20 Seiten, Note: 1,5
Table of figures
1.1 Market structure analysis
1.2 Necessity for storage capacities
2. Electrolysis - Step one
2.1 Technological and operational background
2.3 Potential and utilisation of hydrogen
2.4 Greenpeace Energy - proWindgas
3. Methanation - Step two
3.1 Technological and operational background
3.2 Storage and transportation
3.3 Potential and utilisation of synthetic methane
3.4 Origin of CO2
3.6 Solar Fuel Technology
4.2 Market maturity
Figure 1: Hydrogen Production Paths, P.7- http://www.fsec.ucf.edu/en/consumer/hydrogen/basics/production.htm
Figure 2: Electrolyse/methanation of surpluses and electrification for deficits, P.5 - http://www.zsw- bw.de/fileadmin/ZSW files/Infoportal/Presseinformationen/docs/Vortrag IWES Schmid Einweihung M ethanisierung.pdf
Figure 3: Cost, Volume and Weight of Storage Options, P.9 - http://www.fsec.ucf.edu/en/consumer/hydrogen/basics/storage.htm
Figure 4: Schematic depiction of a fixed-bed, fluidised-bed and bubble column reactor, http://www- alt.igb.fraunhofer.de/www/presse/jahr/1998/en/PI Fixed-bed-reactor.en.html, http://en.wikipedia.org/w/index.php?title=File:Fluidized Bed Reactor Graphic.svg&page=1, http://www.rentechinc.com/rentechReactor.php
The energy efficiency targets of the “Federal Government” are important parameters deciding upon the amount of energy we will need in the future and hence about the storage capacities we will require. The reduction of the primary energy consumption by 20% until 2020 and 50% until 2050 towards 2008’s figures, the reduction in electricity consumption by 10% until 2020 and 25% until 2050, the doubling of the rate of refurbishment from 1% to 2% per year and the reduction of the end energy consumption in the mobility sector by 10% until 2020 and 40% by 2050 towards 2005’s consumption will change the energy market substantially. For instance, houses will need less electricity for their devices and less gas for heating, load profiles will smoothen and passenger and freight traffic will switch from petrol engines to electric and gas engines, fuel cells or will switch to rail.
In Germany, the market structure has been designed to enhance and facilitate the development of renewable energies through the “Renewable Energies Act” (EEG) and the “Energy Economy Law” (EnWG). And actually, in 2011 the share of renewables in the electricity production totalled to over 20% and is expected to rise over 25% this year, whereby especially the photovoltaic is booming with growth rates of nearly 50%. The evolutions are certainly pleasant, still, the very quick development of these, mostly decentralised and location dependent energy sources, is making the market framework conditions come to its limits. The transmission grid capacities are not large enough to transfer the huge amounts of wind energy from the north to the south and the distribution grid is often too weak to feed in the large amounts of photovoltaic energy in the midday. These restrictions have caused 407 GWh of wind energy to get lost in 2011 (150 GWh in 2010), a small but exploding figure, and a valid argument for storage capacities.
This shows that the whole of the energy market has to be evaluated and diverse scenarios for the future have to be created, to forecast the development into one specific area. Additionally, because of the dynamic of this market, these analyses and forecasts have to be updated continuously. In the context of these recent events and developments the following paper will discuss how the need for storage capacities could be met by the “power-to-gas” technology, noting the need for flexibility, close market maturity and economic affordability.
When looking at the German market structure, like also other countries markets structures, the underlying principle for a society dependent on electricity is the security of supply. The power plants capacity development in the past, and to a big extent also in the future, had to orientate themselves along the annual electricity demand and the maximum demand (peak load). This means that there had to be enough capacities not only to meet the total daily required energy but also the daily time curve of this demand. Therefore, the installed and secured capacity had to be compared to the total demand for electricity and balanced continuously. Especially for the future this will become more difficult, since on one hand the development of the demand and its timing have to be forecasted and on the other hand because renewable energies are classified with a lowersecured rate than conventional power plants. In this context, conventional power plants along with deep geothermal and biomass power plants have a secured rate of 85% (losses because of reparation and maintenance) while run-of-the-river hydroelectric, wind and photovoltaic power plants have a secured rate of 50%, 10% and 1% respectively (losses because of lack of water, wind or sun, reparation and maintenance). However, these can still exceed the secured rates by much, creating an excess, as they often do.
