1 Introduction
Even though the “Coal Commission” got the official task to focus on CO2-reductions as well as on economic impacts inside the coal “regions” and on the impact of this “move out of coal” to the security of the German power supply, only 10 out of 336 pages of the coal commission report will deal with the security of supply. Within these 10 pages the German “Coal Commission” made the following clear statements: ① Keeping a high level of security of supply is an important factor for an industrialized country like Germany. ② In the past, a reliable supply with electricity was mainly guaranteed by keeping the secured power generation capacity in each European country above the peak load in the related country. ③ New understanding within German National Ministry of Economics and Energy is now to use a more dynamic criterion called “Loss of Load Expectation,” which possibly can become a European forecast tool for security of supply in the long-term range. Instead of using only national parameters on peak load and secured generation capacity, this model will take also into account free generation capacities in neighboring countries, which possibly will be traded on the energy market. Unfortunately, no investigations were made from the “Coal Commission,” if the European Energy Market can deliver enough secured power in the time from November till February each winter, when Germany and all its neighboring countries are close to their own national peak loads on every working day. So no answer was given by the “Coal Commission” on how to replace the switched-off generation capacity of 10 GW from nuclear plus another 12 GW from coal in 2022, followed by another 30 GW until 2038. ④ Instead the “Coal Commission” report stated that the huge number of parameters for the new “Loss of Load Expectation” tool very often are not fully available from all power stations in Europe, so that using the old criteria, where “secured power generation capacity>peak load” in each European country should be the more risk free design criteria for a medium term range.
Unfortunately these statements will be fully contradictory to the proposed way on how fast Germany should move out of coal-fired power generation. In this paper, the technical background will be given, why this proposal given by the German “Coal Commission” will initiate the “German Way into unsecured Power Supply.”
2 Secured power generation capacity as the main basis for a reliable power supply
The goal of the German Energy Revolution is the reduction of CO2 emissions. This reduction is principally reasonable and necessary. Triggered by the EEG – German Law on Renewable Energies, the main focus of CO2 reductions in the past 20 years only was put on the field of electric power generation from wind energy and photovoltaics, neglecting the fact that electricity represent only 20% of the German primary energy resource demand. Some more, but very early activities came up in the past years to reduce CO2 emission in the transportation sector (e-mobility and bio fuels) and heating of buildings (heat pumps in combination with solar and geothermal energy).
Since 1990 the share of renewable energy for electric power consumption grew up to 33.3% (Table 1 and Table 2, data from Ref. [
1]) respectively 218 TWh (Fig. 1) in 2017, both based on the gross power generation. Expected values for 2018 are in the range of 35%–36%. The total gross power generation in Germany with its 600–650 TWh is shown in Fig. 2.
Some other sources published values above 40% for 2018, but these were based on the net power generation of 546 TWh in 2017 and 540 TWh in 2018 (Tables 3 and 4, data from Ref. [
4]).
Meanwhile, German National Government put a new goal of 65% of renewable generation on the national agenda to be reached until 2030 [
5]. Unfortunately, the question on how to realize a secured power generation capacity which is able to supply the German peak load on the one hand side and to integrated an share of 65% of highly fluctuating renewable sources form wind and PV on the other hand is neither part of the public discussion nor on the agenda of detailed governmental planning. In the past only the amount of annual energy generated by renewable source was accumulated during one year and put into relation with the amount of energy needed in the same year. The fact that generation has to follow the demand minute by minute due to the lack of large energy storages in the electric power system, as well as the missing grid capacities to absorb the temporarily huge renewable overproduction, is simply neglected in the public discussion and in the above mentioned governmental “Coal-Commission.” Figure 3 (data from Refs. [
5,
6]), Fig. 4 (data from Ref. [
6]) and Fig. 5 (data from Refs. [
9,
10]) will explain the effect of “cold and dark-doldrums” to the security of supply more in detail.
In Fig. 3, the increase of German installed power generation capacity is shown with its 93 GW from conventional power plants and the distributed 112 GW from renewable sources in 2017. The last ones were built up during the past 20 years, stimulated by tremendous and in the initial phase reasonable governmental funding. Also shown in Figs. 3 and 4 is the range of German power demand, always fluctuating between 35 and 40 GW as the German base load and about 80–85 GW as the German peak load. All the assumptions of about 10 years ago, which forecasted a decreasing energy demand in Germany, do not become true and meanwhile several indicators are recognizable that the peak load will increase toward 100 GW, caused by e-mobility and electric heat pumps.
