Following are four sets of wind data for the Great Falls area. Each covers different time periods (with overlap), but the data spans at least 1942 until 2003. The sites the data was taken from may vary as well. At least one is from the Airport, one from the NOAA weather station near Gore Hill, and one above the Sun River. The average wind speed varies from 11.9 to 13 mph with the majority of it coming from the southwest.

 

1. Climatic wind data from the National Oceanic and Atmospheric Administration (NOAA) for the period of 1930-1996 (though the period of record for individual sites varies and may begin and end at any time during this period).

 

Great Falls (Direction, Speed, 5-second winds)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
SW SW SW SW SW SW SW SW WSW WSW SW SW
15 14 13 13 11 11 10 10 11 13 15 15
53 48 52 57 39 51 49 47 36 49 54 59

 

Annual direction – SW, speed – 13 mph, 5-second winds – 59 mph

 

2. From NOAA’s National Weather Service Forecast Office in Great Falls:
Prevailing winds are from the southwest to west-southwest, with occasional north to northeasterly winds during late winter and early spring. From 1942-2002, average wind speed is 12.5 mph. Winds averaged on a monthly basis are at a maximum of 15.4 mph during December and lowest at 9.9 mph in July. Daily peak wind gusts average out to 28.8 mph. Monthly averaged peak wind gusts top out at 31.6 mph in December and are at a minimum of 27.6 mph in August.

 

3. From Montana Wind Energy Atlas

 

Great Falls NWS Airport
Data between January 1, 1965 through December 31, 1978 with anemometer at 22 feet.

 

Average annual wind speed was 11.9 mph. Average monthly wind speeds varied from 9.4 mph in July to 14.8 mph in December.

 

Average annual wind power was 183.0 watts/m2. Monthly average wind power ranged from 77 watts/m2 in July to 324 in December.

 

Average seasonal wind speeds were 9.8 mph in summer, 11.9 mph in spring, 12.2 mph in autumn, and 13.9 mph in winter. During the summer, the highest average wind speeds occurred during the late afternoon. During all other seasons, the highest average wind speeds occurred in early to mid-afternoon.

 

Winds most common from the south-southwest through the west-southwest (nearly half the time). The strongest winds blew from the prevailing wind directions.

 

4. From Plains Organization for Wind Energy Resources. Wind Resource Summary for Great Falls, MT. November 2003.

 

Annual summary for October 25, 2002 – October 24, 2003 for tower approximately 7 miles west of Great Falls on a rim above the Sun River.

 

33 ft 98 ft 131 ft
mean wind speed (mph) 10.8 13.2 14.7
max, 10-min mean wind speed (mph) 39.3 45.6 49.8
mean wind power density (w/m2) 141 239 318

 

Winds from the west-southwest (at 16.8%) and the southwest (at 22.9%) had the highest frequency (south-southwest had a frequency of 7.8%, 3rd highest).

 

Recommendations

 

Install a household-size, grid-tied wind system without battery backup. Use it in tandem with a solar system (see Solar section). Using both is more cost effective since they will each use the same components, spreading the fixed cost of the components over more kilowatt-hours.

 

Household-size turbines are usually between 10-23 feet and suitable for homes, farms, ranches, small businesses. They can generate 2,000 kWh to 20,000 kWh per year at 12 mph sites.

 

To get an estimate of performance of a turbine:
AEO = 0.01328 D2V3
where, AEO = annual energy output (kWh/year)
D = rotor diameter (feet)
V = annual average wind speed (mph)

 

Details: Components, Siting, Net metering, Tax incentives/loans

 

1. Components

 

Summary: wind tower, wind turbine, inverter, circuit breaker, wiring

 

Tower: the hub height for a small machine should be between 60-120 feet.

 

Two types of towers:
Guyed
advantages:
• least expensive
• easier to install
disadvantages:
• guy radius must be ½ to ¾ of tower height, the towers require the space to accommodate them

 

Self-supporting (free standing):
advantages:
• easier to maintain
• can tilt down during hazardous weather
disadvantages:
• more expensive

 

2. Siting:

 

Site turbine well away from buildings, trees, and other wind obstructions.

 

Turbine (bottom of rotor blades) should be at least 30 feet above any obstructions within 300 feet of the tower.

 

Under the best of conditions, a tower height of 30 feet is the absolute minimum.

