Wind farm planned near Groton

Duke Energy zero-coal 2050 plan outlines a decarbonized energy mix, aligning with Paris goals, cutting greenhouse gas emissions, driven by investor pressure, shifting to natural gas, extending nuclear power, and phasing out coal.

Key Points

An investor-driven scenario to end coal by 2050, shift to natural gas, extend nuclear plants, and manage climate risk.

✅ Eliminates coal from the generation mix by 2050

✅ Prioritizes natural gas transitions without CCS breakthroughs

✅ Extends nuclear plant licenses to limit carbon emissions

One of America’s largest utility companies, Duke Energy, is set to release a report later this month that sketches a drastically changed electricity mix in a carbon-constrained future.

The big picture: Duke is the latest energy company to commit to releasing a report about climate change in response to investor pressure, echoing shifts such as Europe's oil majors going electric across the sector, conveyed by non-binding but symbolically important shareholder resolutions. Duke provides electricity to more than seven million customers in the Carolinas, the Midwest and Florida.

Gritty details: The report is expected to find that coal, currently 33% of Duke’s mix, gone entirely from its portfolio by 2050 in a future scenario where the world has taken steps to cut greenhouse gas emissions, and where global coal-fired electricity use is falling markedly, to a level consistent with keeping global temperatures from rising two degrees Celsius. That’s the big ambition of the 2015 Paris climate deal, but the current commitments aren’t close to reaching that.

What they're saying: “What’s difficult about this is we are trying to overlay what we understand currently about technology,” Lynn Good, Duke CEO, told Axios in an interview on the sidelines of a major energy conference here.

She went on to say that this scenario of zero coal by 2050 doesn’t assume any breakthroughs in technology that captures carbon emissions from coal-fired power plants. “We don’t see that technology today, and we need to make economic decisions to get those units moving and replacing them with natural gas.”

Good also stressed the benefits of its several nuclear power plants, highlighting the role of sustaining U.S. nuclear power in decarbonization, which emit no carbon emissions. She said Duke isn’t considering investing in new nuclear plants, but plans to seek federal relicensing of current plants.

“If I turn them off, the resource that would replace them today is natural gas, so carbon will go up,” Good said. “Our objective is to continue to keep those plants as long as possible.”

What’s next: A spokesman said the other details of their 2050 scenario estimates will be available when the report is officially released by month’s end.

Axios reports that Duke Energy will release a report later this month that detail the utility's efforts to mitigate climate change risks and plan carbon-free electricity investments across its operations. The report includes a scenario that eliminates coal entirely from the company's power mix by 2050. Coal currently makes up about a third of Duke's generation.

Duke CEO Lynn Good told the news outlet the scenario ending coal-fired generation assumes no technological advances in emissions capture, seemingly leaving open the possibility.

Last year, a report by the Union of Concerned Scientists concluded one in four of the remaining operating coal-fired plants in the U.S. are slated for closure or conversion to natural gas, amid falling power-sector carbon emissions across the country. Duke's report is expected to be released by the end of the month.

Duke's report on its carbon plans comes at the behest of shareholders, a trend utility companies have seen growing among investors who are increasingly concerned about companies' sustainability and their financial exposure to climate policy.

Last year, a majority of shareholders of Pennsylvania utility PPL Corp. called on company management to publish a report on how climate change policies and technological innovations will affect the company's bottom line. Almost 60% of shareholders voted in favor of the non-binding proposal.

The vote, reportedly a first for the power sector, followed a similar decision by shareholders of Occidental Petroleum, which was supported by about 66% of shareholders.

Duke's Good told Axios that right now the utility does not see the coal technology on the horizon that would keep it operating plants. “We don't see that technology today, and we need to make economic decisions to get those units moving and replacing them with natural gas," Good said. However, it does not mean the utility is making near-term efforts to erase coal from its power mix. However, some utilities are taking those steps as they prepare for en energy landscape with more carbon regulations.

