So it produces as much electricity as it uses over the year. That's not zero emissions at all.
If it feeds into the grid in summer and uses electricity derived from natural gas in winter it's simply not emission free.
Actually treating the grid like a battery can cause huge problems. That would result in a lot of overproduction in summer, then in winter when there's virtually no production from solar everyone is starting up their heat-pumps and the demand spikes when the production is lowest.
That being said, this building is producing more electricity than it uses and is also heating neighbouring buildings. Sadly they're almost no numbers provided but it looks promising.
It's energy positive and appearantly has a decent amount of storage, so that it does not rely on the grid as much.