Right now, renewables like solar and wind energy provide 35 percent of Germany's power. Meanwhile, coal and nuclear plants are still being used. These facilities all share the same electrical grid, which is the system that transports electricity from plants to users.
And therein lies the issue. Prices for power on the German market are determined by supply and demand. On the power grids, the electrical output also needs to match the demand for power. Problem is, demand for power is always fluctuating. During the day, people use more electricity than they do late at night. Likewise, power usage goes down on weekends and holidays, when factories are closed and office buildings vacated.
If a grid doesn't distribute enough electricity in an hour of high demand, blackouts can occur. But what happens when the situation is reversed? In other words, what if there's more electricity on the grid than people need?
Well, in a perfect world, that extra power would be stored up for later use. Unfortunately, that's not always possible. "Storage technologies are not yet advanced enough [to] store large amounts of electricity, regardless of whether the electricity comes from renewables or other sources," energy policy expert and associate professor at Indiana University Sanya Carley, Ph.D. told us via email. She went on to explain that "hydro-storage [technology] ... in which water is moved from a low reservoir during times of high electricity supply and low demand, and then released during times of high demand and low supply" is a promising option. But such facilities require specific sets of geographic conditions — and to this end, Germany's physical layout is less than ideal.