In addition to the 25% of coal plants heading for closure or conversion, the UCS report also said that another 17% of the nation’s operating coal plants are uneconomic compared with natural gas-fired generation, and could face retirement soon. But there is plenty of ongoing research into "clean coal" possibilities, and the federal government has expressed an interest in smaller, modular coal units.

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UK EV Per-Mile Taxes are reshaping road pricing and vehicle taxation for electric cars, raising fairness concerns, climate policy questions, and funding needs for infrastructure and charging networks across the country.

Key Points

They are per-mile road charges on EVs to fund infrastructure, raising fairness, emissions, and vehicle taxation concerns.

✅ Propose tax relief or credits for EV owners

✅ Consider emission-based road user charging

✅ Invest in charging networks and road infrastructure

As the UK continues its push towards a greener future with increased adoption of electric vehicles (EVs) and surging EV interest during supply disruptions, a growing number of electric car drivers are voicing their frustration over the current tax system. The debate centers around the per-mile vehicle taxes that are being proposed and implemented, which many argue are unfairly burdensome on EV owners. This issue has sparked a broader campaign advocating for a more equitable approach to vehicle taxation, one that reflects the evolving landscape of transportation and environmental policy.

Rising Costs for Electric Car Owners

Electric vehicles have been hailed as a crucial component in the UK’s strategy to reduce carbon emissions and combat climate change. Government incentives, such as grants for EV purchases and tax breaks, have been instrumental in encouraging the shift from petrol and diesel cars to cleaner alternatives, even as affordability concerns persist among many UK consumers. However, as the number of electric vehicles on the road grows, the financial dynamics of vehicle taxation are coming under scrutiny.

One of the key issues is the introduction and increase of per-mile vehicle taxes. While these taxes are designed to account for road usage and infrastructure costs, they have been met with resistance from EV drivers who argue that they are being disproportionately affected. Unlike traditional combustion engine vehicles, electric cars typically have lower running costs compared to petrol or diesel models and, in many cases, benefit from lower or zero emissions. Yet, the current tax system does not always reflect these advantages.

The Taxation Debate

The crux of the debate lies in how vehicle taxes are structured and implemented. Per-mile taxes are intended to ensure that all road users contribute fairly to the maintenance of transport infrastructure. However, the implementation of such taxes has raised concerns about fairness and affordability, particularly for those who have invested heavily in electric vehicles.

Critics argue that per-mile taxes do not adequately take into account the environmental benefits of driving an electric car, noting that the net impact depends on the electricity generation mix in each market. While EV owners are contributing to a cleaner environment by reducing emissions, they are also facing higher taxes that could undermine the financial benefits of their greener choice. This has led to calls for a reassessment of the tax system to ensure that it aligns with the UK’s climate goals and provides a fair deal for electric vehicle drivers.

Campaigns for Fairer Taxation

In response to these concerns, several advocacy groups and individual EV owners have launched campaigns calling for a more balanced approach to vehicle taxation. These campaigns emphasize the need for a system that supports the transition to electric vehicles and recognizes their role in reducing environmental impact, drawing on ambitious EV targets abroad as useful benchmarks.

Key proposals from these campaigns include:

1. Tax Relief for EV Owners: Advocates suggest providing targeted tax relief for electric vehicle owners to offset the costs of per-mile taxes. This could include subsidies or tax credits that acknowledge the environmental benefits of EVs and help to make up for higher road usage fees.

2. Emission-Based Taxation: An alternative approach is to design vehicle taxes based on emissions rather than mileage. This system would ensure that those driving high-emission vehicles contribute more to road maintenance, while EV owners, who are already reducing emissions, are not penalized.

3. Infrastructure Investments: Campaigners also call for increased investments in infrastructure that supports electric vehicles, such as charging networks and proper grid management practices that balance load. This would help to address concerns about the adequacy of current road maintenance and support the growing number of EVs on the road.

