TVA sees a future in clean coal generation

Texas Electricity Market Bailout proposes securitization bonds and ERCOT-backed fees after Winter Storm Uri, spreading costs via ratepayer charges on power bills to stabilize generators, co-ops, and retailers and avert bankruptcies and investor flight.

Key Points

State plan to securitize storm debts via ERCOT fees, adding bill charges to stabilize Texas power firms.

✅ Securitization bonds finance unpaid ancillary services and energy costs

✅ ERCOT fee spreads Winter Storm Uri debts across ratepayers statewide

✅ Aims to prevent bankruptcies, preserve grid reliability, reassure investors

An approximately $2.5 billion plan to bail out Texas’ distressed electricity market from the financial crisis caused by Winter Storm Uri in February has been approved by the Texas House.

The legislation would impose a fee — likely for the next decade or longer — on electricity companies, which would then get passed on to residential and business customers in their power bills, even as some utilities waived certain fees earlier in the crisis.

House lawmakers sent House Bill 4492 to the Senate on Thursday after a 129-15 vote. A similar bill is advancing in the Senate.

Some of the state’s electricity providers and generators are financially underwater in the aftermath of the February power outages, which left millions without power and killed more than 100 people. Electricity companies had to buy whatever power was available at the maximum rate allowed by Texas regulations — $9,000 per megawatt hour — during the week of the storm (the average price for power in 2020 was $22 per megawatt hour). Natural gas fuel prices also spiked more than 700% during the storm.

Several companies are nearing default on their bills to the Electric Reliability Council of Texas, which manages the Texas power grid that covers most of the state and facilitates financial transactions in it.

Rural electric cooperatives were especially hard hit; Brazos Electric Power Cooperative, which supplies electricity to 1.5 million customers, filed for bankruptcy citing a $1.8 billion debt to ERCOT.

State Rep. Chris Paddie, R-Marshall, the bill’s author, said a second bailout bill will be necessary during the current legislative session for severely distressed electric cooperatives.

“This is a financial crisis, and it’s a big one,” James Schaefer, a senior managing director at Guggenheim Partners, an investment bank, told lawmakers at a House State Affairs Committee hearing in early April. He warned that more bankruptcies would cause higher costs to customers and hurt the state’s image in the eyes of investors.

“You’ve got to free the system,” Schaefer said. “It’s horrible that a bunch of folks have to pay, but it’s a system-wide failure. If you let a bunch of folks crash, it’s not a good look for your state.”

If approved by the Senate and Gov. Greg Abbott, a newly-created Texas Electric Securitization Corp. would use the money raised from the fees for bonds to help pay the companies’ debts, including costs for ancillary services, a financial product that helps ensure power is continuously generated and improve electricity reliability across the grid.

Paddie told his colleagues Wednesday that he could not yet estimate how long the new fee would be imposed, but during committee hearings lawmakers estimated it’s likely to be at least a decade. Several other bills to spread out the costs of the winter storm and consider market reforms are also moving through the Legislature.

ERCOT’s independent market monitor recommended in March that energy sold during that period be repriced at a lower rate, which would have allowed ERCOT to claw back about $4.2 billion in payments to power generators, but the Public Utility Commission declined to do so, even as a court ruling on plant obligations in emergencies drew scrutiny among market participants.

Instead, lawmakers are pushing for bailouts that several energy experts have said is needed, both to ensure distressed companies don’t pass enormous costs on to their customers and to prevent electricity investors and companies from leaving the state if it’s viewed as too risky to continue doing business.

Becky Klein, an energy consultant in Austin and former chair of the Public Utility Commission who played a key role in de-regulating Texas’ electricity market two decades ago, said during a retail electricity panel hosted by Integrate that legislation is necessary to provide “some kind of backstop during a crazy market crisis like this to show the financial market that we’re willing to provide some relief.”

Still, some lawmakers are concerned with how they will win public support, including potential voter-approved funding measures, for bills to bail out the state’s electricity market.

“I have to go back to Laredo and say, ‘I know you didn’t have electricity for several days, but now I’m going to make you pay a little more for the next 20 years,’” state Rep. Richard Peña Raymond, D-Laredo, said during an early April discussion on the plan in the House State Affairs Committee. He said he voted for the bill because it’s in the best interest of the state.

Paddie, during the same committee hearing, acknowledged that “none of us want to increase fees or taxes.” However, he said, “We have to deal with the reality set before us.”

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UK Coal-Free Electricity Record highlights rapid growth in renewables as National Grid phases out coal; wind, solar, and offshore projects surge, green tariffs expand, and energy comparison helps consumers switch to cheaper, cleaner deals.

Key Points

Britain's longest coal-free run, enabled by renewables, lower demand, and grid shifts for cheaper, greener tariffs.

✅ Record set after two months without coal-fired generation

✅ Renewables outpace fossil fuels; wind and solar dominate

✅ Green tariffs expand; prices at three-year lows

On Wednesday 10 June, Britain hit a significant landmark: the UK went for two full months without burning coal to generate power – that's the longest period since the 1880s, following earlier milestones such as a full week without coal power in the recent past.

