*Article* **Experimental Study on Energy E**ffi**ciency of Multi-Functional BIPV Glazed Façade Structure during Heating Season**

#### **Suzana Domjan, Lenart Petek, Ciril Arkar and Sašo Medved \***

Laboratory for Sustainable Technologies in Buildings, Faculty of Mechanical Engineering, University of Ljubljana, SI-1000 Ljubljana, Slovenia; suzana.domjan@fs.uni-lj.si (S.D.); lenart.petek508@gmail.com (L.P.); ciril.arkar@fs.uni-lj.si (C.A.)

**\*** Correspondence: saso.medved@fs.uni-lj.si

Received: 29 April 2020; Accepted: 26 May 2020; Published: 1 June 2020

**Abstract:** Building integrated photovoltaics (BIPV) is technology that can significantly increase the share of renewable energy in final energy supply and are one of essential technologies for the nearly zero-energy buildings (nZEB), new build and refurbished. In the article (a) an experimental semitransparent BIPV glazed façade structure with 60% of PV cell coverage is shown; (b) energy efficiency indicators were developed based on identified impact parameters using experimental data; and (c) multi-parametric models of electricity generation, preheating of air for space ventilation, and dynamic thermal insulation features that enable prediction of solar energy utilization in different climate conditions are shown. The modeled efficiency of electricity production of BIPV was in the range between 8% and 9.5% at daily solar radiation above 1500 Wh/day, while low impact of outdoor air temperature and ventilation air flow rate on PV cell cooling was noticed. Between 35% and 75% of daily solar radiation can be utilized by preheating the air for space ventilation, and 4.5% to 7.5% of daily solar radiation can be utilized in the form of heat gains through opaque envelope walls.

**Keywords:** nZEB, BIPV; room ventilation; dynamic thermal insulation; multi-parametric model