Government Response and Future Directions

The UK government faces the challenge of balancing revenue needs with environmental goals. While there is recognition of the need to update the tax system in light of increasing EV adoption, there is also a focus on ensuring that any changes are equitable and do not disincentivize the shift towards cleaner vehicles, while considering whether the UK grid can handle additional EV demand reliably.

Discussions are ongoing about how to best implement changes that address the concerns of electric vehicle owners while ensuring that the transportation infrastructure remains adequately funded. The outcome of these discussions will be critical in shaping the future of vehicle taxation in the UK and supporting the country’s broader environmental objectives.

Conclusion

As electric vehicle adoption continues to rise in the UK, the debate over vehicle taxation becomes increasingly important. The campaign for fairer per-mile taxes highlights the need for a tax system that supports the transition to cleaner transportation while also being fair to those who have made environmentally conscious choices. Balancing these factors will be key to achieving the UK’s climate goals and ensuring that all road users contribute equitably to the maintenance of transport infrastructure. The ongoing dialogue and policy adjustments will play a crucial role in shaping a sustainable and just future for transportation in the UK.

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China Solar Grid Parity signals unsubsidized industrial and commercial PV, rooftop solar, and feed-in tariff guarantees competing with grid electricity and coal power prices, driven by cost declines, policy reform, and technology advances.

Key Points

Point where PV in China meets or beats grid electricity, enabling unsubsidized industrial and commercial solar.

✅ City-level analysis shows cheaper PV than grid in 344 cities.

✅ 22% can beat coal power prices without subsidies.

✅ Soft-cost, permitting, and finance reforms speed uptake.

Solar power has become cheaper than grid electricity across China, a development that could boost the prospects of industrial and commercial solar, according to a new study.

Projects in every city analysed by the researchers could be built today without subsidy, at lower prices than those supplied by the grid, and around a fifth could also compete with the nation’s coal electricity prices.

They say grid parity – the “tipping point” at which solar generation costs the same as electricity from the grid – represents a key stage in the expansion of renewable energy sources.

While previous studies of nations such as Germany, where solar-plus-storage costs are already undercutting conventional power, and the US have concluded that solar could achieve grid parity by 2020 in most developed countries, some have suggested China would have to wait decades.

However, the new paper published in Nature Energy concludes a combination of technological advances, cost declines and government support has helped make grid parity a reality in Chinese today.

Despite these results, grid parity may not drive a surge in the uptake of solar, a leading analyst tells Carbon Brief.

Competitive pricing

China’s solar industry has rapidly expanded from a small, rural program in the 1990s to the largest in the world, with record 2016 solar growth underscoring the trend. It is both the biggest generator of solar power and the biggest installer of solar panels.

The installed capacity of solar panels in China in 2018 amounted to more than a third of the global total, with the country accounting for half the world’s solar additions that year.

Since 2000, the Chinese government has unveiled over 100 policies supporting the PV industry, and technological progress has helped make solar power less expensive. This has led to the cost of electricity from solar power dropping, as demonstrated in the chart below.

In their paper, Prof Jinyue Yan of Sweden’s Royal Institute of Technology and his colleagues explain that this “stunning” performance has been accelerated by government subsidies, but has also seen China overinvesting in what some describe as a clean energy's dirty secret of “redundant construction and overcapacity”. The authors write:

“Recently, the Chinese government has been trying to lead the PV industry onto a more sustainable and efficient development track by tightening incentive policies with China’s 531 New Policy.”

The researchers say the subsidy cuts under this policy in 2018 were a signal that the government wanted to make the industry less dependent on state support and shift its focus from scale to quality.

This, they say, has “brought the industry to a crossroads”, with discussions taking place in China about when solar electricity generation could achieve grid parity.

In their analysis, Yan and his team examined the prospects for building industrial and commercial solar projects without state support in 344 cities across China, attempting to gauge where or whether grid parity could be achieved.

The team estimated the total lifetime price of solar energy systems in all of these cities, taking into account net costs and profits, including project investments, electricity output and trading prices.

