Projektinfo 12/2012
Detailed information on energy research
Smart regulation
of rural electricity grids
Modern communications technology reduces the voltage
fluctuations and regulates the storage of surplus electricity
In the “Smart Country” model project, researchers in BitburgPrüm were testing out the distribution network of the future.
It is designed to respond flexibly to the increasingly decentralised generation of renewable electricity in the grid. For
this purpose various operating resources were further developed: an optimised biogas plant, which controls the electricity
supplied by the grid, virtually stores surplus electricity with
an efficiency of 98 %. In addition, voltage regulators double
the usable output capacity in the grid. The Eifel project
successfully passed the field test after around one year.
The existing electricity grid is not designed for the diverse manner of ways in
which electricity is fed into the grid. This particularly applies to rural areas. Because of the many decentralised grid injections and low local requirements, new
grid solutions are necessary in order to meet future requirements. New distribution grids – so-called Smart Grids – will provide the basis for sustained energy
use. However, how these intelligent grids will (or should) actually look like is still
not clear.
With traditional electricity provision, the electricity only flows in one direction: from
the power plant to the customers. With smart grids, there are additional small
power plants. Wind turbines, solar power installations and biogas plants generate
additional electricity that is fed into the grid. Because the energy is not constantly
generated, this causes voltage fluctuations, particularly in rural electricity distribution grids.
This research project
is funded by the:
Federal Ministry of Economics
and Technology (BMWi)
BINE-Projektinfo 12/2012
The aim of the “Grids for Future Electricity Supply” research project (“Future Grids / Smart Country” for short)
was to develop and demonstrate innovative grid concepts as a basis for smart grids and provide an economic and technical analysis of them. “All measures are
aimed at enabling more decentralised generation in the
existing grid,” explains Torsten Hammerschmidt, head
of the research project. The investigated grid concepts
consider an increased use of information and communications technology (ICT) as well as intelligent secondary
technology. There are also new components analysed,
ranging from voltage regulators based on power electronics to approaches utilising flexible supply voltages
in the grid, for example by providing the permissible
voltage range for customer devices with inverters at
house connection points. The construction of intelligent grid expansion is also indispensable for connecting decentralised generators, whereby the focus of the
project ranged from the distribution grid to the customer connection. Together with plant manufacturer ABB,
the consultancy company Consentec and the Techni­
sche Universität Dortmund, RWE Deutschland tested the
first smart grid in Germany of this kind in the Eifel region
of Bitburg-Prüm in Rhineland-Palatinate. With just 32
inhabitants per square kilometre, the 173-square-kilometre test area is very sparsely populated, with more
than 12 MW of electricity fed into the grid here from renewable energies (Fig. 1).
MW
2
Region acquires new grids
Fig. 1 Total decentralised generation in the Trier region (three rural districts,
in total 3,900 km²: Bitburg-Prüm, Bernkastel-Wittlich and Trier-Saarburg). Depicted is
only the decentralised generation fed into the medium and low voltage range.
Source: RWE Deutschland
In the Eifel region, the installed capacity of renewable
energy generating systems in the low to medium voltage
range currently exceeds the maximum load by more than
200 % (Fig. 1). This represents a challenge that could occur
in many areas of Germany by 2030. Furthermore, the
expansion of renewable generation has also not yet been
completed in this area. Additional 50 % can be expected
by 2030. The demonstration grid encompasses around
110 kilometres of medium-voltage distribution lines with
around 100 stations. The following components have
been used: data technology, information and communications technology (ICT), a biogas storage system for
balancing out electricity peaks, intelligent grid structures
with powerful cable sections – effectively electricity highways – and voltage regulators that maintain the voltage
in the grid at a constant level (Fig. 2).
