Ended up here searching for Tesla 3 phase powerwalls.
What the OP didn't yet mention (and not necessarily of interest to you all) is that the "salderings regeling", or the possibility to simply erase positive and negative electricity use (or use and production of electricity) against eachother will end in 2020 in the Netherlands. So balancing your own usage and your own production becomes even more important* And there are very little (read NO) decent all-in-one solutions for this yet. And a decent (3-phase) powerwall be at least a step in the right direction.
My 7kWp PV system has a daily surplus of up to 30kWh in the summer, which I obviously have no way of storing until the winter. So what I *can* do is store it and use it as much as possible for nightly usage e.g. for charging an EV (don't have one yet but one can dream) and for cooking (still on natural gas right now).
BTW, I am as of yet still on a single phase connection. I do not know if I can get a 3 phase connection, but chances are pretty good that I can as it is, as said, quite normal.
A single phase connection will be a 35 or 40A main fuse (not accessible for the end-user, so blowing it will need a visit from the electricity company $$$), a 3 phase connection will be 3x25A for the same fixed cost. Anything more, like the 3x40A from the OP or the 3x63A from a house a few doors down without a natural gas connection, will be more coslty in fixed yearly costs.
End result is that I will keep searching for a solution and will keep an eye out for the Tesla solution. But also the PowerEdge solutions, as I might increase my PV to ~10kWp and if so, I will add poweroptimisers and a 10kW 3 phase PowerEdge inverter.
*It is still not clear, but this is how it might be, now and after 2020:
Say you use 4000kWh is a year and supply 3000kWh back into the grid. A kWh is 25cents. You can subtract the 3000kW you supplied into the grid from the 4000kWh you used (btw: my old Ferraris meter does this automatically, so no surprise the electricity want to get rid of these meters!). So NET usage is 1000kWh times 25cents = 250euro (plus whatever fixed cost for the metering, connection, extra-cost-for-3x40A-connection, etc).
Now we are in 2021: You used 4000kWh and supplied back 3000kWh. Say 1000kW was actually made by your solarpanels and immediately used in your own house, so never reached your new meter which can read used and grid-supplied electricity separately.
So the meter actually registered 3000kWh usage times 25cents = 750euro. You also supplied back 2000kWh but you can no longer erase this against your usage, so you get payed for it by the electricity company. But now they obviously don't pay you the full price (25cents of which 2/3 is government tax..., but ony the ~1/3rd which is the bare price per kWh, say 8cents). So the powercompany "pays" you 2000kWh times 8cents = 160euro.
So 2019: you pay 250euro
And 2021: you pay 750 minus 160 = 590euro
And since you will always have extra use in winter which you cannot supply with solar (right now I am happy with 3kWh on a sunny day vs. 30kWh in summer), only part of this difference can be solved with Powerwalls. But still, it may be enough to warrant an investment in them.