Overview of Renewable Energy Tech.pdf

SOLAR CENTER INFORMATION

NCSU • Box 7401 • Raleigh, NC 27695 • (919) 515-3480 • Toll Free 1-800-33-NC SUN

Overview of

Renewable Energy Technologies

As we begin the new millennium, it is evident there is a

growing need to rely more on alternative energy sources and less

on limited conventional energy sources that often are detrimental

to the environment. Fortunately in North Carolina, there are

opportunities to use several renewable energy technologies that

are extremely reliable, technically feasible and sustainable.

These renewable energy technologies are based on an unlimited

source of energy, often directly or indirectly from the sun, that

have little or no negative environmental impact.

This overview presents some of the most feasible renewable

energy technologies in North Carolina. The technologies

reviewed include solar, micro-hydropower, biomass, wind,

biogas and geothermal. The overview also includes references

that provide more information on each of these technologies.

The time is now to invest in renewable energy technologies

because of North Carolina’s 35 percent residential, commercial,

and industrial tax credit. To find out more information about the

tax credits, go to the North Carolina Solar Center website at

http//: www.ncsc.ncsu.edu/tax/revisedtax.htm.

photovoltaics, which convert sunlight to electricity, and

daylighting that is used to light building spaces naturally.

Figure 1 shows a picture of the NCSU Solar House, which

incorporates solar thermal and light-using technologies. Solar

energy conditions the home during the winter using passive

design practices, heats water year round with a state-of-the-art

collector, generates electricity with photovoltaic modules, and

lights the house with properly placed windows.

Solar Energy

The sun has burned for 4.6 billion years and has been the

primary source of energy for life on earth. The sun’s power

comes to us as light or electromagnetic waves and continues to

create most of the forms of energy we use today. The fossil fuels

used today are actually stored solar energy from millions of years

ago. All the renewable energy sources discussed here are

the air temperature differences that provide the air currents that

make wind energy possible. It provides the light to grow biomass

such as wood and provides the force behind the Earth’s water

cycle. Although most forms of renewable energy are a form of

solar energy, when one talks about solar energy, one usually is

talking about direct use of solar energy.

Solar energy traditionally consists of thermal systems and

light-using systems. Solar thermal systems are used to condition

buildings, heat water and generate heat for production of electric-

ity and industrial applications. Light-using systems include

Figure 1: The Solar House at North Carolina State University

For more information on solar energy, request the following

factsheets from the Solar Center: “Solar Energy: An Overview,”

“Passive and Active Solar Domestic Hot Water Systems,” “Siting

of Active Solar Collectors and Photovoltaic Modules,” “Passive

Solar Options for North Carolina Homes,” “Passive Solar Home

Design Checklist,” “Passive Solar Retrofit,” “Selecting A Site for

Your Passive Solar Home,” “Passive Cooling for Your North

Carolina Home,” “North Carolina Consumer’s Guide to Buying A

Solar Electric System,” “Photovoltaics: Electricity from the Sun,”

and “Photovoltaic Applications.”

State Energy Office

North Carolina

Department of Administration

College of Engineering

Printed on Recycled Paper

Micro-hydroelectric Energy

Humans have used the power of falling water for thousands

of years to turn water wheels for the grinding of flour. But only

during the past 100 years or so have humans discovered how to

use this renewable energy source for the creation of electrical

power. One of the earliest uses of micro-hydroelectric technol-

ogy in North Carolina was the development of a 40 kW micro-

hydroelectric plant on the Hominy River in the early 1880s to

power Asheville’s streetcars. Since then the use of micro-

hydroelectric technology has grown so that utility-interconnected

micro-hydroelectric power plants are now providing renewable

energy to customers across the state.

The driving force behind hydro power is the hydrologic

cycle. The hydrologic cycle is illustrated in Figure 2. In this

cycle, the sun’s energy is absorbed by surface water and soil at

low elevations, causing water to evaporate to form water vapor.

Water vapor also is produced from transpiration of plants.

