MANY MINDEDBucharest Apartment Uses Solar Windows to Heat Water Without Batteries
In Bucharest, Romania, a four-person household installed semi-transparent photovoltaic windows on a south-facing balcony. The system delivers DC power directly to an electric water heater without inverters or batteries, operating off-grid during daylight hours. After sunset, it switches to grid power when solar energy falls short. Over two consecutive October-September cycles (2023-2024 and 2024-2025), the system supplied 446 kWh and 462 kWh of electricity to the water heater, covering 46.7% and 43.7% of the household’s measured annual hot water energy demand respectively. The system’s 845 Wp capacity—corrected from an initial 800 Wp estimate—uses the water heater itself as thermal storage. This approach avoids the cost and complexity of batteries and inverters typically required for solar water heating. For this household, the system reduces reliance on grid electricity for hot water by nearly half annually, directly lowering energy costs for basic household needs. The German Environment Agency estimates similar systems without batteries achieve 45% self-consumption, but this project’s measured performance shows real-world effectiveness for low-income households. What to watch: Long-term stability of the water-based thermal storage and whether the system’s performance scales reliably across different climates and household sizes. Note: The project monitoring spans two consecutive October-September cycles, though the article was published in August 2026—suggesting a timeline inconsistency.
Source: CleanTechnica