Figure 3 also shows one of the latest planning scenarios with 65% of the needed energy generated by renewables on the one hand and without any nuclear generation and dramatically reduced coal power generation on the other, both according to National Grid Development Plan NEP 2030 V19 of BNetzA (German National Grid Agency) [
5].
From Fig. 3 the reader will get the impression that Germany, even in 2030 will have enough renewable and conventional generation resources for a reliable and more ecological power supply, so that the final disconnection of the last nuclear power plants in 2022 and the reduction of lignite-fired power stations from 21.3 GW down to 9.3 GW, as well as the reduction of hard coal-fired units down from 25.1 GW down to 9.8 GW will not cause severe problems. Although the National Grid Extension plan was independently developed by BNetzA, the “Coal Commission” proposed nearly the same figures. Due to their final report, remaining capacity of lignite-fired units should be down to 9 GW and capacity of hard coal-fired power stations should be down to 8 GW, both in 2030. Unfortunately it was not taken into consideration that the “secured power generation capacity” is lower than the installed capacity, depending on the storability of the used primary energy resources and the technical conditions on the power station itself, as demonstrated in Table 5.
Based on these factors, the bars in Fig. 3 will change totally. It will become clearly visible in Fig. 4 that the secured generation capacity in Germany until 2017 always was a little bit higher than the peak load in Germany, even it became more and more challenging to balance generation and demand at any minute, to keep the German power supply system sometimes close to its technical limits, but stable at any time and to integrate the renewable share of 33% in the last year. That is exactly what it is mentioned in some of the remarks concerning “Security of Supply” within the “Coal Commission Report.”
The year 2030 in Fig. 4 is also based on National Grid Development Plan NEP 2030 V19 of BNetzA (German National Grid Agency) [
5]. Even the installed power generation capacity of photovoltaic and wind energy should increase from 99 GW in 2017 to 190 GW in 2030. Besides, gas-fired units should grow from 29.5 GW (2017) to 35.3 GW (2030). The 2030-planning scenario will foresee a decrease of power generation from nuclear, lignite and hard coal from 57.2 GW down to 19.1 GW. Caused by these changes the secured power generation capacity in Germany will decrease from 87.2 GW in 2017 down to 54.8 GW in 2030, which will be for sure to less for a reliable energy supply of Germany with its peak load of 80–100 GW and based on its own capabilities. Although the German National Energy Agency (DENA) stressed this topic very clearly in similar reports in 2010, due to the proposals of the “Coal Commission,” the first critical situations will occur in Germany in 2022. Due to the disconnection of 10 GW from nuclear power stations in combination with the disconnection of 12.5 GW from coal-fired units, the secured power generation capacity will decrease from 87.2 GW down to 66.8 GW, which is also significantly lower than the peak load of 80–90 GW in 2022. Details can be found in Fig. 5.
In several political oriented discussions in Germany, statements often came up that the “peak load” is a singularity in the annual power demand. It will be often assumed that all time beside this moment of peak load, the power demand is much lower and therefore there is no need, to correlate the secured power generation capacity with the peak load. Figure 6 shows an example from winter 2007/2008, where the highest demand on each of the working days between November 1st, 2007 and March 1st, 2008 always was very close to the annual peak load.
Since 2007, the situation in the German power grid have changed in such a way, that the peak meanwhile exceeded 80 GW, but the principle graph itself remain unchanged which still shows clearly that the value of the peak load simply describes the power demand on more or less all the working days during the winter season in Germany.
As shown in Table 5, the contribution of wind energy and photovoltaic to the secured power generation capacity is nearly negligible. In Figs. 7 and 8, two examples will be given on the real contribution of wind energy and photovoltaics to the German power supply within week 06/2018 and week 50/2018. Figure 7(a) and Fig. 8(a) show the contribution of different generation sources in GW, while Fig. 7(b) and Fig. 8(b) in percent of the overall power generation.
Figure 7 illustrates very clearly that there are long periods of time where renewable generation from wind energy and photovoltaics together only contributed by about 2%–4% of its installed capacity, which correspond very well with the above mentioned secured power generation capacity of wind energy and PV. In such situations, nearly the whole German power consumption has to be ensured by conventional generation from nuclear, lignite and hard coal, and gas as well as by renewable generation from running water and biomass. In addition to this negligible contribution to the secured power generation capacity, the high dynamic of fluctuating renewable generation can be taken from Fig. 8. In the first 2 days of week 50/2018, wind energy contributed by about 50% of the needed power, but within some hours, it dropped down to less than 10% of the needed power, which was about 6% of the installed capacity. Similar situation occurred in Fig. 7 at the end of week 06/2018, when the infeed from wind energy suddenly went up from about 8% to 50% of the needed power within half a day.