Clouds form from this water vapor. The vapor later condenses to

form water droplets. These water droplets eventually fall as

precipitation. If this precipitation lands on areas of high eleva-

tion, the water will have relatively high potential energy. As

gravity causes this water to run off in streams, the water’s

potential energy is converted into kinetic energy, frictional

heating, and mechanical energy. Hydropower technologies

attempt to convert some of this energy into mechanical or

electrical energy.

Power House

Feeder Canal

Reserve Flow

Intake

Fish Ladder

Penstock

Tail Race

Forebay

Figure 3: Diagram of a Typical 100 kW Micro-hydroelectric

Plant

Power in Water

The power available from a micro-hydroelectric system

depends on the available elevation change, the stream or river

flow rate, and the overall micro-hydroelectric system efficiency.

The equation used to determine the power available in a stream

or river is

Condensation

P=0.19 x Q x H x E 0

Precipitation

where P is in watts, Q is the water flow rate to the turbine in

gallons per minute, H is the head or change in elevation from the

inlet to the outlet of the system in feet, and E o is the overall

system efficiency. Overall system efficiencies of 30 percent to 60

percent are common in micro-hydroelectric systems.

Evapotranspiration

Evaporation

Stream Runoff

System Components

Figure 3 is a diagram of a typical micro-hydroelectric plant

with a generating capacity on the order of 100 kW. Smaller

micro-hydroelectric plants may not include all of the components

shown in Figure 3.

Water flows down the feeder canal from the intake to the

forebay. The canal usually is made of earth stone or concrete and

is fitted with a trash rake and screen to keep floating debris and

marine animals out. The feeder canal dumps into the forebay.

The forebay is a tank that holds water between the feeder canal

and the penstock. The forebay is present to ensure that the

entrance to the penstock is fully submerged so that the designed

head is available and air is excluded from the turbine. The

penstock is the pipe connecting the forebay to the turbine. This is

the high pressure pipe in the system. The head available to the

turbine is developed by the change in elevation between the inlet

of the penstock and the exit of the turbine. The turbine is the

device that converts the power available in water into mechanical

energy. A generator connected to the turbine converts the

mechanical energy into electric energy. As the water exits the

turbine, it is reintroduced to the stream via the tailrace.

Ocean

Figure 2: The Hydrologic Cycle

Hydroelectric systems convert the energy embodied in

flowing water into electrical energy. Micro-hydroelectric

systems are those that generate less than one megawatt of peak

power. These are small-scale systems that can be implemented

by private individuals and small companies with little negative

environmental impact. Most micro-hydroelectric systems extract

power from a portion of the river without causing an appreciable

change in the river flow. Unlike large hydroelectric plants,

micro-hydroelectric systems use no dams or very small dams that

impound little water. Because only small diversion weirs or

intakes are necessary for micro-hydroelectric systems, they do

not typically interfere with fish migration or threaten stream

ecology.

In smaller systems, the dam and fish ladder may be replaced

by a small diversion weir. The feeder canal and forebay also may

be much less defined or may not be present at all.

Many turbine types are available for micro-hydroelectric

systems. Pelton turbines and Turgo turbines are the most

common types of micro-hydroelectric turbines. Other types are

the cross flow turbine, the Francis turbine, the propeller turbine,

and the traditional water wheel. The water wheel is the oldest of

the turbines and is not commonly used these days.

centuries to grind grain, pump water and, more recently, to

generate electricity. Windmills dotted the American West as the

country expanded, and, as early as 1920, wind turbines were

being used to produce electricity in rural parts of the country.

What is Wind?

Wind is a form of solar energy. This is because it is the heat

from the sun that ultimately forms the earth’s wind patterns. On

a micro level, wind is generated by the movement of air from

regions of high pressure to regions of low pressure, with these

differential pressures established by thermal gradients.

While wind directions may seem to change with frequency,

in most places there are prevailing wind patterns that make it

easier to predict and harness the power of wind. For example, in

North Carolina, the coastal regions experience steady easterlies

(wind from the east) coming off the Atlantic Ocean. The state’s

best wind resources are along the coast and in the mountains.

Figure 5 shows that class 5 and class 6 winds are available in the

mountains and class 3 on the coast, where class 6 are very strong

winds and class 1 are weak winds. Generally speaking, you need

class 3 winds for wind systems to work consistently.