Besides establishing that installations in every city tested could supply cheaper electricity than the grid, they also compared solar to the price of coal-generated power. They found that 22% of the cities could build solar systems capable of producing electricity at cheaper prices than coal.

Embracing solar

Declining costs of solar technology, particularly crystalline silicon modules, mean the trend in China is also playing out around the world, with offshore wind cost declines reinforcing the shift. In May, the International Renewable Energy Agency (IRENA) said that by the beginning of next year, grid parity could become the global norm for the solar industry, and shifting price dynamics in Northern Europe illustrate the market impact.

Kingsmill Bond, an energy strategist at Carbon Tracker, says this is the first in-depth study he has seen looking at city-level solar costs in China, and is encouraged by this indication of solar becoming ever-more competitive, as seen in Germany's recent solar boost during the energy crisis. He tells Carbon Brief:

“The conclusion that industrial and commercial solar is cheaper than grid electricity means that the workshop of the world can embrace solar. Without subsidy and its distorting impacts, and driven by commercial gain.”

On the other hand, Jenny Chase, head of solar analysis at BloombergNEF, says the findings revealed by Yan and his team are “fairly old news” as the competitive price of rooftop solar in China has been known about for at least a year.

She notes that this does not mean there has been a huge accompanying rollout of industrial and commercial solar, and says this is partly because of the long-term thinking required for investment to be seen as worthwhile.

The lifetime of a PV system tends to be around two decades, whereas the average lifespan of a Chinese company is only around eight years, according to Chase. Furthermore, there is an even simpler explanation, as she explains to Carbon Brief:

“There’s also the fact that companies just can’t be bothered a lot of the time – there are roofs all over Europe where solar could probably save money, but people are not jumping to do it.”

According to Chase, a “much more exciting” development came earlier this year, when the Chinese government developed a policy for “subsidy-free solar”.

This involved guaranteeing the current coal-fired power price to solar plants for 20 years, creating what is essentially a low feed-in tariff and leading to what she describes as “a lot of nice, low-risk projects”.

As for the beneficial effects of grid parity, based on how things have played out in countries where it has already been achieved, Chase says it does not necessarily mean a significant uptake of solar power will follow:

“Grid parity solar is never as popular as subsidised solar, and ironically you don’t generally have a rush to build grid parity solar because you may as well wait until next year and get cheaper solar.”

Policy proposals

In their paper, Yan and his team lay out policy changes they think would help provide an economic incentive, in combination with grid parity, to encourage the uptake of solar power systems.

Technology costs may have fallen for smaller solar projects of the type being deployed on the rooftops of businesses, but they note that the so-called “soft costs” – including installation and maintenance – tend to be “very impactful”.

Specifically, they say aspects such as financing, land acquisition and grid accommodation, which make up over half the total cost, could be cut down:

“Labour costs are not significant [in China] because of the relatively low wages of direct labour and related installation overhead. Customer acquisition has largely been achieved in China by the mature market, with customers’ familiarity with PV systems, and with the perception that PV systems are a reliable technology. However, policymakers should consider strengthening the targeted policies on the following soft costs.”

Among the measures they suggest are new financing schemes, an effort to “streamline” the complicated procedures and taxes involved, and more geographically targeted government policies, alongside innovations like peer-to-peer energy sharing that can improve utilization.

As their analysis showed the price of solar electricity had fallen further in some cities than others, the researchers recommend targeting future subsidies at the cities that are performing less well – keeping costs to a minimum while still providing support when it is most needed.

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Clean Energy Industry Support includes tax credits, refundability, safe harbor extensions, EV incentives, and stimulus measures to stabilize renewable energy projects, protect the workforce, and ensure financing continuity during economic recovery.

Key Points

Policies and funding to stabilize renewables, protect jobs, and extend tax incentives for workforce continuity.

