The Combined Power Plant: the first stage in
providing 100 % power from renewable energy
Renewable energy is
already contributing over 14 percent to the electricity supply
in Germany. That wind energy, photovoltaic and bioenergy plants
can replace electricity from nuclear and coal plants is no longer
disputed. To what extent this is possible, remains to be proven.
The next consistent step is thus to prove that it is possible
to provide the full electricity supply from renewable sources.
The symposium “On our way to full supply from renewable
energy sources” showed the way ahead. It outlined the current
state of development, explained the medium-term plans for 100
percent electricity from renewable energy and provided an outlook
for 100 percent renewable energy for electricity and heat supply
as well as for mobility. Existing reference projects such as
the “Regenerative Combined Power Plant" formed the
point of departure for this event. The Solarserver is presenting
the pioneering project, carried out by the companies Enercon
GmbH, SolarWorld AG and Schmack Biogas AG together with the Institute
for Solar Energy Supply Technology of the University of Kassel,
as “Solar System of the Month” in January 2008.
The Combined Power Plant consists of
three wind parks (12,6 MW), 20 solar power plants (5,5 MW), 4 biogas
systems (4,0 MW) and the pump storage Goldisthal (Output: 1.060
MW; Storage: 80 hours, i.e. 8480 MWh). Photos: www.kombikraftwerk.de
With this pilot project the participating
parties impressively showed that renewable energy can cover 100
% of electricity demand. "The Combined Power Plant shows
that renewable energy sources can supply sufficient electricity,
can be controlled at any time, function in combination and can
be balanced out across the grid”, says Ulrich Schmack,
Board Spokesman of Schmack Biogas AG. The joint project of Schmack
Biogas, SolarWorld and Enercon links and controls 36 decentralised
wind, hydropower, solar power and biogas installations so that
they can cover the electricity demand in any weather conditions
by tapping into the unequally distributed energy potential across
Germany.
Regenerative full supply on a scale of 1:10.000
The
Combined Power Plant is scaled to meet 1/10 00th of the electricity
demand in Germany using renewable energy. This scale corresponds
to the annual electricity requirements of a small town with
around 12 000 households, such as Stade. The Combined Power
Plant therefore shows in miniature what is also possible on
a large scale: 100 percent electricity provision using renewable
energy sources,” emphasises Frank H. Asbeck, CEO of SolarWorld
AG.
Intelligent controlling and accurate weather forecasts
allow regenerative power supply around the clock. Photo: www.kombikraftwerk.de.
[Wording of images: The regenerative Combined Power Plant; Diagram
of electricity demand and feed-in; Measured values; Forecasts;
Environmental conditions; Time, Date; Current electricity mixing
ratio; Solar, Output; Wind, Output; Biogas, Output, Biogas storage;
Reservoir (water), Output, Storage]
Safe supply from renewable energy, all the time
and everywhere
The power plant that is definitely not only
a “virtual
concept” links and controls 36 wind, solar, biomass and
hydropower plants that are distributed throughout Germany. It
has proven to be just as reliable and powerful as a conventional
large-scale power plant, since it optimally combines the advantages
of the different renewable energy sources. Wind turbines and
solar modules, depending on availability of wind and sunshine,
make their contribution to the generation of electricity. Biogas
and hydraulic power are used to make up the difference and are
converted into electricity as needed in order to balance out
short-term fluctuations, or are temporarily stored. Technically,
there is nothing preventing us from 100 percent provision with
renewables.
Pilot project on the complete energy turn-around
Schmack
Biogas, Solarworld and Enercon realised at an early stage that
reliable electricity supply can only be provided when the different
renewable energy sources are combined. The concept of the Combined
Power Plant is based on establishing a network between different
renewable energy power plants that
allows balancing out. In research the “virtual power plant” is
already a well-known concept. The Combined Power Plant, however,
is more than a mere simulation – it permits an active control
of renewable energy power plants in real-time operation. Variations
in the various underlying conditions, such as electricity demand
or the wind availability, immediately change the interaction between
the networked plants. The project thus demonstrates powerfulness
and ease of control of renewable energy. Together they ensure sufficient
electricity supply to cover the demand. The function of the regenerative
Combined Power Plant can be divided into two stages: anticipatory
control and fine-tuning.
Wind energy and biogas plants generate three
quarters of the electricity output of the Combined Power Plant, photovoltaic
systems provide the rest. Photos: Enercon; Schmack Biogas AG
This is how the Combined Power Plant
works
The eleven wind energy plants, four combined heat and
power (CHP) units based on biogas, twenty photovoltaic plants as well
as a pumped
storage power plant are linked to one another through a central control
unit. The Combined Renewable Energy Power Plant adjusts itself to the
nearest minute to meet daily needs. It covers peak loads, such as at
midday, and stores electricity that is not needed during quiet periods.
