Why are wind turbines being switched off?

WHY ARE WIND TURBINES BEING SWITCHED OFF?

POWER TRANSMISSION IS JUST AS IMPORTANT AS GENERATION

UK windfarms hit an all-time high in wind power last year, generating more than 80 thousand gigawatt hours (GWh) and enough power for over 22 million homes. Yet, reports also came out of wind turbines being switched off due to overcapacity — at the expense of customers.

Despite reaching impressive milestones in recent years, there’s a massive problem with the renewable — and particularly wind sector — power wastage. In 2022, it was reported that Brits paid millions to switch off wind turbines as networks were unable to deal with the levels of power generated.

The UK has set ambitious goals for renewable energy sources for the next few years, aiming for a more sustainable approach while reducing dependency on both fossil fuels and external suppliers. As the past 18 months or so have highlighted, the volatility of global markets means it’s essential that the country is able to secure its own energy supply.

Fortunately, the UK does have the natural resources to do so. With the greatest wind energy potential in Europe, it’s clear why wind power has been a preferred route for planners and developers to take. So why are wind turbines still being switched off, and why is this energy being wasted?

DISTANCE FROM THE GRID

Offshore wind farms are often a significant distance from the Grid. Typically, these farms are connected to the Grid with a specialist, individual cable connection through a converter and into the transmission network, allowing the farm to distribute power.

The issue with this setup is that the offshore system will typically have fewer connections readily available than an equivalent farm on land. Because of this, there are less options available when it comes to distributing power during surges or when there are problems with the on-land network.

DISTANCE FROM DEMAND

Furthermore, many of these wind farm installations are being built in remote areas of Scotland or in the North Sea, where winds are stronger. Though this is certainly positive when it comes to power generation, the issue is that the local area isn’t where the demand is.

More power is needed in the south of the country, far from where the electricity is being generated. And while the transmission networks can transport electricity great distances, without efficient connections and cable routes a lot of power can be lost before it reaches crucial areas.

A FOCUS ON INFRASTRUCTURE

It’s clear from these issues that improving power infrastructure is just as vital as delivering new power generation projects. Reassuringly, there are developments underway to address these issues. One such example is the ‘Eastern Green Link 2’ (EGL2), which involves the manufacture and installation of a high voltage direct current (HVDC) subsea cable from Peterhead in the North of Scotland down to Drax in Yorkshire.

A crucial element of these power transmission systems is the host of resistors within that help to facilitate the safe movement of electricity. Pre-insertion resistors, for example, can absorb and control transient magnetising currents within transformers throughout the network. This control helps keep voltages consistent with minimal dips, reducing potential disturbances for users of the power network. They can also help mitigate against temporary overvoltages, such as those caused by exceptionally strong winds.

Discharge resistors are another vital component, particularly in terms of safety. These can reduce the risk of sudden overvoltages from capacitors and inductors that have become isolated from their networks or in situations where an emergency shutdown is required. In offshore farms that are far from other connections, the inclusion of discharge resistors is essential in having a sufficient ability to remove excess electricity when required.

Implementing resistor technologies as new projects are built helps both to ensure safety from dangerous overvoltages, as well as safeguard electricity on the Grid from fluctuations and dips.

So, as the UK continues to invest heavily in the renewable energy sector, considering how we’ll transport this energy will be just as important as thinking about how we will generate it in the first place. With projects like EGL2 on the horizon, it’s clear that the industry is taking the right steps to secure a reliable network from the turbine all the way to our homes.

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COP 26

COP26 round up: the path to coal-free

Clean energy future and resistors role

INDUSTRY’S NEXT STEPS TO A CLEAN ENERGY FUTUREI

The COVID-19 pandemic has shown the world how quickly global threats can take over, making this years’ Conference of the Parties (COP), COP26, the most imperative yet. As the world’s leaders debated how to limit climate change, phasing out coal power became a vital discussion point. Here Simone Bruckner, managing director Cressall, explores the energy goals made at COP26 and the technology that can help achieve them.

From the UK going coal-free for two months in 2020 to Venice’s canals clearing of pollution, restrictions during the COVID-19 pandemic had several positive effects on the environment. While these consequences were cause for short-term celebration, the pandemic highlighted the significant impact normal lifestyles and industrial operations have on our planet. 

In addition, despite temporary reductions in greenhouse gas emissions during the pandemic, the United Nations (UN) United in Science 2021 report found that their concentration in the atmosphere continues to rise. Alarmingly, the report also concluded that there’s a 40 per cent chance that average temperatures in one of the next five years will be 1.5 degrees Celsius warmer than pre-industrial times.

