Selecting a Small Wind Turbine for the South African Antarctic Research Base SANAE IV

Transcription

1 Selecting a Small Wind Turbine for the South African Antarctic Research Base SANAE IV Johan Stander (e: jstander@sun.ac.za) Stellenbosch University Department of Mechanical and Mechatronic Engineering ( Winter Wind Conference Sweden December

2 Outline Background Small wind turbine selection procedure Local climate Environmental considerations Selection criteria Wind turbine evaluation Small wind turbines proposed 10 m wind mast placed upwind from SANAE IV 2

3 Background SANAE IV and its Energy System South African National Antarctic Expedition IV (SANAE IV) base - managed by SANAP a DEAT sub-directorate km South of Cape Town, 230 km from the Antarctic coast - 80 (summer) and 10 (winter) occupants SANAE IV energy system - diesel-electric generator system consisting of three generators - power system annually converts L to: thermal: MWh th electrical: MWh e - power distributed via a well-balanced 380 VAC 3ø 50 Hz grid - eight-year averaged power demand: Power demands: summer mean = 126 kw e peak = 190 kw e winter mean = 120 kw e peak = 200 kw e Power demand frequency distribution 3

4 Background Why wind energy? 1. Fuelling power system (purchase, logistics, storage) - expensive about 1 million US$/a (May 2008) - wind power will result in diesel fuel savings reduced operation costs - improve base autonomy 2. Environmental protection and sustainability (1991 Madrid Protocol) - minimise the risk of potential fuel spills - reduce greenhouse gas emissions Ship-to-shore cargo transfers Total annual emissions (Taylor et al., 2002) 3. Compared to other sustainable energy options - Solar only marginal i.e. season dependent (Olivier et al., 2006) - Bio-waste feasibility yet to be investigated 4. Antarctica interior known for its extreme wind conditions - SANAE IV falls within a katabatic wind regime - strong highly directional winds at low heights The Discovery in 1902 (Anon., 1985) 5. Utilising wind energy in Antarctica is no novelty 1902: Captain Scott - wind turbine on board the Discovery 1960s: Small WECS power remote AWS (Steel et al., 1993) 2003: Antarctic research stations powered by WECSs 4

5 Background Why considering small wind turbines? Def: Small wind turbines rated capacity between 10 kw and 100 kw (SWIIS 2008) Feasibility of a single NW 100 kw e wind turbine investigated (Teetz et al., 2002) - costly relates to high financial risks - installation problematic a logistical nightmare too time and resource intensive Small wind turbines installation and operation: - parts, tools and wiring are highly transportable - no cranes required - minimal installation and commissioning time: vital in Antarctica - a large wind turbine has lower reliability than a cluster of smaller wind turbines Tested (summer) a 1 kw rated VAWT Small wind turbines have: - simple design can be maintained by a technician - fewer parts relates so less parts storage required Technological and experience - contribution to emerging South African small wind turbine industry Tested (summer) a 0.6 kw rated HAWT 5

6 Small wind turbine selection procedure 6

7 Local climate: Assessment standards Wind turbine and climate? Most commercial wind turbines are designed to operate and survive in normal climates (EN 61400:1-2005) Def: Cold climate a climate with a minimum temperature below -20 C for more than 1 h/day, for nine consecutive days per year, over a period of more than 10 years (Franke et al., 2005) Cold climates are further classified (Laakso et al., 2005) as: - low temperature dominated - dominated by snow/icing events - or both of the above 7

8 Local climate: Temperature Vesleskarvet temperature conditions Eight-year, hourly average temperature records captured by a standard AWS were analysed SANAE IV: - average winter and summer temperatures -23 ºC and -8 ºC - annual average temperature -16 ºC - temperatures below -37 ºC were measured Calculated averaged air density (ideal gas) variations range from 1.17 kg/m 3 to 1.40 kg/m 3 at 10 m AGL 8

9 Icing Local climate: Icing and Snow Icing observed at site glaze (summer) and rime Icing rates prediction models (Harstiveit (2000), Tammelin and Säntti (1998)) require: - humidity, cloud and temperature data No icing rates and occurrence were calculated due to: - inaccurate relative humidity data new methods are explored - lack of cloud data (e.g. cloud base height, type, occurrence) - annual occurrence not monitored Snow Snow drift a common phenomena sastrugi removal a costly operation Wind blown snow: - accumulates on and in exposed surfaces/structures - erodes structures exposed to snow-drift snow-blasting Eroded pole 9

10 Extreme wind conditions Local climate: Wind conditions Upper-air katabatic forcing mechanisms induce strong and highly directional wind conditions in lower surface atmospheric boundary layer (Bintanja, 2000) Eight-year, five minute average 10 m AGL wind speed frequency distribution indicates: - winds between 4 m/s and 25 m/s expected for h/a (84 %) - winds above 25 m/s expected for 290 h/a (3 %) Gusty wind conditions during which wind speeds of above 57 m/s at 10 m AGL were recorded Turbulence intensity was estimated at 8 % at 10 m/s, at 10 m AGL 10

