I think Pumped Hydroelectric Storage is what you are looking for. I've seen a few of them here in Switzerland. I think many were originally built out with the train system's grid for it's reliably scheduled low and high capacity times.
Does Belgium (OPs example) have the geography necessary to support pumped hydro? Your example, Switzerland, is significantly more mountainous than Belgium.
Wallonia has at least one pumped hydro that I know of.
There were plants for a 'energy island' 300MW hydro plant at sea, near the large-scale wind farms. The idea is the same, pump sea water up an artificial horse-shoe shaped island. A nice bonus is that you can play with the tides as well. The height difference does not have to be great, if you can compensate with a large surface area.
As far as I know, those plans were shelved. A quick googling says that similar concepts are being considered for interconnected dutch/danish wind farms.
There is a video in German on youtube where Prof. Hans Werner Sinn explains, why Germany can't store the excessive amounts of renewable energy in Pumped Hydroelectric Storage. You would need too much storage capacity, especially since you need two basins and the geological features necessary aren't there. He even calculated how this would work in a compound with Norway.
I really doubt Germany's "Energiewende" is really possible, since solar doesn't generate energy at night and wind energy has really large spikes. This is not the energy you want to have in a large grid and storage isn't possible at such volume. I even calculated how many Tesla walls a city like Munich would need to have a week worth of energy stored and I really, really doubt, this is physically possible or economically viable.
Germany's "Energiewende" is something politicians would like to have, but the problems and cost this is causing (google "site:heise.de tennet") aren't shared fair.
This is somewhat misleading - there is a Europe-wide energy grid, Germany has many neighbors, and a lot of power has been flowing across borders even before this project started. It doesn't make sense to look at Germany in isolation. While I agree that the German approach is misguided (should have shut down coal first, not nuclear) I don't think it's as problematic as you make it seem - the spikes in wind average out excellently when you look on the scale of several countries, and daytime demand for solar power is large and growing due to industrial use (residential use peaks in the evenings, but residential use is insignificant compared to industry). A significant component of the Energiewende is replacing baseload fossils (coal) with peaker gas plants but the coal industry is very powerful and very much opposed to this, and many local governments are in coal industry pockets and resist any coal reduction (this is one reason why nuclear was shut down first). Peaker gas plants operate only when the demand is high and supply is low, running on a much lower duty cycle than a baseload plant. The way things are going now, there's been a rapid nuclear phaseout and there's a glacial coal phaseout very slowly happening, but solar and wind installations have been growing and are displacing more and more baseload. Eventually this will price baseload coal power out of the market, and then we'll see if the coal terrorists are powerful enough to get a bailout or to get solar legally destroyed like they did in Spain.
A possibly better strategy would be to produce DME using excess capacity and convert diesel vehicle engines to DME. Then export both the cars, the fuel and the tech to produce the fuel locally. Maybe even use it as input for peaker gas plants and shipping fuel. Germany has all the resources necessary to establish and lead such a market. Plus they don't need to throw away decades of investment into diesel ICE R&D. See chapter 2.2 of this article.
Germany already uses large amounts of gas, mainly for heating, hot water, and cooking. It's not like using coal for electricity changes the fact that Germany depends on gas imports.
Is there a way to implement gravity batteries on a household-level scale? Shouldn't we all be using solar to lift a weight during the day that will lower during the night to feed the grid?
http://energystorage.org/energy-storage/technologies/pumped-...