ing to the Plug-and-Play principle: only a minimal addi-tional system setting is required to add or remove com-ponents. The new, standardised components will make it easier to install, operate and expand PV hybrid systems.The entire system is managed by a central control unit that records and evaluates the usual consumption and power output processes from the renewable sources. Based on the data recorded on the operating conditions and costs, the central unit automatically calculates how the generators, storage systems and loads must be combined in order to coordinate the supply and demands as cost-effectively as possible. The system can also be used for setting consumption prices and for invoicing.The UESP project uses DC technology to couple the generators and loads, since applications such as small village electricity networks, telecommunications and measurement data recording use DC appliances. The DC coupling is economic and reliable for small and medium outputs, and enables voltage converters to be dispensed with. PV modules, batteries and fuel cells supply DC voltage. Devices that require AC voltage are supplied directly via an inverter. However, the system can also in principle manage AC-coupled systems.The communication system (predominantly) works with standard components and existing industrial standards ensuring a secure exchange of data independent of the manufacturer. The system is fail-safe with built-in redundancy, whereby the electricity supply and communi-cation are separated. Internally it manages controllable, influenceable and non-controllable loads and storage systems as well as controllable and stochastic generators.The project is designed for DC systems with voltages of 12 V, 24 V, 48 V and 120 V and currents of up to 150 A depending on the system size.A UESP demonstration system has been installed at Fraunhofer ISE to further develop components and to test the system. Various energy supply networks have been set up and tested, including an autonomously supplied environmental measurement station in the Thuringian Forest, a radio mast near Offenburg and a village power supply system in Sri Lanka. In an EU project for operating a water treatment system in Egypt (Fig 3.), the UESP communication infrastructure is being con-verted to the new CiA 454 CANopen specification profile for energy management systems.

Concept for decentralised village power suppliesThe experience garnered by UESP is being incorporated into a new photo-voltaic hybrid system for supplying villages with alternating current, which researchers at Fraunhofer ISE and KACO new energy are developing in a project running until the middle of 2013. It links different loads and energy sources to a standardised communication infrastructure and a superordinate energy management system (EMS). This ensures that the managed stand-alone system works as efficiently and cost-effectively as possible and that the resources used are optimally deployed in energy and economic terms. At the same time it records and controls the energy flows between the gen-erators, storage systems and appliances in order to ensure a secure supply. The EMS prevents the premature wear of components such as batteries and diesel generators. Based on generator and load forecasts that have been previously determined using measurements, the incorporated consump-tion management system controls the user behaviour and connects loads flexibly in accordance with the availability. For example, water pumps are not switched on until there is plenty of cheap energy available. This load management largely enables the system to be kept stable. In addition, in-

2 BINE-Projektinfo 16/2011

Biogas generator

Wind power

Diesel generator

Central power ‚supply

Photovoltaics

Appliance Battery

Energy management

PV generator Wind generator

Remote servicing / monitoring

Statischer Test

Blick von der Seite

Blick von oben

250kN350kN400kN400kN400kN400kN

Rotorblattlänge bis 90 m

Biegung

Hubhydraulik

Dynamischer Belastungstest

Diesel generator

Data transfer

Energy transfer

Fig. 2 The new system concept for larger stand-alone systems combines AC and DC sources to form a regional network and storage system.Source: KACO new energy GmbH

Fig. 1 Simple UESP system for supplying an appliance (with separate connection and supply to the intelligent interface). Source: Fraunhofer ISE / KACO new energy GmbH

Photovoltaic hybrid systems

Whereas in southern countries it is often sufficient to use a PV-only battery system to provide stand-alone electricity, it make sense in regions with less intensive solar irradiation to install hybrid systems that combine photovoltaics with wind energy, biogas or diesel gen-erators. Compared with PV-only systems, considerably smaller PV generators are sufficient to compensate for the “winter hole” in the solar yield and consump-tion peaks.In hybrid systems, an automatic energy management system (EMS) ensures that the electricity supply is available around the clock, the solar energy is optimally used and the battery is charged and discharged sparingly. The EMS monitors the charge state of the battery: if this falls below the predefined limit value, the diesel generator switches on, supplies the connected loads and recharges the battery. De-pending on the size and composition of the loads, hybrid systems are designed as DC, mixed DC/AC or as dedicated AC systems. Mixed systems are often installed on farms or in small businesses. A central element in the network are the solar charge control-lers or multifunctional inverters. They supply the connected loads, charge the batteries with electricity from the PV system or the second electricity source or remove energy from the batteries as required to supply the stand-alone grid.