According to the National Grid, Britain has now run its electricity network without burning coal since midnight on the 9 April. This coal-free period has beaten the country’s previous record of 18 days, six hours and 10 minutes, which was set in June 2019, even though low-carbon generation stalled in 2019 according to analyses.

With such a shift in Britain’s drive for renewables and lower electricity demand following the coronavirus lockdown, as Britain recorded its cleanest electricity during lockdown to date, now may be the perfect time to do an online energy comparison and switch to a cheaper, greener deal.

Only a decade ago, around 40 per cent of Britain’s electricity came from coal generation, but since then the country has gradually shifted towards renewable energy, with the coal share at record lows in the system today. When Britain was forced into lockdown in response to the coronavirus pandemic, electricity demand dropped sharply, and the National Grid took the four remaining coal-fired plants off the network.

Over the past 10 years, Britain has invested heavily in renewable energy. Back in 2010, only 3 per cent of the country's electricity came from wind and solar, and many people remained sceptical. However, now, the UK has the biggest offshore wind industry in the world. Plus, last year, construction of the world’s single largest wind farm was completed off the coast of Yorkshire.

At the same time, Drax – Britain’s biggest power plant – has started to switch from burning coal to burning compressed wooden pellets instead, reflecting the UK's progress as it keeps breaking its coal-free energy record again across the grid. By this time next year, the plant hopes to have phased out coal entirely.

So far this year, renewables have generated more power than all fossil fuels put together, the BBC reports, and the energy dashboard shows the current mix in real time. Renewables have been responsible for 37 per cent of electricity supplied to the network, with wind and solar surpassing nuclear for the first time, while fossil fuels have accounted for 35 per cent. During the same period, nuclear accounted for 18 per cent and imports made up the remaining 10 per cent.

What does this mean for consumers?

As the country’s electricity supply moves more towards renewables, customers have more choice than ever before. Most of the ‘Big Six’ energy companies now have tariffs that offer 100 per cent green electricity. On top of this, specialist green energy suppliers such as Bulb, Octopus and Green Energy UK make it easier than ever to find a green energy tariff.

The good news is that our energy comparison research suggests that green energy doesn’t have to cost you more than a traditional fixed-price energy contract would. In fact, some of the cheapest energy suppliers are actually green companies.

At present, energy bills are at three-year lows, which means that now is the perfect time to switch supplier. As prices remain low and renewables begin to dominate the marketplace, more switchers will be drawn to green energy deals than ever before.

However, if you’re interested in choosing a green energy supplier, make sure that you look at the company's fuel mix. This way, you’ll be able to see whether they are guaranteeing the usage of green energy, or whether they’re just offsetting your usage. All suppliers must report how their energy is generated to Ofgem, so you’ll easily be able to compare providers.

You may find that you pay more for a supplier that generates its own energy from renewables, or pay less if the supplier simply matches your usage by buying green energy. You can decide which option is right for you after comparing the prices.

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Denmark 2019 electricity CO2 intensity shows record-low emissions as renewable energy surges, wind power dominates, offshore wind expands, and coal phase-out accelerates Denmark's energy transition and grid decarbonization, driven by higher CO2 prices and flexibility.

Key Points

It is 135 g CO2/kWh, a record low enabled by wind power growth, offshore wind, and a sharp coal decline.

✅ Average emissions fell to 135 g CO2/kWh, the lowest on record

✅ Wind and solar supplied 49.9% of national electricity use

✅ Coal consumption dropped 46% as CO2 allowance prices rose

Danish electricity producers set a new green record in 2019, when an average produced kilowatt-hour emitted 135 gr CO2 / kWh.

It is the lowest CO2 emission ever measured in Denmark and about one-seventh of what the electricity producers emitted in 1990.

Never has a kilowatt-hour produced emitted as little CO2 as it did in 2019. And that's according to Energinet's recently published annual Environmental Report on Danish electricity generation and cogeneration, two primary causes.

One reason is that more green power has been produced because the Horns Rev 3 offshore wind farm, which can produce electricity for 425,000 households, was commissioned in 2019. The other is that Danish coal consumption fell by 46 percent from 2018 to 2019, as coal phase-out plans gathered pace across the sector. the dramatic decline in coal consumption is partly due a significant increase in the price of CO2 quotas, and thus also the price of CO2 emissions.

'Historically, 135 gr CO2 / kWh is a really, really low figure, showing the impressive green travel that the Danish electricity system has been on. In 1990, a kilowatt-hour produced emitted over 1000 grams of CO2, ie about seven times as much as today, 'says Hanne Storm Edlefsen, area manager in Energinet Power Systems Responsibility.

Wind energy is the dominant form of electricity generation in Denmark, a pattern the UK wind beat coal in 2016 when shifting away from fossil fuels.

17.1 TWh. Danish wind turbines and solar cells generated so much electricity in 2019, corresponding to 49.9 per cent. of Danish electricity consumption, reflecting broader EU wind and solar growth trends as well. An increase of 15 per cent. The wind turbines alone produced 16 TWh, which is not only a new green record, but also puts a thick line that wind energy is by far the most dominant form of electricity generation in Denmark.