System Types

Micro-hydroelectric plants can produce alternating current

(AC) or direct current (DC) electric power. AC micro-hydroelec-

tric plants usually are interconnected with the utility grid but can

be stand-alone systems if ballast loads are used. AC plants

require systems to control the voltage and frequency of the power

being generated. These plants are usually tens to hundreds of

kWs in size. Smaller hydroelectric turbine generator sets usually

produce DC power that is used to charge large battery banks.

These systems can be used to run DC loads or a DC to AC

inverter can be employed, allowing the operation of typical AC

loads. These systems may or may not be interconnected with the

utility.

2,000

Cost

Micro-hydroelectric systems can be installed for $2,000 to

$5,000 per peak kW capacity. Variations in site conditions and

water resources account for the wide variance in price. Low head

applications are more expensive than high head applications.

Low head availability requires high flow rate to reach desired

power output. High flow rates require larger and more expensive

equipment. High head, low flow systems are the most economi-

cal. North Carolina provides a tax credit of 35 percent of the cost

of a micro-hydropower system, up to a maximum credit of

$10,500 for residential and $250,000 for industrial and commer-

cial applications.

1,800

1,600

1,400

1,200

1,000

800

600

400

200

Equipment and Service Availability

Residential-sized micro-hydro turbines with a capacity up to

1.5 kW are readily available from renewable energy catalogs and

can be installed by do-it-yourselfers. Larger systems would need

to be designed and purchased from a micro-hydroelectric

specialty firm and installed by a contractor. Firms that can

provide this service can be found in Hydro Review journal

published by HCI Publications Inc., 410 Archibald Street,

Kansas City, Missouri 64111, (816) 931-1311.

Figure 4: Cumulative Installed U.S. Wind Capacity

Wind Technology Overview

Electric generation has recently become the most common use

for wind energy. This is done by using the spinning of the blades to

turn the armature in a generator located directly behind the blades at

the top of the tower. The energy from this generator is then

rectified before being converted to AC electric output through an

inverter.

The power available from the wind is a function of the cube

of the wind speed, which means that, all other things being equal,

a turbine at a site with 10 miles per hour (mph) winds will

produce twice as much power as a turbine at a location where the

wind averages 8 mph. In general, winds exceeding 11 mph are

required for cost-effective application of small grid-connected

wind machines while windfarms require wind speeds of 13 mph.

For applications that are not grid-connected, of course, these

requirements may vary, depending on the other power alternatives

available and their costs.

As technology has matured, available turbine sizes have

grown. Turbines installed today for utility grid power are

typically 250 kW to 900 kW with some machines available that

Wind Energy

Wind energy currently is the fastest growing energy source

in the world. This fact is promising for renewable energy

supporters because it shows that not only are renewable options

becoming more cost effective, but their cost effectiveness

combined with other advantages is being recognized in the

marketplace. Currently, there is over 1,800 MW of wind capacity

installed in the United States. Figure 4 shows the growth of

installed U.S. wind capacity over the past 20 years.

Like solar, hydro, and geothermal, wind energy can take on

many forms – from small to large and from water pumping to

utility power production. And wind energy is one of the oldest

forms of energy conversion in existence. It has been used for

can produce over 1 MW. These are massive machines that have

blade spans of over 150 feet resting on towers over 200 feet tall.

A single 750 kW turbine can power over 50 United States homes.

Wind farms (clusters of wind turbines) may have as many as 500

turbines producing over 400 MW of power.

And just as wind turbines are getting bigger, they also are

getting smaller, with machines down to 200W commercially

available for residential, recreational and general off-grid use.

Utility grid power is only one of many applications. Small wind

turbines are also used on sailboats to charge batteries, on homes

to offset electricity use, to power research stations in the Arctic,

and by farmers and ranchers to produce electricity for well

pumps.

Sophisticated controls technology enables these systems to

be optimized for nearly all conditions, although large wind farms

are usually located along a ridgeline, mountain pass or the coast

where strong winds come consistently and from the same

direction. Typically, these big machines are designed and

controlled so that their output is AC current, which eliminates the

need for a DC-to-AC inverter.

