An energy-efficient structure, which is defined as using 50 percent less energy than a building built to the International Energy Conservation Code 2008, is the first logical step toward reducing our buildings’ carbon footprints. When applying renewable-energy systems, or RES, to energy-efficient buildings, these systems can be a net-positive-energy generator. When sited properly, wind RES can be more productive and provide a better return on investment than current solar technologies. Small wind systems in the urban environment are the fastest- growing RES market globally because of exploding changes in wind-turbine technology, applications, and development of hybrid systems that combine wind and solar-power generation.
Despite wind power’s growth, building owners and consumers often view RES equipment with a “purchase it, install it and operate it” mentality, which leads to confusion, unproductive equipment and financial woes. Thorough research before installing small wind systems can make them a smart option for the urban environment.
TALKING ABOUT WIND
There are two standard wind-turbine technologies used on individual buildings in the urban environment.
Horizontal-axis turbines are the standard, propeller-type wind turbine. Direct, steady winds are a system requirement. Horizontal-axis turbines can suffer from vibration, noise, and bird and bat strikes caused directly or indirectly by the pressure wave generated by the propeller blade. In urban settings, these issues are not easily mitigated because of population density. Most zoning codes
require roof- or pole-mounted wind-turbine equipments’ noise coefficients to be equal to or less than the noise coefficient of an air-conditioning condenser, which is far less than a horizontal-axis turbine noise coefficient when operating. These turbines must spin a lot to create power, which is part of the reason for their noise coefficient. In addition, they often are mounted on the building edge, which can cause code and zoning issues.
Vertical-axis turbines have vertical blades revolving around a vertical axis. These systems have experienced rapid development in blade technology, increased energy generation because of their ability to operate with omni-directional winds, as well as reduced vibration and noise coefficient based on wing and shaft alignment. Vertical-axis wind turbines represent the fastest- growing technology in the small wind-power market. These systems are being used in many urban applications, including charging batteries for street lighting and pocket power plants on high-rise buildings. Most turbine equipment available today is mounted on a standalone pole. When equipment is building mounted, installers must consider whether the building has a light-framed or castin- place-concrete roof to determine whether additional support is required. On a building, turbines are mounted on a structural-steel support that looks like an H frame; more than one turbine can be mounted to this structure. The H frame includes the base plate of the turbine pole and holds the turbine head at the maximum height allowed by zoning and/or building-code requirements.
COMPARING WIND PERFORMANCE
When comparing wind-turbine equipment, key performance considerations include the following:
Rated power—This is the maximum power the unit will generate at the rated wind speed. The higher the power at a lower wind speed, the better the turbine will perform.
Cut-in wind speed—This is the lowest wind speed at which the unit starts to produce electrical power; 1.8 to 2 meters per second is the lowest in the market at this time.
Rated wind speed—This is the highest wind speed at which the unit produces the rated power.
Field testing—A turbine is set up in the field and is monitored under actual wind and weather loads for a minimum of one year. Most manufacturers can supply power data from a one-year field test and some continue testing for longer than one year. Additionally, the test site will have several weath er stations mounted with in 500 feet (152 m) of the test unit to check wind speed and direction while collecting weather data that might influence turbine performance. A reliable manufacturer will have tested in a number of climate zones and conditions to develop an accurate power curve for its turbine. Wind study—Some manufacturers, most states and all federal incentives require a minimum of a one-year wind study at the location at which turbines are installed. Installers and energy-service companies can be hired to do a wind study and compare the data for accuracy with Washington, D.C.-based National Oceanic and Atmospheric Administration weather sites in the vicinity. The wind study will determine the average wind speed and direction at the site, as well as financial feasibility by comparing results to the field data of equipment. The wind study can be applied to a several-block area if all buildings are of similar heights. Most urban areas are not composed of buildings of a uniform height, which generates a wind differential that must be determined. Zoning and building codes vary and need to be addressed upfront when seeking a permit for a wind study to ensure the study equipment is placed in a location that will ensure accurate results.
American Wind Energy Association Approval—AWEA, Washington, D.C., continues to push for standardized labeling and testing of small-wind turbines and potential sites. Wind- turbine manufacturers submit their field-test data to AWEA as proof of field-performance testing for labeling their turbine. Currently, it is difficult to compare wind-power systems to each other because of a lack of nationwide field-test data of wind-system performance and weather conditions. (To learn more about third-party certification of wind-turbine equipment, see “Certifying Small Wind Turbine Performance,” page 72.)
Hybrid solar—An increasing percentage of vertical-axis wind-turbine manufacturers are incorporating solar panels into their designs as an additional renewable-energy source for power production. Solar thin film and panels can be used with several turbines on a rooftop to meet build- ing-code and zoning-setback requirements while not losing any renewable-energy production. These systems typically are dual metered based on their power production.
TESTING THE WIND
The following wind study is being completed by a large real-estate investment trust to develop an urban wind map for use in setting up several pocket power plants for building energy or to be sold to the grid as green energy.
A neighborhood in a major urban area is composed of 2-story single-family homes and 2- and 3-story rental buildings. The central downtown district runs north and south through the middle of the neighborhood for 12 blocks and is composed of 5- to 8-story buildings. According to NOAA data, the prevailing winds in North America are west to east with an average wind speed of 8 mph (3.6 m/s).
