Is my grid connect solar system 100% compatible with a Tesla Powerwall 2 battery?

Short Answer: Yes

Longer explanation:

The Tesla Powerwall 2 is an AC Coupled battery.

That means it simply connects into your solar system via the 230VAC in your switchboard. It does not connect into your solar panels or inverter, so it will work with any existing grid connected solar system.

This diagram shows how it connects in:

As you can see, because the Powerwall2 has a built-in battery inverter, it is independent of your solar system, and relatively easy to install.

Can the Powerwall 2 provide blackout protection / backup / off grid functions with my solar system?

Yes. The Powerwall2 comes with a box of switching gear - called 'The Tesla Gateway' that disconnects your solar system and Powerwall 2 from the grid in the event of a grid outage:

This allows your Powerwall 2 to still power your home when the grid is down.

Note: I strongly recommend that you ask your installer to segregate your home circuits into essential and non-essential loads, and only power the essential loads with your battery when this happens. Otherwise you risk tripping the powerwall if you draw more than 5kW (easily done with the kettle, toaster and a heater for example), and you are also likely to deplete the energy from the battery very quickly if you have the A/C or oven or hot water heater on.

For example my home battery is only wired to power the lights and kitchen (excluding oven) when in off-grid mode.

Can the Powerwall 2 be charged by my solar panels when disconnected from the grid?

Yes. On single phase homes the Powerwall 2 is clever enough to keep your solar inverter powered up when the grid goes down - so the solar can charge your batteries during a grid outage.

If you have a 3 phase home then it can still do this - but only if you have a single-phase solar inverter or micro inverters.

If you have a 3 phase solar inverter, you can't charge the battery with solar during grid outages - the 3-phase solar inverter will not operate without seeing all 3 phases of the grid - and the PW2 can't create 230V on more than 1 phase - so your 3 phase solar-inverter won't operate in a grid outage.

The problem with charging batteries from the grid with no grid connection is that when the batteries are full, you need to throttle back the solar so that you don't overcharge the batteries. The Powerwall 2 does not communicate with the inverter - so how is this possible?

Cleverly, when disconnected the PW2 shifts the AC frequency slightly as it gets close to filling up with kWhs. The inverter sees the frequency shifting and throttles back the power (this is a feature of AS4777.2 for those who are technical). 

If it is a modern inverter (post October 2016) it will gradually reduce the solar power as the frequency shifts.

If you have electric motors in your house then this may cause them to make funny noises, or malfunction.

If you have other frequency sensitive equipment on your essential loads circuit it may also cause issues.

Older inverters will simply trip off when the frequency too high or too low. I call this Bang-bang control and do not recommend it.

Conclusion: The Powerwall 2 is 100% compatible with any existing single phase grid connect solar system installed after October 2016. If it your system was installed before that, and you want your solar panels to charge the battery without the grid - you'll need to check with a Tesla Certified installer if your inverter is compatible.  Many will be. For example I have 2011 vintage microinverters that work fine with the Powerwall 2 in off grid mode.

If you are not worried about using your solar to charge the batteries without the grid, then it should work fine with any existing solar system including ones with 3 phase solar inverters.