Brisbane ratepayers have been shelling out millions of dollars for solar projects, but it will be almost 10 years before they see any financial return.

In the last two financial years, Brisbane City Council has spent $2.5 million on energy efficiency and emissions reduction projects - including installing solar panels at some of the city’s bus depots and libraries.

Solar spends are expected to remain high until 2028, but the council believes this is a smart investment.