11 Environmental Considerations Restricted areas - Micro reserves Vesleskarvet has geo-science, space science and bio-science micro reserves Geo-science and bio-science reserves (snow-rocky region) no drilling or excavation allowed Space science reserve have antennae arrays area declared as magnetic-quiet region Grid connection constraints All exterior electrical cabling above ground the use of existing power transmission lines required Wind turbine power controller grid coupling: 380 VAC, 3-ph at 50 Hz Sastrugi and access routes Wind turbine siting site accessible all year round, wind turbine sastrugi minimal impact of activities Ice shedding and blade throw Icing conditions may result to ice shedding hence a safety hazard Extreme wind conditions may occasionally exceed wind turbine survival wind speed blade or tower failure As a first estimate, models defined by Seifert et al. (2003) were used in ice shedding distance predictions 11

12 Wind Turbine Selection Criteria Some criteria derived from climate study Low temperature: minimise the use of lubricant dependent (viscosity), flexible (impermeability), thermoplastic and composite material components minimal components and component interfaces less tolerance related problems blades material with high impact resistance Icing and snow: passive de-icing methods must be used e.g. black smoothed blades blades with adequate leading edge erosion protection wind turbine structure design with minimal snow accumulation e.g. tubular tower without guide cables Extreme winds: free or passive yaw control ideal for highly directional winds rotor speed stall controlled wind turbine with survival wind speed above 60 m/s shorter than manufacturer-specific tower 12

13 Wind Turbine Selection Criteria Some criteria derived from environmental assessment Installation: Operation: wind turbine transport weight and size minimal limited space on ship and at base limited erection time, support equipment and access require a selferecting wind turbine rock-anchored pylon or ice-buried foundation options permanent-magnet generator and non-conductive blade materials to minimise potential EMI and RFI wind turbine electronics well insulated to eliminate the impact of static electricity 13

14 Wind turbine specific construction related evaluation Information supplied by manufacturer Wind turbine evaluation 14

15 Wind turbine specific operation related evaluation Information supplied by manufacturer Wind turbine evaluation 15

16 Wind turbine specific theoretical performance evaluation Information supplied by manufacturer Wind turbine evaluation 16

17 Small wind turbines proposed 1. PROVEN 6 kw rated (UK): Self-erecting 9 m galvanised, free-standing tubular tower Black blades, materials suited for temperature operation range: -40 C to +45 C Free yaw, furling i.e. stall controlled rotor Hub height survival wind speed of 70 m/s Estimated diesel fuel savings: 10 kl/a 2. BERGEY Excel-S 10 kw rated (USA): Self-erecting 9 m galvanised, free-standing tubular tower Black blades, materials suited for temperature operation range: -40 C to +60 C Passive yaw (tail vane), stall controlled rotor Hub height survival wind speed of 54 m/s Estimated diesel fuel savings: 14 kl/a 3. FORTIS Alizé 10 kw rated (NL): Self-erecting 18 m galvanised, free-standing tubular tower Black blades, materials suited for temperature operation range: -30 C to +50 C Passive yaw (tail vane), stall controlled rotor Hub height survival wind speed of 60 m/s Estimated diesel fuel savings: 11 kl/a

18 Thanks for your time The Antarctic Dream Catching the winds of change 18 Johan Stander 2008

19 References Anonymous 1985, Antarctica Great Stories from the Frozen Continent, Reader s Digest Publishers, United Kingdom Bintanja R. 2000, Mesoscale meteorological conditions in Dronning Maud Land, Antarctica, during summer: A qualitative analysis of forcing mechanisms, Journal of Applied Meteorology, Volume 39, pp Franke J.B., Freundenreich K., Gehlhaar T., Hausschildt M., Krutsschinna L., Muuss T., Schleesselmann R. and Woebbeking M. 2005, Certification of Wind Turbines for Extreme Temperatures, Germanischer Lloyd WindEnergie Technical Note 067 Revision 2, Hamburg, Germany Harstiviet K. 2000, Using routine meteorological data from airfields to produce a map for ice risk zones in Norway, A Norwegian Meteorological Institute paper Laakso T., Tallhaug L., Ronsten G., Horbaty R., Baring-Gould I., Lacroix A. and Peltola E. 2005, Wind Energy Projects in Cold Climates, An International Energy Agency Program for Research and Development on Wind Energy Conversion Systems paper Seifert H., Westerhellweg A. and Kröning J. 2003, Risk analysis of ice throw from wind turbines, Deutsches Windenerge-Institut GmbH (DEWI) paper, Wilhelmshaven, Germany Stanton C. 1994, The visaul impact and design of wind farms in the landscape, Wind Energy Conversion 1994, A British Wind Energy Association (BWEA) publication, pp Steel J.D. 1993, Alternative Energy Options for Antarctic Stations, Graduate Diploma Thesis, Institute of Antarctic and Southern Ocean Studies (IASOS), University of Tasmania, Tasmania Tammelin B. and Säntti K. 1998, Icing in Europe, 4 th BOREAS conference, Hetta, Finland Teetz H.W., Harms T.M. and Von Backström T.W. 2002, Assessment of the wind power potential at SANAE IV base, Antarctica: a technical and economical feasibility study, Renewable Energy, Volume 28, pp