wind power
The ‘Cost’ of Wind by Eduardo Estelles
2020 was a record year for the global wind industry. With a 53 per cent year-on-year increase, the wind energy industry is set for continued growth in the next five years, despite the impact of the Covid-19 pandemic. With this growth, the spotlight is increasingly focused on safety. Most incidents in the life-cycle of a wind turbine occur during the construction and maintenance stage (rather than during operation). In terms of causality, research points to strong wind and lightning strikes. Without live weather data on site and at crane height during construction, the cost of wind - in terms of safety - is greatly underestimated. Accurate and continuous data is essential in programming and planning lifts, to allow immediate decisions to be made in good time. Access to this recorded data is also essential for claims should there be dispute.
Wind risk in construction
Building a wind turbine requires some of the largest lifting equipment in use today, handling components in excess of 80 tons to heights of over 90 meters (almost 300 feet). Gusts can start in seconds, exerting forces on a crane and any load suspended from it. Ground level measurements at the construction site do not reflect actual conditions at crane height, where wind speeds are considerably greater. Operators must calculate permissible wind speed based on accurate data. Let’s say an operator decides to stop work when the wind reaches 35mph for 30 percent of the day. The wind may be steadily below 30mph when a quick 40mph gust blows in enough to create a panic situation or, worse, an accident. The operator must account for allowable wind speed during rigging/ de‐rigging, which is invariably lower than the maximum in-service wind speed. Performing a lift without knowledge of the expected wind forces and the actual sail area of the load can lead to a failure of components
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and/or tipping of the crane, with potentially fatal consequences. In planning lifts, consideration must be given to: • Anticipated wind speeds from site and height specific forecasts • Different types of crane activity and the maximum wind speed for each • Weight of load, its geometric form, and its air drag factor • Sufficient margin to cover wind induced additional loading • Wind data accuracy to show 3‐second wind gust at the highest point of the boom system
How should wind speed be monitored?
It is not sufficient to rely solely on meteorological office data. Each crane must be fitted with anemometers or other windspeed monitoring devices. The sensor of the indicator should be positioned so that it can measure air flow uninterrupted by the crane or adjacent structures (often on the highest point of the crane). Devices located on other parts of the site will not give an accurate wind-speed. The display must be located in clear view of the crane operator. Live data and constant monitoring and alerts are essential, giving early warning of rising wind speeds and enabling the operator to act before the limiting wind speed is reached. Remote access to wind data by all key site personnel greatly improves the lines of communication. For example, considering the time it takes to lower/raise a crane boom, if a boom is left raised overnight and conditions change, speedy action must be taken.
What is the ‘cost’ of wind?
Strong winds pose significant risks and when an accident occurs, the cost to contractors is high. Direct costs to employers of accidents in construction have been calculated as £433.22 ($613.39) per employee per annum; a contractor with only 30 employees would be liable for direct costs of £12,996 ($18,400) per annum due to health and safety incidents. Often under-calculated are the indirect costs; the time to deal with the consequences of the accident, replacement staff, investigation, and corrective measures. These far outweigh direct costs by more than 2 to 1 (as a conservative estimate):
JULY• AUGUST2021 /// www.nacleanenergy.com
Direct costs due to an accident end up doubling in indirect costs.
Construction requires a continuous balance between safety and program. Winded off activities slow down work and increase costs; a typical 250-750 ton crane installed on site for wind turbine construction costs between £3,000 and £8,000 ($4247 and $11,327) per day.
