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Small wind systems usually make electricity that is used in the home, farm, or ranch. Therefore, it may help to understand how electricity is consumed (or used). First, let’s explore the terms power and energy.
Electricity is used each time you turn on an electrical device. Most devices measure power in “watts.” Usually, power refers to an instantaneous measure, where energy refers to power produced over time. A “watt” is a term for power and a “watt-hour” is a term for energy. A light bulb with a 100-watt power rating will use the energy of 100-watthours if it is turned on for one hour.
A kilowatt is 1,000 watts. In most homes, electricity comes from an electrical utility. The amount of energy used by a customer of the utility is tracked on an electrical meter (also called a kilowatt-hour meter). It records the energy (kilowatt hours) used during a billing period and the customer is billed for that amount. In 2008, the average kilowatt hours consumed by homes in Montana was 843 kilowatt hours per month (887 in Wyoming), or 10,116 kilowatt hours in the year (10,644 in Wyoming).
In small wind systems, the turbine may be described by its power, or kilowatts, but the actual energy generation is measured in kilowatt-hours. In small wind, the terms power and energy often are used interchangeably.
There is no common definition of “small” wind. Grid-connected home systems are typically three to 10 kilowatts. “Small” is usually defined by the electric utility. Most utilities limit the size of wind turbine that they will allow to “net meter.” In Montana, most utilities define small wind as less than 50 kilowatts rated power, while in Wyoming state law specifies systems less than 25 kilowatts rated power. Check with your electric utility to find out how “small wind” is defined in your area.
A small wind system that is connected to a home or business but not to an electric utility is called an “off-grid” system. Off-grid systems are common when it is very expensive to connect to the electric utility, often due to a remote location. Off-grid systems are more complex because of the system design and require batteries to store energy. Off-grid systems require consideration of total electrical usage of the home, battery systems, and alternative (back-up) generation. Consult with a qualified system designer when evaluating an off-grid system.
Most small wind turbines are designed to use “net metering.” Net metering is offered by utilities so people can connect their wind turbines to the electric utility. (In some states, net metering and interconnecting your generator to the utility are managed as two separate processes.) Many homeowners opt to remain connected to the utility because the small wind generator may not supply all of the electrical energy for the home. Remaining connected to the utility allows the home to have electricity supplied from the utility that supplements production from the wind turbine. The amount of energy used is tracked on a special electrical meter. When the wind turbine produces more electricity than the home or business is consuming, the meter spins backward. At the end of a billing period, the customer pays the “net” amount to the utility. The “net” is the difference between the amount of utility energy used and the amount of small wind energy produced. Net metering is for off-setting energy use. It is not meant to generate income, only to credit you for the energy you produce.
The first step in buying a small wind system is to determine your electrical usage. Contact your local utility and ask for a 12-month electrical usage history (in kilowatt-hours) for your home. Some utilities provide this history online or in your monthly statements. You will also need to find the cost per kilowatt hour. When you have your energy information for one year, fill out the table below to calculate the number of kilowatt hours used and the average cost per kilowatt-hour for the 12-month period.
The local utility can provide estimates based on energy usage for similar homes in the area if you are planning new construction or an off-grid system.
Remember: Make sure that energy efficiency measures have been taken before adding renewable energy systems!
Evaluate your utility statement to understand how your wind system will change your bill. This list provides a few common mistakes:
US Department of Energy. (2011, March). State Energy Database. Retrieved April 12, 2011, from EIA Consumption Price and Expenditures Estimates: http://www.eia.doe.gov/states/_seds.html