The security of supply under the circumstances of an increasing share of the renewable energies will only work when the market design will be changed by the regulator. Otherwise, because of the merit order, the development of the renewable energies will force gas- and coal-fired power plants out of the market way too often for them to be profitable. The introduction of capacity markets, which for example could secure combined cycle power capacities, is therefore very likely. Since these power plants are highly efficient, have a low minimal performance and are highly adjustable, they represent an economical balancing power and hence could compensate for fluctuations in the electricity production of renewables. Thus guaranteeing supply security.
Because of these facts, scenarios for the development of the energy demand, the capacities through renewable energy power plants, the amount of the energy these will supply and the time curve of demand, are essential. According to the already mentioned energy efficiency targets of the Federal Government the total consumption of electricity in 2020 should amount to around 548 TWh (-10% of current consumption of 608.8 TWh (2011)). Following the argumentation of the “Federal Government”, according to older plans, the target for the share of renewable energies in the electricity production should exceed 35% by 2020. In the light of recent events, however, the Federal Minister for the Environment, Peter Altmaier, raised this threshold to 40% lately. A called in study from the “Fraunhofer Institute for Wind Energy and Energy System Technology” (IWES) predicts that by then 20% would come from wind energy and 10% from solar energy. Recalling the fact that the secured rate of these generation means are very low, the installed quantities have to be very much higher, the excesses have to be stored through storage capacities or the time curve has to alter until 2020.
When prospecting the future, by looking at scenarios about the market design, the load curve and the energy demand and targets about energy efficiency in different sectors, it is inevitable to see that if Germany wants to achieve a complete supply of electricity through renewable energies, storage capacities will be needed. In total, 8% of the yearly electricity consumption could have to be stored at some point which on the basis of the 2011 net consumption of 511.8 TWh, would total to a storage capacity of about 41 TWh. With decreasing electricity consumption this figure will decrease as well and find itself somewhere between 20 and 40 TWh. For comparison, the installed capacity of pumped storage hydropower stations amounts to 0.06 TWh. These storage capacities need to be filled-up by the excessive electricity production of renewables which in the future could amount to an overproduction of 80-90 GW.
While the necessity for storage capacities is present, the closure to the market and the economical aspect of possible technologies are still questionable. In this context, it is important to look at benchmark studies to identify which technologies are the most reasonable to use and develop. Mirjam Sucher’s seminar paper shows that the power to gas technology could be one of the leading storage systems in the years to come.
The power to gas technology, mainly developed by Prof. Dr.-lng. Michael Sterner (University of Regensburg) and Dr. Jürgen Schmid (Head of the IWES-institute in Kassel), is a method to convert the excessive electricity in the system into the form of electrochemical energy which can then be stored in the gas network, in gasometers or in subterranean caverns. The biggest advantage of this form of storage definitely is the possibility to transport the energy carrier very easily and nearly without restrictions through the whole country. This makes it possible to transform, store and regenerate electricity in completely dispatched locations without making use of the temporarily overloaded electricity grids. Gas from renewable energies will help to decarbonise different sectors, to improve the security of supply in times of electricity grid restrictions and to generate C02-neutral fuel. This will decrease dependencies on energy resources and hence could smoothen international relations and conflicts. The process of transformation comprises the step of electrolysis in which hydrogen is being produced and the step of methanation in which the hydrogen reacts with carbon monoxide or dioxide to form methane, essential part of natural gas. These two steps can be looked at independently as both products, hydrogen and methane, can be used and to a certain degree stored in our current energy system. Therefore, the following will analyse them separately as indeed two steps of a process and two differently marketable products.
