Basics of the photovoltaic thermal module - Solar Energy Sciences and Engineering Applications - page 149

Basics of the photovoltaic
thermal module
Krishnan Sumathy
Department of Mechanical Engineering, North Dakota State University, Fargo, USA
5.1 INTRODUCTION
Energy plays a crucial role in social and economic development. Remarkable increases
in oil prices have stimulated research in the renewable energy field as it contributes to
the diversity in energy supply. Compared to other types of energy, renewable energy
reduces the dependence on fossil fuel resources and carbon emissions to the atmo-
sphere. Nobuyuki (2006) gives the latest data which show that renewable energy
technologies provide 13.3% of the energy need around the world (Baños et al., 2010)
and will be greatly dependent on the future, considering their sustainability and wide
public acceptance. The total incoming solar radiation is about 3.8 million EJ per year,
which can meet the entire energy demand if harnessed properly.
Solar energy can be either utilized for producing electricity directly or to produce
heat. The combination of photovoltaic and thermal systems (PV/T) is particularly
attractive because of its efficiency in directly converting solar energy into electricity
and heat, concurrently. A photovoltaic/thermal (PV/T) module mainly comprises a
photovoltaic panel and a solar thermal collector, forming the core components of a
photovoltaic/thermal (PV/T) system.
Solar thermal systems and PV systems are essentially different because solar
systems generate heat energy while PV systems generate electricity. The differences
between PV system, PV thermal system, and solar collector are demonstrated in Fig-
ure 5.1.1. Solar energy can be captured in various ways: in a PV system, only a small
fraction of solar radiation absorbed by the panel is converted into electricity. That is to
say, a subsection of absorbed solar radiation is used by PV cells to generate electricity;
letting most of the radiation turn into waste heat. This results in the decrease of the
Figure 5.1.1 Comparison between PV, PV/T and solar thermal systems.