 

Site selection:
• observe wind and terrain characteristics
• determine the general wind resource in the area
• if necessary, measure wind speed at each site being considered
• check for legal restrictions

 

3. Net metering (buyback)
See Solar.

 

At the end of the month, if the customer has generated more electricity than was used, the utility credits the net kWhs produced at the wholesale power rate. If customers use more electricity than they generate, they pay the difference. At the beginning of a 12-month billing period, any remaining unused kWh credit accumulated during the previous 12 months must be granted to the electricity supplier, without any compensation to the customer-generator. With wind generation, it makes sense to choose a date that occurs after the least windy part of the year.

 

4. Tax incentives/loans

 

Incentives:
See Solar.

 

Wind Tax Credit: Montana taxpayers (small business corporation) who produce or use wind-generated electricity are entitled to a state tax credit equal to 35% of their investment of $5,000 or more in a commercial system or a net metering system.

 

Loans:
See Solar.

 

Alternative Energy Revolving Loan Program (AERLP): Provides loans to small businesses for the purpose of building alternative energy systems. They are eligible for low-interest loans from the state of up to $10,000 for wind projects. Repayment is due in 5 years.

 

To do:
Check with city or county for zoning regs, building codes, and electrical codes.
Talk with neighbors before installing.
Contact utility before installing.

 

Asses maintenance costs:
usually 2 to 2.5 percent of initial machine cost
for small machine, once- or twice-a-year inspection and possible lubrication

 

Estimate the cost-effectiveness of system:
total cost of installation (electrical materials, hardware, inspections)
expected annual energy output in kWh

 

Wind system cost worksheet – page 15 of Montana Wind Power: A Consumer’s Guide to Harnessing the Wind. March 2006.

 

Best method of assessing wind speed is to measure with anemometer placed on a tower at the location and height you plan to install. Study for one year, preferably two.

 

Check for migratory bird flyways.

 

Notes:
For size and price comparisons, use the rotor diameter or swept area of the turbine since both are more reliable indicators of performance than power curves (how much wind power a turbine will produce at any given wind speed). Only use power curve data if the manufacturer has clearly stated the conditions under which the curve was measured or in “rated power.”

 

Checklist:
• rotor diameter
• annual energy output (kWh) at various avg wind speeds
• rated power output or generator rating (kW)
• rated wind speed – wind speed at which the machine reaches rated power output
• cut-in speed – wind speed at which the machine starts to produce power
• survival wind speed – max wind speed the machine is designed to withstand

 

Step-by-step for purchasing small wind system:
• determine year-round electrical requirements
• determine how to reduce electrical demand
• select likely site, obtaining an anomometer and monitoring wind speeds for 3-12 months
• evaluate site and its wind potential – address the following issues at the site:
o avg annual wind speed
o prevailing wind directions
o vegetation and buildings at the site
o type of energy storage and whether the system will be net metered
o legal and environmental restrictions
• survey available small wind energy systems and obtain info from manufacturers
• make preliminary selection
• consult local utility about interconnection costs and requirements
• evaluate the initial cost, as well as the cost per kWh of electricity
• consider potential tax breaks
• check manufacturer or dealer warranties and/or maintenance contracts
• check electrical equipment for utility connection
• if calculations are favorable, it is wise to do a more sophisticated analysis of wind energy potential and potential profitability before buying a machine
• the utility buyback rate and state incentive payments will affect the profitability

 

The bigger turbines cost more but are often more cost-effective.

 

A general rule of thumb for estimating the cost of a residential turbine is $1,000 to $3,000 per kW.

 

Insure system when it’s installed. Most companies will be satisfied if refer to system as a windmill and tower (not “wind turbine”). Include system as an “appurtenant structure” (on current homeowner policy). Policy should cover the installed cost of the system. Make decision to get liability insurance or not.

 

For grid-tie, make sure that turbine is near a three-phase power line. Some utilities restrict how close a turbine can be to power lines.

 

Place turbine back from property lines in case a neighbor builds an obstruction that affects the flow of wind.

 

Take into consideration the length of the wire run in a grid-tied system. A substantial amount of electricity can be lost as a result of the wire resistance. Wire run losses are greater when using DC, so if there is a long wire run, it is advisable to invert DC to AC.

 

From Bright Ideas in Renewable Energy:
Local RE Businesses:
Alternative Energy Systems, LLC (Mark Gray), Black Eagle
Dearborn Solar Electric Co. (Michael and Lumarie Strickland), Cascade
PineRidge Products (Jenni Bryce), Great Falls