Electricity isn't just expensive

[nzoomed]

Sounds like you have a pretty good system, I would probably need about 15kW on total if I were to get an EV.
I worked out I could just squeeze 10kW of panels on the north side of my home and garage.
I think the RUC system does need reform, I think it would be a great outcome to have all cars pay a fair amount per km rather than your fuel amount.

15kW of solar is huge by domestic standards. As you can see on Solar One's gallery of domestic installations they have done most top out at 10kW. There are reasons for this:

• In most homes the self consumption (which is their best ROI) max's out at around 5kW.
  
• Most electricity retailers have a 10kW limit to PV installations before they have to revert to selling on the variable wholesale market rates rather than at a fixed FIT (Feed In Tariff). More complex back charging situation and highly variable return complicated by PV generation happening during daylight hours which may present a glut as PV increases in NZ. In AU where around 1/3 of homes have PV the lines companies have the ability to throttle, or even disable, PV installations at peak times to protect their infrastructure. We're a long way from that situation but if PV gains incentives here it may well happen.
  
• Many lines companies have a 5kW/phase export limit on their PV customers so 10kW requires three phase supply to your property, or throttling ability on your inverter/s to ensure a 5kW cap. Don't know where this goes beyond 10kW but balancing export between phases would be necessary.
  
• It is unlikely that ownership of an EV would require a 15kW installation. Domestic EV chargers have a 7kW capacity for single phase, or 11kW for a three phase charger. Most EVs return around 5km/kWh so best to estimate your daily driving distances and work back from there. Also bear in mind that if you are driving big kms/day you will more likely be using public charging by necessity rather than being able to gain 35km/hour on a 7kW home charger, or 55km/hour on a 11kW one. Also some EVs have a cap on their AC (home) charging rate (e.g. ex-Japan Leafs are 3.3kW max)
  
• Also there are PV panels now capable of 500W (or more if bifacial) so roof space is becoming less of a restricting factor.
  
• Battery prices are still too high to be viable in most cases and definitely it doesn't make sense to charge an EV from home batteries. Personally we're waiting for V2G/V2H to find its way here so we can use our Leaf in a home storage/supply capacity.
  
• Prices continue to drop on a $/kW basis but 10kW or beyond is still a significant investment so crunch your numbers carefully.
  

If you are serious about going down the PV route get some advice from a reputable installer in your area. This is a rapidly evolving space and the guys that are involved in doing it on a daily basis are best qualified to guide you.

OK, I was looking at roughly doube the capacity (~7kW for the home and another 7kW to charge the EV) I probably dont need the extra power unless I was using that load while charging the vehicle, but if I already have a battery bank, I could just use that  power anyway to minimize taking power off the grid.
Would also mean I would need to charge during the day to maximise the savings?