Wind Powering America Fact Sheet Series

Wind for Schools Project Power System Brief

Wind for Schools Project 

Power System Brief

Wind for Schools Project Power System Brief

This fact sheet provides an overview of the system components of a 

Wind Powering America Wind for Schools project.

Wind Powering America’s (WPA’s) Wind for Schools project uses a basic 

system configuration for each school project. The system incorporates 

a single SkyStreamTM wind turbine, a 70-ft guyed tower, disconnect 

boxes at the base of the turbine and at the school, and an interconnection to the school’s electrical system. A detailed description 

of each system component is provided in this document.

The local power cooperative or utility should be an integral part of 

the Wind for Schools project and assist in the turbine installation and 

associated electrical interconnections. However, special electrical 

permits are not required because the turbine is not expected to 

produce enough energy to supply a large portion of the school’s 

power needs, even at low-load periods during the summer or 

at night. 

The Wind for Schools package will include all of the disconnects and 

tower hardware associated with the project. Depending on the specific 

installation requirements, foundation and guy wire anchors must be 

installed, as well as fencing around the base of the wind turbine. 

System Description

The following components are part of a standard WPA Wind for Schools 

project. Note that all descriptions are explanatory; please consult local 

building and electrical codes.

1) SkyStreamTM 3.7, 1.8-kW wind turbine. Two versions are 

available: a 120/240V split-phase or a 120/208 three-phase. 

Depending on service level to the school, either version can be used. 

The 120/240V split-phase is preferred if the turbine is to be installed 

a large distance from the school (see item 6).

2) A standard 70-ft guyed tower (supplied by Southwest 

Windpower). An electrical connection (with three strands of AWG 10 

wire) must be made between the turbine and the junction box. Guy 

wires should be marked with streamers and other anti-avian 

devices. The tower and areas immediately surrounding the guy wires 

may require fencing.

3) Tower/turbine base fused disconnect and junction box. This 

fused disconnect and junction box allows an electrical separation 

between the wind turbine and the electrical wires connecting the 

power system to the school. It allows the isolation of the buried 

electrical lines and a 

way to safely disconnect 

the turbine from the 

electrical lines at the 

turbine site. The junction 

box also allows different 

wire sizes to be used 

from the turbine to the 

disconnect and from the 

disconnect to the school. 

The electrical connection 

is fused to provide further 

electrical safety.

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6

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4

5

3 9

10

11

7

8

8

7

6

5 4

3

2

1

5

5

5

Drawing not to scale

Andy Swapp/PIX14995
A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner 

environment, and greater energy independence for America. Working with a wide array of state, 

community, industry, and university partners, the U.S. Department of Energy’s Office of Energy 

Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies. 

For more information contact:

EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov

Produced for the U.S. Department of Energy by the 

National Renewable Energy Laboratory, 

a DOE national laboratory

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 20% postconsumer waste

DOE/GO-102007-2460 • August 2007

4) The main foundation for the turbine and tower, including tower 

base electrical grounding. The tower foundation is a 36”-diameter 

steel-reinforced concrete cylinder that extends 42” into the ground. 

The tower foundation will also be electrically grounded using a 

standard grounding rod to protect the tower and turbine from 

lightning and static electricity buildup. The base of the turbine will 

likely be fenced to restrict access and limit liability. The concrete pad 

should be installed at least 28 days before the turbine is installed. 

5) Tower guy wire foundations and electrical grounding. Each 

turbine has four guy wires that maintain the turbine stability. A 36”-

diameter steel reinforced concrete anchor is required at each guy 

wire location, depending on specific soil conditions. In areas prone 

to lightning strikes, each of the guy wires will be grounded with 

standard grounding rods and will potentially be interconnected 

using buried copper cable. The area around the guy wires may 

require fencing.

