Field Validation of a Hot-Air De-icing RetrofitWind turbine blade icing affects 65% of wind farms worldwide. Icing results in a reduction of power production, safety hazards for site workers and the public, and the potential for increased wear and tear on turbine components. Borealis Wind has created an after-market system which can remove and prevent ice accumulation on turbine blades. Borealis has designed an internal heating system which can be installed up-tower without the use of rope-access technicians or cranes within one week and without interrupting the night-time production of the turbine. The Borealis ice protection system circulates hot air inside the blade, targeting critical locations like the leading edge and end third.
By Daniela Roeper and Dylan Baxter, Borealis Wind, Canada
The performance of the Borealis ice protection system (IPS) and its effects on the turbine are being tested at a wind park in northern Ontario, Canada, and at various universities across North America. This report will outline the early stage results of these tests and field validation.
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The Borealis IPS is validated through two main streams: laboratory testing and in-turbine testing. Laboratory testing leverages the expert knowledge and resources of universities across North America to investigate the potential structural and thermal effects of the Borealis IPS on turbine blades. In-turbine testing has been done through the Borealis pilot programme at a wind farm in northern Ontario, Canada. With collaboration from the wind farm operators, Borealis has been able to monitor the internal blade temperatures with resistance temperature detectors (RTDs), air circulation performance with pressure sensors, turbine operation through SCADA, icing conditions from eye witness reports, and external blade temperatures with thermal imaging. The collected data is used to validate the in-house model which predicts the performance of the Borealis IPS in specific weather conditions.
The Borealis Ice Protection System
Inside the turbine blade, Borealis mounts a blower, a heater, a ducting system, and an array of sensors at key locations. All components are specifically designed so that they can easily be brought inside the blade of an assembled turbine and integrated into the existing electrical and physical restrictions of the blade. The end third of the blade is where ice accumulation most drastically impacts the power production, and the leading edge is where ice is most likely to accumulate. With this knowledge, Borealis created its patented product which allows the hot air to circulate to the very tip of the blade and focus the heated air to the leading edge. Figure 1 shows how a typical Borealis IPS might sit inside the turbine blade. RTDs and pressure sensors are located at the blowers, heaters, ducts and at the internal surface of the leading edge. These sensors allow Borealis to monitor the level of internal air circulation and to ensure that internal temperatures stay within a safe operating range.
Inside the turbine blade, Borealis mounts a blower, a heater, a ducting system, and an array of sensors at key locations. All components are specifically designed so that they can easily be brought inside the blade of an assembled turbine and integrated into the existing electrical and physical restrictions of the blade. The end third of the blade is where ice accumulation most drastically impacts the power production, and the leading edge is where ice is most likely to accumulate. With this knowledge, Borealis created its patented product which allows the hot air to circulate to the very tip of the blade and focus the heated air to the leading edge. Figure 1 shows how a typical Borealis IPS might sit inside the turbine blade. RTDs and pressure sensors are located at the blowers, heaters, ducts and at the internal surface of the leading edge. These sensors allow Borealis to monitor the level of internal air circulation and to ensure that internal temperatures stay within a safe operating range.
Modelled Versus Measured
Borealis has developed a model which is used to predict the performance of the IPS for specific weather conditions. This model has been validated with case studies completed in the spring of 2018. Internal temperatures were monitored by the Borealis sensors, and external temperatures were measured using thermal imaging. Figure 2 shows two thermal images of the external blade surface taken during separate run tests and the typical internal temperature distribution during start-up. Case 1 shows that with wind temperatures of −2.8°C and wind speeds averaging 3.0m/s, the Borealis IPS was able to achieve blade surface temperatures up to 21.2°C (±2) and averaging 18°C (±2). Case 2 shows that with wind temperatures of −7°C and wind speeds averaging 5.8m/s, the Borealis IPS was able to reach blade surface temperatures up to 13.6°C (±2) and averaging around 11°C (±2). Under these same conditions, the Borealis model predicted an average surface temperature of 17°C and 10°C for Cases 1 and 2, respectively.
Borealis has developed a model which is used to predict the performance of the IPS for specific weather conditions. This model has been validated with case studies completed in the spring of 2018. Internal temperatures were monitored by the Borealis sensors, and external temperatures were measured using thermal imaging. Figure 2 shows two thermal images of the external blade surface taken during separate run tests and the typical internal temperature distribution during start-up. Case 1 shows that with wind temperatures of −2.8°C and wind speeds averaging 3.0m/s, the Borealis IPS was able to achieve blade surface temperatures up to 21.2°C (±2) and averaging 18°C (±2). Case 2 shows that with wind temperatures of −7°C and wind speeds averaging 5.8m/s, the Borealis IPS was able to reach blade surface temperatures up to 13.6°C (±2) and averaging around 11°C (±2). Under these same conditions, the Borealis model predicted an average surface temperature of 17°C and 10°C for Cases 1 and 2, respectively.
Performance PredictionExtensive case studies and runtime data analyses are being completed on the icing events in winter 2018/2019. Early results have been used to provide the pilot wind farm with a weather envelope showing which conditions suit Borealis operations. The chart shown in Figure 3 is used as a guideline for the wind farm operator to determine whether de-icing or anti-icing modes should be used. De-icing, shown in yellow in Figure 3, refers to the scenario where the IPS is activated in a turbine which has accumulated ice and automatically stopped power production. Anti-icing, shown in green in Figure 3, refers to the scenario where a technician has identified a current or potential icing event and turned on the Borealis IPS pre-emptively. The pilot system discussed in this article was designed solely for de-icing purposes; however, it has shown potential to be a strong anti-icing solution as well.
