24-07-2012, 11:06 AM
PHOTOVOLTAIC SOLAR ENERGY
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Introduction to energy consumption and production
Any change that takes place in the universe is accompanied by a change in a quantity
that we name energy. We do not know what energy exactly is, we use this term to describe a
capacity of a physical or biological system for movement or change. Energy comes in many
forms, such as electrical energy, chemical energy, or mechanical energy, and it can be used to
realize many forms of change, such as movement, heating, or chemical change. Any activity,
and human activity as well, requires energy. Human beings need it to move their bodies, to
cook, to heat and light houses, or to drive vehicles. Human being is a greedy consumer of
energy. An active young man needs about 2500 kcal (2.9 kWh) per day to fulfil his daily
energy requirements. This means the energy of about 1060 kWh per year. The present global
energy consumption is around 19 000 kWh per inhabitant per year. It means that on average a
man consumes about 19 times more energy than is needed for his survival and satisfactory
health.
The mankind has witnessed an enormous increase in energy consumption during last
100 years. While in 1890 the energy use per inhabitant per year was around 5800 kWh it
reached 20200 kWh in 1970. Since 1970 the energy use has dropped to the present level of
19000 kWh per inhabitant per year. The increase in energy use in the 20th century can be
SOLAR CELLS
related to an evolution process that has started about five centuries ago. The underlying
motivation of this process was formulated during the Enlightenment period in the 18th century
as the philosophy of human progress. The aim of the process was an examination of the
surrounding world and its adaptation to the needs of people whose life would become more
secure and comfortable. This process was accompanied by growing industrialization and mass
production, which were demanding more and more energy. At the end of the 19th century coal
was the main source of energy. In this period electricity was introduced in the industrialized
countries as a new and elegant form of energy. This form of energy was quickly applied on a
large scale. The widespread growth of electricity use led to construction of hydroelectric
plants and hydropower became an important source of energy in the first half of the 20th
century.
In the period after the World War II much effort was put into the reconstruction of the
society. The emphasis was directed on the growth and efficiency of the mass production. New
technologies and new materials, such as plastic, were applied in the production. The energy
demand was tremendously growing in this period. Oil and gas started to play an important
role as energy sources in the second half of the 20th century. Coal, oil, and gas form today
dominant sources of energy. These three energy sources, also known as fossil fuels, are called
the traditional energy sources. In this period nuclear energy was introduced as a new source
of energy. Increasing and more efficient mass production resulted in the low price of many
household products. The consumption of the products grew enormously and therefore it is not
surprising that we characterise today society as a consumption society.
Nevertheless, it has become evident at the end of the 20th century that the philosophy
of human progress that has manifested itself in a huge production and consumption of goods
has a negative side too. It has been recognized that a massive consumption of fossil fuels in
order to fulfil the present energy demands has a negative impact on the environment. The
deterioration of environment is a clear warning that the present realization of human progress
has its limitations. The emerging international environmental consciousness was formulated
in a concept of a sustainable human progress. The sustainable human progress is defined as:
“… to ensure that it (sustainable development) meets the needs of the present without
compromising the ability of future generations to meet their own needs”1. A new challenge
has emerged at the end of the 20th century that represents a search for and a utilization of new
and sustainable energy sources. The urge of this challenge is underlined by limited resources
of the fossil fuels on the Earth and increasing demand for energy production. This is the
reason why the attention is turning to the renewable energy sources.
Energy is an essence of any human activity. When we are interested in how the human
civilization has been producing and using energy, we can describe it in terms of an energy
system. The main characteristics of the energy system are: the population, the total
consumption of energy, and the sources and forms of energy that people use. The energy
system at the beginning of the 21st century is characterised by six billion people that live on
the Earth and the total energy consumption of approximately 1.3 × 1010 kW.
Primary energy sources
presents an overview of the present primary energy sources2. The primary
energy sources can be divided in two groups. The first group includes those energy sources
that will be exhausted by exploiting them. These energy sources are called the depleting
energy sources and they are the fossil fuels and nuclear energy. The fossil fuels and nuclear
power are the main source of energy in today’s energy system and they supply 78% of the
energy demand. Under the assumption that the population of mankind does not change
drastically and it consumes energy at the current level, the fossil fuel reserves will be
exhausted within 320 years and the nuclear energy within 260 years. This can seem a very
long time for us. However, when we compare this period of time to the time span of existence
of the Earth or the human civilisation, it is a negligible fraction of time. We have to be aware
that the reserves of fossil fuels on the Earth are limited and will be exhausted.