6) School electrical connection. The interconnection between the 

turbine and the school will be completed with a buried electrical 

cable. The cable size will depend on the distance between 

the wind turbine site and school and the specific turbine (see chart), 

although wires larger than 4 AWG can be used. In nearly all 

instances, the wires should be buried within a grounded steel 

electrical conduit (typically 1-inch schedule 40). PVC may be used, 

but a grounding wire must also be added. Electrical wire and 

trenching may be obtained from the local utility or power 

cooperative. Check local building codes, which typically require 

direct cables to be buried to a minimum depth of 24 inches (61 cm), 

while cables in conduit may be buried at a depth of 18 inches 

(46 cm). 

7) School disconnect and junction box. This junction box is typically 

located where the wind turbine electrical wires enter the school 

building. It allows the isolation of the buried electrical lines and a 

way to safely disconnect the school from the wind turbine. The 

junction box also allows different wire sizes to be used from the 

turbine to the school and within the school’s electrical systems. In 

areas prone to lightning strikes, a grounding rod may be installed 

at this location or simply tied into the school’s electrical grounding 

system. Check with local building codes to ensure proper location 

of the disconnect box (in some cases it may need to be located 

next to the school’s electrical meter).

8) School’s electrical power meter or interconnection point, 

where the turbine is electrically connected to the school’s 

240-V or 208-V electrical system. This should be connected 

on the school’s side of the electrical meter (connection to the 

main or primary node electrical panels is recommended). Check 

local building and electrical codes. Depending on local electrical 

requirements, this will require a certified electrician and may require 

that parts of the school’s electrical system be disconnected for a 

short period of time. If interconnection is made at the schools 

primary circuit panel, only 20A breakers should be used.

Wire Size

Maximum Distance

120 V 120/208 V 230 V 120/240 V

4 AWG (21.2 mm2) 646 ft (197 m) 885 ft (270 m) 934 ft (285 m) 1017 ft (310 m)

6 AWG (13.3 mm2) 407 ft (124 m) 557 ft (170 m) 588 ft (179 m) 640 ft (195 m)

8 AWG (8.4 V mm2) 256 ft (78 m) 351 ft (93.3 m) 371 ft (113 m) 403 ft (123 m)

10 AWG (5.3 mm2) 161 ft (41 m) 220 ft (67 m) 232 ft (70.7 m) 253 ft (77 m)

12 AWG (3.3 mm2) 101 ft (31 m) 139 ft (42.4 m) 146 ft (44.5 m) 159 ft (48.5 m)

14 AWG (2.1 mm2) 64 ft (20 m) 87 ft (26.5 m) 92 ft (28 m) 100 ft (30.5 m)

Use copper conductors only. Minimum wire temperature rating is 167°F (75°C). 

Distances and wire sizes are based on 1800-W power production and maximum 

2% voltage line loss. Distances for 120-V system based on 3000 W power 

production and 8% voltage line loss.

Wind for Schools Project Parts List — Additional Items (to be purchased new)

5” Schedule 40 Steel Pipe, 21’ (6.4m) length 5 comprises the tower; purchased at local farm supply

0.75” Tie Rods 4 foundation rods

3⁄4” x 12 inch galvanized forged eyebolt 2 for two of the guy wire anchors

3⁄4” x 8 inch galvanized forged eyebolt 2 for two of the guy wire anchors

Copper ground rod 1(6) electrical grounding rods; number depends on local grounding requirements

Grounding Wire 10(70ft) connection of grounding rods to towers and guy wires

Concrete (2500 psi rating) 4.5 cubic yds 0.9 cubic yards per anchor (main and 4 guy wires)

Rebar –various sizes and lengths see specific tower foundation design

Tower base fused disconnect box 1 SQUARE D #DU221RB 2-POLE, 30A, 240VAC. Tower base fused disconnect

School disconnect box 1 SQUARE D #DU221RB 2-POLE, 30A, 240VAC. School disconnect box

AWG 10 turbine electrical wire (80-ft length) 3 at 80 ft connects the turbine generator to the tower base disconnect box

Steel exterior grade electrical conduit Varies Depends on distance connects the turbine to the school - may be supplied by supporting utility

Turbine interconnection electrical wire Varies Depends on distance connects the turbine to the school - may be supplied by supporting utility