Yes - First off he needs an Electrical Licence. In some states he also needs a building licence. If you are claiming the solar 'rebate' then the person installing must be Accredited by the Clean Energy Council to install solar. There are 2 levels of Accreditation: On-grid and off-grid. Your installer needs the latter if you have decided to go off-grid. Also, the design of your solar system must be done (and signed off) by a CEC accredited Designer. Ask for the design document with this signature.
If you want to go with a non-accredited installer, and are not claiming any 'rebates' (AKA STCs) you can, but I would not recommend it.
There is also a more detailed blog post about the levels of Clean Energy Council accreditation here.