If you compare quotes for solar power systems in Australia and the USA, you will notice that Australian prices are 2 to 3 times lower in most cases. Of course, this is assuming you compare solar systems of the same capacity installed on similar buildings. These low solar prices have been possible thanks to a combination of factors.
Consider that China has some of the largest solar module manufacturing operations in the world. For the simple reason that Australia is much closer to China than the USA, the shipping cost of solar panels and other complementary equipment is much less.
Another important factor is how each country has decided to address solar power. Australia is not a major manufacturer of PV modules, but there are many local producers in the USA. In other words, imported solar panels have considerable local competition in the USA market, which is not present in the case of Australia.
In a few words, Australia is closer to the global manufacturing hubs of the solar industry, and there are no dedicated import tariffs for solar equipment. However, there are additional reasons why solar power is cheap in Australia.
Australia has subsidy programs for small-scale and large-scale solar power, and Small-Scale Technology Credits (STC) apply for solar installations up to 100 kW. This size threshold covers virtually all residential systems and many commercial systems in small and medium-sized companies. STCs are calculated based on how much generation your solar system can provide by the year 2030, which means the rebate becomes lower each year.
In Australia, you can likely purchase a 5-kW solar system for less than AU$6,000 after subtracting the STC rebate. A system of this capacity can provide around 7,000 kWh per year. This provides savings of AU$1,750 per year for someone paying 25 cents/kWh, and AU$2,800 per year for someone paying a less favorable tariff of 40 cents/kWh. A payback period of 2 to 4 years is excellent for an investment that lasts more than 20 years.
In addition to having more expensive solar panels, the USA lacks a nationwide rebate program that reduces the upfront cost of the technology. There is a federal tax credit for 30% of your investment, but you cannot claim it upfront and instead have to wait until your next tax declaration.