BIPV/T facades – A new opportunity for integrated collector-storage solar water heaters? Part 2: Physical realisation and laboratory testing

Building Integrated Photovoltaic Thermal (BIPV/T) systems which generate electricity and heat simultaneously are promising solutions for Net Zero Energy Buildings (NZEB). Despite BIPV/T offering clear energetic and space saving advantages compared to separate PV and solar thermal, overheating problems occur when no thermal demand exists, resulting in reduced yields, stagnation damage, and excessive fluid flow pressures. This two-part study examines an alternative approach combining BIPV, Planar Liquid-Vapour Thermal Diodes (PLVTD) and Integrated Collector-Storage Solar Water Heaters (ICSSWH) to achieve BIPV/T functionality and retain heat overnight to minimises parasitic demands and reduce overheating. The introductory paper (Part 1 of 2) established novelty and rationale for BIPV-PLVTD-ICSSWH concepts, reviewed state-of-the-art and performance benchmarks, and used theoretical modelling to predict behaviour from key design and operational parameters. This paper (Part 2 of 2) describes prototype realisation and multi-day solar simulator laboratory thermal and photovoltaic testing for covered and uncovered variants exposed to different irradiance levels. Measured solar thermal efficiencies with and without transparent covers were η_T,col = 60% and 58% respectively under zero heat loss conditions whilst overnight heat loss coefficients were U_r,sysA_sys/u = 23.0 and 25.4 W·m^–3 K⁻¹ respectively, showing good agreement with theoretical predictions. Photovoltaic performance reduced with increasing absorber temperature as expected, although maximum power point efficiencies (η_E,mpp = 11.4% at T₁ ≈ 25 °C and 5.6% at T₁ ≈ 89 °C, without cover) were lower than expected owing to partial delamination and PV cell damage. The work demonstrates practical operation of a vertical BIPV-PLVTD-ICSSWH, identifies key areas for design development, and highlights benefits of application in NZEB facades.