Interested in Investing in a Wind System?

Like solar, wind energy systems usually have a high up-

front cost with little or no operating cost for the life of the

system. The viability of a wind system will depend on three

issues:

(1) Available wind at the site to meet your needs;

(2) Regulatory or permitting barriers that may prohibit the

installation of a wind system; and

(3) Whether the initial investment can be recaptured in a

reasonable amount of time.

Figure 5: North Carolina Wind Resource Map. (Map courtesy

of US Department of Energy)

For more information

For more information on wind power, contact the American

Wind Energy Society, 122 C Street, NW, 4th Floor, Washington,

DC 20001, phone (202) 383-2500, fax (202) 383-2505, e-mail:

windmail@awea.org or visit their web site at www.awea.org.

Biogas Energy: Anaerobic Digestion

Creation of biogas is not new to our planet but has been part

of Earth’s natural processes well before the existence of man.

Biogas, which mainly consists of methane and carbon dioxide, is

the primary waste product of anaerobic bacteria as they digest

organic material. This process occurs in the absence of oxygen.

These conditions naturally exist in bogs, swamps, deep bodies of

water, and in digestive systems of many animals. Although

biogas has been generated for millions of years, the first docu-

mented collection of the gas for human use was not until 1895 in

England. The gas was used to fuel street lamps.

Since the late 1800s, anaerobic digestion has been an

invaluable means of treating waste, generating excellent soil

amendments, reducing greenhouse gases, diminishing odor

problems, and providing a renewable energy source. Although

the energy benefits of anaerobic digestion are critical, the

greatest benefits are in its capability of treating waste and

generating high quality end-products. In fact, the first farm-

based biogas system in the United States was built for odor

control at a hog farm in Iowa.

Today anaerobic digestion is used to treat city sewage; hog,

chicken, and cow waste; and municipal solid waste. Biogas is

being used for heating, electricity and steam generation, as well

as to supply fuel for natural gas lines. The by-products, called

the effluent, are rich with nutrients and often can be sold as a soil

amendment for nurseries or farms. Biogas systems are excellent

controlling odors and reducing the release of ozone-depleting

methane into the atmosphere.

There are two general classifications for wind turbines: the

horizontal axis (HAWT) and the vertical axis (VAWT). Figure 6

shows an example of a small HAWT. Although horizontal axis

machines are more common, the vertical axis machines have the

advantage of not being sensitive to wind direction. The most

common type of VAWT is the Darrieus design, which looks like

a giant eggbeater.

Figure 6: A 10 Kilowatt Wind Turbine (Photo courtesy of Bergey

Windpower Co., Inc.)

Anaerobic Process

The digestion process takes place in an enclosed tank or

lagoon, usually called a digester. The digester prevents the

waste from being exposed to oxygen. The process takes place in

three anaerobic stages: (1) fermentation, (2) hydrogen, carbon

dioxide, and acetic acid production, and (3) formation of methane.

During the fermentation stage, fermentative bacteria break down

organic material into fatty acids, alcohol, carbon dioxide, hydro-

gen, ammonia and sulfides. During the second stage, acetogenic

bacteria break the material further down to hydrogen, carbon

dioxide and acetic acid. In the final stage, methanogenic bacteria

form methane, which can then be used as a fuel source.

The anaerobic process is greatly affected by temperature.

Most systems operate in either the mesophilic range (68-113

• Durham operates two anaerobic digesters to process sewage

sludge. The biogas is used to power generators that supply

electric power to run pumps for the aeration systems at the

waste treatment plants.

• Raleigh currently extracts biogas from its landfills. The

extraction is done by capping a landfill and providing a

slight suction on the pipes that are located throughout the

landfill. The Raleigh landfill biogas operation provides gas

for a boiler. The steam from the boiler is used to generate

electric power. Other similar projects can be found in

Greensboro and Mitchell County. The Mitchell County

system also is used to provide heating to greenhouses in the

winter.