IMPORTANT TARGETS

It’s clear that, while much of the world’s operations paused during the pandemic, climate change continued. This placed particular importance on COP26, with some viewing it as the last chance to save the planet from climate disaster. The resulting COP26 agreement calls for countries to accelerate the phasing out of coal and subsidies for fossil fuels. This is a world first, as previous UN climate agreements have not specifically mentioned fossil fuels. 

In pledges made at COP26, more than 40 countries committed to transitioning away from coal. In order to phase out coal power, countries must increase the proportion of clean energy in their networks. This will not only require scaling up of renewable projects, but also incorporating technology that increases their efficiency.

RELYING ON RENEWABLES

For instance, solar tracking can increase the efficiency of solar panels by using motorised systems to move the panels so that they are always in direct alignment with the sun. This increases efficiency by overcoming a common issue seen with solar panels, where their power generation peaks at midday. 

Incorporating a solar tracking system can increase average solar panel power output by 35 per cent, and high efficiency can be further ensured by incorporating a dynamic braking resistor. In the motorised system, a dynamic braking resistor can be installed to dissipate the excess voltage of a decelerating motor. This makes sure that the motor doesn’t overshoot, which would cause the panel to land in a sub-optimal position.

Another renewable energy system that can benefit from additional technology is wind turbines. The majority of wind turbines use a doubly fed induction generator (DFIG), which enables them to operate at variable speeds. However, in exceptionally high winds, the rotor speed of a DFIG can exceed the maximum operating range of the system. This in turn can lead to high voltages that destroy elements of the system.

To avoid this issue and ensure high efficiency of the wind turbine system, a crowbar resistor can be fitted to the DFIG. Connected to the rotor windings of a DFIG, a crowbar resistor can prevent damage to the generator by disconnecting the converter when the rotor speed reaches its limit. 

RESISTORS TO THE RESCUE

With over 100 years’ experience in electrical engineering, Cressall is a trusted supplier of resistors to the renewable energy industry. For instance, our crowbar resistors for wind turbines can withstand high currents while remaining operational. In addition, our braking resistors for solar panels have no wearing components, so last as long as the panels themselves.

A commitment to phasing out coal power was a key outcome of COP26, and countries must increase their reliance on renewable energy if society is to bid farewell to fossil fuels. However, incorporating more clean energy into the network requires not only scaling up installation projects, but also taking advantage of advanced technology that can increase the efficiency of power generation. 

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Powering a coal-free future

IS THE UK’S COAL-FREE HIATUS HERE TO STAY?

Britain passed a significant landmark in June 2020, as the nation went for two months without burning coal to generate power. A decade ago, around 40 per cent of the UK’s electricity came from coal and, while the recent plummet in demand accounts for some of the success, it isn’t the full story. Simone Bruckner managing director of Cressall, explains why the country no longer depends on burning coal that has, for so long, been the backbone of Britain’s power.

Britain’s new coal-free period has smashed the previous record from June 2019, which lasted for 18 days, six hours and ten minutes. While that hiatus was caused by the unprecedented shutdown of many of the National Grid’s coal-fired power plants, the disruptions in 2020 have been even more remarkable. They are, however, by no means the sole contributor to coal’s decline.

RENEWABLES ON THE RISE

Two examples illustrate the recent changes in Britain’s power network. Ten years ago, wind and solar energy made up a meagre three per cent of the country’s power mix. Compare this to the first six months of 2020, where renewables were responsible for a significant 37 per cent of electricity supplied to the network — this outstripped fossil fuels by two per cent.

Secondly, a company that has historically been one of the biggest players in coal power appears to be moving on from its history. Drax, the UK’s largest power plant, was once the biggest consumer of coal in the UK. Now, the plant is making the switch to compressed wood pellets with the goal of phasing-out coal entirely by March 2021.

While some environmental activists still question the efficiency of burning wood, which still produces carbon emissions in its own right, this change would leave the UK with just three coal-powered plants.

WINDS OF CHANGE

There is one major reason why Britain’s 2020 shift away from coal power will have more longevity than a passing trend. That’s because renewable technology is far more sophisticated than it was ten years ago.

Renewable energy has undergone a massive scale-up in recent years. This is largely as a result of the Paris Climate Agreement, but also because new technologies have made it more possible for renewables to outshine fossil fuels.

In solar panel developments, for instance, research into capturing and using waste heat emitted by solar panels could help to reduce solar costs even more, while doubling the efficiency of solar cells. Photovoltaic tracking panels have also become increasingly popular, which use tracking systems to tilt and shift the angle of the panel as the day goes by to best match the sun’s position.

Wind turbines are much larger nowadays. One example is the 9.6 mega Watt (MW) turbine from Danish producer, MHI Vestas, that alone is able to power more than 8,000 homes. Power storage is increasingly possible, and many companies have partnered with battery producers to store extra power so it can be used on less windy days.

KEEPING TECHNOLOGY TURNING

As renewable resources grow in sophistication, it is vital that other systems also keep pace in order to effectively manage the power they create. 

