Is the storage of solar energy a problem?

Energy storage - a key problem for renewable energies?

Extra article> Fukushima

(This article appeared in a similar form in Energie & Umwelt 1/2006, the magazine of the Swiss Energy Foundation.)

Author: Dr. Rüdiger Paschotta

One often hears that the widespread use of renewable energies requires new technologies for the storage of energy. At least for Central Europe, however, this can hardly be justified.

In addition to many advantages, electricity as an energy source has one major disadvantage: it can hardly be stored in significant quantities. New supercapacitors are expensive and quite limited in their capacity. Rechargeable batteries (accumulators) for storage in the form of chemical energy are expensive, have significant energy losses, have a limited service life and are uncomfortably heavy for mobile applications. The same applies to flywheel accumulators. The only large-scale storage technologies that can be used well are based either on hydropower plants (possibly with pumped storage, i.e. additional “charging” with electricity in times of low network load) or on underground compressed air storage. Essentially, therefore, the generation of electricity in an electricity network must follow current consumption. Rapidly controllable gas turbines and the like are available on the one hand for short-term adaptation, and on the other hand in particular pumped storage units. To compensate for longer-term (e.g. seasonal) fluctuations, z. B. large gas or coal-fired power plants are used.

Some renewable energies, especially wind and solar energy, contribute to generation depending on the time of day and weather - somewhat predictable in the short term, but not controllable at will. Obviously, this would be a big problem if a certain city were to be supplied 100% by such power plants: At night and when there was no wind, there would be bottlenecks that would be very expensive to bridge with storage. Regardless of this, it cannot be concluded from this that the development of better storage technologies would be the central prerequisite for the widespread use of solar and wind energy. In particular, Central, Southern and Eastern Europe is covered with a powerful network with which almost all producers and consumers work. This network is of inestimable value for a safe and efficient supply based on fossil fuels and atomic energy as before, as well as for the use of renewable energies in the future. It drastically reduces the need for storage capacity and additional generation that can be called up at short notice. B. in the event of a sudden unexpected failure to distribute the lost generation to widely distributed other power plants, or to compensate for short-term shutdown of not absolutely necessary large consumers in other locations. Further development of the European networks will be necessary and this will require significant investments. However, the resulting challenges are likely to be minor in comparison with others, for example with the broad conversion of the power plant fleet for climate-friendly electricity generation.

Propaganda and ignorance

Unfortunately, these circumstances are sometimes hidden, be it in the service of propaganda against renewable energies or simply out of ignorance. One example is the assertion that a wind turbine enables certain amounts of energy to be generated, but does not contribute to the safe provision of power. In a more stringent form: every wind power plant requires the provision of a fossil-fired power plant of the same output, which is operated in idle mode when there is wind and can step in at any time, but causes enormous additional costs (and energy losses).

One should transfer this way of thinking to a nuclear power plant: This too can suddenly fail at any time, which means that the full capacity has to be taken over immediately elsewhere. Exactly this is z. This happened, for example, at the Leibstadt nuclear power plant (Switzerland) on Easter Monday 2005; without any warning, suddenly more than 1000 MW were missing. But where was the fossil-fired power plant that was idle and took over the power of the KKL? Nowhere, of course - even this major failure could be absorbed by the European network by distributing the lack of power over many “shoulders”. It is just strange that in the discussion we never hear the reserve argument applied to nuclear power plants, but only to wind power plants. Their output fluctuates significantly more frequently, but can usually be predicted fairly well over days in advance, and never in such a way that production fails completely over many months (as in the KKL Leibstadt). Therefore, even if, for example, Europe will one day cover 20 to 30% of its electricity needs with wind energy, for example, no major technical or economic problems will arise from the required reserve capacity.

One should consider here that wind power from different regions (e.g. the North Sea and North Africa) will be combined, which means that fluctuations in generation will be averaged out far more than would be the case for a small region considered in isolation. And the Swiss water storage power plants (with or without pumped storage) will - mind you, with corresponding financial benefits for all involved - contribute an even larger part to a secure electricity supply in Europe.

