Principles Of Solar Cooling Technologies

PRINCIPLES OF SOLAR COOLING TECHNOLOGIES

1. INTRODUCTION

Summer weather conditions in Europe and in other regions or countries which have warm weather and the temperatures are higher than 26 Celsius degrees demand the use of air conditioning to keep the people welfare inside the buildings.
Apart from keep the people welfare, the buildings must have a complete air conditioning system inorder to obey the international laws as well.
The production, storage and marketing of medicaments and perishable foods require refrigeration systems for guarantee the product quality.
For these reasons we should have efficient refrigeration systems to maintain the life quality of some people and improve the way of life of some others, but in some regions of the world people cannot use theelectric grid that is why is convenient find different energy sources, which can be use in insulated villages as well.
Investigations to use other energy sources are being made rapidly because fossil fuels have few reserves. To give an example, petroleum reserves are approximately one billion barrels (source www.bp.com). Taking into account the world population growing and the growing demand of someemerging economies like China and India, these reserves could supply the planet just for 40 years.
Additionally, fossil fuels have a high environmental impact due to the fact that they affect considerably the ozone layer and they are the major contributor to global warming.
Among the energy sources alternative to fossil fuels, renewable energies such as solar energy, are gaining importance owingto they have fewer adverse effects on the environment and they can be used on insulated places where people cannot use the electric grid. Therefore, the aim of the current report is to show the basic principles of the cooling technologies that utilize solar energy and review their advantages and disadvantages compared to the conventional ones.

2. SOLAR COOLING TECHOLOGY

There are twodifferent classifications: depending on the energy conversion and based on the principle used in the systems.
Florides and Tassou (2002) are based on the principle used in the refrigeration systems, which are: solar sorption cooling, solar-mechanical systems and solar-related systems.
Hwang and Radermacher (2007) showed a solar cooling technology classification depending on the energy conversionoptions. According to them, solar cooling technology can be classified into three categories: solar electrical cooling, solar thermal cooling, and solar combined power and cooling, as illustrated in Figure 1.
Both classifications are valid, but for this report is better use the second option shown above, because it covers more technologies, although some systems shown by Florides and Tassou shall betaken into account as well. Detailed discussion of each solar cooling technology follows.

Figure 1. Energy conversion options for solar cooling.
2.1. Solar Electrical Cooling
In these systems, electrical power is supplied either to the Peltier cooling systems or to the vapor-compression systems with a dc compressor motor. This can be done by converting solar energy into electricity by meansof photovoltaic devices.
Photovoltaic devices transform sunlight energy into electrical energy through photoelectric effect, as French physicist Edmond Becquerel discovered as early as 1839. Also photovoltaic (PV) cell is known as “solar cell” and it can be defined as a semiconductor device that generates electricity when light falls on it.
The process inside the PV cell starts when sunlightstrikes the cell, afterwards the photons of the absorbed sunlight dislodge the electrons form the atoms of the cell. The free electrons then move through the cell, creating and filling in holes in the cell. It is this movement of electrons and holes that generates electricity.
Commonly two different types of PV cell are used: flat plate and concentrators. As the most prevalent type of PV systems,...