German wind and solar integration

Schiermeier, Q. April 10, 2013. Renewable power: Germany’s energy gamble. An ambitious plan to slash greenhouse-gas emissions must clear some high technical and economic hurdles. Nature 496: 156–158

The rapid rise in wind and solar power has created a nightmare scenario for grid operators, who face power surges when the wind blows and the Sun shines, and shortages when they don’t. In 2011, more than 200,000 blackouts exceeding three minutes were reported — and experts warn of a growing risk of major power failures.

For the Energiewende to succeed, the grid must be able to accommodate millions of extra small solar installations and wind turbines, as well as autonomous sub-grids such as those that connect offshore wind farms, which intermittently send floods of power into the onshore grid.

Some companies have floated plans to build large thermal solar plants in the Sahara Desert, which gets enough sunshine to meet most of Europe’s electricity demand. But this scheme, the multibillion-euro DESERTEC initiative, lost momentum late last year, when two major industry partners — Siemens and Bosch — backed out (see Nature 491, 1617; 2012). Energy analysts, moreover, doubt that Germany or any other European country would be willing to rely on substantial electricity imports from a politically unstable region.

NREL. 2012. Integrating Variable Renewable Energy in Electric Power Markets: Best Practices from International Experience. National Renewable Energy Laboratory.

Germany has developed a fund to encourage new fossil-fired power plants to use the most flexible technology available to maximize their ability to ramp to meet the system’s balancing need.

The Greennet study determined that additional balancing costs in Germany, at around 10% penetration, would be around €2.5 ($3.3)/MWh (Holttinen et al. 2009).

Germany’s wind industry association believes an additional 25 GW could be installed on land and at sea by 2020, on top of the 29 GW today (GWEC n.d.). ENTSO-E estimates that in the Nordic region as a whole, meanwhile, wind capacity could rise to approximately 15-20 GW in the same year (ENTSO-E 2010), at which point less than half of Nordic wind capacity would be located within Danish borders. Output throughout this northern region is likely to be highly correlated. This means that competition for flexible resources such as Norwegian hydropower, to balance these largely wind power ambitions, is going to increase. Denmark may need to increase its domestic flexibility.

Denmark is a small system, heavily interconnected with both Scandinavian neighbors in the Nordic power market and Germany to the south, with a transfer capacity equal to approximately 80% of its peak demand. In other words, surpluses and deficits of power production resulting from a large variable RE share can relatively easily be compensated for. Other systems are likely to have a far smaller potential to trade, relative to their size.

Germany must manage very large flows of wind energy into and around its grid area. Until recently, with the scaling up of solar photovoltaic power plants (PV) in the south of the country, almost all variable renewable energy (RE) generation (i.e., wind power) has been in the middle and north if the country. The lack of balance between rural areas with high wind energy shares and principal consumption areas all over Germany has led to transmission congestion between these different areas. The challenge is likely to be compounded by growing flows of variable electricity from outside Germany’s borders. Germany’s immediate neighbor to the north is Denmark, which targets 50% wind power. Moreover, wind penetration is likely to be highest in the Jutland Peninsula, which is part of the same power system as Germany (i.e., the synchronous grid of continental Europe). Instantaneous shares in Jutland can already rise above 100% today. Grid congestion in the border region during times of high wind is likely to increase without reinforcement.

In addition, flows of electricity from Germany to and through Eastern neighbors are already challenging, to the extent that eastern neighbors are considering remedial measures. Finally, fast-growing, distributed solar photovoltaic (PV) installations in the south of the country will increase the complexity of the system operation task, particularly because the distribution grid is managed passively.

The 2010 Energy Concept includes a “Government-Länder Initiative on Wind Energy,” which intends to improve cooperation between federal and state levels in the search for higher quality wind resources on land. This is particularly important as the majority of the best resources may already have been exploited.

Protecting the Revenue of Existing Flexible Resources. As wind and solar PV electricity production increases, and because of their low marginal cost and priority dispatch, less production is needed from existing conventional plants, such as gas and coal, which have higher operating costs (mainly fuel). This is known as the “merit-order effect” (i.e., whereby conventional power plants are pushed down the order in which plants are used). This “missing revenue” problem may adversely affect the economics of those plants to the point that owners no longer consider their continued production to be profitable and retire them from service. If this would occur, it would not only reduce the amount of flexible power on the system able to balance fluctuating variable RE output, it might also undermine the adequacy of the system (i.e., its ability to meet its peak power requirements).