Hydrogen is the simplest element in the world and makes up for most of the known matter, however, it is locked up in water, in hydrocarbons (such as methane) or in other organic material. The production of hydrogen (fig. 1) from these components was a big challenge in the past and will be for the future development of more efficient procedures.
Until recently the production of hydrogen was achieved through the direct utilisation of one primary energy source (solar-based, fossil), explaining that hydrogen is an energy carrier and not source. The current developments in the energy market, with fossil fuels predestined to vanish, biomass fully dedicated to other means, and other renewable energies showing big fluctuations in their electricity production, make it necessary to produce hydrogen indirectly through water and a secondary energy source, electricity, and therefore through the process of electrolysis. Additionally, it is essential to make this more efficient for a wide-scale application. In this sense, different procedures are being deployed to split the components ofwater into hydrogen and oxygen.
Abbildung in dieser Leseprobe nicht enthalten
While especially the production through steam reformation (95% of US hydrogen production ) or gasification (cracking), fuelled by fossil fuels, is most cost efficient, the costs of electrolysis are twice to three times as high. Moreover, as soon as electricity from renewable resources is being directly employed for the electrolysis process the costs tend to increase as their price is mostly higher. In fact, the costs rise according to the cost developments of renewable energy sources, which show onshore wind power in the lead and solar power considerably more expensive. However, if not analysed in the context of a combined production facility (wind power plant attached to electrolyser) these costs are dependent on the price projection at the energy exchange markets or individual agreements with electricity producers. In this context, and especially through the known price fluctuations at the “European Energy Exchange” (EEX) with a generally decreasing trend, the costs for the hydrogen generation are volatile.
The history of the electrolytic process goes back to the time around the 18th century when Galvani’s and Volta’s first experiments were followed by William Nicholson who firstly broke down water into hydrogen and oxygen. “Electrolysis involves passing an electric current through water. The current enters the electrolysis device through the cathode (a negatively charged electrode), passes through the water, and leaves through an anode (a positively charged electrode). Hydrogen is evolved and collected at the cathode and oxygen is generated and collected at the anode.” The chemical reaction is defined as 2 H20 + energy « 2 H2 + 02. Electrolysers can be hand-sized but research is being committed to increase the scale of electrolytic operational plants which can be integrated at renewable power plants, allowing to shift production to best match resource availability and market factors (demand, price level), or produce big quantities of hydrogen centrally.
There are three electrolytic processes which are being used more frequently, the PEM-Electrolysis, the Alkaline-Electrolysis and the High-Temperature-Electrolysis. “In a polymer electrolyte membrane (PEM) electrolyser, the electrolyte is a solid specialty plastic material. Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons). The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode. At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas.” This method is rather new and the best suitable catalysts are still in development as a new catalyst, 97% more cost efficient, shows. “Alkaline electrolysers are similar to PEM electrolysers but use an alkaline solution (of sodium or potassium hydroxide) that acts as the electrolyte. These electrolysers have been commercially available for many years.”
Additionally, the process of high-temperature water splitting, which different than a pure electrolytic is a thermochemical process, is a future technology in the early stages of development. “High-temperature heat (500°C-2000°C) drives a series of chemical reactions that produce hydrogen. Chemicals used in the process are reused within each cycle, creating a closed loop that consumes only water and produces hydrogen and oxygen. The high-temperature heat needed can be supplied by next- generation nuclear reactors under development (up to about 1000°C) or by using sunlight with solar concentrators (up to about 2000°C).” However, considering the enormous local and source-specific risk of nuclear energy plants, this option should be discharged by conscious governments. In the last months different alternative procedural ways (more than 200 cycles) have been tested and further research is focused on twelve specific cycles which can improve the efficiency in the future. Further, the
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