Weather stations that monitor wind speed, direction, temperature and precipitation were set up four blocks west of the central downtown corridor on 2- and 3-story rooftops; on the west and east side of the main business street on select 5- to 8-story rooftops; and two-, four- and six-blocks east of the downtown corridor on 2- and 3-story rooftops. Data was collected from the weather stations every two weeks and then aggregated for one year.
The study results determined that four blocks west of the central downtown district, average wind speed is 7 1/2 mph (3.7 m/s). The west side of the downtown district has a 14 7/10 mph (6.6 m/s) AWS while the east side has an AWS of 8 3/5 mph (3.8 m/s). The AWS two blocks east of downtown is 3 1/2 mph (1.6 m/s), four blocks east of downtown has an AWS of 10 1/5 mph (4.7 m/s) and six blocks east of downtown AWS is 8 1/5 mph (3.7 m/s). Wind directions from the reporting stations were omni-directional.
Based on architectural and structural factors of the built environment, three considerations determined what wind equipment ultimately was purchased for the buildings. The buildings that were 4 stories or less in height had light-framed roofs, which required structural-steel H frames from parapet wall to parapet wall to support the loads of the vertical-axis wind equipment. Buildings that were 5 stories or more in height were cast-in-place-concrete structures that used structural steel that wasn’t required to span parapet walls to support the vertical-axis equipment. Zoning requirements for both building types controlled where the turbines could be mounted on the buildings’ roofs.
The west side of the central downtown district has the highest average wind potential in this study. The consultant responsible for the wind study cross referenced several power curves for equipment and selected a vertical-axis turbine that will generate 350 watts at an average wind speed of 14 7/10 mph (6.6 m/s). The rated power for this turbine is 1.8 kW; on windy days the power output would increase. Calculation: [(350W)24 hours per day] x 365 days = 3,066 kilowatt hours per year per turbine
Primary, or source, energy is the amount of energy it takes to deliver energy to a site. It is much higher than site energy because of production and transmission losses. In the example, one turbine produces 3,066 kWh per year. The primary- energy coefficient is 2.7 kWh/kWh, according to the Washington-based U.S. Department of Energy and Sacramento-based California Energy Commission’s Calculation of Source Energy. Calculation: 3,066 kWh per year x 2.7 kWh/kWh = 8,278.2 kWh per year of saved primary energy
Carbon credits are generated by saving primary energy and generating renewable energy on-site. To calculate the carbon credits generated by one turbine, add primary energy saved to energy produced from the turbine, which equals total energy. Calculation: 8,278.2 kWh per year + 3,066 kWh per year = 11,344.2 kWh per year.
One turbine would save 0.68 kg/kWh of CO2, which is a DOE constant for CO2 per kWh of power-plant-generated energy. Calculation: 0.68 kg/kWh x 11,344.2 kWh per year x 1 metric ton/1000 kg = 7.714 metric tons of CO2 saved per turbine
The cost of 1 metric ton of CO2 is $30, according to the 2008 global average at www.carbon-cred it-trading.com/index.html. This could generate an annual carbon-credit income of $231.42 per turbine per year. The credits currently can be certified and traded in the European Union and Asia. If the turbine life is 20 years, it would generate y $4,628.40 in carbon credits during its life.
EMBRACING THE WIND
An energy-efficient structure is the first priority before thinking about any RES. Review local zoning, building and grid-interconnection codes and requirements for the project location to determine feasibility of RES. A wind study to determine the site wind profile will be required for at least one year before grants are awarded. Select a consultant that has aggregated wind data and can cross reference your results for accuracy. Use the AWEA guidelines for field testing of wind-turbine equipment. Ask for supporting documents of the field testing, such as power data curves from windtunnel testing compared to field data, as well as testing length and climate zones. Compare your site wind potential to current wind-turbine equipment to select a turbine that maximizes your power production for the site wind profile. Compare wind-turbine warranty and maintenance requirements. Choose a certified installer, RES provider, ESCO, and architecture and/or engineering firm that specializes in RES to ensure the wind-turbine installation follows all codes, permit and connection requirements. Once these steps have been taken, you will maximize the likelihood of installing a productive, economically feasible wind-power system for a building with a minimal carbon footprint.
GREG T. BLUE is chief operating officer of Synergy Viridis LLC, Chicago. He can be reached at greg@syn ergyviridis.com or (630) 341-1690. George D. Sullivan is chief executive officer and principal of Eco Smart Building PC, Chicago. He can be reached at gds@ ecosmartbuilding.com or (773) 230-4462.
[ COST BREAKDOWN ] The cost of a weather station typically is $500 to $2,000 for installation and permits. A wind study to collect and review data from a site typically is $800 to $1,000 per month; cost is minimized if the wind-study data automatically is uploaded to a weather-station-instrument Web site where it can be downloaded and reviewed by the consultant. The return on investment of the turbine is dependent on the power generation, which is dependent on the equipment selected for the wind profile of the site. Turbine and installation costs vary widely depending on equipment.