Sure, it's only part of the solution. But due to their intermittent character, they can also be used to buffer energy, e.g. with Hydro-pumped storage (using old mines filled with water, pumped to a higher level during surplus production, and by use of gravity drive turbines as the water drops to a lower level, and so on). Besides, Germany is part of the European grid system, which increases the likelihood that somewhere the sun will shine or the wind will blow.
And, while currently not very efficient, excess solar-power during sunny summer-days can be converted to Hydrogen gas as a storage medium that will provide Carbon emission-free power when burned again when needed. Hydrogen gas can use the current existing natural gas pipeline infrastructure with relatively small modifications.
Cheers,
Bart
Bart, first off, it is not the case that if the sun does not shine then the wind must be blowing and vis versa. So to assume that their will be sun shining and wind blowing always to produce energy is a fallacy. This was shown to be the case in 2016, which was a much less windy and sunny year in Europe. Actually the total amount of electricity produced in Germany from wind/solar that year was less then the previous even though they increased their potential production by over 20%.
So what do you do in less windy/sunny years?
Second, it cost money to transport power, and in many cases, when the distances are great, more then what you can actually charge for it. This too has been shown to be the case. The odd thing about wind and solar is that it produces a lot of energy when we typically don't need it. Problem though is that an overcharged power grid can damage the grid from blow outs. So when this happens, states/countries need to effectively pay their neighbors to take the excess energy because the cost of transport is higher then the price of it. So Germany being part of the EU grid does not solve anything.
Third, neither of the energy storage options you listed would actually work. In the case of the water storage, it turns out you need a very specific storage vessel, not just some abandoned mine. On top of this, even if abandon mines could work, they are not water tight, so a certain amount of construction will be needed. Third, since salt water is so corrosive, fresh water will have to be used in these cases and their are much more important things to use fresh water for, such as irrigation or making sure the population does not go thirsty. Remember, fresh water only constitutes 1% of all water on the planet; it is a more valuable resource then what we think it is.
Insofar as the hydrogen suggestion, it takes a lot of energy to split water into hydrogen, so much so that nearly all commercially available hydrogen comes from other sources then water, like fossil fuels. This is not to say you could not build a hydrogen production plant using electricity, but the fact remains you will loose a lot of energy in the process of splitting water. On top of this, of all the flammable gases, hydrogen has the lowest energy potential.
This is similarly the case with batteries. You loose about 20% to 40% of your energy when you charge a battery and retrieve it later. Compared to a electric grid, batteries are incredibly energy inefficient as well.