'Thanks to our large wind resources, turbines are by far the largest supplier of renewable energy in Denmark, and this will be for many years to come. The large price drop in new wind energy in recent years - for both onshore and offshore winds - will ensure that wind energy will drive a large part of the growth in renewable energy in the coming years, as new wind generation records are set in markets like the UK, 'says Soren Klinge, electricity market manager at Wind Denmark.

Conversely, total electricity generation from fossil and bio-based fuels decreased by 26 PJ (petajoule ed.), Corresponding to 34 per cent. from 2018 to 2019, mirroring renewables overtaking coal in Germany. Nevertheless, net electricity generation was just under 30 TWh both years.

'It is worth noting that while fossil fuels are being phased out, Denmark maintains its annual net production of electricity. The green, so to speak, replaces the black. It once again underpins that green conversion, high security of supply and an affordable electricity price can go hand in hand, 'says Hanne Storm Edlefsen.

Danish power system is ready for a green future

Including trade in electricity with neighboring countries, 1 kWh in a Danish outlet generates 145 gr CO2 / kWh.

'There has been a very significant development in the Danish electricity system in recent years, where the electricity system can now be operated solely on the renewable energy. It is a remarkable development, also from an international perspective where low-carbon progress stalled in the UK in 2019, that one would not have thought possible for just a few years ago, 'he says.

More than expected have phased out coal

The electricity from the Danish sockets will be greener , predicts Energinet's environmental report , which expects CO2 intensity in the coming years. This is explained by an expectation of increased electrification of energy consumption, together with a continued expansion with wind and solar.

'Wind energy is the cornerstone of the green transition. With the commissioning of the Kriegers Flak offshore wind farm and several major onshore wind turbine projects within the next few years, we can well expect that only the wind's share of electricity consumption will exceed 50 per cent hopefully as early as 2021,' concludes Soren Klinge.

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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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COVID-19 Impact on Electricity Demand, per IEA data, shows 15% global load drop from lockdowns, with residential use up, industrial and service sectors down; fossil fuel generation fell as renewables and photovoltaics gained share.

Key Points

An overview of how lockdowns cut global power demand, boosted residential use, and increased the renewable share.

✅ IEA review shows at least 15% dip in daily global electricity load

✅ Lockdowns cut commercial and industrial demand; homes used more

✅ Fossil fuels fell as renewables and PV generation gained share

The daily demand for electricity dipped at least 15 per cent across the globe, according to Global Energy Review 2020: The impacts of the COVID-19 crisis on global energy demand and CO2 emissions, a report published by the International Energy Agency (IEA) in April 2020, even as global power demand surged above pre-pandemic levels.

The report collated data from 30 countries, including India and China, that showed partial and full lockdown measures adopted by them were responsible for this decrease.

Full lockdowns in countries — including France, Italy, India, Spain, the United Kingdom where daily demand fell about 10% and the midwest region of the United States (US) — reduced this demand for electricity.

Reduction in electricity demand after lockdown measures (weather corrected)

Source: Global Energy Review 2020: The impacts of the COVID-19 crisis on global energy demand and CO2 emissions, IEA

Drivers of the fall

There was, however, a spike in residential demand for electricity as a result of people staying and working from home. This increase in residential demand, though, was not enough to compensate for reduced demand from industrial and commercial operations.

The extent of reduction depended not only on the duration and stringency of the lockdown, but also on the nature of the economy of the countries — predominantly service- or industry-based — the IEA report said.

A higher decline in electricity demand was noted in countries where the service sector — including retail, hospitality, education, tourism — was dominant, compared to countries that had industrial economies.

The US, for example — where industry forms only 20 per cent of the economy — saw larger reductions in electricity demand, compared to China, where power demand dropped as the industry accounts for more than 60 per cent of the economy.

Italy — the worst-affected country from COVID-19 — saw a decline greater than 25 per cent when compared to figures from last year, even as power demand held firm in parts of Europe during later lockdowns.

The report said the shutting down of the hospitality and tourism sectors in the country — major components of the Italian economy — were said to have had a higher impact, than any other factor, for this fall.

Reduced fossil fuel dependency

Almost all of the reduction in demand was reportedly because of the shutting down of fossil fuel-based power generation, according to the report. Instead, the share of electricity supply from renewables in the entire portfolio of energy sources, increased during the pandemic, reflecting low-carbon electricity lessons observed during COVID-19.

This was due to a natural increase in wind and photovoltaic power generation compared to 2019 along with a drop in overall electricity demand that forced electricity producers from non-renewable sources to decrease their supplies, before surging electricity demand began to strain power systems worldwide.

The Power System Operation Corporation of India also reported that electricity production from coal — India’s primary source of electricity — fell by 32.2 per cent to 1.91 billion units (kilowatt-hours) per day, in line with India's electricity demand decline reported during the pandemic, compared to the 2019 levels.

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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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