Unlocking the Energy Potential of Existing Residential Buildings
Germany’s building stock possesses a vast energy potential that has so far only been partially exploited. Multi-family housing, in particular, should be at the heart of the energy transition. These buildings combine extensive roof areas, stable load profiles, and a high concentration of consumers on a single connection point – a combination that makes them one of the most effective levers for delivering secure and affordable energy. Increasingly, studies are confirming this. For example, analysis by IW Medien GmbH, carried out as part of the Ariadne project, indicates that more than 20 million apartments could, in technical terms, be supplied through residential on-site solar schemes. On paper, this would cover a significant share of the required photovoltaic expansion.
Current conditions are favourable. Photovoltaic systems installed on residential buildings can provide a substantial proportion of annual electricity demand directly on site, relieving pressure on the grid and reducing costs. Their load profile aligns well with modern energy systems, particularly when combined with heat pumps, EV charging infrastructure and, in future, electricity storage. The advantage of such systems is clear: electricity is generated where it is needed. This eliminates grid fees, transmission-related costs, and exposure to price volatility. For tenants, it translates into lower service charges; for owners, stable returns; and for the wider energy system, a reliable source of decentralised generation.
Roofs as Strategic Resources for the Energy Transition
Despite these favourable conditions, progress in expanding rooftop solar has been slow. This is due less to a lack of willingness among property owners than to bureaucratic and technical hurdles that complicate the adoption process. Many landlords are deterred by metering concepts, billing processes, and coordination with grid operators. Yet proven solutions already exist. Residential on-site solar schemes are currently the most practical approach for making PV systems economically viable in existing buildings. Under this model, specialist service providers manage the technical operation, energy management, billing, metering, and customer service. Tenants have a single contract covering both on-site solar electricity and any required top-up power from the grid, while property owners are primarily responsible for providing the roof space and deciding whether to invest directly or use a contracting arrangement.
Roofs offer ideal conditions for such solutions. According to Fraunhofer ISE, Germany’s rooftop surfaces have a potential of several hundred gigawatts. Even today, more than three million systems already generate a considerable share of the country’s solar electricity. Experience shows that rooftop projects can be implemented quickly, whether owners invest themselves or use leasing or contracting models. For commercial properties, onsite power purchase agreements (PPAs) provide an additional route, supplying electricity directly on the premises. Recent regulatory clarifications on the distinction between customer energy networks and private direct supply lines have increased legal certainty in this area. For residential buildings, shared building electricity supply schemes simplify internal power distribution, though they do not offer the full economic benefits of a comprehensive residential on-site solar scheme model.
Economical Deployment of Photovoltaics on Roofs
Another area with significant benefits is the combination of photovoltaics and green roofs. Green roofs improve the microclimate, reduce solar panel temperatures, and can enhance system performance. They also increase heat resistance, ease pressure on the sewer system, and extend the lifespan of roof membranes. In urban districts, this delivers a dual benefit of energy generation and climate adaptation.
The role of multi-family housing will become even more important in the years ahead. These buildings offer technical, economic, and environmental advantages: they help curb energy costs, provide stable revenue streams, and contribute to relieving pressure on the grid. At the same time, they create a robust foundation for heat pumps and electric mobility. To harness this potential, clear and reliable framework conditions are needed. These include transparent regulations for metering and billing, standardized processes for grid and metering point operators, and a stronger policy focus on existing buildings as the core of the energy transition.
The technology is available, and the business models are proven. The next step is to further develop existing structures so that the opportunities in multi-family housing and on urban rooftops are fully exploited.