Data Analysis Strategy
The most frequently requested metric used to evaluate the performance of the Borealis IPS is the per cent reclaimed production. To determine the portion of the power reclaimed due to de-icing or anti-icing, Borealis compares the test turbine with a control turbine. The test turbine is outfitted with the Borealis IPS, whereas the control turbine is the nearest and most similar turbine at the wind farm not outfitted with the Borealis IPS. Borealis carefully filtered IPS runtime information and production data from both the test and control turbines in order to determine the reclaimed production for two turbines. Turbine 1 reclaimed 30, 80 and 46% of lost production in November, December and January 2018, respectively. Turbine 2 reclaimed 19, 61 and 32% of lost production in November, December and January 2018, respectively. Site-level observations and runtime data show that there were predominantly anti-icing events in November and de-icing events in December. In total, 47% of production which would have been lost to icing was reclaimed for the two turbines during three months. Borealis is in early discussions with the National Renewable Energy Laboratory and Nergica to conduct third party data analyses on these pilot test results.
The most frequently requested metric used to evaluate the performance of the Borealis IPS is the per cent reclaimed production. To determine the portion of the power reclaimed due to de-icing or anti-icing, Borealis compares the test turbine with a control turbine. The test turbine is outfitted with the Borealis IPS, whereas the control turbine is the nearest and most similar turbine at the wind farm not outfitted with the Borealis IPS. Borealis carefully filtered IPS runtime information and production data from both the test and control turbines in order to determine the reclaimed production for two turbines. Turbine 1 reclaimed 30, 80 and 46% of lost production in November, December and January 2018, respectively. Turbine 2 reclaimed 19, 61 and 32% of lost production in November, December and January 2018, respectively. Site-level observations and runtime data show that there were predominantly anti-icing events in November and de-icing events in December. In total, 47% of production which would have been lost to icing was reclaimed for the two turbines during three months. Borealis is in early discussions with the National Renewable Energy Laboratory and Nergica to conduct third party data analyses on these pilot test results.
Icing Event Example
A specific icing event was investigated during the month of December 2018 to further understand the system performance. Figure 4 shows the actual power production of the test turbine in blue, the predicted power production of the test turbine in yellow, and the actual power production of the associated control turbine. A short icing event occurred in the final days of November causing both turbines to stop production. The Borealis IPS was able to successfully remove the ice and regain power production to the expected capacity. The weather conditions prevented the ice from melting naturally from the control turbine, which attempted to start production again throughout the week. It was not until the end of the week that the ice was naturally shed from the control turbine and normal power production could resume.
A specific icing event was investigated during the month of December 2018 to further understand the system performance. Figure 4 shows the actual power production of the test turbine in blue, the predicted power production of the test turbine in yellow, and the actual power production of the associated control turbine. A short icing event occurred in the final days of November causing both turbines to stop production. The Borealis IPS was able to successfully remove the ice and regain power production to the expected capacity. The weather conditions prevented the ice from melting naturally from the control turbine, which attempted to start production again throughout the week. It was not until the end of the week that the ice was naturally shed from the control turbine and normal power production could resume.
Lab TestingLaboratory testing has been done in-house at Borealis Wind, with the Composite Research Network (CRN) at the University of British Columbia and with the Advanced Structures and Composites Center (ASCC) at the University of Maine to determine the potential effects that the Borealis IPS might have on the structural integrity of the turbine blade. ASCC investigated the level of strain which is added to the turbine blade due to the weight of the Borealis IPS, whereas CRN investigated the level of strain due to the temperature gradients across the thickness of the turbine. Conclusions from the ASCC experiments on a 34-metre cantilevered blade show that Borealis components add less than 70µ when operational loads equivalent to 25rpm are induced. This is drastically less than 10% of the IEC 61400-23 strain limit of 3,000µ, which demonstrates that the Borealis IPS adds negligible mechanical strain. CRN has completed multiple thermal tests on blade samples, the results of which will be used in simulations to determine the thermally induced strain and cyclic loading.
Conclusion
The Borealis IPS is undergoing multiple streams of validation and testing during 2018/2019. Early results show that the IPS can predictably remove ice accumulation, has the potential to prevent ice accumulation, was able to reclaim 47% of production losses due to icing events during three months, and has an insignificant effect on the integrity of the turbine blade. Thermal tests and simulations are underway. The performance of the system for winter 2018/2019 will be analysed by Borealis Wind and third parties in the coming year.
The Borealis IPS is undergoing multiple streams of validation and testing during 2018/2019. Early results show that the IPS can predictably remove ice accumulation, has the potential to prevent ice accumulation, was able to reclaim 47% of production losses due to icing events during three months, and has an insignificant effect on the integrity of the turbine blade. Thermal tests and simulations are underway. The performance of the system for winter 2018/2019 will be analysed by Borealis Wind and third parties in the coming year.
Acknowledgements
Borealis Wind would like to thank all parties involved at ASCC and CRN, and Riley Doering from Borealis Wind, for their contribution to the information provided in this article.
Borealis Wind would like to thank all parties involved at ASCC and CRN, and Riley Doering from Borealis Wind, for their contribution to the information provided in this article.
Biography
Daniela Roeper is the CEO and Founder of Borealis Wind. She began building the company while completing her BASc in Mechanical Engineering at the University of British Columbia and has been in the renewable energy industry for eight years.
Daniela Roeper is the CEO and Founder of Borealis Wind. She began building the company while completing her BASc in Mechanical Engineering at the University of British Columbia and has been in the renewable energy industry for eight years.
Dylan Baxter is the Simulation and Mechanical Designer at Borealis Wind. He has obtained his BASc in Mechanical Engineering and conducted graduate level research for multiple universities in Canada and Germany pertaining to thermal, fluid and mechanical simulations.
