Community Wind Handbook/Select the Final Design & System Specifications
Select the Final Design & System Specifications
One of the final steps in the installation of a small community wind system is selecting the turbine. When finally selecting your turbine size and model, it is important to conduct a performance assessment for each system you are interested in. It is essential to understand that a wind turbine's power rating is an incorrect metric to use when comparing different models. You should compare turbine models by looking at the number of kilowatt-hours of electricity the system will produce at your site per year. Comparing that number to the number of kilowatt-hours you use and the net metering policy of your utility will help in assessing which turbine will best suit your needs. To determine the annual energy output, you need to know the:
- Power curve for each turbine
- Average annual wind speed at your site
- Height of the tower that you plan to use
- Frequency distribution of the wind (an estimate of the number of hours that the wind will blow at each speed during an average year).
It is also recommended that you adjust the calculation for the elevation of your specific site. To conduct a preliminary estimate of the performance of a particular wind turbine, you can use the following formula:
AEO= 0.01328 D2 V3
- AEO = Annual energy output (kilowatt-hours/year)
- D = Rotor diameter, feet
- V = Annual average wind speed, miles-per hour (mph), at your site.
In terms of the actual system design, there are typically three types of small turbine configurations for a small wind turbine: self-commutated inverters, line-commutated inverters, and induction generators.
Self-commutated inverters, due to their own oscillators, need a reference from the utility grid to hold synchronization. When linked with a battery they may become part of an uninterrupted power supply, which is important in the event of a blackout.
Line-commutated inverters are actuated by utility line power and will cease to function during a blackout.
Induction generators produce grid-quality, constant-speed, AC power without the need for an inverter. An induction generator's output is regulated by the utility power; therefore if the grid blacks out, the generator will not produce output.
After researching your options for turbine size, model, and configuration type based on performance and project economic assessments, it is time to weigh the other characteristics that are important to you (certified or not, vertical-axis or horizontal-access) and finalize your turbine selection and project specific details (location, height, and site plan).