Renewable Energy and Sum-Zero Energy Buildings - Energy-Efficient HVAC Design - page 115

As per National Energy Foundation website which is based in the UK, “ http://
www.nef.org.uk/renewableenergy/pv-basics.htm , ” the most effi cient exposure for
locating the PV panels is on the roofs facing an exposure between southeast and
southwest. But the most important fact regarding these units is that even a minimal
amount of shading can reduce the effi ciency of the panels considerably. Common
effi ciency of these panels depending on the type of the used semiconductor and
manufacturing technology usually is somewhere between 5 to 15 %.
High temperature on the surface of the PV panels can also cause the loss of effi -
ciency of the PV panel. This effi ciency loss can be calculated by multiplying a fac-
tor that is called temperature coeffi cient by the difference between the environment
temperature and rated temperature of the PV panels. Depending on the type of the
used technology the temperature coeffi cient can be anywhere between two tenth to
fi ve tenth percent per one degree of Celsius (0.2-0.5 %/°C).
On average for a properly installed panel assembly of 1 kW-peak (maximum
output), an annual 750 kW h of output can be expected.

12.2.2 Concentrating Solar Power Systems

A Concentrating Solar Power (CSP) is an assembly in which sun light is concen-
trated to heat up a working fl uid. This heated working fl uid then will be utilized to
run a turbine or an engine which starts a generator in order to generate electricity.
Main utilized systems for this purpose are Linear Concentrator Systems, Design-
Engine systems, and Power Tower systems. It is common for these systems to be
designed with a supplemental thermal storage system in order to make up for the
periods of time that Sun power is not available.
Two popular types of Linear Concentrator systems are Parabolic Trough and
Linear Fresnel Refl ector systems. In a parabolic trough system (Fig. 12.4 ), para-
bolic refl ectors are installed in a general north-south direction. The control system
swings these refl ectors in such way to follow the movement of the Sun as much as
possible.
These refl ectors direct the maximum possible Sun energy towards a group of
collector pipes which carry working fl uid. These collector pipes are located in the
focal point of the parabolic surfaces and their function is to heat up the working
fl uid inside them using the absorbed Sun energy. The contained heat inside the
working fl uid then via utilization of a heat exchanger will be transferred to a steam
generating water cycle. Generated steam in this cycle then will be delivered to a
turbine. Steam will run the turbine shaft which fi nally will be transferred to an
electricity generator for generation of electricity.
In a linear Fresnel refl ector system, similar procedure happens through fl at long
mirrors individually following the movement of the sun and heating up the working
fl uid inside of the collector pipes located at the focal point of the mirrors (Fig. 12.5 ).
A Dish-Engine system is a relatively small size electricity generator with an
electricity generation target of mostly less than 25 kW. It is made of a parabolic dish