The switch to renewable electricity will be technically challenging because solar and wind power are not dispatchable, meaning that you cannot turn wind turbines and solar panels on the way that you can ramp up central coal and nuclear plants to match power demand. A number of solutions are possible.
The general problem is that the exact amount of electricity that is needed at a given moment has to be available at that moment, lest the grid collapses. We have therefore traditionally tailored power production to demand. A number of storage options are currently being discussed, from underground compressed air in natural caverns to pumped storage (hydropower), flywheels, and batteries. Most importantly, Germany plans to use natural gas in the interim as a bridge fuel to be eventually replaced by sustainable biogas and hydrogen made from excess wind power and solar power. Solar and wind power could be stored as a gas (called “power to gas” or P2G), allowing it to be used as a motor fuel, for heat applications, or to produce dispatchable power. Finally, "smart grids" will help tailor power demand to the available renewable power supply – the opposite of what we do now.
The need for power storage
European integration could be a solution, especially in light of Germany's limited pumped-storage capacity (hydropower). It has been proposed that Germany could export large amounts of power to Norway and Switzerland, for instance, which have tremendous hydro-storage potential, but at the moment connections are insufficient. But work is being done: in 2015, plans were finalized for a new 1.4 gigawatt connection between Norway and Germany. Called Nordlink, the cable is to go into operation in 2020. It remains to be seen, however, whether Norway or Switzerland (neither of which is a member of the EU) would be willing to flood more of their pristine valleys and fjords so that Germans can have a stable supply of renewable electricity.
Over the midterm, most experts believe that the need for power storage will be minimal in Germany. A study produced for the WWF found that there would not be a major market for storage technologies until 2030, and the German engineering organization VDE does not expect much demand for storage until Germany has 40 percent renewable power, a target that is admittedly likely to happen closer to 2020. Furthermore, Fraunhofer ISE points out that the amount of storage needed is not relative to the share of fluctuating renewable power alone, but rather to the combination of fluctuating renewables and inflexible baseload power. In other words, the need for power storage can be reduced by decreasing baseload generation capacity, mainly lignite and nuclear plants.
Putting renewable grid expansion into perspective
To put all of this in perspective: First, Germany has gone from 3% renewable power at the beginning of the 1990s to 32 percent in 2016 without any major changes to its grid. After all, wind power, biomass, and solar power are largely distributed sources of energy – at least the way Germany is doing it.
Critics of renewables sometimes complain when the grid has to be expanded for renewables: The problem with wind farms is that they are built in places where there is no need for electricity. As a result, the produced electricity has to be moved elsewhere.
In fact, this describes coal power better than wind power. You can spread solar, wind power, and biomass fairly evenly across the landscape in a way that you cannot do with conventional power. In contrast, brown coal plants are never built where power is needed, but rather where the brown coal is dug out of the ground. Even power plants fired with hard coal, which is traded globally, were traditionally built close to the source of the coal, such as in Germany's Ruhrgebiet (Ruhr Area). Clearly, however, it is much easier and less expensive to transport large amounts of power across power lines than it is to haul loads of coal. And while one could argue that coal plants are often located close to industry (as is the case in the Ruhr Area), this description puts the cart in front of the horse. Go back some 200 years to the beginning of industrialization – most of the towns in the Ruhrgebiet were small villages. Coal plants were not built in the Ruhr because industry was there; rather, industry developed there because the area was full of coal reserves.
Furthermore, while nuclear plants are built more or less where power is needed, not where uranium is mined, all central plants are so huge that the grid is always expanded for them. In the 1960s and 70s, new nuclear power plants in Germany not only required the grid to be expanded, but also led to the installation of a large number of electric home heating systems that generated heat from power overnight so that the nuclear plants would not have to be ramped down each day. A distributed supply of renewable power is a much softer approach with a much smaller impact on the environment. Hermann Scheer, the late German expert on renewables, once compared distributed power supply to our conventional centralized power supply by saying that the latter is like "cutting butter with a chainsaw."
There is a consensus that the grid needs to be expanded for more renewables to be integrated, but there is less agreement about a number of details, such as how many lines need to be added, where they need to go up, and what kind of lines should be used. Furthermore, the renewables sector itself has an interest in making the energy transition affordable and has therefore come up with a number of inexpensive alternatives to extensive grid expansion. In addition, people do not want to live near power lines, so public input is needed for planning – and that requires greater transparency.