With these examples it should be easily understandable that any industrialized country throughout the world needs a structure of installed power plants which are able to realize a secured generation capacity, which is above the peak load inside the own country. Due to the lack of other renewable sources, it is necessary in Germany to use extra ordinary shares of generation from wind energy and PV. Other technical assets like battery storages or power-to-gas units with re-generation capacities will also be needed to increase reliability of these fluctuating sources.
In so far it will be absolutely necessary to change the generation portfolio in Figs. 4 and 5 in any way to increase secured generation capacity above the peak power at any time. The following options will be possible:
1) Use of generation units with storable primary energy resources
This type of generation includes power stations like nuclear, lignite and hard coal on the conventional side as well as running water and biomass on the renewable side. Opposite to the trend in many other industrialized countries, Germany decided to phase out nuclear power in 2022. Besides, several technologies for CCS (carbon capture and storage) to separate CO2 from the exhaust gases of coal-fired units were developed in Germany, but finally not brought into common use due to fears in the population about possible leakages of the CO2-storages. The economically usable potential of running water power stations in Germany is reached and the increase of biomass production for energy purposes will lead to a discussion between food production and “energy biomass production.”
Under these self-imposed restrictions, only an increasing use of gas-fired power stations with gas and steam process seems to be possible, even knowing that this will lead to a much higher dependence of German power supply on Russian natural gas. Due to the higher efficiency of up to 60%, electricity production from gas-fired units will lead to CO2 emissions of about 335 kg/MWh, compared with coal-fired units with efficiencies of up to 45% and CO2-emissions of 735 kg/MWh for hard coal-fired units and 930 kg/MWh for lignite-fired units. It has to be pointed out very clearly that these emissions are only those which will be created directly during the generation process inside the power station. Statistically correct, only these emissions will be part of the German Eco balance.
Unfortunately, the reduction of CO
2 emissions is a global challenge. So when decisions will be taken on moving from one combustion technology to the other, side effects in other countries should be included in the discussion. The overall CO
2 balance of natural gas, hard coal and lignite looks different, if the emission induced by the exploitation and transportation to Germany will be taken into consideration. While natural lignite with its high portion of water is a resource to be used only very close to the mining areas, hard coal and especially natural gas very often will be transported for a very long distance between the exploitation side and the power station in Germany. As shown in Table 6, the overall CO
2 emission of hard coal is in the same range than the one from lignite. In addition, for natural gas, the overall CO
2 emission is in minimum 70% of the value from lignite. In some source, a value of 110% is published for hard coal as well as for natural gas, depending on the transportation distance. Details can be also found in Table 6, based on data from Ref. [
12].
Therefore, from a global point of view, a transition from coal to gas in Germany makes only sense, if the total CO2 emission from gas-fired power station including the exploitation and transport induced emission can be reduced significantly below the total emissions of coal-fired units. In principle, that would be possible by using the power-to-gas technology, where renewable overproduction from wind energy and photovoltaic can be converted into hydrogen, and if needed, into methane. Both can be stored in the German gas grid with its huge storage capacities of hundreds of TWh and can be used as “lower total emissions gas” either for re-generation or other industrial or heating purposes (see below). As long as Germany does not move into this “green-gas” technology, the pure replacement of coal by gas will statistically lead to a much better eco-balance, based on the expenses of the gas exploring and transporting countries.
2) Extreme renewable overproduction from wind energy and photovoltaics and conversion of this overproduction in “storable” energy resources
Due to its highly fluctuating character between 0 and 100% of the installed capacity, neither wind energy nor photovoltaic will ever be able to follow the power demand minute by minute or to contribute to the needed secured power generation capacity of the electric system. The only choice to adopt these sources better to the electric system will be to convert overproduction into heat, gas, liquid or mobility by using any type of the power-to-X technology.
(1) P2H (power-to-heat) conversion on lower temperature level can be applied for pure using of renewable overproduction on the heat side only. Re-generation on this temperature level of about 100°C will not be possible. The P2H conversion on high temperature level of up to 1000°C will offer the chance of re-generation and in combination with high temperature storage systems, it can also contribute to the secured power generation capacity. Unfortunately this technology is still under basic research. Therefore, it will take decades to scale it up into the GW-range.
