Building integrated concentrating solar systems - Solar Energy Sciences and Engineering Applications - page 579

17.3 CONCLUSIONS

Concentrating solar energy systems can reduce system cost if the cost of the reflector
or the lens system (and tracking system where applicable) is less than the cost of the
replaced receiver material (i.e. PV). A concentrating panel separates the functions of
light collection and conversion into electricity that are integrated in a flat photovoltaic
panel (Luque, 1986) or converted into thermal energy in flat-plate thermal modules. In
solar thermal collection the benefit of using concentrating technologies is mostly related
to the achievement of higher fluid temperatures. In relation to higher temperatures,
the materials involved must be adequate for temperature ranges and present proper
thermal tolerance. In PV applications, an advantage of concentrating panels is the
tendency for solar cell efficiency to increase when the cell is under high irradiance.
However concentrators for photovoltaic applications present some drawbacks when
compared to flat PV panels, as follows:

• Complexity of the tracking mechanism that may for remote applications (either

geographically or in terms of façade accessibility) make them less attractive
(Luque, 1989);

• Inability at high concentration ratios to collect diffuse light, which limits their use

in locations where high diffuse radiation prevails;

• Large size of the basic concentrator module (due to the need to spread the structure

and tracking costs by producing a larger amount of electricity) as compared to
flat-panel is too large for small applications where photovoltaic electricity is cost-
competitive today;

• High cost of the more sophisticated cells and the more complex structures used

previously with concentrators jeopardizes the advantages obtained in cell area
reduction;

• Increased solar cell temperatures decrease PV efficiency and differential heating

(hot spot) increases mismatch errors;

• Lack of radiation uniformity leading to mismatch errors.

These drawbacks can be avoided by using low or low-medium concentration ratio
systems, as for instance the cylindrical Fresnel lens with CPC or the asymmetric com-
pound parabolic concentrator described above. In cloudy and overcast sky conditions,
low concentration systems accept a significant component of the diffuse solar radiation
because of their high acceptance-half angle (Mills and Giutronich, 1978).
In summary, detailed technological advancements have been discussed in this
chapter, including description of low, medium and high concentrating solar energy
systems, their applications and the current issues for building integration.

REFERENCES

Absolicon Solar Concentrator AB (2012). www.absolicon.com.
Adsten M. (2002) Solar thermal collectors at high latitudes: Design and performance of non-
tracking concentrators . PhD Thesis, Uppsala University, Sweden.
Adsten, M., Helgesson, A. and Karlsson, B. (2005) Evaluation of CPC-collector designs for
stand-alone, roof- or wall installation. Solar Energy , 79, 638-647.