WIND AND SOLAR POWER SYSTEMS DESIGN ANALYSIS AND OPERATION BY WIND AND SOLAR POWER SYSTEMS PDF
The total electricity demand in 1997 in the United States of America was
three trillion kWh, with the market value of $210 billion.
demand was 12 trillion kWh in 1997, and is projected to reach 19 trillion
kWh in 2015. This constitutes the worldwide average annual growth of
The growth rate in the developing countries is projected to be
approximately 5 percent, almost twice the world average.
Most of the present demand in the world is met by fossil and nuclear power
A small part is met by renewable energy technologies, such as the
wind, solar, biomass, geothermal and the ocean.
Among the renewable power
sources, wind and solar have experienced a remarkably rapid growth in the
past 10 years.
Both are pollution free sources of abundant power. Additionally,
they generate power near the load centers, hence eliminate the need of running high voltage transmission lines through rural and urban landscapes.
Since the early 1980s, the wind technology capital costs have declined by
80 percent, operation and maintenance costs have dropped by 80 percent
and availability factors of grid-connected plants have risen to 95 percent.
These factors have jointly contributed to the decline of the wind electricity
cost by 70 percent to 5 to 7 cents per kWh.
The grid-connected wind plant
can generate electricity at cost under 5 cents per kWh. The goal of ongoing
research programs funded by the U.S. Department of Energy and the
National Renewable Energy Laboratory is to bring the wind power cost
below 4 cents per kWh by the year 2000.
This cost is highly competitive with
the energy cost of the conventional power technologies.
For these reasons,
wind power plants are now supplying economical clean power in many
parts of the world.
In the U.S.A., several research partners of the NREL are negotiating with
U.S. electrical utilities to install additional 4,200 MW of wind capacity with
capital investment of about $2 billion during the next several years. This
amounts to the capital cost of $476 per kW, which is comparable with the
conventional power plant costs.
A recent study by the Electric Power
Research Institute projected that by the year 2005, wind will produce the
cheapest electricity available from any source.
The EPRI estimates that the
wind energy can grow from less than 1 percent in 1997 to as much as
10 percent of this country’s electrical energy demand by 2020
1.1 Industry Overview
The total annual primary energy consumption in 1997 was 390 quadrillion
(1015) BTUs worldwide1 and over 90 quadrillion BTUs in the United States
of America, distributed in segments shown in Figure 1-1.
About 40 percent
of the total primary energy is used in generating electricity.
Nearly 70 percent
of the energy used in our homes and offices is in the form of electricity. To
meet this demand, 700 GW of electrical generating capacity is now installed
in the U.S.A. For most of this century, the U.S. electric demand has increased
with the gross national product (GNP).
At that rate, the U.S. will need to
install additional 200 GW capacity by the year 2010.
The new capacity installation decisions today are becoming complicated
in many parts of the world because of difficulty in finding sites for new
generation and transmission facilities of any kind.
In the U.S.A., no nuclear
power plants have been ordered since 19782 (Figure 1-2). Given the potential
for cost overruns, safety related design changes during the construction, and
local opposition to new plants, most utility executives suggest that none will
be ordered in the foreseeable future.
Assuming that no new nuclear plants
are built, and that the existing plants are not relicensed at the expiration of
their 40-year terms, the nuclear power output is expected to decline sharply
after 2010. This decline must be replaced by other means.
With gas prices
expected to rise in the long run, utilities are projected to turn increasingly
to coal for base load-power generation.
The U.S.A. has enormous reserves
of coal, equivalent to more than 250 years of use at current level. However,
that will need clean coal burning technologies that are fully acceptable to
The first use of wind power was to sail ships in the Nile some 5000 years
The Europeans used it to grind grains and pump water in the 1700s
The first windmill to generate electricity in the rural U.S.A. was
installed in 1890.
Today, large wind-power plants are competing with electric
utilities in supplying economical clean power in many parts of the world.
The average turbine size of the wind installations has been 300 kW until
the recent past.
The newer machines of 500 to 1,000 kW capacity have been
developed and are being installed. Prototypes of a few MW wind turbines
are under test operations in several countries, including the U.S.A.
is a conceptual layout of 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 per kWh
in 1980 to less than 5 cents per kWh in 1997 in favorable locations
(Figure 2-2). At this price, wind energy has become one of the least-cost
power sources. Major factors that have accelerated the wind-power technology development are as follows:
• high-strength fiber composites for constructing large low-cost blades.
• falling prices of the power electronics.
• variable-speed operation of electrical generators to capture maximum energy.
• improved plant operation, pushing the availability up to 95 percent.
• economy of scale, as the turbines and plants are getting larger in size.
• accumulated field experience (the learning curve effect) improving
the capacity factor.
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.
The cell converts the sunlight into direct
Numerous cells are assembled in a module to generate
required power (Figure 3-1). Unlike the dynamic wind turbine, the pv installation is static, does not need strong tall towers, produces no vibration or
noise, and needs no cooling.
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 from
more than $20 per watt to less than $5 per watts (Figure 3-2). During the
same period, the cost of pv electricity has declined from almost $1 to about
$0.20 per kWh, and is expected to decline to $0.15 per kWh by the year 2000
(Figure 3-3). The installed capacity in the U.S.
has risen from nearly zero in
1980 to approximately 200 MW in 1996 (Figure 3-4). The world capacity of
pv systems was about 350 MW in 1996, which could increase to almost
1,000 MW by the end of this century (Figure 3-5).
The pv cell manufacturing process is energy intensive.
Every square centimeter cell area consumes a few kWh before it faces the sun and produces
the first kWh of energy.
However, the manufacturing energy consumption
is steadily declining with continuous implementation of new production
processes (Figure 3-6).
The present pv energy cost is still higher than the price the utility customers pay in most countries. For that reason, the pv applications have been
limited to remote locations not connected to the utility lines.
With the declining prices, the market of new modules has been growing at more than a
15 percent annual rate during the last five years.
The United States, the
United Kingdom, Japan, China, India, and other countries have established
new programs or have expanded the existing ones.
It has been estimated
that the potential pv market, with new programs coming in, could be as
great as 1,600 MW by 2010.
This is a significant growth projection, largely
attributed to new manufacturing plants installed in the late 1990s to manufacture low cost pv cells and modules to meet the growing demand.
Wind Speed and Energy Distributions
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.
wind turbines are installed at one site to build a wind farm of the desired
power production capacity. Obviously, sites with steady high wind produce
more energy over the year.
Two distinctly different configurations are available for the turbine design,
the horizontal axis configuration (Figure 4-1) and the vertical axis configuration (Figure 4-2). The vertical axis machine has the shape of an egg beater,
and is often called the Darrieus rotor after its inventor.
It has been used in
the past because of specific structural advantage.
However, most modern
wind turbines use horizontal-axis design.
Except for the rotor, all other components are the same in both designs, with some difference in their placement.
Wind Power System
The wind power system is fully covered in this and the following two
This chapter covers the overall system level performance, design
considerations and trades.
The electrical generator is covered in the next
chapter and the speed control in Chapter 7