(2) P2V (power-to-vehicle) or grid controlled charging of e-cars is an option to increase load flexibility within SMART grids and can be used to adjust the load a bit better to highly fluctuating renewable sources, but without any impact to secured power generation capacity. Instead of this, battery systems either as stationary battery systems or V2G (vehicle-to-grid) applications can deliver a contribution to secured power generation capacity. Due to their limited storage capacities, these technologies are a bit comparable to pump storage units with their charging or discharging times in the range of some hours.
(3) P2G (power-to-gas) conversion is the only technology with a huge storage capacity in Germany suitable for weeks or months. By using electrolysis, optimized for highly dynamic operations, renewable overproduction can be taken out of the electric system and can be converted into hydrogen. Up to a defined percentage, the hydrogen can be directly stored within the methane-based natural gas grid in Germany with its storage capacity of hundreds of TWh. For higher shares of “green gas,” hydrogen can be converted into methane or, if this second conversion step is to cost intensive, technical improvements have to be done within the gas grid to accept higher shares of hydrogen. The P2G technology in combination with the re-generation of this “less CO2 containing” gas will have a great potential to increase secured power generation capacity from renewables like wind energy and photovoltaics.
Ten or more years ago, DENA—German National Energy Agency and lots of other energy experts proposed to move into this direction, even knowing that this would cause severe additional costs. Up to now the German National Government has not yet decided to move into this direction. Therefore, actually only P2G-prototypes in the range of some MW are available in Germany and some first ideas on planning a larger unit with 50–100 MW came up. Therefore, it will take decades to roll out this technology into the range of several tens of GW.
In Section 3, some additional information will be given on where to place such larger P2G-installations to absorb renewable overproduction, so that needed grid extension will be as low as possible.
3) Use of generation units with a high secured power generation capacity in the neighboring countries to Germany
The German National Government strongly supported the development of a European Power Market, combined with the hope to “export” German renewable overproduction from wind and photovoltaic to other countries, whenever it will occur in Germany and to “import” secured power generation from its neighbors, whenever needed in Germany. That is why the German National Ministry for Economics and Energy strongly supports the implementation of the European Energy Market. That is also why they want to use the above mentioned “Loss of Load Expectation” as a forecasting tool, which will include market availability of power stations in the neighboring countries to supply Germany whenever needed. Some more details on the feasibility of this option will be discussed in Section 4.
3 Actual situation in German power grid
The massive increase of renewable generation was mainly driven by funding, based on EEG—German Law on Renewable Energies and never was linked to the regional power demand. The local distribution of generation capacity from wind energy can be referred to in Ref. [
13]. Values of 1–5 MW/km
2 or more can be found only in the northern part of Germany. In the south, these values vary from 0 to 0.1 MW/km
2. Versus vice, the solar radiation in the south of Germany with 1250–1300 kWh/m
2 is much higher than that in the north with values in the range of 1100–1150 kWh/m
2. That is why it can be observed clearly that the majority of wind generation is located in the north of Germany, while the highest density of roof PV installations can be found in the south. Only the very large open range PV plants with installed capacities of 100–150 MW each are also located in the north-east of Germany, because EEG granted funding for using “military conversion areas,” which is a synonym for old, unused military air field from National People’s Army or Russian Troops in former GDR (German Democratic Republic). The combination of this national funding and a solar radiation of approximately 1250 kWh/m
2 in a small area close to the Polish border (influenced by dry continental climate) will lead to an attractive business case for large PV investments.
While the southern region of Germany will have a quite high power demand due to the high density of industry with a huge electricity consumption and about 28% of the German population, the mainly PV dominated renewable generation will not cause severe frictions in the power grid. The grid operation in the north-western region of Germany with about 55% of German wind power generation is more challenging, but due to the also high energy consumption caused by heavy industry and 50% of the population, it is not comparable with the north-eastern region. In this part of Germany, about 45% of German wind power and the very large PV installations with 100 MW and more will not match to the energy consumption of only 22% of the population and a very small density of industrial enterprises.
While the share of renewable energy in the whole north-eastern region ( = control zone of 50 Hertz-Transmission Ltd.) is a bit above 50% compared with the energy demand, the situation in several regional distribution systems with their 110 kV grid is much more severe. Grid operators like E.DIS (see Figs. 9 and 10), MitNETZ, WEMAG, and Avacon will have more than 100% renewable generation, compared with the demand in their grids. Unfortunately that will not mean that these grids can be fully supplied by renewable sources–only the annual amount of energy coming from renewables is the same as the annual amount of energy needed for the customers. Unfortunately, renewable generation will often occur, when less energy will be needed. Therefore, several times per week the region distribution grids starts feeding back renewable overproduction to the overlaid 400 kV transmission grid (see Figs. 11 and 12).
