It took a bit of effort but when we finally got our X22 installed with working solar diversion we faced the same issue as others; a 5kW solar system and very little chance of 3 phase solar charging. Three phase switching (to single phase) looked like the answer and it certainly works, BUT…
3 phase homes with 3 phase solar will be given a meter with two “registers” that record the half hour power use; a consumed register, and an export (feed-in) register. Both sum across the 3 phases, but they do not sum across each other.
I’ll use an ultra simplistic example of why this is an issue, where we generate 3 kW at 1 kW per phase continuously for a half hour period and there is no load using power, X22 target export set to zero. Two cases:
Three phase switching off. Not enough generation, so X22 does not charge the car. Consumed register records zero kWh for the half hour while the export register records 3kWh/2. You will be billed zero for consumption, and given your feed-in pittance for 1.5kWh.
Three phase switching on. There is now enough generation, X22 switches to single phase charging feeding the car 3kW to match detected solar power. At the end of the half hour the consumption register records zero for 2 phases and 3kWh/2 minus 1kWh/2 = 1kWh. The export register records zero on the phase being used to charge plus 1kWh/2 for each of the other two phases = 1kWh. These values do not cancel out. You will be billed 1kWh at your day rate, and get a 1kWh feed-in pittance.
I dumped the half hour data from our retailer (by law this has to be available) and checked - this really looks like how they charge it.
Have I overlooked something here? Are X22 users better off disabling three phase switching, accepting they will mostly end up charging at their night rate? Should X22 owners be warned about this so they make informed decisions?
[Note for anyone reading this, the above describes how things work in NZ but not AU, where the meter registers generally are summed together]
If you are in NZ, then as with many solar scenarios it will depend on your situation. As you have identified, in your case it does look like disabling phase switching will be the right choice, and thank you for highlighting that we ought to give more guidance around this to help X22 owners make the right choice for their situation.
Here are some pointers for others:
The most important is how your retailer handles billing. My understanding is that most retailers bill as described above, but some do bill you for net consumption across all three phases. In this case phase switching will always be beneficial.
The next most important thing is how your inverter behaves. Many modern inverters will output different amounts on each phase so that import is minimised. With phase switching enabled, by default the charger will look for a total of 1.5kW export - likely 500W on each phase. It will then start charging at 1.5kW on one phase, so temporarily that phase will import 1kW while the other two continue exporting 500W. The inverter will then recognise the imbalance and correct for it by outputting everything onto the phase being used by the charger.
Finally for some tariffs it may even make sense to charge during the day because the night time price is not sufficiently low to make it worthwhile.
In future we are also looking at adding another option for phase switching which would be beneficial even if none of the above apply.
Ideally your charger will be wired so that the first input is on the least loaded phase in your home. Often this phase would have 1.5kW of export even if the other two don’t, and so you could do single phase solar charging on this phase. Then you could jump to three phases if there were enough capacity to make this worthwhile (e.g. 4kW excess on L1 and 2kW on L2 and L3 would make it beneficial to charge on three phases).
The above change hasn’t been made yet, but we are looking to do it in future so if you are getting an X22 installed I’d recommend that the least loaded phase gets wired into the first terminal of the charger.
Thanks for a detailed response. Everyone with 3 phase solar really does need to understand too much - how they are billed, do they have an inverter that can adjust output to match phase loading, are they on the best plan in their area for EV ownership and more.
The billing thing could be fixed easily by the NZ Electricity Authority making a regulatory change but don’t hold your breath.