Turning Building Façades into Power Sources

A two-year pilot in Bucharest has demonstrated the real-world potential of photovoltaic glazing to generate hot water and reduce urban energy waste. Conducted by PhotoVoltaic Windows SRL and validated by the Romanian Association of Energy Auditors for Buildings (AAECR), the project tested a façade-integrated CdTe photovoltaic (PV) glass system designed for domestic hot water (DHW) production in a multi-apartment building.

Between October 2023 and September 2025, the system proved that building façades can serve as reliable energy generators, even in dense urban environments and without traditional energy storage or inverters.

Direct Solar-to-Heat Innovation

The 7.9 m² system, rated at 683 Wp (88 W/m²), was installed as a south-facing vertical façade powering an 80-liter electric boiler through a direct DC-to-heat configuration. This approach eliminates the inefficiencies and costs of conventional PV systems that rely on inverters and batteries.

Automatic AC fallback was integrated via Wi-Fi smart sockets and power contactors, ensuring uninterrupted hot water availability. In essence, the system provides a seamless, low-maintenance way to use building envelopes as both energy producers and architectural elements.

Performance: Reliable Energy, Measurable Savings

Continuous monitoring over two years produced consistent results. Solar generation averaged 454 kWh per year, covering 45–50% of the household’s DHW needs. The remainder was met by grid backup, averaging 551 kWh annually.

The average annual solar yield reached 58 kWh/m², a strong result considering the panels’ vertical orientation and Bucharest’s temperate climate.

Parameter	Year 1	Year 2	Average
Solar production (kWh)	446	462	454
Grid backup (kWh)	508	594	551
Solar share of DHW (%)	45–50%	45–50%	47%

Economic Impact: Strong Case for Decentralized Hot Water

Economic analysis compared the PV-assisted system with Bucharest’s district heating network (SACET), which operates on a flat-rate basis. Results show that the Boiler + PV configuration delivered substantial annual savings.

Case	Annual Cost (lei)	Savings vs SACET (lei/year)
SACET (flat rate)	2,585	–
Boiler + PV (HE tariff 1.04 lei/kWh)	1,065	1,520
Boiler + PV (PPC tariff 1.62 lei/kWh)	1,378	1,207

Even under higher energy tariffs, savings remained strong. Sensitivity analysis confirmed positive results across ±10% scenarios, with total savings ranging between 1,007 and 1,721 lei per year.

The study also quantified the impact of the municipal district heating subsidy (PMB) for “hot water” billing, revealing that roughly 58% of the subsidy (1,007 lei/year) corresponds to water waiting losses. By eliminating these inefficiencies, decentralized solar-heated systems could reduce both municipal costs and emissions.

Environmental and Urban Benefits

The pilot highlights several tangible sustainability outcomes:

• 45–50% reduction in gas use for DHW in homes with individual gas boilers
• Elimination of 20–40 liters of water waste per person per day
• Six-year simple payback period under current electricity tariffs

These findings reinforce the potential of façade-integrated photovoltaics (FIPV) as part of Nearly Zero Energy Building (NZEB) renovation programs under EU directives.

“Even with vertical façade orientation, direct DC heating achieves high solar utilization and measurable urban benefits,” the report concludes. The combination of decentralized energy generation, efficiency gains, and avoided water losses positions the technology as a scalable solution for cities aiming to modernize their building stock.

Context: Solar Integration in European Cities

Across Europe, façade-integrated solar technology is emerging as a vital component of building decarbonization strategies. While rooftop PV remains dominant, façades offer significant untapped potential, especially in dense urban environments where roof space is limited.

Romania’s NZEB regulations, aligned with the EU Energy Performance of Buildings Directive (EPBD), encourage integration of renewable energy in both new constructions and retrofits. The Bucharest pilot demonstrates that PV glazing can contribute meaningfully to energy performance while preserving architectural aesthetics.

Such systems are also compatible with thermal retrofits, enabling apartment blocks to upgrade façades while improving energy self-sufficiency. By coupling local electricity generation with direct-use applications like water heating, cities can reduce grid demand peaks and lower reliance on fossil fuels.

Toward Scalable Application

PhotoVoltaic Windows SRL’s pilot adds to a growing body of evidence that façade PV systems can be economically and technically viable under real-world conditions. The success of this project strengthens the case for integrating solar-active façades into municipal renovation and subsidy programs.

As energy prices fluctuate and cities seek to modernize their building stock, direct solar-to-heat systems present a pragmatic path forward: simple, low-maintenance, and locally efficient.

With proven savings, reduced water waste, and alignment with European climate targets, the Bucharest pilot shows how even modest façades can play a big role in the urban energy transition.