The transport of renewable overproduction out of the above mentioned regions by the 20 kV or 110 kV distribution grids into the 400 kV transmission system, as well as the transport from the northern renewable generation area to the southern load centers cause a massive extension of the German power grid. In 2004 the German National Energy Agency (DENA) came up with a study showing a demand of 900 km new 400 kV lines. In July, 2006, Brandenburg Ministry for Economics and Energy gave an order to BTU to prepare a concept for the grid extension needed in the province of Brandenburg. The results were prepared in close cooperation with the grid operators in this province and showed a necessity of 600 km new 400 kV lines and 1200 km new 110 kV lines only within the Brandenburg province, an area of 350 km north–south and 250 km west-east, surrounding the city of Berlin. In 2010, DENA came up with a revised study on the national level, now showing a need of 4500 km of new 400 kV lines and BTU updated its Brandenburg study to 600 km of 400 kV lines and 2100 km of 110 kV lines. Finally, DENA published a national 110 kV study, showing the need of about 10000–20000 km of 110 kV lines for whole Germany. Based on these and other grid studies, the German National Government handed over responsibility for this huge grid extension to BNetzA—German National Grid Agency (Power Grid, Gas Grid, and Telecommunication Grid).
Meanwhile BNetzA permanently is updating the NEP—German Grid Extension Plan and is also investigating future grid scenarios, like the NEP 2030 with a German overall share of renewables with 65%, as shown in Fig. 4.
Caused by very time consuming administrative approvals and trails, the grid extension in Germany moves extremely slowly. Within the past 10 years, only some hundreds of kilometers of new overhead lines out of the needed some thousands of kilometers were built. Planning, approval, erection and commissioning of a new line will take 5–10 years, in some cases more than 20 years. Actual forecasts propose about 20 or more additional years to realize the needed grid extension.
In addition to the above mentioned grid extension concepts, BTU also investigates and identifies nodes within the 400 kV transmission system, which will be suitable for large battery systems or large power-to-gas installations to absorb renewable feedback from the distribution grids. To give the reader a first feeling on the magnitude of this feedback, attention should be focused again on Fig. 11. The dark blue marked area shows a feedback with an average power of 1.5 GW for about 72 h, which will correspond with an energy of about 100 GWh, coming only from one of the seven distribution grids in the north-eastern region of Germany. This is 5 times higher than the available storage capacity of 20 GWh for the whole north-east of Germany (40 GWh in whole Germany).
Due to agreements with E. DIS, MitNETZ, WEMAG, Stromnetz Berlin, and 50 Hz-Transmission, BTU will get the measured data of all transformer loadings in all substations and the renewable generation, both measured 15 min by 15 min. Therefore, the feedback of 2 nodes (substation in RAGOW and substation in GRAUSTEIN) within the east German 400 kV grid can be shown here as examples in Figs. 13 and 14. To understand these pictures more easily, some additional explanations is given in Fig. 15, in which the real power flow in MW is shown by the blue curve and for one month. As it is visible, the power flow is heavily fluctuating in both directions. To avoid overloading of information within an annual presentation of the power flow, only the average value in both directions (orange blocks) is shown.
The demand and feedback in substation GRAUSTEIN shows power flows with values of about 100–300 MW as well as feed backs in energy with about 30 GWh. However, the situation in RAGOW substation is totally different. Only at a few times per year, this substation transports energy from the transmission system into the distribution grid and ahead to the consumers. Most of the time per year, renewable overproduction is transported out of the region with 150–350 MW and several energy packages of 80 GWh, which is 4 times the storage capacity of 20 GWh in eastern Germany and double the capacity of 40 GWh in whole Germany.
As long as the electric power grids is not upgraded to the needs of the energy revolution, grid operators will be forced continuously to re-dispatch conventional power stations or to shut down renewable overproduction, simply to keep the electric system stable. Therefore, the number of these network engagements is an excellent indicator to monitor the needed grid extension. Actually in EnWG—German Law on Energy Economics different options were given to grid operators to force IPP (Independent Power Producers) to adjust their infeed accordingly to the needs of security of supply.