1,500
1.419
+ 47 %
967
1,000
+ 16 % 837
494
500
535
450
Original grid transportation
capacity / max. load
267
180
131 131
32 34
0
Biogas
Water
31.12.2010
PV
Wind
Total
Total
2030
31.12.2011
Load balance in the demonstration grid
When operating distribution grids without decentralised generation, the grid is sufficiently monitored by
conducting electricity measurements in the mediumvoltage terminations in the primary substations. However, this is no longer the case with increasingly de­
centralised generation. The grid must therefore be
monitored with additional ICT. The actual load flows are
recorded and transferred with the data transmission. In
addition, individual status reports on operating equipment are continually checked and remote control concepts analysed in technical and economic terms,
whereby switching commands are given and responses
evaluated.
Virtual electricity storage
To enable the grid to be loaded more equally and thus
enable additional decentralised generation units to be
connected without grid enhancements, an intermediate
Fig. 2 Investigated voltage regulator in the low-voltage grid (left) and voltage
regulator in the medium-voltage grid (right).
Source: RWE Deutschland
gas storage system was used at a biogas plant as part of a field experiment
(Fig. 3). “To store the solar-generated electricity that is available in excess
during the midday hours, we deployed a biogas storage system. It actually
stores biogas, but is used as a PV storage system by shifting the generation
of electricity from biogas from the midday hours to the evening,” explains
Hammerschmidt. The biogas storage system is sized so that the PV feed-in
is imitated in reverse, i.e. during the period with increased PV feed-in the
electricity generated from the continually produced biogas is throttled
down or stopped.
The largest storage period for the biogas storage system is required during
the summer months. In the winter months, on the other hand, this method
of operation makes it possible to generate electricity from the biogas a
­ lmost
BINE-Projektinfo 12/2012
More flexible operational management
PV electricity generation
PV
t
Medium voltage
AC
DC
The feed-in and load situation has reached a stage
where the limits of the voltage range are now being
reached at certain points. An analysis was therefore initially conducted to examine the effectiveness of central
(medium-voltage branch point), semi-central (secondary station) or decentralised control (house connection
point). For this purpose, a branch point, four local grid
stations and two house connections were equipped
with electronic voltage regulators. This minimised voltage fluctuations, increased the voltage quality and, as a
result, created capacity in the grid for other connections
to decentralised generators.
In addition, using 20-kV technology, a main supply axis
has been laid in the demonstration grid that is more
powerful and reliable than the surrounding 20-kV grid,
since intelligently structured cable connections also form
part of efficient smart grids. The increased short-circuit
power of this main distribution line provides increased
connection possibilities for decentralised generators.
The main distribution line has been executed as a powerful dual cable in the demonstration grid, to which the
rural overhead power lines are connected. The supply
quality is supported by the use of break switches or remote-controlled load disconnectors between the overhead power lines and the main distribution line.
PV panel
Biogas electricity generation
Biogas
Digester
t
3~
Grid
t
Storage system
Biogas
storage
reservoir
t
3~
Fig. 3 Virtual PV electricity storage: Buffering of the PV electricity generation
for grid- and needs-oriented feeding into the electricity grid.
Source: RWE Deutschland
Successful first operating year
D
C
B
A
J
E
I
H
F
G
A External membrane
E Anchorage ring
I Pressure-relief valve
B Internal membrane
F Air valve
J Inspection panel
C Air flow system
G Air blower
D Belt system
H Vacuum valve
Fig. 4 Sketch of the implemented storage strategy:
The biogas plant acts as photovoltaic storage system.
Source: Ceno-Tec
without having to use the storage system. The 300 kWel produced at the
site (160 Nm3/h raw biogas) has to be distributed during the day and year in
such a manner that the biogas produced can also be completely used for
generating electricity.
Coupling the biogas storage system to the electricity injected by renewable
energy sources such as photovoltaic and wind power balances out deviations in the electricity grid. The farm-produced biogas is used for generating
electricity and heat in a CHP plant when insufficient photovoltaic or wind
energy is available in the grid; conversely the production of electricity from
biogas stops when the solar and wind energy can meet demand. With an
efficiency of 98 %, this makes it possible to store renewable electricity produced from wind, photovoltaics and biomass (Fig. 4).
Practically throughout the entire trial year for the “Smart
Country” project, a growing surplus of renewable energybased electricity prevailed throughout the demonstration
grid area – the generation there was almost constantly
greater than the demand. After one year of testing, the
project participants have drawn a positive balance.