The current German grid is divided up as follows:
The transit grid consisting of some 35,000 kilometers of 220 and 380 kV lines. This is the ultra high-voltage level at which Germany is connected to its neighbors and power is transported across long distances. The distribution grid consisting of the following:
- Some 95,000 kilometers of high-voltage lines (60 to 110 kV) for conglomerations and large-scale industry.
- Some 500,000 kilometers of medium-voltage lines (6 to 30 kV) for many large facilities such as hospitals.
- Some 1,100,000 kilometers of low-voltage lines (230 and 400 V) for households and small businesses.
Germany has four investor-owned utilities operating the four sections of its transit grid, but there are some 900 distribution grid operators.
How many kilometers?
So what needs to be done for the country's Energiewende? At the moment, a lot of wind power is in the north and a lot of solar is in the south. The German Energy Agency (dena) published two studies (Grid Study I and II) estimating that some 4,500 kilometers of ultra high-voltage lines would need to be added if Germany is to increase its wind power capacity from 27 gigawatts to 51 gigawatts by 2020 – ten gigawatts of which would be offshore in the North Sea and Baltic Sea. But some experts believe that this length could be cut by more than half. Starting in 2016, the Grid Development Plan is to be updated every two years. It currently contains 22 projects covering a total of 1,876 kilometers of new lines, 487 of which had been completed by mid-2015.
Indeed, these plans have been met with great criticism among proponents of renewables in Germany, mainly because the underlying data was not published, so the findings could not be further scrutinized. But even at the proposed level, a near doubling of wind power capacity would still apparently only require the transit grid to be expanded by less than 13 percent. Furthermore, a lot of these lines would not be needed if the government promoted more onshore wind in the south rather than additional offshore and onshore wind in the north. In the past few years, the wind industry has come up with special wind turbines with taller towers and longer blades designed especially for use in weak-wind locations, such as southern Germany. Such onshore turbines in the south would not require as many power lines, thereby reducing the overall cost of Germany's energy transition, and onshore wind is also much less expensive than offshore wind to boot.
Likewise, some proponents of solar would also like to see feed-in tariffs for photovoltaics adjusted by region (as is done in France) so that more PV is installed in the north, thereby facilitating grid integration.
Grid upgrades often face local opposition (people do not wish to live next to overhead power lines), and complicated red tape and financing also slow things down. Underground cables are an option, but they are more expensive. As of 2016, the government has decided to prefer underground cables over overhead power lines for the high voltage direct current lines, which are built to connect northern Germany with southern Germany. For AC lines, the number of underground cables has been increased compared to earlier plants, too. As part of the revised Renewable Energy Act, it is also discussed to reduce the number of new wind energy installations that are auctioned in areas with grid bottlenecks.
But again, keep in mind that we are talking about adding roughly 1,900 kilometers to a grid consisting of hundreds of thousands of kilometers set up exclusively for the country's nuclear and fossil energy supply.
In 2017, the German Network Agency announced that the three main north-south lines to be added would be finished until 2025. In the interim, Germany plans to bridge the gap with reserve power plants. For the winter of 2017/18, 10.4 gigawatts has been set aside for that purpose.
Alternatives to grid expansion
Germany's renewables sector is not, however, just sitting back and waiting for the government to provide a future-proof grid. The solar sector has come up with a way of making the use of ultra high-voltage lines more efficient: solar power plants can act as "phase-shift oscillators" to stabilize the grid's frequency. The solar sector hopes that this approach will reduce the number of lines that need to be built.
The wind sector is also full of ideas. Under German law, there is a regulation called "n+1"; it means that whenever a line is set up, there has to be a reserve line that can take up its capacity in case it fails. The wind sector has come up with a solution that could mean that this requirement is no longer necessary: dedicated power lines to connect renewables.
Furthermore, the European Union - as part of its Energy Union plans - aims to step up interconnections between countries to strengthen the continent's energy security and keep costs down. At the same time, however, surges in wind and solar power production in Germany are already pushing power into Poland and the Czech Republic, in particular, so further integration would be a challenge for those countries. Phase shifter, which actively control real power flows in order to enfore or block load, have been installed at the German-Polish border so the Poles can have better control of their own grid.