The phenomenal growth and new developments in wind and solar power technologies have made the second edition of this book necessary.

It reflects the need for an
expanded, revised, and updated version of the well-received first edition in just 5
years. During that time, the capital and energy costs of wind power have declined
by 20%. Today, the cost of electricity from grid-connected wind farms is below 4
cents/kWh, and that from photovoltaic (PV) parks below 20 cents/kWh.

The goal
of ongoing research programs funded by the U.S. Department of Energy (DOE) and
the National Renewable Energy Laboratory (NREL) is to bring wind energy cost
below 3 cents/kWh and the PV energy cost below 15 cents/kWh by 2010.

In capital
and energy costs, wind now competes on its merits with the conventional power
technologies, and has become the least expensive source of electrical power —
traditional or new — in many parts of the world. It is also abundant and environmentally clean, bringing many indirect social benefits not fully reflected in the market

For these reasons, wind power now finds importance in the energy
planning in all countries around the world.

According to the DOE, prime wind
locales of the world have the potential of supplying more than ten times the global
energy needs. In the U.S., the DOE has established 21 partnerships with public and
private bodies to develop turbines to generate economical power in low-wind-speed
regions that would open up much larger areas of the country for rapid development
of wind power.

The Electric Power Research Institute (EPRI) estimates that wind
energy will grow from less than 1% at present to as much as 10% of the U.S.
electricity demand by 2020.
Around the world, the wind power generation capacity has seen an average
annual growth rate of 30% during the period from 1993 to 2003.

More than 8,000 MW of new wind capacity was added globally in 2003 with an investment value of
$9 billion. This brought the total cumulative wind capacity to 40,000 MW.

The most explosive growth occurred in Germany.

Offshore wind farms are bringing a new
dimension to the energy market.

Many have been installed, and many more, each
exceeding 300-MW capacity, are being installed or are in the planning stage. Most
offshore farms are less than 10 km from the shore in less than 10 m depth of water.
Denmark’s plan to install 750 MW of new wind capacity by 2008, bringing its total
to 4,000 MW for supplying 25% of the country’s electricity, includes aggressive
offshore plans.

U.S. wind capacity is projected to reach 12,000 MW by 2015. Utilities
and wind power developers have announced plans for more than 5,000 MW of new
capacity in 15 states by 2006. Hydro-Quebec plans 1,000 MW of new capacity to
be added between 2006 and 2012.

In these new installations, 3-MW turbines are
being routinely installed in many countries, with 5-MW machines available today
for large offshore farms; 7-MW units are in prototype tests

On the solar PV side, the cost of PV electricity is still high: between 15 and 25
cents/kWh. With the consumer cost of utility power ranging from 10 to 15
cents/kWh, PV cannot economically compete directly with utility power as yet,
except in remote markets where utility power is not available and transmission line
cost would be prohibitive.

Many developing countries have large areas falling in
this category, and that is where the most PV growth is taking place, such as in India
and China. The worldwide solar PV is about $7 billion in annual business, mainly
driven by Germany.
Worldwide, PV installations grew at an average annual rate of 25 to 30% during
the period from 2000 to 2004.

By the end of 2004, the cumulative PV capacity was
2,030 MW, with 1,000 MW in the U.S.

The annual production of PV modules was
530 MW in 2004 and is projected to reach 1,600 MW by 2010. The present module
prices are $6 to $7 per watt for 1-kW modules and $3 to $4 per watt for 1-MW

The emerging thin-film and concentrating PV cells are expected to reduce
the module prices substantially in the near future

About This Book
The second edition of this book is an expanded, revised, and updated version, which
was prepared when I was invited to teach a course as a visiting professor in emerging
electrical power technologies at the University of Minnesota, Duluth.

Teaching the
full course to inquisitive students and short courses to professional engineers
enhanced the contents in many ways.

It is designed and tested to serve as textbook
for a semester course for university seniors in electrical and mechanical engineering

For practicing engineers there is a detailed treatment of this rapidly growing
segment of the power industry.

Government policymakers will benefit by the overview of the material covered in the book, which is divided into 4 parts in 19 chapters.
Part A covers wind power technologies and ongoing programs in the U.S. and
around the world. It includes engineering fundamentals, the probability distributions
of wind speed, the annual energy potential of a site, the wind speed and energy maps
of several countries, and wind power system operation and the control requirements.
As most wind plants use induction generators for converting turbine power into
electrical power, the theory of the induction machine performance and operation is
reviewed. The electrical generator speed control for capturing maximum energy
under wind fluctuations over the year is presented.

