The role of HVDC in energy transition

THE ROLE OF HVDC IN ENERGY TRANSITION

power transmission

With the rise of offshore windfarms and international grid links, effectively and efficiently transmitting electricity over long distances is more crucial than ever before.

Simone Bruckner, Managing Director of Cressall, explains the role of high voltage direct current (HVDC) and filter resistors in making long-distance energy transition possible.

The UK has four times more offshore windfarms in operation than in 2012, with the number set to rise significantly as the government looks to reach its goal of generating 50 gigawatts (GW) of offshore wind by 2030.

Along with this rise, international and intercontinental grid links have increased as the UK trades excess power with other countries, much of which is generated by renewable means. Trading the surplus not only saves energy, but also prevents Brits paying to turn off turbines when more energy is generated than the grid can take.

As the UK currently has 13.9GW offshore wind capacity compared to its 50GW goal, it is important that this output is used efficiently and energy loss is kept at a minimum. Although alternating current (AC) is standard in electrical power transmission, the current often concentrates near the conductor’s surface – known as the skin effect – which causes energy loss.

HOW HVDC HELPS

HVDC is a transmission system that uses direct current (DC) for the transfer of power over long distances. As remote offshore windfarms and the grid are often far apart, HVDC enables effective transmission due to its uniform current density throughout the line.

Additionally, HVDC supports the trading of excess power between unsynchronised AC distribution systems, which run at a set frequency and cannot be connected to those with a different frequency. As HVDC does not have a frequency, multiple circuits can be interconnected and converted to both system voltage and frequency levels of the system at point of use.

While HVDC is used for international grid links, it must be converted back to AC at the local grid level. However, converters create harmonic distortion, which in turn can cause lower efficiency, overheating and increased chance of equipment failure.

Therefore, harmonic filter resistors are a vital part of HVDC and SVC converter stations, helping to remove harmonics by dissipating them as heat. This ensures a safe and assured power supply for the UK and countries across the continent.

The UK’s rollout of offshore windfarms currently puts it among world leaders, and with the pipeline of projects close to 100GW, Britain could soon supply many countries with surplus energy. With the ever-increasing need for sustainable energy, HVDC ensures that countries across the world can safely and securely benefit from wind power.

Floating wind farms for the future

FLOATING WIND FARMS FOR THE FUTURE

pre-insertion resistors for turbines

ARE FLOATING WIND TURBINES THE ANSWER TO RENEWABLE POWER?

Back in 2019, then-Prime Minister Boris Johnson promised 40 GW of UK offshore wind power by 2030. In early 2022, the Government raised that target to 50 GW, with an additional five GW from floating wind turbines. But are floating wind farms the solution to existing offshore power problems?

Many of us will be familiar with the sight of wind turbines. After all, there are more than 10,000 of the structures on land and at sea in the UK. In terms of efficiency, offshore wind turbines often have more favourable wind conditions, producing more electricity per turbine than their onshore counterparts.

But traditional offshore wind turbines have their limitations. Traditional offshore turbines are built onto a large steel column, fixed into a concrete foundation on the seabed. These can only be installed in relatively shallow waters, up to depths of around 60m. Not only does this limit the potential areas for turbine installations, it also means that the turbines have less access to the stronger winds that are often found further out to sea.

FLOATING FARMS

To capitalise on the stronger winds further out, floating wind turbines can be built instead. These are turbines built on huge floats, anchored to the seabed with weighted subsea cables.

Operating in much deeper water, floating wind farms make use of vast areas that were previously considered not suitable for offshore wind power. Being further out to sea also means that turbines can be a lot larger in size than their counterparts, producing even more electricity per turbine.

Kincardine, the world’s largest floating wind farm based in Scotland, has five operational floating wind turbines. Three cylindrical floats arranged in a triangular formation support each turbine, and pipes between the floats allow liquid ballast to be pumped around the structure. In this manner, the weight of the turbine can be shifted to stabilise it in harsh conditions, as well as orientating it for the wind direction.

Are we on track to meet solar power targets?

ARE WE ON TRACK TO MEET SOLAR POWER TARGETS?

MAXIMISING EFFICIENCIES TO MEET RENEWABLE TARGETS

In April 2023, a report published by the House of Commons stated that, at the UK’s current pace of change, it will miss its target of decarbonising the power sector by 2035. As the UK fights to secure its energy supply, what progress is being made in the renewable sector, and what needs to change? In this article, Simone Bruckner, managing director of resistor manufacturer Cressall, explores.

More and more applications are going electric. Whether it’s the cars we drive or the heat pumps in our homes, rising electrification is putting more pressure on the grid. In fact, the UK’s electricity demand is expected to double by 2035.

60 per cent of our current electricity usage comes from low-carbon sources, which includes renewables and nuclear power. But within the next twelve years, renewables are expected to supply up to 90 per cent of the country’s power if we’re to meet decarbonisation targets. In real terms, this sets a target of around 150 GW of renewable energy. But this is a long way off our current capacity of just 40 GW.

Further efforts to secure the UK’s energy independence while meeting decarbonisation targets have resulted in additional goals. The British Energy Security Strategy has outlined a 50 GW target for offshore wind by 2030, as well as a 70 GW target for solar by 2035.

But with a current solar capacity of just 14 GW, is the UK on track to meet such targets?

DELVING INTO SOLAR

One of the biggest issues faced by those in the solar sector is obtaining planning permissions and approvals. Industry body Solar Energy UK reported back in 2021 that around 17 GW of new projects were in the planning pipeline, with just under 800 MW of new projects entering the pipeline each month. But typically only around 500 MW of capacity is added each year, much lower than the approximate 4.5 GW required to meet the Security Strategy’s 70 GW target.

In Sleaford, Lincolnshire, a 600 MW solar farm able to power 190,000 homes is currently undergoing consultation with local residents. Despite being in talks now, if the plans for the farm are approved, it’s not expected to start construction until at least 2026.

Another problem with solar power is efficiency. Solar panels tend to operate with efficiencies between 15 and 20 per cent, compared to between 30 and 50 per cent for wind. Evidently, there’s improvements to be made to the efficiency of solar power if the UK is to hit its targets. But what can be done?

SAFE, EFFECTIVE MAINTENANCE

Maintenance is a key factor in improving efficiency. Regular cleaning and inspection ensures that the solar panels are working properly. But there might be times when the solar panel needs to be disconnected for more extensive maintenance or repairs, presenting an electrical safety challenge.

While there is still sufficient light, the solar panel will continue to produce electricity. This electricity must be discharged so that the panel can be handled safely. This can be done using a load bank, which dissipates excess electricity to allow safe disconnection, installation, and maintenance of solar panels.

THE BENEFITS OF MOTORISATION

Ground-mounted solar panels have the advantage of space, compared to those fixed onto rooftops. This means that the panels can be tilted and moved with respect to the sun’s position in the sky. An electric drive system is used to move the panels, either along a pre-programmed path or using information obtained via solar radiation sensors.

Moving the solar panels helps to maximise their efficiency throughout the day, as well as accounting for minute changes in the sun’s position and trajectory throughout the seasons. In fact, these systems can increase the output of solar farms by up to 35 per cent.

Motorising solar panels requires electronics that can ensure they move precisely and safely. To achieve this, a dynamic braking resistor (DBR) can be used. A DBR dissipates the excess voltage generated by the motors as they decelerate. As a result, the panels stop exactly when required, resulting in a more accurate positioning.

Though these slight changes in positioning may only be minute, when multiplied across an entire solar farm, they represent a significant proportion of its overall output and efficiency.

Finding suitable resistors for the solar sector can be a challenge. Cressall has vast experience in providing resistors for a variety of applications, including renewables. Offering resistors with no wearing components, they can last as long as the solar panels themselves, minimising downtime.

