Technically you are only limited by the space on your roof. However, with great power comes great responsibility. What this really means is that a number of energy providers have put limits on the number of Kilo-watts (kW) you can have on a residential and this amount varies from state to state, and even regionally in Australia. As well as this an inverter can only withstand a 1.3:1.0 ratio between the kW rating of the system and the kW rating of the inverter itself; this means you can only have, for example, a 6.5kW on a 5kW inverter. While larger inverters are available they come at a greater cost.