A system over 9kW is becoming a lot more common for single and three-phase supply households with high energy usage. With feed-in tariffs reducing and daytime consumption increasingly getting higher due to flexible working hours, larger system sizes are the perfect way to offset high daytime usage. High usage could be because of an increase in working/schooling at home, or you may have a pool, high heating and cooling costs and/or other expensive electricity guzzlers. It would make sense and be beneficial for you to install a larger system with the goal of self-consuming as much of the solar energy as possible.
You will need space on the roof for around 24-35 panels depending on the panel output or watt size. Complement a system this size with battery storage for storing excess solar energy not used during the day. Battery storage can then be released back to the house when the sun goes down, further reducing your reliance on grid supplied energy. Recommended for a household of 4-6 + persons.