For example, wind turbines are typically connected to the distribution network through step-up transformers. When energised by high inrush currents, these transformers can experience overvoltage on the distribution network. This can potentially damage equipment.

Overvoltage issues can be remedied by using technologies like pre-insertion resistors (PIRs). PIRs, such as those offered by Cressall, are a three-phase resistor with a high thermal mass that allows them to absorb energy from high inrushes, while still being compact enough to fit efficiently in a transformer substation. 

Resistor technologies can also help manage power in solar panels. One example is electric motors that help solar panels move to “track” the position of the sun. These motors can be fitted with braking resistors to ensure that the panels stop at the optimum angle when tracking the sun for maximum efficiency.

Braking resistors can also be used on wind turbines, particularly on fixed-speed winder generators where sudden changes in wind speed can have a detrimental impact on the stability of the system. By inserting a dynamic braking resistor in series with the generator circuit, designers can help the system to dissipate the excess power created by stronger winds, before it has chance to damage the entire system.

The UK’s current coal-free reign may not last forever — at least not yet — but the pause from burning fossil fuels certainly marks a brighter future. As renewable resources form an increasing part of our energy mix, it will be ever more essential to ensure that the technologies which power them, and those that manage the power, support the nation’s net zero goal.

For more information on Cressall’s resistor technologies for renewables, click here

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Futureproofing tidal power

FURURE PROOFING TIDAL POWER

HOW TECHNOLOGY CAN HELP TIDAL POWER TO REALISE ITS POTENTIAL

The UK Government estimates that tidal energy could meet around 20 per cent of the country’s electricity demands. Considering the UK is an island and entirely surrounded by water, this comes as no surprise. Despite this fortunate position, uptake of tidal power has been slow. How should we encourage the development of this promising resource?

Tidal power functions in a similar way to wind power. Tidal turbines are placed underwater where the change in tide from high to low and low to high turns the blades to produce electricity. Tidal power is more reliable than solar or wind because we can easily predict the movement of the tides, which is determined by the Moon.

However, tidal power comes with extremely high upfront costs. To make the resource more feasible, its technology needs to deliver a high performance, allowing this cost to be recovered more quickly and making tidal power more appealing.

BIOFOULING PROTECTION

Biofouling occurs when plants and animals attach themselves to underwater constructions as often seen on the hulls of ships. However, biofouling also alters the hydrodynamics of submerged tidal turbines, presenting a productivity problem.

The biofouling organisms attach themselves to the surface of turbine blades making them rougher, which increases losses due to friction and therefore reduces the efficiency of the turbine. This, in turn, will lower tidal power’s performance and make it less cost-efficient.

Antifouling methods, such as a non-toxic coating with a low friction, can prevent organisms from attaching to surfaces whilst avoiding damage to surrounding marine life. These coatings are currently used in the shipping industry, but we must explore their applications in tidal power to reduce maintenance costs and improve efficiency.

CALMING THE STORM

Protecting submerged turbines from their marine co-habitants isn’t the only step tidal power plants should take. Sudden changes in water flow can be equally challenging for tidal turbines. Although the time between high and low tide is consistent, the distance between them, known as tidal range, is not. The tides are determined by the Moon and the Sun, and in some circumstances, extreme tidal forces such as spring tides can occur.

Tidal turbines need to be able to cope with these forces, as well as any unexpected and extreme weather conditions. By placing a dynamic braking resistor (DBR) in the generation and control circuit, can protect against any excess power generated by strong currents can be safely dissipated. The turbine system will therefore be less prone to damage, increasing its performance capacity and decreasing the chance of regular repairs.

The use of Cressall’s EV2 advanced, water-cooled resistor, which is suitable for low and medium voltage applications. The range is modular, so multiple resistors can be combined to handle power outputs up to one Megawatt. The EV2 also boasts an IP56 ingress protection rating, making it able to withstand harsh marine environments and suitable for the tidal turbine application.

BLADE DEVELOPMENT

Location also plays a major role in tidal electricity generation, with generator requirements including the need for a flow speed greater than two metres per second. Locations that can offer this are limited, which is one of the reasons for tidal power’s slow uptake. In the UK, only the north coast consistently meets this requirement.

Turbine blades with a high tip-speed ratio are slimmer and produce less drag. With less drag, the turbines can achieve a larger number of rotations at a lower speed. Through the development of blades that can operate at lower flow speeds, the number of sites at which tidal power can operate can increase, making it a more viable option.

Expensive installation costs cannot be avoided when increasing tidal power. However, by investing in technological developments that ensure less maintenance, higher efficiency and increased site suitability, tidal power can realise its potential and increase the prevalence of renewables globally.

For more information on Cressall’s tidal resistor technologies click here

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