Page 295 - A Comprehensive Guide to Solar Energy Systems

14

Advanced Building Integrated

Photovoltaic/Thermal Technologies

Fangliang Chen, Frank Pao, Huiming Yin
COLUMBIA UNIVERSITY, NEW YORK, NY, UNITED STATES
hy2251@columbia.edu

14.1 Introduction
Integrated technologies for harvesting solar energy in the building sector, such as building-
integrated photovoltaic (BIPV) systems [1–3], building-integrated solar thermal systems
[4–6], or building-integrated photovoltaic/thermal (BIPVT) systems [7–9], have evolved
as viable technologies toward the nearly zero energy building scenario. Those integrated
systems replace parts of the conventional building materials and the components in the
climate envelope of buildings, such as facades and roofs, and simultaneously serve as both
a building envelope material and power generator [10–12]. Compared with most conven-
tional nonintegrated systems, in addition to the power supply function, the integrated sys-
tem offers several advantages: (1) there is no need for the allocation of land or facilitation
of the PV system, (2) it does not require additional assembly components such as brackets
and rails, and (3) it thus achieves significant savings in terms of the total building material
costs and associated labor fees [13, 14].
Today, most photovoltaic (PV) modules in production are based on crystalline silicon
wafer technologies. The electricity conversion efficiency of silicon solar modules available
for commercial application is about 12%–20% [15]. However, the majority of the incoming
solar energy is either reflected or absorbed as heat [16]. Consequently, the working tem-
perature of the solar cells increases considerably after prolonged operations. Solar panel
temperature is one of the important factors that affects electricity conversion efficiency, yet
−1
most solar cells show a heat-related performance loss of about 0.4%–0.5% (°C) [17]. With-
out a cooling system, in-service surface temperatures can be up to 40–50°C above ambient
temperature, resulting in 16%–25% reductions in electricity generation or malfunction be-
yond the operational temperature range [18]. The rise in PV temperature not only reduces
electricity generation, but also shortens the life-span of the module itself. The BIPVT system
appears as an exciting new technology as it merges PV and thermal systems, simultaneously
harvesting both electrical and the thermal energy [19]. The most common BIPVT systems
are realized through a heat transfer fluid in an open-loop (usually air) [20–22] or closed-loop
(usually liquid) configuration [23–25], which are shown in Fig. 14.1A and B, respectively.
A Comprehensive Guide to Solar Energy Systems. http://dx.doi.org/10.1016/B978-0-12-811479-7.00014-2 299
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