Wind EnergyResource, Advantages, and

Constraints

Dr. Richard Nelson

Engineering Extension

Renewable Resourcesand Technologically Viable End-

uses

Wind - electricity and hydrogen production

No Greenhouse Gas Emissions

Insurance Against Conventional Fossil-based Price Risk No Sulfur Dioxide (SO2),

Nitrous Oxide (NOx), or Mercury Emissions

Why Wind Energy?Wind, for now, is the renewable energy resource/technology of choice

“Free” resource

A “clean” resource due to: Replacement of a “dirty” energy source (coal) and, No emissions associated with its use

Can be utilized on underutilized land or on lands currently in commodity crop production (“harvest” on the surface and “harvest” above the surface)

Will primarily be used for electricity generation for immediate end-use or as a “driver” for hydrogen production

Energy Production and the Environment

Energy use in power plants accounts for:

67% of air emissions of SO2, the primary cause of acid rain. SO2 causes acidification of lakes and damages forests and other habitats.

25% of NOx, which causes smog and respiratory ailments.

33% of Hg (mercury), a persistent, bio-accumulative toxin which increases in concentration as it moves up the food chain, e.g. from fish to birds, causing serious deformities and nerve disorders.

SOURCES: Union of Concerned Scientists (UCS)

Wind Energy Benefits

No air emissions

No fuel to mine, transport, or store

No cooling water

No water pollution

No wastes

Wind Resources in the United States

Wind resources are characterized by wind-power density classes, ranging from class 1 (the lowest) to class 7 (the highest).

Good wind resources (class 3 and above) which have an average annual wind speed of at least 13 miles per hour, are found along the east coast, the Appalachian Mountain chain, the Great Plains, the Pacific Northwest, and some other locations.

Wind Resources in the United States Wind speed is a critical feature of wind resources, because the

energy in wind is proportional to the cube of the wind speed.

Kansas Wind Potential

Kansas is one of the three best wind states in the country

Total “windy” land equals more than 108,000 square kilometers (about 1/2 of state)

Total Energy Potential = 1.07 trillion kWh or 121,900 MWa

Most of that potential probably won’t be developed . . .

Wind Energy Basics

Physical & Engineering Aspects

Wind Power EquationP = ½ * air density * Area Swept by Rotor * Wind Speed3

P = ½ * ρ * A * V3

1) Power in the wind is correlated 1:1 with area and is extremely sensitive to wind speed (the cubic amplifies the power significantly)

2) If the wind speed is twice as high, it contains 23 = 2 x 2 x 2 = 8 times as much energy

3) A site with 16 mph average wind speed will generate nearly 50% more electricity and be more cost effective than one with 14 mph average wind speed (16*16*16) / (14*14*14) = 1.4927

4) Therefore, it “pay$” to hunt for good wind sites with better wind speeds

Energy from the Wind Turbine output drives wind economics and output is a strong function of wind

speed

Wind speed increases with height above the ground Power = 1/2 × (air density) × (area) × (wind speed)³

Energy in the wind increases as height increases (theoretically)

V2/V1 = (H2/H1)1/7

Wind Turbines

Turbines: Different Sizes and Applications

Small (10 kW)• Homes (Grid-connected)• Farms• Remote Applications

(e.g. battery changing, water pumping, telecom sites)

Intermediate

(10-500 kW)• Village Power• Hybrid Systems• Distributed Power

Large (500 kW – 5 MW)

• Central Station Wind Farms

• Distributed Power• Offshore Wind

Large Wind Systems

Range in size from 100 kW to 5 MW

Provide wholesale bulk power

Require 13-mph average wind sites

Technology OverviewLarge Wind Projects

Over 98-99% availability

Can deliver power for less than 5 cents/kWh (with Production Tax Credit) in many locations

~6,000 MW to be installed nationwide at end of 2003

In 2004, will generate about 3x Vermont’s total use

Typical Turbine Size1.3 to 1.8 MW rated capacity

Rotor diameter 60 to 80 meters

Tower height 60 to 80 meters

Turbine footprint 10 m x 10 m

Lowest ground clearance is at least 100 ft.

165-

220

ft T

OW

ER

245-

330

ft. T

IP

Ap

x. 1

00 f

t.

Next Generation Wind Turbines

Wind Turbine Schematic

Nacelle for 1.65-MW turbine

Cross section of blade for 1.65-MW turbine

VariabilityQuantifying Wind Power Performance

99% Availability

>90% Operating Time*

30 – 40% Capacity Factor

* Lake Benton, Minnesota Analysis of Windfarm Operation

Expected Output/Capacity Factor

The capacity factor is simply the wind turbine's actual energy output for the year divided by the energy output if the machine operated at its rated power output for the entire year

A reasonable capacity factor would be 0.25 to 0.30. A very good capacity factor would be 0.40

Capacity factor is very sensitive to the

average wind speed

Power Curves

The turbine would produce about 20% of its rated power at an average wind speed of 15 miles per hour (or 20 kilowatts if the turbine was rated at 100 kilowatts).

Operating Characteristics of Wind Turbines

0.66 MW 1.5 MW 1.8 MW 2.5 MW 3.0 MWVestas GE Vestas GE Vestas

Hub Height (m) 55 80-85 67-70 80 80-90

Rotor Diameter (m) 47 70.5 80 88 90

Swept Area by Rotor (m2) 1,735 3,904 5,027 6,082 6,362

Cut-in Speed (m/s) 4 3 4 3 4

Cut-out Speed (m/s) 25 25 25 25 25

Rated Speed (m/s) 15 12 16 12 15

“Value” of Wind Energy

The value of a wind turbine or wind farm depends upon many factors

locationterrainwind speed = f(location, terrain)cost of competing energy sourcerate structure of competing energy source

Wind Insures Against Fuel Price Risk

Platts “conservatively estimates that generating electricity from renewable sources can ultimately save consumers more than $5/MWh (1/2¢ per kW-h) by eliminating fuel price risk”*

*4/8/03 announcement re “Power Price Stability: What’s it Worth?”

Value of domestic fuel source (wind) would have a direct benefit on the Kansas/community

Wind energy “Fuel” is inflation-proof; therefore impervious to fuel price hikes

Wind - Natural Gas Comparison

WindLow Operating CostHigh Capital CostNon-dispatchableNo Fuel Supply/Cost

RiskNo Emissions

Natural Gas

High Operating Costs

Low Capital Cost

Dispatchable

Fuel Supply/Cost Risk

Smog, Greenhouse Gas Emissions

Wind Power CostsWind Speed

Assuming the same size project (total MW installed), the better the wind resource, the lower the cost; capture more energy for the same capital/ installed/ maintenance cost

Wind Power CostsProject Size

Assuming the same wind speed, a larger wind farm is more economical; economy-of-scale associated with wind farm installation

Wind Power Isn’t Perfect

Wind Power output varies over time; it isn’t dispatchable

Wind Power is location-dependent (rural vs. urban where it is needed most)

Wind Power is transmission-dependent for tie-in to the grid

Wind Power has environmental impacts (pro / con)

Wind Power can only meet part of the electrical load

Common Misunderstandings

Wind turbines are only generating electricity about one third of the time.

Wind turbines generate electricity essentially all the time, but only at their rated capacity about 30-40% of the time

Wind Web Sites

• www.awea.org

• www.wwea.org

• www.windpower.org