The development of a wind-diesel project can be a complex process, but with a wind resource identified, the first step of the process is already completed.
Initial Site Selection
The next step is to assess the land availability in conjunction with the wind resource map. The Alaska Wind Map can be downloaded from the AEA website. This map covers most of the State and can be used as an initial guideline of where to look, but it should not be considered completely accurate. Since the wind turbine needs to be connected to the existing grid and have good road access, sites close to the road, river, and/or power lines are preferred. Once several potential sites have been identified, they should be surveyed by a wind energy or wind resources assessment specialist. The sites should then be ranked based on a number of general criteria, such as:
- Likely wind resource (higher the better)
- Limited environmental impact
- Siting constraints including land availability, land cost, proximity to the airport, accessibility, and historical significance
- Proximity to the power plant and electrical distribution
- Geotechnical considerations
At www.awea.org more information on siting can be found.
Detailed Resource Assessment
Following identification of the most likely sites for wind turbines, an anemometer tower should be installed. Typically, the anemometers are installed at the planned wind turbine installation height. For most small to medium-sized communities a 30 m (~100 ft) anemometer tower should be sufficient. Larger communities may want to install taller towers. If there are multiple high quality sites that are not in close proximity, multiple anemometer towers may be needed. On their website, AEA has resource data for a large number of Alaskan communities, but in most locations site specific wind data collection should take place for a period of one year before project financing is obtained.
Detailed Load Assessment
The second key piece of data is the current and expected load for the community. This information can initially take the form of a daily total generation log. As the assessment process becomes more detailed, it will become important to have time series data representing a full year, in a minimum of one hour increments. This load data should take into account any new plans for the community, such as new buildings or services, as well as standard load growth. Generally speaking, load data should be collected at the power plant bus bar and should be an average reading as compared to a series of instantaneous measurements.
Other factors play into the decision to implement a wind-diesel power system. One important factor is the age and condition of the existing diesel plant. Wind is a variable resource, and if harnessed it needs to be combined with other base load generation technologies. In most remote Alaskan communities this means diesel generators. Diesel generators are specifically designed to provide power to a fluctuating load. They are a perfect match to the fluctuating power produced by a wind turbine.
As discussed in the section on wind penetration, if the amount of wind relative to the load, and thus the number of operating diesel engines, is small, then older diesel technology will be able to handle the inherent variability in the load and wind generation. As wind penetration increases, the controls of older diesels are not able to react as quickly as needed.
Additionally, the fuel performance of older diesels drops off more rapidly at lower loads. The efficiency of these diesels suffers as more energy is produced by the wind turbines. This limits the amount of diesel fuel that can be offset by the wind turbines. In contrast, modern fuel-injected diesel engines with electronic controls can maintain high efficiencies even at low load levels and should be employed for all higher wind penetration systems. It should be noted that the majority of diesel engines deployed in Alaska are fuel-injected with electronic controls that help to manage efficiency.
A second consideration is the overall age of the diesel powerhouse and associated switchgear and controls. As with any new energy project, integrating new equipment into an old power house is problematic, especially when this integration involves shutting down power to the community. In low penetration applications, the additional control panels and integration are probably not a significant concern, however, as the level of desired wind penetration increases, these integration and switchgear issues become more complicated. For this reason, if the intention is for wind energy to become a major supplier of energy to the community, thought must be given to the state of the diesel plant and to a complete replacement of the whole power system, diesel engines and all.
A community should also carefully consider the motivation behind moving to wind generation. Usually, the cost of energy is a key driver; however, this is only one of the issues to be studied. Other important issues are the environmental impact of energy generation, the price volatility of the ‘fuel’ used to create that energy, the security of the resource supply, as well as the personal feelings of community members. Ultimately, the purchase of new power generation equipment is a long-term commitment and may not result in near-term reductions in the cost of energy. While wind turbines themselves are not more complex in regards to maintenance and operations compared to diesel generators, the integration of wind turbines into a diesel system can add to the overall complexity of the the entire system. A strategy for ensuring long-term success must be developed beforehand.
While wind does not require fuel as a resource, the costs associated with installing a wind generation system are significant. Determining if the price of harnessing free energy makes sense is key to deciding how much wind, if any, to incorporate into a community’s power system.
Using the data collected it is possible to assess different power system configurations and different scenarios for load, fuel prices, wind penetration, and equipment cost. A software tool like the HOMER model produced by the National Renewable Energy Laboratory (NREL) is a good tool to conduct these initial assessments. Another available screening tool is RETScreen, developed by the Department of Natural Resources Canada. Both tools have their individual qualities that have been evaluated depending on the project needs in the early phases of assessment. It should be noted that as different options are assessed, care must be given to insure that all key parameters and system efficiencies are properly considered. Organizations like AEA or private consultants can assist with this analysis.
As the project develops, more detailed technical and economic assessments will be required. For example, if initial analysis indicates that 500 kW of wind energy is optimal, consideration of which turbines could be used would be based on the available land area. This, in turn, will better define the cost of the required infrastructure and turbine foundations, which can then be used to update the system cost calculations and performance modeling. At this stage, more detailed performance modeling using software such as the Hybrid2 model also developed through NREL, should be considered.
As with any development project in a community, environmental impact is expected and must be assessed. The installation of a wind turbine may impact birds, local wildlife and, fauna, directly or indirectly. These impacts can be clear and easily documented and mitigated; however, some impacts are more difficult to quantify.
Environmental impacts will be site specific, and a site environmental survey should be conducted at any location considering wind power generation. Depending on the source of funds, different levels of environmental impact study are required. The total environmental impacts of any project should be understood in relation to those of other energy options. Results of any environmental survey should be discussed openly so that all options to minimize these impacts are considered.