Smart Grid is a two-way street

London Underground Power Outage 2025 disrupted Tube lines citywide, with a National Grid voltage dip causing service suspensions, delays, and station closures; TfL recovery efforts spotlight infrastructure resilience, contingency planning, and commuter safety communications.

Key Points

A citywide Tube disruption on May 12, 2025, triggered by a National Grid voltage dip, exposing resilience gaps.

✅ Bakerloo, Waterloo & City, Northern suspended; Jubilee disrupted.

✅ Cause: brief National Grid fault leading to a voltage dip.

✅ TfL focuses on recovery, communication, and resilience upgrades.

On May 12, 2025, a significant power outage disrupted the London Underground during the afternoon rush hour, affecting thousands of commuters across the city. The incident highlighted vulnerabilities in the city's transport infrastructure, echoing a morning outage in London reported earlier, and raised concerns about the resilience of urban utilities.

The Outage and Its Immediate Impact

The power failure occurred around 2:30 PM, leading to widespread service suspensions and delays on several key Tube lines. The Bakerloo and Waterloo & City lines were completely halted, while the Jubilee line experienced disruptions between London Bridge and Finchley Road. The Northern line was also suspended between Euston and Kennington, as well as south of Stockwell. Additionally, Elizabeth Line services between Abbey Wood and Paddington were suspended. Some stations were closed for safety reasons due to the lack of power.

Commuters faced severe delays, with many stranded in tunnels or on platforms. The lack of information and communication added to the confusion, as passengers were left uncertain about the cause and duration of the disruptions.

Cause of the Power Failure

Transport for London (TfL) attributed the outage to a brief fault in the National Grid's transmission network. Although the fault was resolved within seconds, it caused a voltage dip that affected local distribution networks, leading to the power loss in the Underground system.

The incident underscored the fragility of the city's transport infrastructure, particularly the aging electrical and signaling systems that are vulnerable to such faults, as well as weather-driven events like a major windstorm outage that can trigger cascading failures. While backup systems exist, their capacity to handle sudden disruptions remains a concern.

Broader Implications for Urban Infrastructure

This power outage is part of a broader pattern of infrastructure challenges facing London. In March 2025, a fire at an electrical substation in Hayes led to the closure of Heathrow Airport, affecting over 200,000 passengers, while similar disruptions at BWI Airport have underscored aviation vulnerabilities. These incidents have prompted discussions about the resilience of the UK's energy and transport networks.

Experts argue that aging infrastructure, coupled with increasing demand and climate-related stresses, poses significant risks to urban operations, as seen in a North Seattle outage and in Toronto storm-related outages that tested local grids. There is a growing call for investment in modernization and diversification of energy sources to ensure reliability and sustainability.

TfL's Response and Recovery Efforts

Following the outage, TfL worked swiftly to restore services. By 11 PM, all but one line had resumed operations, with only the Elizabeth Line continuing to experience severe delays. TfL officials acknowledged the inconvenience caused to passengers and pledged to investigate the incident thoroughly, similar to the Atlanta airport blackout inquiry conducted after a major outage, to prevent future occurrences.

In the aftermath, TfL emphasized the importance of clear communication with passengers during disruptions and committed to enhancing its contingency planning and infrastructure resilience.

Public Reaction and Ongoing Concerns

The power outage sparked frustration among commuters, many of whom took to social media to express their dissatisfaction, echoing sentiments during Houston's extended outage about communication gaps and delays. Some passengers reported being trapped in tunnels for extended periods without clear guidance from staff.

The incident has reignited debates about the adequacy of London's transport infrastructure and the need for comprehensive upgrades. While TfL has initiated reviews and improvement plans, the public remains concerned about the potential for future disruptions and the city's preparedness to handle them.

The May 12 power outage serves as a stark reminder of the vulnerabilities inherent in urban infrastructure. As London continues to grow and modernize, ensuring the resilience of its transport and energy networks will be crucial. This includes investing in modern technologies, enhancing communication systems, and developing robust contingency plans to mitigate the impact of future disruptions. For now, Londoners are left reflecting on the lessons learned from this incident and hoping for a more reliable and resilient transport system in the future.

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Western Denmark Negative Electricity Prices stem from wind energy oversupply, grid congestion, and limited interconnector capacity via Nord Pool and TenneT, underscoring electrification needs, renewable integration, special regulation, and system flexibility.