Even if fossil-fueled plants are displaced to some extent by new variable RE output, they will be needed to compensate for the nuclear power plants already retired (nearly 10 GW), alongside imports of electricity from France.

Challenges for Neighboring Countries Polish and Czech system operators are considering blocking action in the face of large wind-based flows into and through their systems. Poland is considering installing devices to enable this (Platts 2011). Austria, for example, buys wind power to fill its pumped-hydropower reservoirs, and 35% of electricity flowing from Germany to Austria passes through the Czech Republic.

The task of TSOs, which manage the high-voltage grid in areas with very large shares of variable RE electricity, is increasingly complex. Very large amounts of data need to be managed and continually updated, while more dynamic management of power plants, such as re-dispatching or using curtailment, requires high-speed decision-making.

Serious delays to essential grid expansion work are also apparent in the increasing need to curtail wind plants in the north of the country. Though an important system management tool, the curtailment of power plants (or “feed-in management”) leads essentially to the waste of what was wanted in the first place (i.e., clean energy) so it should be minimized. Curtailment in 2010 increased by up to 69% over the previous year. Even if it only amounted to 0.2% – 0.4% (72-150 GWh) of total wind electricity, in some northern wind farms as much as 25% of output was curtailed (Ecofys 2011).

Figure D-1. Development of electricity generation from RE in Germany since 1990 Source: BMU 2011a Table 1 shows the average annual share of wind power in total electricity generation increasing from 1% in 1999 to 6% in 2010. Solar PV, from a much later start, reached nearly 2% in 2010. While these figures seem still quite modest, instantaneous shares can be very challenging.

Table D-1. Shares of Wind and Solar Wind Share Solar PV (%) Share (%) Table 2 shows the maximum ratio of solar PV and wind power output to power demand in Germany as a whole and in the four TSO control areas into which it is divided (See Figure 2). Perhaps surprisingly, given the modest annual figures above, penetration reached over 60% on Sunday May 8 at 1:00 p.m., when demand dropped to a low on a quiet, sunny afternoon. At the same time, in the area managed by TenneT, which stretches from the north to the south of the country-picking up power both in the windy north and in the sunny south-penetration reached 160% of the entire demand of the area. Eastern Germany saw similarly little activity at 6:00 a. m. on January 1, 2011, and the system operator (50Hertz) had to manage wind output amounting to 124% of the area’s demand.

It remains to be seen whether the Energy Concept will solve the biggest challenge: rolling out and reinforcing the grid.

Table D-2. Maximum Ratio of Wind and Solar PV to Load, by TSO, in Germany in 2011. The Market Stimulation Program has provided grants since 2000. These initially included the power sector, but they are now exclusively for the heat sector. Another important driver is the public bank, Kreditanstalt fuer Wiederaufbau (KfW).44 KfW provides long-term, fixed, low interest investment loans, and loan guarantees, to projects, amounting to some €10bn by 2008 (RETD 2008). Recently KfW announced EUR 5 billion ($6.6 billion) of loan guarantees to offshore wind projects up to 2020 (Platts 2011). In 2010 alone, it provided EUR 11 billion ($15.5 billion) “for the construction of facilities using renewable energies,” including heat).

The German Renewable Energy Concept targets are as follows: 18% of energy consumption by 2020; 30% by 2030; 45% by 2040; and 60% by 2050 o 35% electricity consumption by 2020; 50% by 2030; 65% by 2040; and 80% by 2050. These targets are highly ambitious. The Energy Concept was updated in summer 2011 following the government’s decision to phase out nuclear power by 2022, which represented approximately 23% of German capacity in 2011, after the events at the Fukushima Daiichi nuclear plant in Japan in March 2011. The change of policy resulted in additional promotion of renewable electricity as well as conventional options such as coal power. A recent study, which modeled balancing costs in a number of European countries, found that in Germany, additional balancing costs of wind power at approximately 10% penetration of electricity (i.e., more than present penetration) amounted to approximately EUR 2.5 per MWh wind).

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