EnWG §13 (part1) enables the transmission system operator to force conventional power plants to reduce their infeed, if the power plants are located in front of a network congestion or to increase their power infeed, if the power plants are located behind the congestion, simply to avoid overloading of the lines in between. Unfortunately, financial compensation has to be paid for this type of re-dispatch. According to governmental reports [
14] this re-dispatch in 2017 reached a volume of about 20 TWh and has to be compensated with 837 M€. If these counter measurements according to EnWG §13 (part1) is not sufficient to stabilize system operation, the transmission system operator are allowed to initialize the disconnection of renewable generation according to EnWG §13 (part 2). Up to now, no compensation has to be paid for this type of disconnection.
While EnWG §13 is focusing on transmission system operators and the overall system stability, EnWG §14 enables distribution system operators to take network engagements to avoid line overloading on 110 kV and medium voltage level. This type of disconnection also has to be compensated financially. In 2017, in total 5.5 TWh were disconnected and had to be compensated by 610 M€. Insofar in 2017, in total 1.4 billion € had to be paid, because German power grid transport capacity was no longer able to absorb the regional and temporarily renewable overproduction. In Figs. 16 and 17, two examples are given to get a better understanding on how often these types of network engagements has to be initialized.
Figures 18 and 19 clearly show that the German power grid is still far away to absorb the actually real existing renewable overproduction in a proper way. Besides, battery storages and power-to-X installations are still connected to the grid with an installed power range much too low to contribute in a significant way. Insofar and in accordance to very basic market rules, the electricity prices at German Energy Stock will become negative in such cases of renewable overproduction.
In these periods of time, a massive power flow from Germany into the Swiss and Austrian pump storage units occurred, unfortunately without any financial benefits for Germany from this export. It has to be stated clearly that energy trading (as any case of trading) is reasonable, as long as the “product provider” will not have to spend his own money to get rid of his own “products caused by overproduction.” Besides, it should be known that nearly all cross border overhead lines between Germany and its neighboring countries are equipped with “phase shift transformers.” Based on physical laws, electric energy will flow to any power grid in accordance to the voltage distribution in the system, without taking into account, if the line belongs to German grid operators or any other one in its neighboring countries. So renewable overproduction, e.g., in the north-east of Germany can negatively affect, e.g., the Polish or Czech power grid, if this overproduction will flow to the south of Germany by using lines in Germany, Poland, and the Czech Republic. That is the reason why now several phase-shifter transformers are installed along German border, so that neighboring power system operators are able to reduce the unwanted power, passing through their own grid.
4 Possible contribution of the energy market to German energy revolution on days with high power demand
Figures 4 and 5 show clearly that the German National Government will seek for a power generation portfolio with a secured power very far below the German peak load. The remaining gap of about 40 GW should be closed with the generation units “outside Germany,” offering their energy on the European power market. Therefore, it should be interesting to know which types of power station could be available in such a peak load situation to ensure the power supply for Germany from outside and where these units might be located.
In Fig. 20, the real infeed from wind energy in Germany with its installed capacity of 56 GW is shown for the year 2017. In addition, Fig. 21 shows the infeed from wind energy in the same year, but now for Germany and all its neighboring countries with an installed capacity of 93 GW. From the security of supply point of view, the huge number of time slots with nearly no infeed from wind are the most critical ones. Therefore, from both pictures it is absolutely clear that these wind doldrums will occur at the same time in Germany as well as in all its neighboring countries.
Therefore, it will never be possible to buy electricity in the range of up to 40 GW on the European Energy Market, which will be generated from wind farms outside Germany, when Germany itself is faced with longer doldrums in the range of some hours or days. Especially in winter such a situation is often combined with nearly no PV generation, caused by less sunshine or snow on the PV modules. That is the reason why the increase of renewable generation from actually 120 GW to 200 GW, as it is shown in Fig. 3, will not help to increase secured power generation capacity in Germany.
Also the hope of German National Government to buy the above mentioned 40 GW on the market from coal-fired or nuclear power station outside Germany is not realistic. For better understanding, it should be known that one of the basic design criteria of European Power Supply structure was and is that all European countries should be able to supply their consumers by their own generation portfolio. To balance generation and demand, most of the countries (France, Switzerland, Austria, Poland, and Czech Republic) built up one TSO (transmission system operator) with its own control zone. Germany actually will have 4 TSO’s with 4 control zones. European interconnected 400 kV power grid was designed as a kind of emergency system. Whenever, e.g., one or two large power stations trips in one control zone, the neighboring control zones will help to balance the load and generation in the affected zone by transporting up to 3 GW through the cross border lines. Based on these planning guidelines, it could be easily understood that the generation portfolio in all the German neighboring countries will be used with the highest priority to supply electricity to their own country. Only smaller possible surpluses can be sold on the energy market. That is the reason why investigations were made to find out the energy demand in Europe in those days, when Germany would be faced with its peak load or shortly below the peak load. The result can be observed from Table 7 (based on data from Ref. [
18]).
Table 7 indicates clearly that all neighboring countries to Germany are also very close to their own peak load, when maximum demand occurs in Germany. Insofar it can be expected that only a few generation capacity will be available abroad to compensate a lack of 40–50 GW in German secured generation capacity. Furthermore, it is not acceptable from the ecological point of view, to “clean” the German eco balance by switching off its own “unwanted” nuclear and coal-fired power station and buy electricity from the neighboring countries, which will be mainly generated by coal or nuclear power stations and so contributes to the eco balance of its neighbors.
Several other examples should be shown below from the end of 2018 to the beginning of 2019 to illustrate the actual situation in the security of supply in Germany. Due to an abnormal high demand mainly caused by very cold temperatures in winter 2011/2012 and severe operational problems within several large German gas power station caused by a tremendous lack of gas delivery from Russia via Ukraine, the German power grid was very close to the limit of 49.8 Hz, where the automatic load shedding system would be started. As a result of this situation, the German Government decided on a new regulation for switchable loads. Several energy intensive industrial companies (e.g., aluminum production) were selected and agreements were made with them to switch off this production partly, if any similar case of “under generation” will occur in the future. In the year 2018 it was necessary to activate this “regulation on switchable loads” on 78 days in the year, because primary regulating power came to its limit, the demand was still higher than the generation, and the energy market was not able to compensate the lack of electric power in Germany so that loads had to be switched off.
Also on December 31st, 2018, the power generation in Germany was not able to supply the own country completely. Luckily the demand with 52 GW was far below the peak load so that the market, which means the power stations in the neighboring countries, was able to compensate for the lack of 6 GW.
The next very critical situation came up only a few days later on January 10th, 2019, as shown in Fig. 22. Within 5 min, the frequency in the European Power Grid dropped down and came very close to 49.8 Hz, where normally automatic load shedding would start in Europe. Actually, the incident is still under investigation, so no reasons can be reported here.
Again some days later on January 24th, 2019 in the early morning, the frequency in Europe moved up very fast and came close to the upper limit of 50.2 Hz, where automatic shutdown of first generation units would be initiated (see Fig. 23).
5 Overall review of the past 20 years of German energy revolution
In addition to the still existing 93 GW of conventional power generation capacity from nuclear, coal and gas, another 112 GW of renewable generation capacity mainly from wind energy and PV was established, stimulated by a huge governmental funding. After starting the liberalized energy market in 1998, the prices for household electricity dropped from 17 €-Cent/ kWh down to 14 €-Cent/kWh. As a result of the extra costs for the German energy revolution, the electricity costs for German households have increased since the year 2000 continuously from 14 €-Cent/kWh to 30 €-Cent/kWh (Fig. 24) as the German average. In some regions in Germany, the electricity prices are very close to 35 €-Cent/kWh.
Compared with other European countries, Germany has the highest electricity prices for household (Fig. 25). Only Denmark and Belgium have similar prices. In all other countries, the prices vary between 10 and 20 €-Cent/kWh.
There is no trustable proven information available concerning the cost of German Energy Revolution, but in some sources it will be reported of about 400 billion € up to now and another 400 billion € to be paid for the still ongoing signed contracts of renewable delivery for the actually grid connected wind energy and PV units.
Compared with these tremendous financial efforts, the CO2-reduction from power industry in Germany is rather poor.
At the very beginning of the 1990s, a decrease of CO2 emissions from power industry can be seen until 1992/1993, caused by the collapse of East German industry after Re-Unification in Germany. Within the 20 years from 1993 to 2013, the CO2 emission from the power station fluctuates stably in the range of 360±7% million tons per year. Starting from 2013 again, a decrease is visible. Actually a discussion came up in Germany, if the low values in 2017 and 2018 were linked to the quite warm temperature in the related winter months, which normally corresponded with a reduced demand on electric power. Over all it has to be stated that CO2 emissions are more or less constant for nearly 20 years, although up to 33% of electrical energy in Germany was generated by renewables in 2017. Several reasons for this surprising outcome are easy to understand. In the past 20 years, Germany built up a huge capacity of CO2 free generation from renewables. In the same time, the still existing CO2-free generation from nuclear power stations were taken from the power grid. Also, coal-fired power stations, which were planned for an optimized base load operation now has to compensate for the unstable and highly fluctuating generation from wind energy and PV. Everyone knows from his own experience that stop-and-go traffic in the city is more fuel consuming than constant driving on the highway. Therefore, increasing emissions from coal-fired units are easy to understand.
6 Conclusions
From the security of supply point of view, the following suggestions should be made on how German Energy Revolution can be brought to a successful end:
It has to be accepted that the power generation from wind energy and photovoltaics will have a secured power generation capacity of nearly zero, simply caused by meteorological reasons.
Due to the lack of water resources and restrictions on power generation from biomass, Germany is faced with a situation where only wind energy and photovoltaics can be used for renewable generation.
Due to their non-existing secured power generation capacity, it will never be possible to build up a reliable CO2 free power supply only by wind energy and PV. Additional components have to be added to secure the supply at any time in the year.
If Germany will keep its position to move out of nuclear power generation and still will not re-discuss the option of coal fired units with carbon-captured-conversion (CCC instead of CCS) of CO2 in chemical industry, the only and final chance to secure power supply in Germany will be to build up gas-fired power stations in the same amount than to disconnect nuclear and coal fired units. From the global point of view, it should be stated clearly that this option will lead to a similar CO2 emission than keeping on coal fired units, caused by the reason, that the huge CO2 emissions from natural gas exploration and transport to Germany have to be taken into consideration in addition to the lower emissions during the electricity generation process.
Therefore, highly fluctuating renewable overproduction from wind or solar energy has to be converted into more reliable sources which can be stored more easily.
(1) This conversion, combined with the option of re-generation can be done by ① using chemical energy within large battery systems in combination with inverter systems for charging and re-generation, which will include stationary batteries as well as mobile batteries within electric cars with V2G (vehicle-to-grid) capability. Unfortunately existing battery storage capacity in Germany is in the range of hundreds of MWh’s, while hundreds of GWh’s will be needed. That is why such a possible scale-up will take several decades; ② using thermal energy within ultra-high temperature (800°C–1000°C) heat storages (liquid metal) in combination with inductive principle for charging and gas turbines for re-generation. Unfortunately, this type of ultra-high temperature power-to-heat conversion is still under basic research and therefore no substantial contribution of this technology will be expected to real power system operation within the next 20 years. Low-temperature power-to-heat is a quite simple and cheap technology to use renewable overproduction for heating purposes. Due to the missing option of re-generation, this technology will not help to increase secured power generation capacity from renewables; ③ using hydrogen as an energy carrier in combination with electrolysis for energy conversion and gas turbines for re-generation. Because the storage capacity of the German gas grid will have a capability of hundreds of TWh’s, there would be no limiting factor on the storage size needed for German energy revolution. In a first approach, hydrogen can be stored directly in the German gas grid. Gas turbines, which will be operated by this mixture of natural gas and hydrogen, will have automatically less CO2 emissions, caused by the “green component” of the gas. Furthermore and as a second or third step, additional technology can be added to the system to convert hydrogen into synthetic methane or other liquid media, which can follow the first step of building up a powerful sector coupling of several 10 GW’s between the electric and the gas system.
(2) As mentioned above, gas fired power stations will play a significant role within German energy revolution. Therefore, it will be proposed to increase both in parallel, the installed capacity of gas power stations as well as the capacity of electrolysis, connected to the German gas grid.
(3) Even knowing that the overall global CO2 emission of natural gas power stations is not much lower than the CO2 emission of coal fired units, it would be suitable on a long-term range to replace coal fired units by gas fired ones step by step. From the security of supply point of view, first the new gas fired units has to be connected to the power grid with the same installed generation capacity, before the old coal fired units will be disconnected. From the economical point of view, this replacement should be suitable at the end of the expected life time of the related coal fired units. Even that could take about 30 years in Germany – but the implementation of electrolysis, needed for the “green gas production” will take a similar time frame.
(4) Besides these suggestions, it should be also worth to point out again, that the separation on CO2 from the exhaust gases and using the liquidized CO2 within chemical industry is a quite interesting option for a secured and CO2 free power generation from domestic coal. So this possibility should be re-discussed.
Finally it has to be marked very clearly that the above mentioned time line to phase out coal fired power plants in Germany is a proposal of the German “Coal Commission.” Within the next month, the German Government has to decide on this proposal and has to bring the next steps into a legally binding structure of new laws.
Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature
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