Key Points

They are sub-zero power prices from wind oversupply, weak interconnectors, low demand, and balancing needs.

✅ Caused by high wind output, low demand, and export bottlenecks

✅ Limited Nord Pool interconnector capacity depresses prices

✅ Special regulation and district heating absorb excess power

A downturn in the cable connection to Norway and Sweden, together with low electricity consumption and high electricity production, has pushed down European electricity prices to a negative level in Western Denmark.

A sign that the electrification of society is urgently needed, says Soren Klinge, head of electricity market at Wind Denmark today.

The heavy winds during the first weekend of July, unlike periods when cheap wind power wanes in the UK, have not only had consequences for the Danes who had otherwise been looking forward to spending their first days at home in the garden or at the beach. It has also pushed down prices in the electricity market to a negative level, which especially the West Danish wind turbine owners have had to notice.

'The electricity market is currently affected by an unfortunate coincidence of various factors that have a negative impact on the electricity price: a reduced export capacity to the other Nordic countries, a low electricity consumption and a high electricity generation, reflecting broader concerns over dispatchable power shortages in Europe today. Unfortunately, the coincidence of these three factors means that the price base falls completely out of the market. This is another sign that the electrification of society is urgently needed, 'explains Soren Klinge, electricity market manager at Wind Denmark.

According to the European power exchange Nord Pool Spot, where UK peak power prices are also tracked, the cable connection to Sweden is expected to return to full capacity from 19 July. The connection between Jutland and Norway is only expected to return to full capacity in early September.

2000 MWh / hour in special regulation

During the windy weather on Monday morning, July 6, up to 2000 MWh / hour was activated at national level in the form of so-called special regulation. Special regulation is the designation that the German system operator TenneT switches off Danish electricity generation at cogeneration plants and wind turbines in order to help with the balancing of the German power system during such events. In addition, electric boilers at the cogeneration plants also contribute by using the electricity from the electricity grid and converting it to district heating for the benefit of Danish homes and businesses.

'The Danish wind turbines are probably the source of most of the special regulation, because there are very few cogeneration units to down-regulate electricity generation. Of course, it is positive to see that we have a high degree of flexibility in the wind-based power system at home. That being said, Denmark does not really get ahead with the green transition, even as its largest energy company plans to stop using coal by 2023, until we are able to raise electricity consumption based on renewable energy.

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Ontario Electricity Transition faces surging demand, GHG targets, and federal regulations, balancing natural gas, renewables, battery storage, and grid reliability while pursuing net-zero by 2035 and cost-effective decarbonization for industry, EVs, and growing populations.

Key Points

Ontario Electricity Transition is the province's shift to a reliable, low-GHG grid via renewables, storage, and policy.

✅ Demand up 75% by 2050; procurement adds 4,000 MW capacity.

✅ Gas use rises to 25% by 2030, challenging GHG goals.

✅ Tripling wind and solar with storage can cut costs and emissions.

Ontario's electricity sector stands at a pivotal crossroads. Once a leader in clean energy, the province now faces the dual challenge of meeting surging demand while adhering to stringent greenhouse gas (GHG) reduction targets. Recent developments, including the expansion of natural gas infrastructure and proposed federal regulations, have intensified debates about the future of Ontario's energy landscape, as this analysis explains in detail.

Rising Demand and the Need for Expansion

Ontario's electricity demand is projected to increase by 75% by 2050, equivalent to adding four and a half cities the size of Toronto to the grid. This surge is driven by factors such as industrial electrification, population growth, and the transition to electric vehicles. In response, as Ontario confronts a looming shortfall in the coming years, the provincial government has initiated its most ambitious energy procurement plan to date, aiming to secure an additional 4,000 megawatts of capacity by 2030. This includes investments in battery storage and natural gas generation to ensure grid reliability during peak demand periods.

The Role of Natural Gas: A Controversial Bridge

Natural gas has become a cornerstone of Ontario's strategy to meet immediate energy needs. However, this reliance comes with environmental costs. The Independent Electricity System Operator (IESO) projects that by 2030, natural gas will account for 25% of Ontario's electricity supply, up from 4% in 2017. This shift raises concerns about the province's ability to meet its GHG reduction targets and to embrace clean power in practice. 