• Chicken and hog farmers in the eastern part of the state have

successfully used anaerobic digestion to process manure

while generating electricity and developing an excellent soil

amendment. A reduction in offensive odors is an added

benefit. Most of the systems in the state are of the lagoon

type and operate in the psychrophilic temperature range. An

EPA program, AgSTAR, has provided technical assistance to

many of these farms in developing appropriate systems for

their particular situations.

• A meat processing plant in Smithfield has been very success-

ful at using anaerobic digestion to reduce its waste products

while generating energy and reducing hauling fees.

F). The thermophilic range

allows for the largest loading rate of a digester as well as increas-

ing the destruction of harmful pathogens. Although little research

has been done at lower temperatures, digestions can also take

place in the psychrophilic range of less than 68

F. Higher

temperature systems generally have a greater rate of waste

processing per unit volume of digester but tend to be more

complicated to operate and require more equipment. Many of the

recently installed systems in North Carolina are of the psychro-

philic and mesophilic type.

The biogas generated from either of the three digester types

and operating temperatures consist of primarily methane (60% to

80%, about 600-800 BTU/ft 3 ) and carbon dioxide (20% to 40%).

There are normally traces of corrosive hydrogen sulfide, which

must be scrubbed out before utilizing the biogas as a fuel source.

System Components and Digester Types

A biogas system normally consists of a waste collection

system, waste preprocessing system, digester, and some final

effluent handling and storage. If electric power is generated

directly from the biogas, a gas scrubber and generator are part of

the system.

A waste collection system varies dramatically and is depen-

dent on the type of waste stream and waste handling practices.

Before entering a digester, the waste may need to be mechanically

shredded to improve system performance. Often the waste stream

also is preheated before entering a digester.

The three types of digesters most commonly used today are

(1) covered lagoons, (2) complete mix digesters, and (3) plug flow

digesters. Covered lagoons are used when the waste stream is less

than 2 percent solids. The waste is stored in a deep lagoon and

covered with a floating cover to trap escaping biogas. A complete

mix digester has engineered tanks, located above or below

ground, that treat waste in the range of 3 percent to 10 percent

solid content. Complete mix digesters generally require less land

and have a shorter treatment time than covered lagoons. Plug

flow digesters are engineered, heated rectangular tanks that treat

solid waste in the range of 11 percent to 13 percent solid content.

Biogas also can be generated from the decomposition of

municipal solid waste. Currently, there is ongoing research to

develop digesters that will break down the organic portion of a

waste stream to generate biogas while reducing the amount of

garbage that must be landfilled. For the waste already in the

landfill, biogas can be recovered and utilized. This is currently

happening at over 100 landfills around the country.

Biogas production has great potential in our state to generate

renewable energy while also protecting the environment by

reducing greenhouse gas emissions and creating an organic soil

amendment.

For More Information

Contact the AgSTAR Program at 800-95-AgSTAR for

information on biogas generation from agriculture byproducts.

Contact the Landfill Methane Outreach Program at 888-782-7937

for more information on methane recovery from landfills. Both

programs also can be contacted at U.S. EPA, 6202-J, 401 M

Street SW, Washington, DC 20460 or through the web site

www.epa.gov/methane/

Geothermal Energy

Geothermal energy under the Earth’s surface comes from hot

rocks and liquids produced by recent volcanic activity. One of

the principal sources of geothermal energy comes from large

reservoirs of hot water trapped in the permeable rock formations

below the surface. These reservoirs are called hydrothermal

reservoirs. This energy is located at shallow enough depths that

it can be recovered and put to use. In the western part of the

United States, high-temperature geothermal energy is used to

produce over 2,800 megawatts of electric generation power. In

many areas of the country, low-temperature geothermal is

available for residential, commercial and industrial uses.

Thermal capacity is another type of geothermal energy. The

ground just below the surface at ambient temperatures can serve

as a heat reservoir. The stable ground temperature just below the

surface can be used to heat and cool residential and commercial

buildings with geothermal heat pumps. Thermal capacity is

the principal form of geothermal energy available in North

Carolina.

Current Applications in North Carolina

Biogas is being actively used today around our state to collect

a renewable energy resource, process waste in an environmentally

sound manner, and reduce greenhouse gas emissions. Some of

the successful projects around our state include:

or the thermophilic range (113-150

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: