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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A transcontinental renewable network?

A TRANSCONTINENTAL RENEWABLE NETWORK?

HOW HIGH VOLTAGE DIRECT CURRENT TRANSMISSION COULD TRANSFORM POWER SUPPLY

The SuperSmart Grid (SSG) is a theoretical concept that involves the creation of a transcontinental electricity network connecting Europe, the Middle East and North Africa to deliver low cost, high capacity, low loss electricity. To support global efforts to decarbonise power generation, could the SSG become a reality?

The SSG is a fusion of a super grid, a wide-area, often transcontinental transmission network and a smart grid, which uses digital technology, such as smart meters, to react to fluctuations in energy demand.

By implementing this system across Europe, the Middle East and Africa, this geographical area could benefit from an entirely renewable energy supply, which in turn supports the United Nations’ Sustainable Development Goal Seven: ensure access to affordable, reliable, sustainable and modern energy for all.

Offshore wind farms and solar power are the two resources that offer great potential, given the large number of suitable sites for both systems throughout the region. Having identified potential energy resources, how can this energy be transmitted to meet demand over such a vast area?

DEVIATING FROM THE AC NORM

High voltage direct current (HVDC) uses direct current (DC) for most electrical power transmission. Although DC is less common than standard alternating current (AC) systems, it meets the demands of the SSG for a variety of reasons.

HVDC transmission is a proven method of achieving power transmission over very long distances. It would play a vital part of the SSG, since it allows power to be transmitted from areas where it is in abundance to areas experiencing a shortage, which would secure the energy supply across the entire region. It would also facilitate the use of offshore wind farms — whose natural location is so distant from areas of electricity demand that HVDC is essential to ensuring efficient transmission.

HVDC also allows power transmission between unsynchronised AC distribution systems. AC systems operate at a set frequency and if these frequencies are different, the systems cannot be connected. HVDC circuits do not have a frequency, eliminating this problem and allowing multiple circuits to be interconnected.

Most significantly, HVDC suffers lower electrical losses than AC transmission. It has a uniform current density throughout the line, so there is no skin effect as there is in AC circuits. Although the corona effect, which is an electrical discharge that appears around a charged conductor, is still generated in a HVDC system, it is considerably lower than in AC systems, facilitating more efficient electricity transmission across the vast area encompassed by the SuperSmart Grid.

CONVERTING BACK TO AC

HVDC is ideal for transmitting over long distances, but when transmitting electricity into the local AC transmission grid, the direct current must be switched back to alternating current using a converter system. All converters, including HVDC converters, generate harmonic distortion to some degree.

If harmonics are not controlled, they can wreak havoc with the transmission system, jeopardising power quality and increasing the chances of equipment malfunction and electrical losses on the line. Therefore, it is important to integrate harmonic filters into the HVDC converter stations to block these unwanted currents.

Harmonic filters allow current at the frequency of the AC network to pass through, while redirecting distorted harmonic currents into a harmonic filter resistor, where they are dissipated as heat. This ensures that the unwanted currents are safely removed from the transmission network in a controlled way, which helps to secure the power supply when converting from DC to AC.

Although the SuperSmart Grid is purely theoretical, it’s clear that the technology necessary to realise this concept already exists. With countries all over the region setting ambitious renewable energy targets, perhaps this could be the solution to providing a secure, sustainable power source across all three continents.

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Offshore wind

ADVANCING OFFSHORE WIND

HOW CAN WE EXPAND OFFSHORE WIND TO REACH 2030’S 40 GW TARGET?

The UK’s history is enriched with maritime activity. Surrounded by water from John o’ Groats to Lands’ End, the surrounding waters have played a pivotal role in trade, travel, and most recently, electricity production. Achieving the Government’s target of generating 40 gigawatts (GW) of offshore wind power every year by 2030 will require continued investment and development in power equipment.

Offshore wind power plays to the nation’s geographical strengths while also providing a clean energy source to fuel the country’s path to net zero. The North Sea’s high quality wind resources and relatively shallow water make it an ideal location for offshore wind farms. According to the International Renewable Energy Agency (IRENA), around 90 per cent of global offshore wind capacity is located in the North Sea, which is why the UK is already a world leader in this renewable power source.

However, to reach the Government’s 2030 production goal, energy suppliers must make advancements in wind turbine technology, while simultaneously considering how their generated power will be safely transferred to the grid.

IMPROVED TURBINE TECHNOLOGY

Turbines capable of producing more power per rotation are essential for the development of efficient offshore wind farms. One way of improving turbine efficiency is to increase the blade length.

An increased blade length means that stronger forces will act on the turbine, so the blade material needs to be appropriately chosen. To achieve an adequate stiffness-to-weight ratio to avoid deflection, carbon fibre or fibreglass blades are typically favoured. However, there is an expanding market for hybrid reinforcements, which combine the two materials together for optimum sturdiness.

Improvements in wind turbine technologies have already triggered a move into deeper waters to use sites with better wind resources. Static wind turbines are still restricted to waters at a maximum depth of 60 metres, so to upscale the UK’s wind power output, floating wind turbines will be essential.

MORE SUITABLE SITES

Once all viable sites within 60 metres of shore have been constructed, floating wind projects will become vital to offshore’s growth. Floating offshore wind farms, which can be located up to 80 kilometres (km) from land, could play a key role in the long-term decarbonisation of the power sector.


Floating wind turbines sit on a steel and concrete floating system instead of a fixed base, meaning they can be placed in a larger number of sites up to 200 metres deep. They can also be towed, allowing them to be relocated without much additional cost. This broadens the potential output that offshore wind could provide and brings it one step closer to the 40 GW target.

SECURED POWER SUPPLY

Like all renewable energy, offshore wind can be unpredictable and inconsistent, which can make grid connection challenging. In periods of high wind, large inrush currents occur, which can lead to overvoltages on the grid and subsequent equipment malfunctioning.

It’s important to prepare for these inevitable inrush currents by integrating technologies such as pre-insertion resistors (PIRs). Already in use across many of the UK’s windfarms, Cressall’s PIRs have a high thermal mass, which allows them to absorb excess energy produced by the inrush current and safely dissipate it as heat. This prevents damage to the grid and improves the reliability of offshore wind’s power supply.

Offshore wind holds great potential in the shift towards renewable energy and could be the key to decarbonising electricity generation. However, we must continue to advance critical power protection technologies to prevent any obstacles in its upscaling and to enable this powerful resource to flourish.

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