The expansion of gas-fired plants, including broader plans for new gas capacity, such as the Portlands Energy Centre in Toronto, has sparked public outcry. Environmental groups argue that these expansions could undermine local emissions reduction goals and exacerbate health issues related to air quality. For instance, emissions from the Portlands plant have surged from 188,000 tonnes in 2017 to over 600,000 tonnes in 2021, with projections indicating a potential increase to 1.65 million tonnes if the expansion proceeds as planned. 

Federal Regulations and Economic Implications

The federal government's proposed clean electricity regulations aim to achieve a net-zero electricity sector by 2035. However, Ontario's government has expressed concerns that these regulations could impose significant financial burdens. An analysis by the IESO suggests that complying with the new rules would require doubling the province's electricity generation capacity, potentially adding $35 billion in costs by 2050, while other estimates suggest that greening Ontario's grid could cost $400 billion over time. This could result in higher residential electricity bills, ranging from $132 to $168 annually starting in 2033.

Pathways to a Sustainable Future

Experts advocate for a diversified approach to decarbonization that balances environmental goals with economic feasibility. Investments in renewable energy sources, such as new wind and solar resources, along with advancements in energy storage technologies, are seen as critical components of a sustainable energy strategy. Additionally, implementing energy efficiency measures and modernizing grid infrastructure can enhance system resilience and reduce emissions. 

The Ontario Clean Air Alliance proposes phasing out gas power by 2035 through a combination of tripling wind and solar capacity and investing in energy efficiency and storage solutions. This approach not only aims to reduce emissions but also offers potential cost savings compared to continued reliance on gas-fired generation. 

Ontario's journey toward a decarbonized electricity grid is fraught with challenges, including balancing reliability, clean, affordable electricity, and environmental sustainability. While natural gas currently plays a significant role in meeting the province's energy needs, its long-term viability as a bridge fuel remains contentious. The path forward will require careful consideration of technological innovations, regulatory frameworks, and public engagement to ensure a clean, reliable, and economically viable energy future for all Ontarians.

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Toronto Flood Cleanup details the citywide response to storm damage after heavy rain, stressing drainage system upgrades, emergency services, transit disruptions, infrastructure repair, financial aid, insurance claims, and climate resilience planning for future weather.

Key Points

Toronto Flood Cleanup is the city's flood response, restoring infrastructure, aiding residents, and upgrading drainage.

✅ Emergency services and public works lead debris removal.

✅ Repairs to roads, bridges, transit, and utilities underway.

✅ Aid, insurance claims, and drainage upgrades prioritized.

Toronto is grappling with significant cleanup efforts following severe storms that unleashed heavy rains and caused widespread flooding across the city. The storms, which hit the area over the past week, have left a trail of damage and disruption, prompting both immediate response measures and longer-term recovery plans.

The intense rainfall began with a powerful storm system that moved through southern Ontario, with Sudbury Hydro crews working to reconnect service as the system pressed toward the GTA, delivering an unprecedented volume of water in a short period. The resulting downpours overwhelmed the city's drainage systems, leading to severe flooding in multiple neighborhoods. Streets, basements, and parks were inundated, with many areas experiencing water levels not seen in recent memory.

Emergency services were quickly mobilized to address the immediate impact of the floods. Toronto’s Fire Services, along with other first responders and skilled utility teams, as Ontario recently sent 200 workers to Florida to help restore power, were deployed to assist residents affected by the rising waters. Rescue operations were carried out to help people trapped in their homes or vehicles, and temporary shelters were set up for those displaced by the flooding.

The storm's impact was felt across various sectors of the city. Public transportation services were disrupted, as strong gusts led to significant power outages in parts of the region, with numerous subway stations and bus routes affected by the high water levels. Major roads were closed due to flooding, causing significant traffic delays and affecting daily commutes for many residents. Local businesses also faced challenges, with some forced to close their doors as a result of the water damage.

The city's infrastructure bore the brunt of the storm's fury. Several key infrastructure components, including roads, bridges, and utilities, suffered damage. The city's water treatment plants and sewage systems were stressed by the volume of water, raising concerns about potential contamination and the need for extensive maintenance and repair work.