The actual course of the electricity demand is the central starting
point for all power plant functions. The forecast of the electricity
requiremenst,
the “load profile”, is communicated to the central control
unit. This is also where the forecasts for the wind and solar power installations
arrive. The German Weather Service (DWD) provides the forecasts for wind
strength and hours of sun. In the central control unit this data is then
evaluated. Wind and solar energy cannot precisely meet the electricity
demand since the amount of wind and solar radiation fluctuates. This
creates oversupplies and shortages, which have to be balanced out in
order to ensure security of supply and grid stability.
Additional solar power plants guarantee highest outputs.
Photo: SolarWorld AG
Adjusting to the actual electricity demand
The central control unit controls the installations included in the
Combined Power Plant in order to produce electricity in accordance with
demand. If wind and solar power installations do not produce enough electricity,
additional plant power is required, which comes from two sources: firstly,
combined heat and power (CHP) plants are used to produce electricity
and heat from biogas. Secondly, energy can be stored temporarily in a
pumped storage power plant and can be quickly made available again. If
electricity is needed, water flows downwards from high-level reservoirs
and drives a generator. If there are electricity surpluses, water is
pumped through pipes back into the reservoirs. Forecasting of the output
requirement makes it possible to draw up schedules in sufficient time
for controlling the combined heat and power plants and the storage systems.
If the amount of electricity produced by wind and solar power installations
exceeds demand, the surplus of energy is used for filling up the pumped
storage reservoirs. The electricity can also be exported or used for
driving electrical cars. In exceptional cases, the wind and solar plants
can be throttled back, but this would mean that existing potential energy
is not utilised.
Principle of how the regenerative Combined Power Plant functions,
1. stage: anticipatory control. Photo: www.kombikraftwerk.de. [Wording
of image: Forecast, Required values; Central control unit; Operating schedule;
Biogas; Reservoir; Electricity demand, Forecast]
Fine-tuning on the basis of accurate measuring values
The
accurate forecast of the output of all involved power plants enables
the Combined Power Plant to specify anticipatory control models. However,
there is still a need for balancing out in terms of the actual electricity
fed into the grid. Despite precise weather forecasts, there is generally
a slight deviation in the actual electricity production and in the
electricity demand. This requires fine-tuning of the central control
unit. It adjusts
the original schedule to the actually measured values.
Principle of how the regenerative Combined Power
Plant functions, 2. stage: fine-tuning. Photo: www.kombikraftwerk.de. [Wording
of image: Output; Central control unit; Adjusted operating schedules; Biogas;
Reservoir; Electricity demand, Output.
If there is insufficient electricity available, the biogas/CHP plants
and the reservoirs release their available capacities. The central control
unit receives continuous data on the current output of all power plants
involved and, if necessary, requests additional power. Thus, the Combined
Renewable Energy Power Plant is able to immediately meet electricity
demand entirely from renewable energy sources. The use of biogas, in
particular, plays a central role in controlling the Combined Power Plant.
Biogas covers peak load and balances out the natural fluctuations in
wind and solar energy.
German Minister of Economic Affairs Michael Glos:
Innovative solutions such as the Combined Power Plant are to be taken
into consideration in the renewable energy law
The wind and the sun
cannot be influenced, which places particular importance on linking
wind, solar
and biogas plants. “The decentralised network enables wind, solar
and biogas installations to be controlled like a conventional large-scale
power station and thus meet Germany’s fluctuating energy requirements,” says
Kurt Rohrig from ISET, explaining the Combined Power Plant’s central
control unit.
Words of praise for the Combined Power Plant were also
expressed by the German Minister of Economic Affairs Michael Glos, "This
demonstration project shows that a virtual Combined Power Plant provides
the possibility to make available electricity in the same way as a conventional
large-scale power plant by jointly controlling smaller, dencentralised
energy plants.” The use of intelligent controlling and regulatory
technology allows the combination of decentralised wind and solar systems
with biogas and hydraulic power plants so that fluctuations in the feed-in
of wind electricity can be compensated. Glos was in favour of further
developing such solutions in order to ensure the required grid stability,
even if an increasing amount of electricity is fed in from wind and solar
plants. "Particularly with regard to the coming amendment of the
German law on renewable energy, we must provide adequate incentives so
that such solutions will not remain mere demonstration projects but can
be realised in future because they present the most economically feasible
utilisation of renewable energy,” the Minister said. Thus far the
law on renewable energy does not make provision of load-specific compensation.
A bonus for “continuous electricity” could provide an incentive
for the realisation of further Combined Power Plants and could boost
the decentralised production of electricity from renewable energy sources.
This is precisely the point where politics will come into play.
Ulrich Schmack, Andreas Düser and Frank
H. Asbek presented the Combined Power Plant to the public on 9 October
2007. The Business Institute Solar Strategy (BISS), Sunbeam GmbH, the German
Weather Service (DWD), SMA Technologie AG, Stadtwerke Schwäbisch Hall
GmbH and Tauber Solar support this project. Photo: "deutschland hat
unendlich viel energie”
Contributions
to the symposium "On our way to full supply from renewable
energy sources" can be downloaded from the following website:
www.unendlich-viel-energie.de
Video clip: "The Combined Power Plant" (7:20 minutes; MPEG)
can be downloaded from the following website www.unendlich-viel-energie.de
