Building integrated concentrating solar systems - Solar Energy Sciences and Engineering Applications - page 546

reduce the complexity and the cost of the system. When comparing such a system with
a flat-panel PV device built for the same application, the additional cost of the tracker
and its maintenance must be compensated by the advantages that are provided by the
use of a concentrating technology. On the other hand, flat-panel systems can be used
to replace structural elements of a building and this (in most cases) is not possible by
means of concentrating technologies (Swanson, 2000).
In terms of the concentrators (reflectives or refractives), their integrability depends
on its concentration factor, C (defined as the ratio between the aperture area of the
primary concentrator and the active cell area). Concentrating systems with C > 2.5X
generally use tracking, whereas systems with C < 2.5X can be static. However, in
the long term static concentrators with higher ratios which make use of luminescence
and photonic crystals may appear (Luque-Heredia et al., 2007). Low concentrating
ratio systems (C < 10X) are of great interest as they are mostly of linear geometry
and thus one tracking axis is sufficient for efficient operation (Tripanagnostopoulos,
2008). The combination of improved sheet metal capability with the high capacity
of the PV industry can lead to a large deployment of low concentration PVs (Kurtz,
2008). CPV is a feasible method to reduce the high initial cost of PV solar energy since
concentrating solar radiation onto solar cells means that the area of semiconductor
devices is diminished. Considering that a higher concentration factor has higher cost
reduction, within the concentration range where single-axis tracking may be used,
the most desirable concentration factor is that which approaches the upper limit of
single-axis concentrators.
On the other hand, solar thermal systems can be considered as an alternative
solution for instances where the priority is the production of heat. Several promising
technologies are included in this category, including solar collectors with vacuum tubes,
reflectors combined with simple concentrating thermal (CT) systems. Moreover for
solar thermal, solutions with low cost and low complexity should be preferred.
For all applications of BI systems, certain requirements must be fulfilled. These
requirements are associated with factors such as the design of the building, the
conformity to the context of the building, an architecturally pleasing design, etc.
The first part of this chapter describes the characteristics of BI systems without
concentration, and later focuses on concentrating systems specifically. We begin by
considering general concepts relating to building integration of solar thermal and pho-
tovoltaic systems. In the second part, all the terms and characteristics are adapted and
applied to the concentring systems, thermal and photovoltaic.
17.1.1 Solar thermal systems and building integration
requirements
Building Integration of Solar Thermal (BIST) systems involve incorporating a solar heat
generator while preserving and considering the other functions of the building enve-
lope. Some of these functions are, for example, to protect the building interior space
from weather conditions, to prevent noise, control daylight, regulate air renovation,
and to achieve good insulation conditions leading to energy efficiency.
The characteristics of solar thermal collectors present difficulties when being
integrated into buildings, due to their size, materials, rigidity, colour and auxiliary
installations. Accordingly, thermal collectors are mostly added to fulfil only a technical