Cities are the modern era’s undisputed drivers for economic growth and development. But cities are also highly energy and resource intensive. Therefore, it is predictable that cities would be active participants in the global effort to creatively strike a balance between resources consumption and economic growth for a sustainable future. Part of this is exploiting the often neglected, but vital, solar photovoltaic (PV) resource and rooftop real estate within cities.

At face value, a city with the real estate infrastructural sophistication of the City of Johannesburg (CoJ), presents an attractive opportunity for generating renewable energy from its building rooftops. However, the magnitude of this potential is yet to be fully characterised. Assessments of the rooftop solar PV potential of buildings in inner city locale are made complex by the variety of building typologies and rooftop accessibility.

The main objective of this research was to assess the technical potential of rooftop PV generation in the inner city core of the CoJ, using a rapid, simple, accessible, effective, and computationally light methodology. The sample for the study was the entire population of buildings located in the central business district (CBD) of the CoJ, made up of 202 buildings across a 1.64 km2 area. Digital images of the individual building rooftops were used.

The inner city core of the CoJ was found to have a rooftop availability factor of 46% (375 985 m2 ), 17% (140 995 m2 ) of which was considered to be available and suitable for system installations. The area could accommodate a system with a technical capacity of 22.6 MW and an average annual production of 38 399 915 kWh, which constitutes a mere 0.23% of the CoJ’s current annual electricity consumption. The full installation of such a system would reduce the CoJ’s electricity services revenue by 0.31%, whilst positively impacting its carbon emissions inventory through the offsetting of 36 096 tCO2e.

The outcome of the research shows that the technical potential for rooftop PV installation in the central business district of CoJ, whilst seemingly attractive at face value, was, in reality, insignificant. The immateriality of the determined technical potential – as is reasonable to expect – would be aggravated further by the incorporation of economic and financial constraints, as well as real-time building-tobuilding shadow analysis.

Whilst the research has demonstrated that rooftop PV in the inner city core of the CoJ, and possibly in CBD areas of other cities displaying similar building typology, is limited in scope and impact, the same argument cannot be made about the entirety of the building rooftops in the CoJ. After all, building typology beyond the inner city core boundaries is dominated by less dense, low-rising, residential, industrial and commercial roof space, which possibly holds immense potentials for rooftop PV. This means that the CoJ, in seeking to transform its energy supply options through exploitation of its real estate, should focus attention away from the inner city core for optimised impact.