Power Electronics in Solar Energy Systems
Part 1 – Introduction to Solar Energy
I – How important is electrical energy in our modern existence?
Energy is one of the most vital resources for our modern existence. Our survival depends
on the availability of energy. Every day, we consume energy to perform our daily activities that
are vital for our survival. Electrical energy, which is just one form of energy, is considered to be
the most important form of energy in our modern world. Everything is powered by electrical
energy in our modern world. We cook our food using electric stoves. We refrigerate our food
using electric refrigerators. We wash our clothes using washing machines. We entertain
ourselves using computers and electronic appliances. We use air-conditioners to stay comfortable
during hot weather. The list just goes on and on. All of the gadgets just mentioned are powered
by electrical energy. It is clear that without cheap and abundant sources of electrical energy our
modern civilization will be put in jeopardy.
II – Where does the electrical energy that we use come from?
At present, most of the electrical energy produced by electric power companies comes
from nonrenewable sources like fossil fuels (coal, gas, and oil) and nuclear sources. A very
small part of it comes from renewable sources (wind, tidal, hydroelectric, geothermal, and solar).
Figure 1
III – So, what is the problem with non-renewable fossil fuels?
Our fossil fuel emissions have increased dramatically over the past century. The massive
amount of carbon dioxide in the atmosphere has dire implications for the delicate balance of our
ecosystem and could eventually lead to environmental problems.
Figure 2
Back in 1956, an American geophysicist, Marion King Hubbert, stated in one of his
papers that the production of oil in the USA would peak toward the end of the 1960s and, would
peak worldwide in the year 2000. The theory of Hubbert states that production of fossil fuels
follows a bell-shaped curve, where production begins to gradually increase, then as the
technology becomes mainstream there is a sharp upturn in production, followed by a flattening
off when production has to continue against rising costs. As the cost of extraction increase,
production begins to plateau, and then fall—falling sharply at first, and then rapidly.
Figure 3
The International Energy Agency has stated that energy production is in decline in 33 out of the
48 largest world oil producers. In the same way that production of oil has reached its limits, other
fossil fuels such as gas and coal will also reach their limits.
Nuclear power plants use radioactive materials (e.g. uranium) which is not only also
limited but also pose as an environmental threat.
IV – Why choose solar energy?
Solar energy is clean, green, free, and best of all it will last as long as the sun will last.
Actually, solar energy is the main energy source of our planet. Plants rely on the sun to produce
their food. The wind is caused by the heat that comes from the sun. The waves in the sea are
caused by the wind which is caused by the heat of the sun. The hydrological cycle depends on
the sun for it to continue. The bottom line is, the sun is our main power source.
V – Relationship between Solar Energy Photovoltaic Systems and Power Electronics
One of the advantages of solar photovoltaic systems is the potential to provide
sustainable electricity in areas not served by the conventional power grid. The growing market
for renewable energy technologies such as solar photovoltaic systems has resulted in a rapid
growth in the need for power electronics. Solar photovoltaic systems produce DC power and
hence power electronics and control equipment are required to convert the DC into AC power.
Inverters are used to convert DC to AC. There are two types of inverters for this purpose:
(a) stand alone and (b) grid-connected. A stand-alone inverter is used in off-grid applications
with battery storage. With back-up diesel generators (such as photovoltaic/diesel/hybrid power
systems, the inverters may have additional control functions such as operating in parallel with
diesel generators and bidirectional operation (battery charging and inverting). Grid interactive
Inverters must follow the voltage and frequency characteristics of the utility generated power
presented on the distribution line. For both types of inverters, the conversion efficiency is a very
important consideration.
VI – Photovoltaic Power
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A solar photovoltaic device is one which takes light from the sun and turns it into
electricity. In doing so, it produces no emissions or harmful waste, and does so
completely silently!
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The photovoltaic (pv) power technology uses semiconductor cells (wafers), generally
several square centimeters in size. From the solid-state physics point of view, the cell
is basically a large area p-n diode with the junction positioned close to the top
surface.
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The cell converts the sunlight into direct current electricity. Numerous cells are
assembled in a module to generate required power.
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Because much of the current pv technology uses crystalline semiconductor material
similar to integrated circuit chips, the production costs have been high. However,
between 1980 and 1996, the capital cost of pv modules per watt of power capacity has
declined.
Major advantages of the photovoltaic power are as follows:
• short lead time to design, install, and start up a new plant.
• highly modular, hence, the plant economy is not a strong function
of size.
• power output matches very well with peak load demands.
• static structure, no moving parts, hence, no noise.
• high power capability per unit of weight.
• longer life with little maintenance because of no moving parts.
• highly mobile and portable because of light weight.