✅ Extend PTC/ITC and remove phase-outs to sustain projects

✅ Enable direct pay or refundability to unlock financing

✅ Preserve safe harbor timelines disrupted by supply chains

U.S. Senator Catherine Cortez Masto (D-Nev.) led 17 Senate colleagues, as the Senate moves to modernize public-land renewables, in sending a letter calling on Congress to include support for the United States' clean energy industry and workforce in any economic aid packages.

"As Congress takes steps to ensure that our nation's workforce is prepared to emerge stronger from the coronavirus health and economic crisis, we must act to shore up clean energy businesses and workers who are uniquely impacted by the crisis, echoing a power-sector call for action from industry groups," said the senators. "This action, which has precedent in prior financial recovery efforts, could take several forms, including tax credit extensions or removal of the current phase-out schedule, direct payment or refundability, or extensions of safe harbor continuity."

"We need to make sure that any package protects workers and helps families stay afloat in these challenging times. Providing support to the clean energy industry will give much-needed certainty and confidence, as the sector targets a market majority, for those workers that they will be able to keep their paychecks and their jobs in this critical industry," the senators also said.

In addition to Senator Cortez Masto, the letter was also signed by Senators Ed Markey (D-Mass.), Martin Heinrich (D-N.M), Sheldon Whitehouse (D-R.I.), Debbie Stabenow (D-Mich.), Tina Smith (D-Minn.), Jack Reed (D-R.I.), Cory Booker (D-N.J.), Richard Blumenthal (D-Conn.), Amy Klobuchar (D-Minn.), Chris Van Hollen (D-Md.), Dianne Feinstein (D-Calif.), Jacky Rosen (D-Nev.), Tammy Duckworth (D-Ill.), Chris Coons (D-Del.), Mazie Hirono (D-Hawaii), Dick Durbin (D-Ill.), and Kyrsten Sinema (D-Ariz.).

Dear Leader McConnell, Leader Schumer, Chairman Grassley, Ranking Member Wyden:

As Congress takes steps to ensure that our nation's workforce is prepared to emerge stronger from the coronavirus health and economic crisis, we must act to shore up clean energy businesses and workers who are uniquely impacted by the crisis, with wind investments at risk amid the pandemic. This action, which has precedent in prior financial recovery efforts, could take several forms, including tax credit extensions or removal of the current phase-out schedule, direct payment or refundability, or extensions of safe harbor continuity.

First and foremost, we need to take care of workers' health and immediate needs to stay in their homes and provide for their families, and the Families First Coronavirus Response Act is a critical down payment. Now, we must make sure the workforce has jobs to return to and that employers remain able to pay for critical benefits like paid sick and family leave, healthcare, and Unemployment Insurance.

The renewable energy industry employs over 800,000 people across every state in the United States. This industry and its workers could suffer significant harms as a result of the coronavirus emergency and resulting financial impact. Renewable energy businesses are already seeing project cancellations or delays, as the Covid-19 crisis hits solar and wind across the sector, with the solar industry reporting delays of 30 percent. Likewise, the energy efficiency sector is susceptible to similar impacts. As the coronavirus pandemic intensifies in the United States, that rate of delay or cancellations will only continue to skyrocket. Global and domestic supply chains are already facing chaotic changes, with equipment delays of three to four months for parts of the industry. A major collapse in financing is all but certain as investment firms' profits turn to losses and capital is suddenly unavailable for large labor-intensive investments.

To ensure that we do not lose years of progress on clean energy and the source of employment for tens of thousands of renewable energy workers, Congress should look to previous relief packages as an example for how to support this sector and the broader American economy. The American Recovery and Reinvestment Act of 2009 (also known as the Recovery Act or ARRA) provided over $90 billion in funding for clean energy and grid modernization, along with emergency relief programs. Specifically, ARRA provided immediate funding streams like the 1603 Cash Grant program for renewables and the 30 percent clean energy manufacturing tax credit to give immediate relief for the clean energy industry. As Congress develops this new package, it should consider these immediate relief programs for the renewable and clean energy industry, especially as analyses suggest green energy could drive Covid-19 recovery at scale. This could include direct payment or refundability, extensions of safe harbor continuity, tax credit extensions, electric vehicle credit expansion, or removal of the current phase-out schedules for the clean energy industry.