The rapidly developing offshore
wind farms with their engineering, operational, and legal aspects are covered in
Part B covers solar photovoltaic (PV) technologies and current developments
around the world.

It starts with the energy conversion characteristics of the photovoltaic cell, and then the array design, effect of the environment variables, suntracking methods for maximum power generation, the controls, and emerging trends
are discussed.

1 Introduction
Globally, the total annual primary energy consumption in 2005 is estimated to be
500 quadrillion (1015) Btu.1 The U.S. consumes 105 quadrillion Btu, distributed in
segments shown in Figure 1.1. About 40% of the total primary energy consumed is
used in generating electricity.

Nearly 70% of the energy used in our homes and
offices is in the form of electricity.

The worldwide demand of 15 trillion kWh in
2005 is projected to reach 19 trillion kWh in 2015. This constitutes a worldwide
average annual growth of 2.6%.

The growth rate in developing countries is projected
to be approximately 5%, almost twice the world average.
Our world has been powered primarily by carbon fuels for more than two
centuries, with some demand met by nuclear power plants over the last five decades.
The increasing environmental concerns in recent years about global warming and
the harmful effects of carbon emissions have created a new demand for clean and
sustainable energy sources, such as wind, sea, sun, biomass, and geothermal power.
Among these, wind and solar power have experienced remarkably rapid growth in
the past 10 yr. Both are pollution-free sources of abundant power.

Additionally, they
generate power near load centers; hence, they eliminate the need of running highvoltage transmission lines through rural and urban landscapes.

Deregulation, privatization, and consumer preferences for green power in many countries are expanding
the wind and photovoltaic (PV) energy markets at an increasing pace.
The total electricity demand in the U.S. approached 4 trillion kWh in 2005, with
a market value of $300 billion. To meet this demand, over 800 GW of electrical
generating capacity is now installed in the U.S. For most of this century, the countrywide demand for electricity has increased with the gross national product (GNP).
At that rate, the U.S. will need to install an additional 200-GW capacity by the year

2 Wind Power
The first use of wind power was to sail ships in the Nile some 5000 yr ago. Many
civilizations used wind power for transportation and other purposes: The Europeans
used it to grind grains and pump water in the 1700s and 1800s.

The first windmill
to generate electricity in the rural U.S.

was installed in 1890. An experimental gridconnected turbine with as large a capacity as 2 MW was installed in 1979 on Howard
Knob Mountain near Boone, NC, and a 3-MW turbine was installed in 1988 on
Berger Hill in Orkney, Scotland.
Today, even larger wind turbines are routinely installed, commercially competing
with electric utilities in supplying economical, clean power in many parts of the world.
The average turbine size of wind installations was 300 kW until the early 1990s.
New machines being installed are in the 1- to 3-MW capacity range. Wind turbines
of 5-MW capacity have been fully developed and are under test operation in several
countries, including the U.S. Figure 2.1 is a conceptual layout of a modern multimegawatt wind tower suitable for utility-scale applications.1
Improved turbine designs and plant utilization have contributed to a decline in
large-scale wind energy generation costs from 35 cents/kWh in 1980 to 3 to 4
cents/kWh in 2004 at favorable locations (Figure 2.2). At this price, wind energy
has become the least expensive new source of electric power in the world, less
expensive than coal, oil, nuclear, and most natural-gas-fired plants, competing with
these traditional sources on its own economic merit.

Hence, it has become economically attractive to utilities and electric cooperatives, with 30% growth from 1993
to 2003. Worldwide, over 40,000 MW of wind capacity has been installed, and more
than 100,000-MW capacity by 2010 is predicted.

3 Wind Speed and Energy
The wind turbine captures the wind’s kinetic energy in a rotor consisting of two or
more blades mechanically coupled to an electrical generator.

The turbine is mounted
on a tall tower to enhance the energy capture.

Numerous wind turbines are installed
at one site to build a wind farm of the desired power generation capacity.

Obviously, sites with steady high wind produce more energy over the year

4 Wind Power Systems
The wind power system is fully covered in this and the following two chapters. 

This chapter covers the overall system-level performance, design considerations, and

The electrical generator is covered in the next chapter, and generator drives
in Chapter 6.