On a new home, my advice is to fit at least 6.6kW of solar with a 5kW inverter. This is the maximum you are allowed to install on a single phase home in most parts of Australia, and is usually the best value per kW due to the way the rebate works.
If you want more than this (up to 20kW) then you need to ask your builder to install a 3 phase power supply.
A solar system can generate about 150W per m² of roof. So for 6.6kW you want about 50m² of roof space. Ideally North facing, but East and West can work too, or a combination.
When you are talking to your architect or home builder, these are the things to discuss to ensure your solar system works at max capacity:
- Is there room next to the switchboard for the solar inverter? Will this be shaded from full sun? An alternative is to place the inverter in the garage.
- Where will be a good place to add a future battery? Ideally this should be a shaded spot close to the switchboard and inverter.
- Where will the drain vent pipe exit the roof? Will this shade the solar? Can it go on the south facing roof - out of the way. Can you should specify an 'Air Admittance Valve' instead of a roof penetration?
- Where will your TV aerial go? Can it also go on the south roof out of the way of any solar?
- If using rooftop wireless internet, where will your internet transceiver go? South facing roof again please!
- If the sparky is laying new cables to the street, can he make them thicker than normal to avoid voltage rise issues? On a single phase home tell the sparky you want a voltage drop less than 2V when your inverter is exporting 100% - typically pushing 5kW into the grid.
- Can you get a 3 phase electricity supply installed from the outset? This gives you the option of a much bigger solar system, reduces issues with voltage rise, and will allow you to charge a future electric car up 6 times faster! Installing 3 phase after the build is incredibly expensive.
I strongly advise pre-installing the conduit for your solar system during the build. A good electrician can easily and neatly put the conduit in the house for solar before the walls are gyp-rocked. If this saves the installers save time and money then the savings can be passed to you. Also - if the inverter will be some distance from your switchboard, ask them to pre-wire the mains cable from the switchboard to the inverter. Finally - a data cable from the switchboard to the inverter, and a data cable from the house modem/router to the inverter will allow you to hard wire the inverter's data comms, which is more reliable than wi-fi.
Say this to your house-builder's electrician:
"Run a 25mm HD SOLAR conduit from where the solar inverter will go, to the roof. Also run the AC from the main switchbard to the inverter location: 10mmTPS for single phase, and 4mm orange circ three phase. Also run a data cable from the inverter to the MSB for smart meter, and from the modem/router to the inverter. "
The all electric future means that you are likely to add big appliances to your home over time. Ask for a bigger switchboard with lots of room for extra breakers. Upgrading your switchboard later is a big, expensive job!
In a few years you are likely to own an electric car. I'm serious! Get 3 phase cabling put in from your switchboard to wherever you would put a charger in the future. This will be much cheaper than laying the cable later. Tell the sparky a future electric car charger could pull 11kW so he puts in a chunky enough connection. (If you are really keen you might want to consider a 22kW connection - as some Teslas will charge this fast).
Monitoring systems need a data connection. Wi-fi can be unreliable and stops working if someone changes the wifi password. Consider running a Cat5e data cable to the switchboard so you can have a wired data connection that will be rock solid.
Get a solar-ready electricity meter installed from the outset. Then you won't have to replace it. This will save you hundreds of dollars. Ensure the builder's sparky knows to do this. By default you'll get a non-solar meter and then have to pay to replace it!
If you’re building a multi-storey house put your solar panels on the roof before the scaffolding comes down. You don't want to pay for scaffolding twice.
Incredibly - some new homes come as standard with roofs that cannot support a decent sized solar system. Ensure you get written assurances from your builder that every roof face can be filled with solar panels. If you have to 'upgrade' to do this it should only be a few hundred dollars. More info here.
Get A Firm Quote (or quotes) 3-4 months before handover - this timing is usually ties in nicely with getting the walls pre-wired before the gyprocking happens.