In the wake of the flooding, the Toronto Municipal Government has launched a comprehensive cleanup and recovery effort. The city's Public Works Department is spearheading the operation, focusing on clearing debris, repairing damaged infrastructure, and restoring essential services, as Hydro One crews restore power to hundreds of thousands across Ontario. Teams of workers are diligently addressing the damage to roads and bridges, ensuring that they are safe for use and functioning properly.

Efforts are also underway to assist residents and businesses affected by the flooding. Financial aid and support programs are being implemented to help those who have suffered property damage or loss, including customers affected by Toronto power outages as repairs continue. The city is working closely with insurance companies to facilitate claims and provide relief to those in need.

In addition to the immediate cleanup, there is a heightened focus on evaluating and improving the city's flood management systems. The recent storms have highlighted vulnerabilities in Toronto’s infrastructure, prompting calls for enhanced flood prevention measures. City officials and urban planners are assessing the current drainage systems and exploring ways to bolster their capacity to handle future extreme weather events.

The storms have also sparked discussions about the broader implications of climate change and its impact on urban areas. Experts suggest that increasingly severe weather events, including heavy rainfall and flooding, may become more common, as seen with Houston's extended power outage after severe storms, as global temperatures rise. This has led to a call for more resilient and adaptable infrastructure to better withstand such events.

Community organizations and volunteers have played a vital role in the recovery process. Local groups have come together to support their neighbors, providing assistance with cleanup efforts, distributing supplies, and offering emotional support to those affected by the disaster. Their contributions underscore the importance of community solidarity in times of crisis.

As Toronto works towards recovery, there is a clear recognition of the need for a comprehensive strategy to address both the immediate and long-term challenges posed by severe weather events. The city’s response will involve not only repairing the damage caused by this storm but also investing in infrastructure improvements, drawing lessons from London power outage disruption cases to harden critical systems, and adopting measures to mitigate the impact of future floods.

In summary, the severe storms that recently struck Toronto have led to widespread flooding and significant disruption across the city. The immediate response has involved extensive cleanup efforts, damage assessment, and support for affected residents and businesses. Looking ahead, Toronto faces the challenge of enhancing its flood management systems and preparing for the potential impacts of climate change. The collective efforts of emergency services, city officials, and community members will be crucial in ensuring a swift recovery and building resilience against future storms.

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Offshore wind power accelerates low-carbon electrification, leveraging floating turbines, high capacity factors, HVDC transmission, and hydrogen production to decarbonize grids, cut CO2, and deliver competitive, reliable renewable energy near demand centers.

Key Points

Offshore wind power uses offshore turbines to deliver low-carbon electricity with high capacity factors and falling costs.

✅ Sea-based wind farms with 40-50% capacity factors

✅ Floating turbines unlock deep-water, far-shore resources

✅ Enables hydrogen production and strengthens grid reliability

The need for affordable low-carbon technologies is greater than ever

Global energy-related CO2 emissions reached a historic high in 2018, driven by an increase in coal use in the power sector. Despite impressive gains for renewables, fossil fuels still account for nearly two-thirds of electricity generation, the same share as 20 years ago. There are signs of a shift, with increasing pledges to decarbonise economies and tackle air pollution, and with World Bank support helping developing countries scale wind, but action needs to accelerate to meet sustainable energy goals. As electrification of the global energy system continues, the need for clean and affordable low-carbon technologies to produce this electricity is more pressing than ever. This World Energy Outlook special report offers a deep dive on a technology that today has a total capacity of 23 GW (80% of it in Europe) and accounts for only 0.3% of global electricity generation, but has the potential to become a mainstay of the world's power supply. The report provides the most comprehensive analysis to date of the global outlook for offshore wind, its contributions to electricity systems and its role in clean energy transitions.

The offshore wind market has been gaining momentum

The global offshore wind market grew nearly 30% per year between 2010 and 2018, benefitting from rapid technology improvements. Over the next five years, about 150 new offshore wind projects are scheduled to be completed around the world, pointing to an increasing role for offshore wind in power supplies. Europe has fostered the technology's development, led by the UK offshore wind sector alongside Germany and Denmark. The United Kingdom and Germany currently have the largest offshore wind capacity in operation, while Denmark produced 15% of its electricity from offshore wind in 2018. China added more capacity than any other country in 2018.

