I get a lot of enquiries from clients who are looking to install solar on a new house or renovation. It’s a great idea to consider solar when you have the skeleton of the house exposed as it means that the wiring can be done as efficiently and neatly as possible; some houses can be very difficult to run concealed wiring from the panels to the inverter to the switchboard and surface wiring may be inevitable. By taking the shortest possible route between the components we can also reduce losses in the cables and increase the efficiency of the system (it’s likely a minor gain, but a gain none-the-less).
The problem with designing a system for a new house (or renovation) however, is that the historical data showing energy usage is not available (or not relevant). Typically I look at how much power is historically used throughout an average day (for a few seasonal variances) and overlay that with a estimated solar output; coming up with a suitably sized system for your needs. Given that the price of solar is still dropping and feed in tariffs (in Victoria) have recently risen, it’s not such a big deal to oversize the system any more.
The other way to size the system is to base it on both the available roof space and the the average consumption for the house/family size. This gives a good ball park figure to work with, and any local variances that may increase or decrease from this average can be factored in.
Something else that you may want to consider is integration of batteries and backup systems into your house. If your power and lighting circuits are carefully planned, then you can select which appliances you might wish to keep running if the grid was to go down (and you have a hybrid system with backup functionality). Most current hybrid systems can’t just power the whole house in the event of a grid failure, so you have to choose what you want to connect to the emergency output, which is best done whilst the plaster is off the walls.
The main thing I want to convey from this post is that whether or not you intend to put on solar at the time of building, it is highly worthwhile talking to a local solar contractor about pre-wiring the house for solar. It will likely give you a cost saving as the job is done quicker, and will also result in a cleaner installation.