It should also be noted that other renewable energies can also make valuable contributions to securing the supply. Wind power is generated more in winter, when the demand is higher. The fact that solar power is generated during the day instead of evenly distributed is another advantage. Both of these reduce the need for other generation that fluctuates seasonally or with the time of day. And biogas plants are ideally suited to feed in electricity preferentially when the demand is highest, as the gas can be stored easily.

Sensible priorities

It can be assumed that the European network will be used much more intensively in the future than before. For this, certain expansions are necessary, the costs of which, however, are spread over decades and among many millions of consumers and are therefore hardly noticeable. Moderate investments in the region of northern Germany and Denmark will make it possible to increasingly bring not only new wind power from large offshore wind farms, but also very cheap electricity from Norwegian hydropower plants to Central Europe. It should be more cost-effective to carry out certain expansion of power lines and Scandinavian power plant capacities and also to curb the waste of cheap electricity in Norway than to create additional capacities in Central Europe itself. It will also be profitable to generate electricity on cheap land in good wind conditions in North Africa and to conduct it via Spain and Italy to Central Europe. If thermal solar power plants with day storage systems are developed that can produce distributed over day and night, this may be useful in isolated cases, but it is never the prerequisite for the widespread use of renewable energies.

Thus it becomes clear: What would be a big problem for an island supply of a small area (with high costs for the necessary energy storage) becomes a manageable problem by European standards.

Incidentally, these considerations also shake the dogma cultivated in some circles that regional self-sufficiency is fundamentally better than extensive exchange. What might make sense for many agricultural products appears questionable for electricity: It is difficult to imagine how a financially viable supply, especially with renewable energies, should be possible without the advantages of the interconnected grids. And a supply that cannot be financed is certainly not our future. It is true that small-scale, scattered generation can reduce the amount of energy to be transported and thus reduce the requirements for network expansion. However, a region that is mostly supplied with wind and solar power to a large extent needs power from other regions again at times - and that only comes from appropriately developed grids.

See also the newer article "Energy storage and power grids - what does the energy transition need?".

Questions and comments from readers


The article is based on a magazine article from 2006 and suggests that there is already sufficient RE power somewhere in Europe, and that it only has to be distributed via an appropriately developed energy network. Today is 2018, and we are not even able to expand in Germany.

However, if am accepts the author's theses as meaningful, the (safe) solar power can only be used to cover a possibly existing peak consumption during the day, the entire base load would have to be provided by a Europe-wide wind energy network.

This would have to be dimensioned in such a way that the supply of energy to Europe at night would be ensured even with low wind levels.

I wish you a lot of fun with the anti-power line and anti-wind power citizens' initiatives.

Answer from the author:

As is well known, we already have high RE capacities and will soon need reinforced grids in order to be able to use them better. The construction of these networks is actually a challenge - but in my opinion at least a much smaller one than solving the problem with energy storage. They cost much more and have much higher losses.

Of course, photovoltaics alone is not enough, but it can make a useful contribution, especially for covering the midday peak and for air conditioning.


The Federal Network Agency, as a politically occupied authority, can probably only fulfill the wishes of politics and certainly not act according to rational-economic criteria. The hundreds of billions of euros in costs for the energy transition must finally be “explained” (

“And so far the grid stability and the security of supply have even improved in the course of the German energy transition.”: This statement contradicts any physics. The withdrawal of control reserve and the addition of highly unstable new generators must inevitably lead to a more unstable network. I would be interested in an independent and apolitical source without an agenda that conclusively explains this blatant contradiction that you are writing here.

Answer from the author:

So you assume that the Federal Network Agency is hiding the enormous risks for network stability on the instructions of the politicians, and that you know everything better based on a simple argument. Such allegations are certainly trendy, but I think they are unfounded.

Reality is definitely too complex to clarify such points with a simple physical argument. There is also hard data on these points, such as the frequency of power outages, which has decreased significantly in recent years. In the USA, for example, such outages are much more frequent, despite a much lower share of renewable energies, and the risk of large-scale power outages is also much greater there. This is due to the outdated and poorly maintained infrastructure.

Here you can suggest questions and comments for publication and answering. The author of the RP-Energie-Lexikon will decide on the acceptance according to certain criteria. In essence, the point is that the matter is of broad interest.

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