Building integrated concentrating solar systems - Solar Energy Sciences and Engineering Applications - page 575

The idea of holographic solar concentrators was first proposed in the early 1980s
(Horner and Ludman, 1981; Ludman, 1982a,b; Bloss et al., 1982). Holographic
elements have a number of advantages over conventional optical elements: they are
lightweight, easy to reproduce and one holographic element can be used to perform
several different functions. For example, there is a demonstration project which uti-
lizes light-directing holograms for both daylighting and PV power generation (Müller,
1994). Holograms can be fabricated, which concentrate the spectrally disperse solar
radiation (Ludman et al., 1992).
There has been a surge of interest in this kind of technology thanks to the recent
appearance of the Holographic Planar Concentrator™ (HPC) designed by the Amer-
ican company Prism Solar Technologies, Inc. This is the key technology in Prism
Solar products. The HPC acts as an extremely low-cost concentrator (3 suns) without
mechanical tracking or cooling systems. The bi-facial HPC configuration uses 72% less
silicon than a standard module, leading to a more cost-effectiveness product. Further-
more, this new type of concentrator can be installed on rooftops or even incorporated
into windows and glass doors (Castro et al., 2010; PrismSolar, 2012).
Finally, it should be mentioned that for concentrating systems an important factor
is their economic viability. In this direction there are some companies which aim at
the development of cheap devices. An example is the “Cool Earth Solar'' company
with its innovative design of an inflated, balloon-shaped concentrator. Each 8-foot-
diameter concentrator is made of plastic film with a transparent upper hemisphere and
a reflective lower hemisphere. When the concentrator is inflated with air, it forms a
shape which focuses or concentrates sunlight onto a PV cell placed at the focal point
(Coolearthsolar, 2012). Another example is the “Pacific Solar Tech'' company with its
MicroPV TM Concentrator Photovoltaic Modules and a “silicone-short environment''
(Pacificsolartech, 2006).
17.2.4 Building integrated solar thermal (concentrating)
As mentioned previously, the category of BICST may include configurations similar
to the aforementioned BICPV, provided that there is a CT (instead of a PV) receiver.
Of the examples of BICST systems which follow, some of the technologies have the
potential for BI applications, while other devices have low-level potential.
1) Parabolic troughs (on a small-scale)
The POWER ROOF™ is a new concept in solar energy because it is a high-temperature
solar collector which at the same time also serves as an insulating system. The system
integrated building approach is an important characteristic of this technology, along
with energy cost savings. POWER ROOF™ is an attractive solution for large industrial
and commercial energy users and is designed for new as well as for existing facilities.
A basic advantage is the fact that its temperature range can fulfil an important array
of issues. Collection temperatures above 398 ◦ C can be achieved, thus the system can
provide energy in the form of steam for uses such as space heating and domestic hot
water (as well as for industrial applications: desalination, absorption cooling, water
purification, etc). In a commercial-building level, Solargenix Power Roof was installed
in 2002 on a 930 m 2 office building in Raleigh, North Carolina. This system utilizes
a fixed parabolic reflector and tracking receiver and provides 50 tons (176 kW) of