The untapped potential of offshore wind is vast

The best offshore wind sites could supply more than the total amount of electricity consumed worldwide today. And that would involve tapping only the sites close to shores. The IEA initiated a new geospatial analysis for this report to assess offshore wind technical potential country by country. The analysis was based on the latest global weather data on wind speed and quality while factoring in the newest turbine designs. Offshore wind's technical potential is 36 000 TWh per year for installations in water less than 60 metres deep and within 60 km from shore. Global electricity demand is currently 23 000 TWh. Moving further from shore and into deeper waters, floating turbines could unlock enough potential to meet the world's total electricity demand 11 times over in 2040. Our new geospatial analysis indicates that offshore wind alone could meet several times electricity demand in a number of countries, including in Europe, the United States and Japan. The industry is adapting various floating foundation technologies that have already been proven in the oil and gas sector. The first projects are under development and look to prove the feasibility and cost-effectiveness of floating offshore wind technologies.

Offshore wind's attributes are very promising for power systems

New offshore wind projects have capacity factors of 40-50%, as larger turbines and other technology improvements are helping to make the most of available wind resources. At these levels, offshore wind matches the capacity factors of gas- and coal-fired power plants in some regions – though offshore wind is not available at all times. Its capacity factors exceed those of onshore wind and are about double those of solar PV. Offshore wind output varies according to the strength of the wind, but its hourly variability is lower than that of solar PV. Offshore wind typically fluctuates within a narrower band, up to 20% from hour to hour, than solar PV, which varies up to 40%.

Offshore wind's high capacity factors and lower variability make its system value comparable to baseload technologies, placing it in a category of its own – a variable baseload technology. Offshore wind can generate electricity during all hours of the day and tends to produce more electricity in winter months in Europe, the United States and China, as well as during the monsoon season in India. These characteristics mean that offshore wind's system value is generally higher than that of its onshore counterpart and more stable over time than that of solar PV. Offshore wind also contributes to electricity security, with its high availability and seasonality patterns it is able to make a stronger contribution to system needs than other variable renewables. In doing so, offshore wind contributes to reducing CO2 and air pollutant emissions while also lowering the need for investment in dispatchable power plants. Offshore wind also has the advantage of avoiding many land use and social acceptance issues that other variable renewables are facing.

Offshore wind is on track to be a competitive source of electricity

Offshore wind is set to be competitive with fossil fuels within the next decade, as well as with other renewables including solar PV. The cost of offshore wind is declining and is set to fall further. Financing costs account for 35% to 50% of overall generation cost, and supportive policy frameworks are now enabling projects to secure low cost financing in Europe, with zero-subsidy tenders being awarded. Technology costs are also falling. The levelised cost of electricity produced by offshore wind is projected to decline by nearly 60% by 2040. Combined with its relatively high value to the system, this will make offshore wind one of the most competitive sources of electricity. In Europe, recent auctions indicate that offshore wind will soon beat new natural gas-fired capacity on cost and be on a par with solar PV and onshore wind. In China, offshore wind is set to become competitive with new coal-fired capacity around 2030 and be on par with solar PV and onshore wind. In the United States, recent project proposals indicate that offshore wind will soon be an affordable option, even as the 1 GW timeline continues to evolve, with potential to serve demand centres along the country's east coast.

Innovation is delivering deep cost reductions in offshore wind, and transmission costs will become increasingly important. The average upfront cost to build a 1 gigawatt offshore wind project, including transmission, was over $4 billion in 2018, but the cost is set to drop by more than 40% over the next decade. This overall decline is driven by a 60% reduction in the costs of turbines, foundations and their installation. Transmission accounts for around one-quarter of total offshore wind costs today, but its share in total costs is set to increase to about one-half as new projects move further from shore. Innovation in transmission, for example through work to expand the limits of direct current technologies, will be essential to support new projects without raising their overall costs.

Offshore wind is set to become a $1 trillion business

Offshore wind power capacity is set to increase by at least 15-fold worldwide by 2040, becoming a $1 trillion business. Under current investment plans and policies, the global offshore wind market is set to expand by 13% per year, reflecting its growth despite Covid-19 in recent years, passing 20 GW of additions per year by 2030. This will require capital spending of $840 billion over the next two decades, almost matching that for natural gas-fired or coal-fired capacity. Achieving global climate and sustainability goals would require faster growth: capacity additions would need to approach 40 GW per year in the 2030s, pushing cumulative investment to over $1.2 trillion. 

