In 2021, Vienna introduced a subsidy for solar PV systems on green roofs, up to a maximum of €400 per kilowatt-peak. While these kinds of public support are welcome, “It’s like a drip on a hot stone,” Ms Zluwa says, in view of the costs. For the PV roof garden design in the BOKU research project, the estimated cost was around €1,000 per square metre.