“This is the first time that we have deployed voltage
regulators based on semiconductor technology in public
energy distribution grids. These control the voltage precisely to the set value,” summarises Torsten Hammerschmidt. In this case the operational locations of the
voltage regulators double the usable output capacity in
the existing medium-voltage grid. The alternative measurement technology installed in another medium-voltage grid enables the voltage fluctuations to be reduced
by up to 38 %. “That is considerably important for rural
supply tasks, since decentralised generation is developing particularly rapidly in the countryside,” explains
the project manager.
The project results provide a basis for future grid planning and for developing new strategies for managing
the grid. Although the operating equipment used in the
field test has provided very positive results, the operational results will have to be further validated, since
there is still no long-term experience. RWE Deutschland
has therefore secured the validation of the operational
equipment as part of a 3-year follow-up project.
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BINE Projektinfo 01/2010
BINE-Projektinfo
12/2012
Better energy distribution in smart grids
According to the German Federal Environment Agency, approximately 600 TWh of
electrical energy are consumed each year in Germany, of which roughly 25 % is lost
during the energy transmission and conversion. By developing the electricity networks
to form an intelligent grid – the Smart Grid, it should be possible to use the available
energy much more efficiently and therefore considerably reduce energy losses.
The aim of the 3-year “Energy to Smart Grid” (E2SG) research project is to reduce the
losses created when distributing the energy by 20 %. The focus of interest is on smart
electricity meters and the interfaces (communications processes and voltage converters)
between the end devices (household peripherals, lamps, etc.) and the Smart Grid.
In order to reduce the energy losses on route from the energy generators to the consumers,
the German E2SG project partners are focussing their research on components for the
secure, cost- and energy-efficient networking of devices. The devices include electricity
meters that have particularly secure communications processes for transmitting the
electricity consumption from the households to the energy provider and smart power
supply units that take into account the grid load for domestic appliances, internal and
external lighting and energy storage systems. It is also intended to take into account when
the consumers want to use the energy, for example to operate domestic appliances during
low-tariff periods or when the local PV installation is currently providing electricity – without
sacrificing comfort or reducing the accustomed safety and invoicing standards.
Under the management of Infineon, 31 partners from business and research from
9 countries are working on the European E2SG research project. In addition to Infineon,
the German E2SG partners include the Fraunhofer Institute for Integrated Systems and
Device Technology (IISB), Insta Elektro, NXP Semiconductors Germany, RWTH Aachen and
Telefunken Semiconductors GmbH. A total of 34 million euros is being spent on the
research project throughout Europe, of which the German partners are contributing
4.9 million euros and the German Federal Ministry of Education and Research is
funding 4.4 million euros.
Project organisation
Federal Ministry of Economics
and Technology (BMWi)
11019 Berlin
Germany
Project Management Organisation Jülich
Research Centre Jülich
Dr. Ralf Eickhoff
52425 Jülich
Germany
Project number
03KP101 A-D
Imprint
ISSN
0937 - 8367
Publisher FIZ Karlsruhe · Leibniz Institute
for Information Infrastructure
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen
Germany
Author
Anna Durst
Cover image
Gerhard Hirn, BINE Informationsdienst
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.
Contact · Info
Questions regarding this Projektinfo
brochure? We will be pleased to help you:
Project participants
+49 228 92379-44
>> Project management: RWE Deutschland AG, Essen, Germany, Torsten Hammerschmidt,
BINE Information Service
Energy research for practical applications
A service from FIZ Karlsruhe
[email protected]
>> Operating resources: ABB AG, Mannheim, Germany, Dr. Thomas Benz, [email protected]
>> Evaluation methods: Consentec GmbH, Dortmund, Germany, Dr. Wolfgang Fritz, [email protected]
>> Scientific monitoring: Technische Universität Dortmund, Dortmund, Germany, Dr. Christian Rehtanz,
[email protected]
Links and literature
>> www.zukunftsnetze.de | www.smart-country.de
>> Grid integration of decentralised power generators. BINE-Projektinfo brochure 02/2008
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