Power - Wind turbine - 150 kW - Isolated-grid / Canada

Case study assignment

You have been hired by a northern Canadian utility to prepare a preliminary feasibility study on their behalf. The utility wants to explore wind energy for its remote grid. This grid has base load generation by hydroelectric sources, with winter peak supply from diesel generators. The local grid peaks at 78 MW, and about 450 GWh are consumed annually. The firm wants to use a modestly sized, proven wind turbine. The Nordex N27 150 kW model is one possibility.

Among the challenges of the project are the steep and difficult access to the site, complicating transportation, construction, and power transmission, and the significant rime icing experienced in the area, which may cause losses approaching 10%.

Site information

The site is located in the community of Whitehorse, Yukon Territory, Canada, on the end of a low mountain ridge. The ridge reaches an elevation of nearly 2,000 m; the site is at roughly 1,400 m. The nearest location for which weather data is available is Whitehorse, YT; the weather station is in the valley below, at about 700 m, and the wind speed that would be measured on a 10 m tower at the site is estimated to be about 2.2 m/s higher than the station. There already exists a power line to the site, but it is too small for the power produced by the turbine, and must be upgraded. Being close to Whitehorse, the cost of travel and accommodation to the site is modest.

Financial information

Financial figures for the analysis are provided by the utility (inflation at 2.5%, debt ratio of 60%, debt interest rate of 8%, discount rate of 8%, and a debt term of 20 years). The utility is a government-owned corporation and therefore does not pay taxes. The project is expected to last for 25 years. The price for the energy from the wind turbine is compared to the system marginal price for diesel power in the winter, which is $0.10/kWh.

This is considered a research & development project, rather than a commercially viable project. It is still important to reduce costs and maximise benefits. The principal justification for the project will be the opportunity to learn about the operation and viability of wind energy in such a situation.

Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.

Solution

The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.

Teacher's notes

• This is clearly a research and demonstration project. It is not financially viable without consideration of the valuable information and experience gained during planning, installing, operating, monitoring and reporting. The high losses due to icing and remote grid failure detract from the financial viability of the project, but the critical factors are the high capital costs: installation, foundations, transportation, and maintenance.
• If this project is followed up with additional installations, and uses the knowledge gained from this project to enhance future ones, it should be possible to considerably improve the financial viability of wind energy in this particular community.
• In order to accurately calculate the energy produced by the wind turbine, the effect of the difference in altitude between the weather station and the site needs to be accounted for:
  • The temperature falls by roughly 6.5 ºC for every 1,000 m increase in altitude;
  • The atmospheric pressure falls with increasing altitude. Up to about 5,000 m altitude, the mean atmospheric pressure, P, at an altitude of z meters above sea level can be estimated by: P = Psealevel e (-z/8200) where Psealevel is the atmospheric pressure at sea level (i.e., 101.33 kPa).
• For a single turbine with a distribution line nearby, no substation is required - the turbine transformer is specified to match the distribution line voltage.
• It can be expected that major components such as the blades or the drivetrain will eventually fail and require replacement. A set of blades or a drivetrain costs roughly 20% to 25% of the purchase price of the turbine. This is accounted for as a periodic cost. Due to the research & development nature of this project and the harsh environment in which this turbine is installed, this periodic cost is incurred every 10 years - more frequently than normal.
• Because of the small size of the project (150 kW) relative to the grid peak load of 78,000 kW, it is assumed that all of the energy produced by the wind turbine will be used by the grid.

Real project

Results

In 1992 and 1993, the Yukon Energy Corporation, a government-owned utility of the Yukon Territory, Canada, went out for tender, purchased and installed a 150 kW Bonus wind turbine. It was installed on Haeckel Hill, a shoulder of Mt. Sumanik, at 1,430 m, about 750 m above the valley floor where the Territory's capital of Whitehorse is located.

The total project costs, not including pre-feasibility phases, was about $800,000. A track leading up the mountain to a fire lookout tower was upgraded to a road, and the existing single-phase power line was upgraded at a cost of $170,000 (included in the total amount).

The wind turbine has experienced significant icing events, and has proven to be a very important testing platform for icing mitigation technologies. The project is considered a success, and as a result Yukon Energy Corporation installed a 660 kW Vestas wind turbine in 2000, in order to assess the possibility of a utility scale windfarm on Mt. Sumanik.

System description

A Bonus 150 kW Mark III turbine was used, and the manufacturer, Bonus A/S of Denmark, was highly involved in the implementation of the project. The turbine was modified to include aftermarket leading edge blade heaters, heated wind monitoring sensors on the turbine (used for control purposes), and a tilt-up tower system (to avoid crane requirements). The low-voltage, 3-phase electricity generated by the turbine is transformed to 25 kV and delivered to the grid.

Lessons learned

• Research & development projects must be implemented efficiently, but need not be financially viable. The value of such projects is in what is learned, what they can and do lead to, and in the successes and failures that are monitored, reported, and analysed.
• Single turbine costs for remote grids are high, especially when the best sites are not close to the load. This is, in fact, very likely, since communities are not typically built in good wind sites, but rather close to shelter, water and transportation routes.
• Northern wind sites have additional challenges, in terms of severe weather conditions (such as rime icing), extended cold temperatures, available equipment and "logistics." In some communities in the far North, there may be only one annual delivery of goods - meaning project management for a wind facility must be at least 100% on time!
• There are many remote communities in Canada and other parts of the world that have significantly higher diesel fuel costs and/or higher wind speeds, than those found in Whitehorse. For many of the sites, wind energy is financially viable (see: http://www.retscreen.net/retpii_e/).

The big picture

Yukon Territory is growing, and will likely need more power in the future. One of the largest loads in the Territory is a mine that operates intermittently, requiring large amounts of energy when it operates and causing large surpluses when it does not. With high levels of environmental awareness in the Yukon, wind energy has good potential. Yukon Energy Corporation has conducted a number of wind energy resource studies, and has demonstrated a long-term commitment to examining wind energy. The Yukon government has instituted a Green Plan, and has committed to exploration of green power. It is likely that in the future, larger scale wind energy facilities will be installed and operated in the Yukon.

Photo

Wind turbines - Isolated-grid - Haeckel Hill , Yukon, Canada

References

• Edworthy, Jason, "Personal communication," Nor'wester Energy Systems Ltd., 2000.
• Maissan, John, "Adaptation of a Wind Turbine for Sub-Arctic Conditions with Severe Rime Icing", Proceedings of Canadian
• Wind Energy Association Conference, Kananaskis Country, Alberta, 1996, Pp. 152-161.
• Yukon Energy Corporation, Website: http://www.yec.yk.ca.
• Yukon Government, Website: http://www.gov.yk.ca.