As deadlines get closer, pressure is mounting to provide a secure supply of green energy. Evidently, governments, planning regulators, energy companies and manufacturers will all have a part to play in the UK’s journey to green energy. As the House of Commons’ report states, the achievement of a decarbonised energy system will not come easily ─ but it is not impossible.

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Are EVs too heavy?

ARE EVS TOO HEAVY?

light weight car

THE IMPORTANCE OF LIGHTWEIGHTING ELECTRIC VEHICLES

In June 2023, the Institution of Structural Engineers published a report suggesting that the weight of our cars is too much for many multi-storeys built in the 60s and 70s. Known for being heavier, EVs have been the first to be blamed ─ but is this fair?

It’s clear that cars have come a long way in design and development over the past 50 years. But while their safety, range, and ride have improved drastically, there’s something else that has increased too ─ their weight.

Looking at some of the most prevalent vehicles of the 60s and 70s highlights the increase in weight. The BMC AD016 was Britain’s best-selling car for more than five years and had a kerb weight of just over 830 kg. Other popular cars included the Ford Escort at 867 kg, and the estate Ford Cortina at 940 kg. So, what’s the comparison to modern vehicles?

CARS IN THE 2020s

Let’s consider last year’s most popular car ─ the Nissan Qashqai. Comparing petrol and equivalent hybrid models within the range, such as the Acenta Premium, shows a weight increase of approximately 250 kg with the partially electric version. The 1.3L petrol comes in at 1348 kg, versus the hybrid 1.5L version at 1612 kg. While the slightly larger engine will contribute to the weight increase, it’s clear that the battery itself ─ even for just a hybrid ─ adds up to the weight. And the Tesla Model Y, the UK’s best selling electric car, boasts a weight of 1980 kg, with 771 kg belonging to the battery alone.

But is it fair to place all the blame on electric cars? It’s worth noting that, while electric and hybrid equivalents are likely to be heavier, there are still plenty of larger petrol and diesel cars on the upper end of the scale. New Range Rovers typically weigh upwards of 2400 kg, and the trend towards larger vehicles in general is another important factor in the weight debate.

Therefore, making more lightweight vehicles is likely to become a growing priority ─ not just in achieving higher fuel efficiency, but also to support older and aging infrastructure.

BUILDING LIGHTER EVS

When it comes to electric vehicles, the battery is likely to be an area of focus. Simply opting for smaller batteries won’t do; this will only negatively impact the range of usability of the vehicle. Therefore, if we’re going to make EV batteries lighter, a more sophisticated approach is required.

One option is the implementation of regenerative braking technology. Regenerative braking allows the surplus energy generated by braking to be directed back into the battery. This improved efficiency can extend the EV’s range by ten to 15 per cent, and even higher in optimum conditions. Therefore, by implementing regenerative braking technology, it becomes possible to slightly reduce the size of the battery, without a huge effect on range.

To safely implement regenerative braking technology, a dynamic braking resistor (DBR) is essential. The DBR dissipates any excess energy in the system, such as that generated when the car is braking on a full battery. Providing a safe way of dispelling this excess energy is crucial to protect the electrical components in the vehicle and to prevent overvoltages.

In line with lightweighting measures, it’s therefore important to choose a compact DBR. Here at Cressall, we have a range of lightweight DBRs available. Our flagship EV2 resistor is just 15 per cent of the weight of an equivalent air-cooled resistor, making it an ideal choice for EV manufacturers seeking to cut vehicle weight with no loss to safety or performance.

While there’s truth in that EVs are typically heavier than their petrol equivalents, it’s clear that the trend towards larger cars in general has contributed to the strain being placed on our infrastructure. But with EV uptake only set to increase within the next few years, making them lighter must be a priority. Regenerative braking is just one example of a technology crucial to improving EV efficiency and weight ─ and with new technologies emerging all the time, it certainly won’t be the last.

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