Dealing with severe weather

Whether a hurricane or flooding, the effects of climate change are being felt increasingly frequently. This also applies to companies like Enercon – a pioneer in wind energy technology that specialises in the development, manufacture, distribution and servicing of onshore wind turbines. “As a company, we’re no different to any other citizen, as climate change is affecting our daily lives, our actions and our business model,” explains Enercon Group spokesperson Felix Rehwald.

This also has a political dimension that influences Enercon’s business. “The ambitious targets set by politicians for the expansion of renewable energies, wind and onshore are leading to the designation of more new areas and to easier repowering. This, in turn, is boosting the wind industry and increasing our incoming orders,” he continues. “It’s an issue for our product development, too, as we might have to adapt the design or configuration of certain turbine types in the medium and long term.”

The company receives the data required for this from service providers, or it collects it – such as wind direction, strength, gust intensity, precipitation and humidity – via its own turbines. Enercon also takes wind and weather forecasts into account when planning new wind farm locations and then works with additional simulation tools and software to optimise the design of the wind farms to the local conditions.

A new lifting device is used to install the rotor blades. This device uses two propellers to grip the rotor blades and automatically holds them in position during the installation process.

Extreme winds are already being taken into account in standard safety tests

“Climate change has long since influenced wind farm planning,” Rehwald states. For example, stability tests in northern Germany are now set higher than was usual in the past due to extreme winds (gusts). “This is due to the increase in extreme wind events,” he emphasises. Consequently, the German Institute for Construction Technology’s (DIBt) wind zones have also shifted with the boundary of wind zone 4, which has the highest wind speed, now running further south than before. The certifiers have also adapted their guidelines accordingly.

However, climate change poses no new risks to existing facilities. “They’re generally designed to be robust and have the appropriate reserves,” says Rehwald. Plus, facility monitoring and control ensure that they are automatically throttled back during extreme weather.

All the company’s wind turbines are equipped with a storm control system as standard. “When the wind picks up, the turbine continuously regulates this by reducing the angle at which the rotor blades are set to the wind. This can go as far as the blades being fully retracted from the wind – referred to as the ‘feathered position’, where the rotor blades no longer experience any lift and the turbine only spins.”

The wind speed at which the turbine is down-regulated depends on its type. “For our new top model, the ‘E-175 EP5’, which has a rated output of 6 to
6.3 megawatts, the cut-out speed is 25 metres per second, for example,” explains Rehwald. “The extreme wind speed at hub height – a three-second gust – is 59.5 metres per second for this type of turbine.”

According to the company, quantifying how much the work of the service and project planning teams has increased due to more severe and frequent gales and strong wind events is not possible. What is certain, however, is that the increase in strong-wind days has not impacted the product portfolio, for example the size of the turbines. “We offer our customers products for all wind situations, i.e. for strong-wind locations, such as on the Mediterranean islands of Greece, for medium-wind locations such as in northern and central Germany, and for weak-wind locations in southern Germany,” Rehwald continues. Accordingly, the range of products, tower variants and hub heights are extensive.

More frequent storms put a considerable additional strain on the plant and challenge service and project planning teams.

Challenging difficult weather conditions

One thing is also clear – climate change is making installation planning more complex for the construction teams. “With more windy days during the installation phase, ‘wind windows’ with little wind or no wind at all have to be used very effectively in order to install wind-prone components, such as rotor blades, without delay,” Rehwald explains. After all, costs are still incurred if the weather prevents installation work from being carried out.

The wind speed up to which work can be carried out on the construction site depends on the type of work and the technology used, in particular the available crane technology. “Ultimately, it’s up to the on-site site manager to decide at what wind speed work must be stopped,” reports Rehwald.

Enercon relies on the use of new technologies on construction sites. “For example, a new lifting device is used to install the rotor blades. This device uses two propellers to grip the rotor blades and automatically holds them in position during the installation process,” Rehwald continues. These propellers can compensate for higher wind speeds and stabilise the rotor blades better than was previously possible using the guide ropes guided from the ground. This allows the rotor blades to be installed at wind speeds of up to ten metres per second – previously, the limit was usually eight metres per second.

Moreover, adapting to climate change is part of the company’s sustainability strategy. “We’re working on this strategy because climate change is real,” Rehwald explains. “We don’t just want to develop green products, but also use them in order to conserve the environment and resources as far as possible.” (cb)