Germany now generates over 35% of its yearly electricity consumption from wind and solar sources. Over 30 000 wind turbines have been built, with a total installed capacity of nearly 60 GW. Germany now has approximately 1.7 million solar power (photovoltaic) installations, with an installed capacity of 46 GW. This looks very impressive.
Unfortunately, most of the time the actual amount of electricity produced is only a fraction of the installed capacity. Worse, on “bad days” it can fall to nearly zero. In 2016 for example there were 52 nights with essentially no wind blowing in the country. No Sun, no wind. Even taking “better days” into account, the average electricity output of wind and solar energy installations in Germany amounts to only about 17% of the installed capacity.
The obvious lesson is: if you want a stable, secure electricity supply, then you will need reserve, or backup sources of electricity which can be activated on more or less short notice to fill the gaps between electricity demand and the fluctuating output from wind and solar sources.
The more wind and solar energy a nation decides to generate, the more backup capacity it will require. On “bad days” these backup sources must be able to supply up to 100% of the nation’s electricity demand. On “good days” (or during “good hours”) the backup sources will be used less, or even turned off, so that their capacity utilization will also be poor. Not very good economics.
Much better would be to limit wind and solar to a relative minimum, and rely instead upon controllable, non-fluctuating power sources operating with a high capacity factor, to meet the nation’s base load electricity requirements and to adjust total output in accordance with varying demand. This corresponds to world-wide practice prior to the recent huge buildup with renewable energy.
In theory the ideal backup for wind and solar energy would be to store excess electricity produced when the Sun is shining and strong winds are blowing, and inject it back into the grid when needed. Unfortunately, electricity is a difficult and expensive commodity to store.
By far the most efficient presently available solution for storing excess electric power is to use it to pump water against gravity into a reservoir. When electricity is needed again, it is produced by letting water flow down again via a turbine generator. In this process about 25% of the energy is lost.
Naturally, the costs of construction and operation of such pump storage plants will add to the real costs of providing electricity. Plus, these installations use up a large amount of land area.
Here, too, Germany provides an instructive example. A 2014 study by the Bavarian Ministry of Energy came to the conclusion that pump storage plants were not an economically viable solution. Much better would be to exploit already existing water reservoir resources in Norway and Sweden, where the capacity of pump storage plants can be greatly expanded and new ones built at much lower cost.
This “solution,” however, would require transporting large amounts of electricity over long distances back and forth between Germany and those countries – which in turn would require additional high-voltage lines and cables that have not been built and that no one wants to pay for.
Given the high costs and other obstacles to creating large electricity storage systems, it is not surprising that Germany’s electricity storage capacity amounts today to less than 2% of total electricity output.
There has been much discussion and research concerning alternative ways to store electricity. Theoretically one could be to use excess power to produce hydrogen, store it somehow and then use fuel cells to generate electricity back from the hydrogen. This would be vastly more expensive than pump storage, however, and with much greater losses.
Overdose of renewables?
Today, in order to guarantee stable baseline power and fill the gaps left by its fluctuating wind and solar generators, Germany is forced to rely on (1) CO2-spouting coal and natural gas power plants; (2) its remaining handful of nuclear plants, which it plans to shut down by 2022; and most notably (3) importing electricity from other European nations.