Projektinfo 16/2011
Detailed information on energy research
New operating system
for stand-alone grids
Photovoltaic 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 “standalone” 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.
This research project
is funded by the:
Federal Ministry for the Environment,
Nature Conservation and Nuclear
Safety (BMU)
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 generators and loads in decentralised power supplies. If a superordinate energy management 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.
2
BINE-Projektinfo 16/2011
Another application area is provided by measurement
and transport control systems as well as telecommunications 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 energies, since it is often more economic to generate electricity with a solar power system than to develop a supply
network or use diesel generators.
Controlling smaller stand-alone grids
with the UESP system
To set up a stand-alone grid, the UESP protocol combines – as an open source platform – all components
together such as the generators, inverters, storage systems and loads. These are equipped with an intelligent
interface that enables them to communicate with one
another, whereby part of the system intelligence is outsourced to them. The system offers device interfaces as
well as communication and data software for operating
stand-alone hybrid systems. Everything functions according to the Plug-and-Play principle: only a minimal additional system setting is required to add or remove components. 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 communication 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 converted to the new CiA 454 CANopen specification profile
for energy management systems.
PV generator
Wind generator
Diesel generator
Data transfer
Remote servicing / monitoring
Energy management
Energy transfer
Appliance
Battery
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
Diesel generator
Central power ‚
supply
Biogas generator
Wind power
Photovoltaics
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
Concept for decentralised village power supplies
The experience garnered by UESP is being incorporated into a new photovoltaic 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 standalone 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 generators, 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 consumption 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-
BINE-Projektinfo 16/2011
Photovoltaic hybrid systems
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
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 generators. Compared with PV-only systems, considerably
smaller PV generators are sufficient to compensate
for the “winter hole” in the solar yield and consumption 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. Depending 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 controllers 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
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
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.
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 “EnergyBus” 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 Automation) application profile for energy management
systems. This protocol, which was originally developed 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 Network) fieldbus. Only the superordinate applicationoriented protocol has changed and is now based on
the CANopen standard. For the consumption management, data recording and remote servicing, interface
standards such as PLC, Mbus and TCP/IP are used.
The advantages of UESP remain in place: the standardised 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.
3
BINE Projektinfo 01/2010
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 throughout the year, particularly in central Europe it may be necessary to combine different renewable 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 components 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.
Project organisation
Federal 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, B
0325121
Imprint
ISSN
0937 - 8367
Publisher FIZ Karlsruhe · Leibniz Institute
for Information Infrastructure
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen
Germany
Author
Gerhard Hirn
Cover image
Fraunhofer ISE
Copyright
Text 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.
Projektbeteiligte
Contact · Info
>> Coordination of the UESP research and development: Fraunhofer Institute for Solar Energy
Questions regarding this Projektinfo
brochure? We will be pleased to help you:
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-Systemtechnik für die Dorfstromversorgung der nächsten Generation) is described under project number
0325121 in “Forschungsjahrbuch Erneuerbare Energien”.
More from BINE Information Service
b This Projektinfo brochure is available as an online document at www.bine.info under
­ ublications/Projektinfos. Additional information in German, such as other project addresses
P
and links, can be found under “Service”.
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.
b
+49 228 92379-44
BINE Information Service
Energy research for practical applications
A 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
Concept and design: iserundschmidt GmbH, Bonn – Berlin, Germany · Layout: KERSTIN CONRADI · Mediengestaltung, Berlin, Germany
4