New communication standard

Researchers at Fraunhofer ISE have developed and tested a standardised communication bus as a kind of “driver software” for the hybrid system. The content of the UESP has been incorporated into this “Energy-Bus” system. In the current state of development the individual devices are linked via the CANopen protocol, a widely used standard in automation technology. The central EMS works with the CiA 454 (CAN in Auto-mation) application profile for energy management systems. This protocol, which was originally devel-oped for electric bikes and lightweight electric vehicles, has been adapted for controlling PV systems. It enables communication between the devices in the PV system as well as their control and diagnosis. As with the UESP, the EMS continues to communicate with the system components via the CAN (Controller Area Net-work) fieldbus. Only the superordinate application-oriented protocol has changed and is now based on the CANopen standard. For the consumption manage-ment, data recording and remote servicing, interface standards such as PLC, Mbus and TCP/IP are used. The advantages of UESP remain in place: the stand-ardised communication infrastructure simplifies the planning and installation of photovoltaic hybrid systems, and new system components can be added according to the Plug-and-Play principle. In the village electricity supply research project conceived together with KACO new energy, the newly developed CiA communication protocol enables manufacturer- independent communication between the individual components.

telligent measurement devices help to calculate the consumption and control it via a variable electricity price. The mini-grid concept is also designed to enable it to be connected to the national grid in the long term.The central components of the system consist of grid-forming inverters, MPPT (Maximum Power Point Tracking) charge controllers, intelligent meters and an innovative high-voltage hybrid battery that combines the high efficiency and cycle durability of lithium-ion batteries with the economic efficiency of lead acid batteries. An integrated battery management system monitors the charge state, reports errors and records the ageing and energy content. The transformerless inverter achieves an efficiency of more than 97% and can work bi-directionally, i.e. it either feeds into the AC grid or charges the battery with energy generated by a diesel generator integrated on the AC side. The stand-alone grid can be supplemented as required and modularly expanded to 600 kW, whereby the uniform communications standard enables DC and AC generators to be flexibly integrated.The forthcoming field tests will investigate grid-parallel operation as well as a stand-alone grid with a diesel generator.

Fig. 4 The trunked radio system on the Brandeckkopf tower near Offenburg, Germany, which is used for communicating with and monitoring a regional railway line, is operated with a PV hybrid system. Source: Steca Elektronik GmbH

3BINE-Projektinfo 16/2011

Fig. 3 The tracker directs the concentrating PV modules precisely to the position of the sun. In the stand-alone system at Wadi Al Natroon in Egypt, the water pumps are powered with electrical energy and the communication is achieved via the standardised CANopen protocol. Source: Fraunhofer ISE

