How often does it happen that this is financially viable? The way the European electricity market is set up is quite interesting, so I wonder how the ArenA-sys

How often does it happen that this is financially viable? The way the European electricity market is set up is quite interesting, so I wonder how the ArenA-system ties in. Also, is the system also charging up when there's negative electricity prices like there were recently? And get payed to take in power?