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398 CHAPTER 12 Concentrating Solar Power

The National Laboratory of Renewable Energy of the United States, within its
software Solar Advisor Model (SAM), version 2014-01-14, utilizes a value of
0.7169 for the conversion efficiency of a PTC. This software was developed to
help evaluate performance and costs of PV and solar concentrating systems.
During sun hours (6 h were considered), the thermal power at the outlet of the
solar field must satisfy the demand of the power system (ORC) and also provide
thermal energy for the storage system (also 6 h). Therefore, 50% of the heat at
the outlet of the solar field goes to the power cycle and 50% goes to the storage sys-
tem. This means that during sun hours, the thermal power at the outlet of the solar
field must be double the requirements for the ORC. The value of heat in Eq. (12.2) is
double the heat required for power generation. From Eq. (12.2), and using
h ¼ 0.7169, the values of aperture areas for PTC were calculated in function of local
solar radiation.
As shown in Eq. (12.2), if the value of the heat exiting the collector is fixed, the
necessary collector area is inversely proportional to solar radiation. This is why the
value of solar radiation is fundamental for the development of projects involving so-
lar energy.
However, the required land area for installation of solar collectors is higher than
the aperture area of collectors. This value varies approximately between three to four
times the aperture area of collectors. The land area is greater because there is a dis-
tance between collectors besides the required space for pipes and other accessories
of the system. Table 12.7 shows the land area required for the installation of solar
collectors, adopting a value three times higher than the collector area (A a ), for
several radiation values (I).
Table 12.8 shows the costs associated with a solar system based on PTC. These
values are based on technical report NREL/TP-550-47605 (July 2010), of the Na-
tional Laboratory of Renewable Energy of the United States. 24
The 2014 version of SAM software utilizes a more recent value, which was adop-
2
ted here in: USD 270/m for the solar field.
With the solar collector areas calculated in Table 12.7 and the costs presented in
Table 12.8, final costs were calculated, as shown in Table 12.9.
2
For the ORC-solar system that considered average radiation (450e550 W/m ),
the costs associated with the solar system represent over 96% of total costs, while
the components of the ORC system corresponded to under 4%. Local improvement
costs were responsible for 5% of total costs, solar field costs corresponded to 55% of
total costs, the HTF system contributed with 18%, and the storage system with 22%
of total costs.
From these values, the cost per kW installed was calculated for different radia-
tion levels, and the main results are presented in Fig. 12.15.

24
C. Turchi, Parabolic Trough Reference Plant for Cost Modeling With the Solar Advisor Model
(SAM), 2010.