BINE Projektinfo 01/20104 BINE-Projektinfo 16/2011

Cheap PV electricity for stand-alone systems The development of secure energy supplies provides an important impetus for the economic development of remote regions in Europe and worldwide. Stand-alone PV hybrid systems make it possible to supply cost-effective and reliable renewable energy to individual buildings, entire villages as well as measurement and transmission systems. There is expected to be considerable demand for such systems, which work more cheaply than diesel generators.The developers also believe that there is a considerable market potential for hybrid systems and forecast a volume of two gigawatts for Brazil alone, whereby in order to achieve this just 10% of the diesel-operated stand-alone grids there need to be replaced with renewable energies. The European Photovoltaic Industry Association (EPIA) estimates that the proportion of autonomous PV systems will increase worldwide to 30 per cent by 2030 – whereby this is a constantly growing trend. PV supply systems for homes are already widespread in off-grid regions in Africa, Asia and Latin America. Mini-grid systems in villages can also supply larger individual loads. That enables craft-based businesses to use larger machines and helps to promote the local economy.In order to ensure that stand-alone systems can reliably secure electricity supplies through-out the year, particularly in central Europe it may be necessary to combine different renew-able energy sources such as the wind, sun and biomass to form a hybrid system.The new soft- and hardware makes it possible to develop flexible, Plug-and-Play-capable village electricity networks. In order to enable hybrid stand-alone systems to become more widespread, researchers believe that it is very important to establish a company-independent platform that can securely link different technologies, generators and loads. Such a uniform standard also makes it much easier to modify and expand existing systems.The newly developed energy management system makes it possible to optimise the stand-alone system: on the one hand this ensures the efficient interaction of all compo-nents ranging from the generator and the storage system to the appliances; on the other hand this keeps the life cycle cost of the entire system as low as possible. The new, open platform provides an excellent basis for considerably expanding PV hybrid systems. However, whether the expected high market potential can be realised in practice will not be shown until the new renewable systems can be operated more cheaply than the previously used diesel generator systems.

Projektbeteiligte >> Coordination of the UESP research and development: Fraunhofer Institute for Solar Energy

Systems (ISE), Freiburg im Breisgau, Germany, Georg Bopp, georg.bopp@fraunhofer.ise.de >> UESP industry coordination: Steca Elektronik GmbH, Photovoltaik Off Grid, Memmingen,

Germany, Michael Müller, michael.mueller@steca.de>> Project coordination of the Inno-System project: KACO new energy GmbH, Neckarsulm, Germany,

Volker Dietrich, volker.dietrich@kaco-newenergy.de

Links and literature (in German)>> www.ise.fraunhofer.de | www.steca.de | www.kaco-newenergy.de | www.forschungsjahrbuch.de>> Müller, M.; Bopp, G.: Entwicklung eines universellen Managementsystems mit offener System-

architektur für DC-gekoppelte dezentrale technische Stromversorgungen – UESP. Steca GmbH, Memmingen (Hrsg.); Fraunhofer ISE, Freiburg (Hrsg.). Juni 2009. 52 S. FKZ 0329922A-B.

>> The KACO new energy GmbH’s Inno-System project (Innovative Photovoltaik-Hybrid-Systemtech-nik für die Dorfstromversorgung der nächsten Generation) is described under project number 0325121 in “Forschungsjahrbuch Erneuerbare Energien”.

More from BINE Information Serviceb This Projektinfo brochure is available as an online document at www.bine.info under

Publications/Projektinfos. Additional information in German, such as other project addresses and links, can be found under “Service”.

b BINE Information Service reports on energy research projects in its brochure series and newsletter. You can subscribe to these free of charge at www.bine.info/abo.

Project organisationFederal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)11055 Berlin Germany

Project Management Organisation Jülich Research Centre Jülich Dr. Christoph Hünnekes 52425 Jülich Germany

Project number 0329922A, B0325121

ImprintISSN0937 - 8367

Publisher FIZ Karlsruhe · Leibniz Institute for Information InfrastructureHermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany

AuthorGerhard Hirn

Cover imageFraunhofer ISE

CopyrightText and illustrations from this publication can only be used if permission has been granted by the BINE editorial team. We would be delighted to hear from you.

Contact · InfoQuestions regarding this Projektinfo brochure? We will be pleased to help you:

+49 228 92379-44BINE Information Service Energy research for practical applicationsA service from FIZ Karlsruhe

Kaiserstrasse 185-197 53113 Bonn Germany Phone + 49 228 92379-0 Fax + 49 228 92379-29 kontakt@bine.info www.bine.info

Conc

ept a

nd d

esig

n: is

erun

dsch

mid

t Gm

bH, B

onn

– B

erlin

, Ger

man

y · L

ayou

t: K

ERST

IN C

ON

RAD

I · M

edie

nges

taltu

ng, B

erlin

, Ger

man

y