The promising outlook for offshore wind is underpinned by policy support in an increasing number of regions. Several European North Seas countries – including the United Kingdom, Germany, the Netherlands and Denmark – have policy targets supporting offshore wind. Although a relative newcomer to the technology, China is quickly building up its offshore wind industry, aiming to develop a project pipeline of 10 GW by 2020. In the United States, state-level targets and federal incentives are set to kick-start the U.S. offshore wind surge in the coming years. Additionally, policy targets are in place and projects under development in Korea, Japan, Chinese Taipei and Viet Nam.

 The synergies between offshore wind and offshore oil and gas activities provide new market opportunities. Since offshore energy operations share technologies and elements of their supply chains, oil and gas companies started investing in offshore wind projects many years ago. We estimate that about 40% of the full lifetime costs of an offshore wind project, including construction and maintenance, have significant synergies with the offshore oil and gas sector. That translates into a market opportunity of $400 billion or more in Europe and China over the next two decades. The construction of foundations and subsea structures offers potential crossover business, as do practices related to the maintenance and inspection of platforms. In addition to these opportunities, offshore oil and gas platforms require electricity that is often supplied by gas turbines or diesel engines, but that could be provided by nearby wind farms, thereby reducing CO2 emissions, air pollutants and costs.

Offshore wind can accelerate clean energy transitions

Offshore wind can help drive energy transitions by decarbonising electricity and by producing low-carbon fuels. Over the next two decades, its expansion could avoid between 5 billion and 7 billion tonnes of CO2 emissions from the power sector globally, while also reducing air pollution and enhancing energy security by reducing reliance on imported fuels. The European Union is poised to continue leading the wind energy at sea in Europe industry in support of its climate goals: its offshore wind capacity is set to increase by at least fourfold by 2030. This growth puts offshore wind on track to become the European Union's largest source of electricity in the 2040s. Beyond electricity, offshore wind's high capacity factors and falling costs makes it a good match to produce low-carbon hydrogen, a versatile product that could help decarbonise the buildings sector and some of the hardest to abate activities in industry and transport. For example, a 1 gigawatt offshore wind project could produce enough low-carbon hydrogen to heat about 250 000 homes. Rising demand for low-carbon hydrogen could also dramatically increase the market potential for offshore wind. Europe is looking to develop offshore "hubs" for producing electricity and clean hydrogen from offshore wind.

It's not all smooth sailing

Offshore wind faces several challenges that could slow its growth in established and emerging markets, but policy makers and regulators can clear the path ahead. Developing efficient supply chains is crucial for the offshore wind industry to deliver low-cost projects. Doing so is likely to call for multibillion-dollar investments in ever-larger support vessels and construction equipment. Such investment is especially difficult in the face of uncertainty. Governments can facilitate investment of this kind by establishing a long-term vision for offshore wind and by drawing on U.K. policy lessons to define the measures to be taken to help make that vision a reality. Long-term clarity would also enable effective system integration of offshore wind, including system planning to ensure reliability during periods of low wind availability.

The success of offshore wind depends on developing onshore grid infrastructure. Whether the responsibility for developing offshore transmission lies with project developers or transmission system operators, regulations should encourage efficient planning and design practices that support the long-term vision for offshore wind. Those regulations should recognise that the development of onshore grid infrastructure is essential to the efficient integration of power production from offshore wind. Without appropriate grid reinforcements and expansion, there is a risk of large amounts of offshore wind power going unused, and opportunities for further expansion could be stifled. Development could also be slowed by marine planning practices, regulations for awarding development rights and public acceptance issues.

The future of offshore wind looks bright but hinges on the right policies

The outlook for offshore wind is very positive as efforts to decarbonise and reduce local pollution accelerate. While offshore wind provides just 0.3% of global electricity supply today, it has vast potential around the world and an important role to play in the broader energy system. Offshore wind can drive down CO2 emissions and air pollutants from electricity generation. It can also do so in other sectors through the production of clean hydrogen and related fuels. The high system value of offshore wind offers advantages that make a strong case for its role alongside other renewables and low-carbon technologies. Government policies will continue to play a critical role in the future of offshore wind and  the overall pace of clean energy transitions around the world.