We need to make sure that any package protects workers and helps families stay afloat in these challenging times. Providing support to the clean energy industry will give much-needed certainty and confidence for those workers that they will be able to keep their paychecks and their jobs in this critical industry.

These strategies to provide assistance to the clean energy industry must be included in any financial recovery discussions, particularly if the Trump Administration continues its push to aid the oil industry, even as some advocate a total fossil fuel lockdown to accelerate climate action. We appreciate your consideration and collaboration as we do everything in our power to quickly recover from this health and economic emergency.

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Alberta Coal Phase-Out signals a clean energy transition, replacing coal with natural gas and renewables, cutting greenhouse gas emissions, leveraging a carbon levy, and supporting workers in Alberta's evolving electricity market.

Key Points

Alberta Coal Phase-Out moves power from coal to lower-emission natural gas and renewables to reduce grid emissions.

✅ Last coal plant closed: Genesee Generating Station, Sept 30, 2023

✅ Shift to natural gas and renewables lowers emissions

✅ Carbon levy and incentives accelerated clean power build-out

The closure of the Genesee Generating Station on September 30, 2023, marked a significant milestone in Alberta's energy history, as the province moved to retire coal power by 2023 ahead of its 2030 provincial deadline. The Genesee, located near Calgary, was the province's last remaining coal-fired power plant. Its closure represents the culmination of a multi-year effort to transition Alberta's electricity sector away from coal and towards cleaner sources of energy.

For decades, coal was the backbone of Alberta's electricity grid. Coal-fired plants were reliable and relatively inexpensive to operate. However, coal also has a significant environmental impact. The burning of coal releases greenhouse gases, including carbon dioxide, a major contributor to climate change. Coal plants also produce air pollutants such as sulfur dioxide and nitrogen oxide, which can cause respiratory problems and acid rain, and in some regions electricity is projected to get dirtier as gas use expands.

In recognition of these environmental concerns, the Alberta government began to develop plans to phase out coal-fired power generation in the early 2000s. The government implemented a number of policies to encourage the shift from coal to cleaner energy such as natural gas and renewable energy. These policies included providing financial incentives for the construction of new natural gas plants and renewable energy facilities, as well as imposing a carbon levy on coal-fired generation.

The phase-out of coal was also driven by economic factors. The cost of natural gas has declined significantly in recent years, making it a more competitive fuel source for electricity generation as producers switch to gas under evolving market conditions. Additionally, the Alberta government faced increasing pressure from the federal government to reduce greenhouse gas emissions.

The transition away from coal has not been without its challenges. Coal mining and coal-fired power generation have long been important parts of Alberta's economy. The closure of coal plants has resulted in job losses in the affected communities. The government has implemented programs to help workers transition to new jobs in the clean energy sector.

Despite these challenges, the closure of the Genesee Generating Station is a positive development for Alberta's environment and climate. Coal-fired power generation is one of the largest sources of greenhouse gas emissions in Alberta, and recent wind generation outpacing coal underscores the sector's transformation. The closure of the Genesee is expected to result in a significant reduction in emissions, helping Alberta to meet its climate change targets.

The transition away from coal also presents opportunities for Alberta. The province has vast natural gas resources, which can be used to generate electricity with lower emissions than coal. Alberta is also well-positioned to develop renewable energy sources, such as wind power and solar power. These renewable energy sources can help to further reduce emissions and create new jobs in the clean energy sector.

The closure of the Genesee Generating Station is a significant milestone in Alberta's energy history. It represents the end of an era for coal-fired power generation in the province, a shift mirrored by the UK's last coal station going offline earlier this year. However, it also marks the beginning of a new era for Alberta's energy sector. By transitioning to cleaner sources of energy, Alberta can reduce its environmental impact and create a more sustainable energy future.

