Page 137 - A Comprehensive Guide to Solar Energy Systems

136 A COmPREHEnSIVE GuIdE TO SOlAR EnERGy SySTEmS

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CSTP plants involve solar fields greater than 250 000 m , while solar fields for IPH applica-
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tions are usually smaller than 50 000 m .
A solar field with PTC is composed of parallel rows, with several PTC connected in se-
ries within each row. The total length of each row depends on how much the working fluid
must increase its temperature as it circulates from the row inlet to outlet: the higher the
temperature increase, the more PTC connected in series are required in each row. The
number of parallel rows depends on the power of the plant; the higher the power, the more
parallel rows are installed in the solar field. The number of parallel rows for IPH applica-
tions is usually small, while solar fields with more than 100 parallel rows are common in
CSTP plants. The length of each row is usually smaller in IPH applications, while the length
of the rows in a CSTP plant is usually 600 m (each row is composed of four 150 m collectors
or six 100 m collectors connected in series).
The maximum working temperature is also lower in IPH applications, with maximum
temperatures usually below 300°C. These lower operation temperatures make the use of
pressurized liquid water a feasible option as working fluid instead of thermal oil. Sev-
eral companies are commercializing PTC solar fields using pressurized water for IPH
applications. The mexican company Inventive Power (http://inventivepower.com.mx)
and the Turkish company lucida Solar (https://lucidasolar.com/) are two companies of-
fering PTC solar fields to provide hot liquid water at temperatures of about 200°C for IPH
applications.
Another difference that is usually found in PTC used for IPH applications is the type
of sun tracking system, because the systems used for small PTC are usually based on an
electric motor with a speed-reducing gear box, while hydraulic units are preferred for big
PTC because they can provide higher torque at lower cost.
Although electricity generation is the commercial application most widely used
for PTC so far, IPH applications are of interest because of the huge commercial po-
tential. According to Ref. [13], the total energy consumption of the industry in 2014
was 115 EJ, and 16% out of these 115 EJ was thermal energy consumption within the
temperature range from 150°C to 400°C, which is very suitable for PTC systems. This
means that each year 18.7 EJ could be delivered by solar systems using PTC. This is
the reason why the number of companies interested in IPH applications for PTC is in-
creasing and a high number of IPH commercial projects are expected to be developed
in the coming years.

7.3 Central Receiver Systems

In a central receiver system, the receiver is placed at the top of a tower and many reflecting
elements called heliostats are placed around the tower reflecting and focusing the direct
solar radiation onto the receiver (Fig. 7.6). Though commercial systems using this technol-
ogy are working at temperatures below 600°C, temperatures of 1000°C and even higher can
be achieved with this technology because the solar flux incident on the receiver is signifi-
cantly higher than in a PTC (about 1 mW m ).
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