|Fig. 1: Distribution of windmills.  (Courtesy of dena.)|
On June 30th 2011 83% (513 out of 620) of the German Bundestag voted to forever close all German nuclear power plants, eight immediately and the other nine by 2022. This decision was a direct consequence of the Fukushima nuclear accident, after which the German public was no longer willing to risk the dangers of nuclear energy.  This legislation was not a pushed by the left, right, or green special interests. It was clear to all parties that the maintaining the existing plants would cost them the upcoming election. I will not seek to justify that decision in this article; instead I will take that decision as given and discuss the practical realities of maintaining the grid without nuclear power. The German energy transition is a highly complex process and it remains to be seen how much it will cost the German people, if they will maintain their resolve through 2022. Regardless, Germany is now running the experiment, so we can watch and learn.
A good place to start when determining the cost of replacement for German nuclear energy is the power output of those soon-to-be decommissioned plants. Table 1 shows various sources of German energy and their total output for 2012.  Coal and natural gas are the primary energy sources, but 11% of the energy is generated by nuclear. Therefore, it does not seem unreasonable to replace that nuclear power with either natural gas or coal. However, Germany is quite committed to the Kyoto protocol must therefore fill in that capacity with emission free energy. The government hopes to fill the void with a mixture of wind and photo voltaic renewable energy. To that end, government funds have been used to kick start the wind and solar infrastructure. Furthermore, the government hopes to curtail usage so as to meet the energy deficit.  Fig. 2 shows the change in primary energy consumption (EC) compared to the GDP versus time. Primary energy consumption is the sum of household EC, industry EC, traffic EC, system losses and so on.  Interestingly, Germany has succeeded in keeping its energy consumption constant while growing GDP from 1990 until 2010, but has been unable to drastically reduce in energy usage. Fig. 2 also shows a future prediction, which assumes high energy savings while still growing GDP.  Given that Germany was unable to both reduce EC and grow the GDP over the past 20 years, it is unclear where the energy needed to make up the nuclear deficit should come from.
|Table 1: Energy mix of Germany in 2012. |
This article does not go into the implementation details of wind or solar power, the interested reader is referred to the web and resources like, which explain how they work. [4-10] However, the implementation of these two energy sources does share one important shortcoming: their dependence on the weather. Without wind and sunshine these two power sources generate no electricity. And since the weather is beyond our control their power output is highly volatile. [2,3] Today wind energy can fluctuate between 0 and 20 GWh. That difference is similar to turning on 20 nuclear power plants in just a few days' time. The existing power grid was not designed for such fluctuations. The addition of solar power further complicates matters. In one day of this past spring German solar plants produced 20 GW in one hour.  The absolute size of this one number may be promising in that it proves that there is a large amount of renewable energy available, but it represents a nightmare for the operators of the power grid. Furthermore, the highly volatile renewable energy sources are highly localized. Most wind energy is produced in the north, near the coast or even off-shore (Fig. 1), and must be transmitted to the energy hungry industries of southern Germany.  Therefore, the grid must fight two battles: large fluctuations in power output, and massive power transmission. Before these new energy sources neither was an issue.
Reference  investigates three different scenarios for the evolving German power grid, and all of them required substantial expansion of the existing grid. The total length of new power lines that must be built, according to the models, ranges from 1700 to 3600 km and costs between 0.98 billion and 1.64 billion Euros a year (for 10 years). The annual German budget is 313 billion Euros (2012), suggesting that money is not an issue.  However, the grid expansion is impractical due to the small villages that cover the German countryside and the homeowners who live there. Germany is a very densely populated country, which means that every new power line must pass thousands of homes. As a result, new power lines are guaranteed to engender costly law suits and political resistance. Germans may not want nuclear power, but they don't want a power line in front of their house either. According to  the most practical solution involves 380 kV three-phase overhead power lines, and classical HVDC technology with overhead line transmission where that proves impractical. HVDC is most useful for connecting to offshore wind farms or for directly connecting the north to the south over 600-700 km. The interested reader is referred to  which contains more detailed information on the various transmission alternatives, including the principles of operation and their advantages and drawbacks.