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Nighttime Thermoelectric Generator converts radiative cooling into renewable energy, leveraging outer space cold; a Stanford-UCLA prototype complements solar, serving off-grid loads with low-power output during peak evening demand, using simple materials on a rooftop.

Key Points

A device converting nighttime radiative cooling into electricity, complementing solar for low-power evening needs.

✅ Uses thermocouples to convert temperature gradients to voltage.

✅ Exploits radiative cooling to outer space for night power.

✅ Complements solar; low-cost parts suit off-grid applications.

Two years ago, one freezing December night on a California rooftop, a tiny light shone weakly with a little help from the freezing night air. It wasn't a very bright glow. But it was enough to demonstrate the possibility of generating renewable power after the Sun goes down.

Working with Stanford University engineers Wei Li and Shanhui Fan, University of California Los Angeles materials scientist Aaswath Raman put together a device that produces a voltage by channelling the day's residual warmth into cooling air, effectively generating electricity from thin air with passive heat exchange.

"Our work highlights the many remaining opportunities for energy by taking advantage of the cold of outer space as a renewable energy resource," says Raman.

"We think this forms the basis of a complementary technology to solar. While the power output will always be substantially lower, it can operate at hours when solar cells cannot."

For all the merits of solar energy, it's just not a 24-7 source of power, although research into nighttime solar cells suggests new possibilities for after-dark generation. Sure, we can store it in a giant battery or use it to pump water up into a reservoir for later, but until we have more economical solutions, nighttime is going to be a quiet time for renewable solar power. 

Most of us return home from work as the Sun is setting, and that's when energy demands spike to meet our needs for heating, cooking, entertaining, and lighting.

Unfortunately, we often turn to fossil fuels to make up the shortfall. For those living off the grid, it could require limiting options and going without a few luxuries.

Shanhui Fan understands the need for a night time renewable power source well. He's worked on a number of similar devices, including carbon nanotube generators that scavenge ambient energy, and a recent piece of technology that flipped photovoltaics on its head by squeezing electricity from the glow of heat radiating out of the planet's Sun-warmed surface.

While that clever item relied on the optical qualities of a warm object, this alternative device makes use of the good old thermoelectric effect, similar to thin-film waste-heat harvesting approaches now explored.

Using a material called a thermocouple, engineers can convert a change in temperature into a difference in voltage, effectively turning thermal energy into electricity with a measurable voltage. This demands something relatively toasty on one side and a place for that heat energy to escape to on the other.

The theory is the easy part – the real challenge is in arranging the right thermoelectric materials in such a way that they'll generate a voltage from our cooling surrounds that makes it worthwhile.

To keep costs down, the team used simple, off-the-shelf items that pretty much any of us could easily get our hands on.

They put together a cheap thermoelectric generator and linked it with a black aluminium disk to shed heat in the night air as it faced the sky. The generator was placed inside a polystyrene enclosure sealed with a window transparent to infrared light, and linked to a single tiny LED.

For six hours one evening, the box was left to cool on a roof-top in Stanford as the temperature fell just below freezing. As the heat flowed from the ground into the sky, the small generator produced just enough current to make the light flicker to life.

At its best, the device generated around 0.8 milliwatts of power, corresponding to 25 milliwatts of power per square metre.

That might just be enough to keep a hearing aid working. String several together and you might just be able to keep your cat amused with a simple laser pointer. So we're not talking massive amounts of power.

But as far as prototypes go, it's a fantastic starting point. The team suggests that with the right tweaks and the right conditions, 500 milliwatts per square metre isn't out of the question.

"Beyond lighting, we believe this could be a broadly enabling approach to power generation suitable for remote locations, and anywhere where power generation at night is needed," says Raman.

While we search for big, bright ideas to drive the revolution for renewables, it's important to make sure we don't let the smaller, simpler solutions like these slip away quietly into the night.

This research was published in Joule.

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