In Australia, scientists are figuring out how to determine fair rates for paying back solar energy investments more quickly. They looked at how long it takes to recoup the money spent on solar panels (the payback year). By using a special calculation method, they discovered the right payout ranges for different sizes of rooftop solar systems. For example, for the 3 kW and 5 kW systems in Victoria, Australia, the ideal rates were found to be between 20.29 and 28.25 cents per kilowatt-hour. This information could help policymakers design fair incentives for people who invest in solar energy.