|Fig. 2: Primary energy consumption (EC) of Germany compared to GDP. |
Another way to relax the stresses placed on the power grid by renewable energy is through the use of storage, which were investigated by  as well. Unfortunately, they conclude that most of today's storage technologies are not compatible with the needs of renewable energy. With the exception of pump storage, no available technology has enough storage capacity to effectively level the variations in renewable energy, and increasing the amount of pump storage is infeasible because all possible sites are either in use already or blocked for environmental reasons. It remains to be seen however, if additional capacity is available in Switzerland, Austria, or Norway.
An interesting solution to the storage problem that was not explored in  may be through renewable methane, as reported in . Renewable methane is produced with electricity, which can then be stored in a more traditional manner until needed. The efficiency converting electricity to methane and back is unfortunately low (approx. 38%), but it is better to save that 38% than to throw it away during peak production. As it stands, wind and solar power plants are shut down when production exceeds grid capacity.
In conclusion, it would not be difficult to replace Germany's nuclear power plants with gas or coal, but doing so and remaining carbon neutral is impossible. Wind and solar energy present attractive alternatives, but both suffer from inconsistent weather, which then requires more complicated transmission and storage to utilize properly. It appears to be technologically possible, but it remains to be seen whether the German citizens are willing to pay for the transition. There will be at least two general elections before the last nuclear plant is shut down, which leaves ample opportunity to politicize the subject.
© Martin Kramer. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Entwurf eines Dreizehnten Gesetzes zur Änderung des Atomgesetzes," Deutscher Bundestag, Drucksache 17/6246 , 22 Juni 2011 ["Proposed Legislation for a Thirteenth Change to the Atomic Energy Law," German Parliament, Docket 17/6246, 22 Jun 11].
 "Bericht zum Zustand der leitungsgebundenen Energieversorgung im Winter 2011/12," Bundesnetzagentur, 3 May 12 ["Report on the Status of the Electric Grid Energy Supply in the Winter of 2011/2012," Federal Electric Grid Agency, 3 May 12].
 J. Nitsch et al., "Langfristszenarien und Strategien für den Ausbau der Erneuerbaren Energien in Deutschland bei Berücksichtigung der Entwicklung in Europa und global," Schlussbericht BMU-FKZ 03MAP146 für Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit, 29 März 2012 ["Long-Term Scenarios and Strategies for the Buildup of Renewable Energy in Germany in the Context of Development in Europe and the World," Final Report BMU-FKZ 03MAP146 to the Federal Ministry for Environment, Nature Conservation and Reactor Safety, 29 Mar 12].
 T. Parise, " Wind Turbine Design," PH240, Stanford University, 2011.
 M. Shu, "Modern Wind Power," PH240, Stanford University, 2011.
 S. Agaian, "Wind Energy: Benefits, Design, and Challenges," PH240, Stanford University, 2011.
 A. Aguilar, "Solar Power Conversion," PH240, Stanford Unviersity, 2011 .
 F. Abuzaid, "Offshore Wind Energy," PH240, Stanford University, 2010.
 J. Brown-Cohen, "Photon-Enhanced Thermionic Emission," PH240, Stanford University, 2010.
 C. Bruner, "Organic Photovoltaics," PH240, Stanford University, 2010.
 E. Kirschbaum, "Germany Sets New Solar Power Record, Institute Says," Reuters, 26 May 12.
 "Integration of Renewable Energy Sources in the German Power Supply System from 2015 - 2020 with an Outlook on the year 2025," Deutsche Energie-Agentur GmbH, November 2010.
 "Abstract of the Federal Ministry of Finance's Monthly Report" German Federal Ministry of Finance, July 2012.
 M. Sterner, "Bioenergy and Renewable Power Methane in Integrated 100% Renewable Energy Systems," (Kassel University Press, 2009).