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Polycrystalline Tin Selenide Thermoelectrics enable waste heat recovery with ZT 3.1, matching single crystals while cutting costs, powering greener car engines, industrial furnaces, and thermoelectric generators via p-type and emerging n-type designs.

Key Points

Low-cost tin selenide devices that turn waste heat into power, achieving ZT 3.1 and enabling p-type and n-type modules.

✅ Oxygen removal prevents heat-leaking tin oxide grain skins.

✅ Polycrystalline ingots match single-crystal ZT 3.1 at lower cost.

✅ N-type tin selenide in development to pair with p-type.

So-called thermoelectric generators turn waste heat into electricity without producing greenhouse gas emissions, providing what seems like a free lunch. But despite helping power the Mars rovers, the high cost of these devices has prevented their widespread use. Now, researchers have found a way to make cheap thermoelectrics that work just as well as the pricey kind. The work could pave the way for a new generation of greener car engines, industrial furnaces, and other energy-generating devices.

“This looks like a very smart way to realize high performance,” says Li-Dong Zhao, a materials scientist at Beihang University who was not involved with the work. He notes there are still a few more steps to take before these materials can become high-performing thermoelectric generators. However, he says, “I think this will be used in the not too far future.”

Thermoelectrics are semiconductor devices placed on a hot surface, like a gas-powered car engine or on heat-generating electronics using thin-film converters to capture waste heat. That gives them a hot side and a cool side, away from the hot surface. They work by using the heat to push electrical charges from one to the other, a process of turning thermal energy into electricity that depends on the temperature gradient. If a device allows the hot side to warm up the cool side, the electricity stops flowing. A device’s success at preventing this, as well as its ability to conduct electrons, feeds into a score known as the figure of merit, or ZT.

 Over the past 2 decades, researchers have produced thermoelectric materials with increasing ZTs, while related advances such as nighttime solar cells have broadened thermal-to-electric concepts. The record came in 2014 when Mercouri Kanatzidis, a materials scientist at Northwestern University, and his colleagues came up with a single crystal of tin selenide with a ZT of 3.1. Yet the material was difficult to make and too fragile to work with. “For practical applications, it’s a non-starter,” Kanatzidis says.

So, his team decided to make its thermoelectrics from readily available tin and selenium powders, an approach that, once processed, makes grains of polycrystalline tin selenide instead of the single crystals. The polycrystalline grains are cheap and can be heated and compressed into ingots that are 3 to 5 centimeters long, which can be made into devices. The polycrystalline ingots are also more robust, and Kanatzidis expected the boundaries between the individual grains to slow the passage of heat. But when his team tested the polycrystalline materials, the thermal conductivity shot up, dropping their ZT scores as low as 1.2.

In 2016, the Northwestern team discovered the source of the problem: an ultrathin skin of tin oxide was forming around individual grains of polycrystalline tin selenide before they were pressed into ingots. And that skin acted as an express lane for the heat to travel from grain to grain through the material. So, in their current study, Kanatzidis and his colleagues came up with a way to use heat to drive any oxygen away from the powdery precursors, leaving pristine polycrystalline tin selenide, whereas other devices can generate electricity from thin air using ambient moisture.

The result, which they report today in Nature Materials, was not only a thermal conductivity below that of single-crystal tin selenide but also a ZT of 3.1, a development that echoes nighttime renewable devices showing electricity from cold conditions. “This opens the door for new devices to be built from polycrystalline tin selenide pellets and their applications to be explored,” Kanatzidis says.

Getting through that door will still take some time. The polycrystalline tin selenide the team makes is spiked with sodium atoms, creating what is known as a “p-type” material that conducts positive charges. To make working devices, researchers also need an “n-type” version to conduct negative charges.

Zhao’s team recently reported making an n-type single-crystal tin selenide by spiking it with bromine atoms. And Kanatzidis says his team is now working on making an n-type polycrystalline version. Once n-type and p-type tin selenide devices are paired, researchers should have a clear path to making a new generation of ultra-efficient thermoelectric generators. Those could be installed everywhere from automobile exhaust pipes to water heaters and industrial furnaces to scavenge energy from some of the 65% of fossil fuel energy that winds up as waste heat. 

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