Solar Energy

Radiative cooling and solar heating from one system, no electricity needed

Published

4 years ago

February 9, 2021

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Radiative cooling and solar heating from one system, no electricity needed

Passive cooling, like the shade a tree provides, has been around forever. Recently, researchers have been exploring how to turbo charge a passive cooling technique – known as radiative or sky cooling – with sun-blocking, nanomaterials that emit heat away from building rooftops. While progress has been made, this eco-friendly technology isn’t commonplace because researchers have struggled to maximize the materials’ cooling capabilities.

New research led by University at Buffalo engineers makes significant progress in this area.

A study published Feb. 8 in the journal Cell Reports Physical Science describes a uniquely designed radiative cooling system that:

+ Lowered the temperature inside a test system in an outdoor environment under direct sunlight by more than 12 degrees Celsius (22 degrees Fahrenheit).

+ Lowered the temperature of the test box in a laboratory, meant to simulate the night, by more than 14 degrees Celsius (25 degrees Fahrenheit).

+ Simultaneously captured enough solar power that can be used to heat water to about 60 degrees Celsius (140 degrees Fahrenheit).

While the system tested was only 70 centimeters (27.5 inches) squared, it could eventually be scaled up to cover rooftops, engineers say, with the goal of reducing society’s reliance on fossil fuels for cooling and heating. It also could aid communities with limited access to electricity.

“There is a great need for heating and cooling in our daily life, especially cooling in the warming world,” says the study’s lead author Qiaoqiang Gan, PhD, professor of electrical engineering in the UB School of Engineering and Applied Sciences.

The research team includes Zongfu Yu, PhD, University of Wisconsin-Madison; Boon Ooi, PhD, King Abdullah University of Science and Technology (KAUST) in Saudi Arabia; and members of Gan’s lab at UB, and Ooi’s lab at KAUST.

System design and materials key to success

The system consists of what are essentially two mirrors, made of 10 extremely thin layers of silver and silicon dioxide, which are placed in a V-shape.

These mirrors absorb incoming sunlight, turning solar power from visible and near-infrared waves into heat. The mirrors also reflect mid-infrared waves from an “emitter” (a vertical box in between the two mirrors), which then bounces the heat they carry into the sky.

“”Since the thermal emission from both surfaces of the central thermal emitter is reflected to the sky, the local cooling power density on this emitter is doubled, resulting in a record high temperature reduction,” says Gan.

“”Most radiative cooling systems scatter the solar energy, which limits the system’s cooling capabilities,” Gan says. “Even with a perfect spectral selection, the upper limit for the cooling power with an ambient temperature of 25 degrees Celsius is about 160 watts per square meter. In contrast, the solar energy of about 1000 watts per square meter on top of those systems was simply wasted.””

Spinoff company aims to commercialize technology

Gan co-founded a spinoff company, Sunny Clean Water LLC, which is seeking partners to commercialize this technology.

“One of the key innovations of our system is the ability to separate and retain the solar heating and radiative cooling at different components in a single system,” says co-first author Lyu Zhou, a PhD candidate in electrical engineering in the School of Engineering and Applied Sciences. “During the night, radiative cooling is easy because we don’t have solar input, so thermal emissions just go out and we realize radiative cooling easily. But daytime cooling is a challenge because the sun is shining. In this situation, you need to find strategies to separate solar heating from the cooling area.”

The work builds upon previous research Gan’s lab led that involved creating a cone-shaped system for electricity-free cooling in crowded cities to adapt to climate change.

“The new double-sided architecture realized a record local cooling power density beyond 280 watts per square meter. Under standard atmospheric pressure with no vacuum thermal isolation, we realized a temperature reduction of 14.5 degrees Celsius below the ambient temperature in a laboratory environment, and over 12 degrees Celsius in an outdoor test using a simple experimental system,” says the other co-first author, Haomin Song, PhD, a research assistant professor of electrical engineering in the School of Engineering and Applied Sciences.

“Importantly, our system does not simply waste the solar input energy. Instead, the solar energy is absorbed by the solar spectral selective mirrors, and it can be used for solar water heating, which is widely used as an energy efficient device in developing countries,” says Gan. “It can retain both the solar heating and radiative cooling effects in a single system with no need of electricity. It’s really sort of a ‘magic’ system of ice and fir.”

The research team will continue to investigate ways to improve the technology, including examining how to capture enough solar power to boil water, making it suitable for drinking.

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Solar Energy

UK announces new investment in green energy projects

Published

23 hours ago

October 11, 2024

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UK announces new investment in green energy projects

by AFP Staff Writers

London (AFP) Oct 10, 2024

The UK government on Thursday announced that it had secured more than �24 billion ($31.3 billion) of private investment in green energy projects, as it gears up for an international investment summit.

Prime Minister Keir Starmer called the investments “a huge vote of confidence” in his Labour government and its long-term growth plans, despite a stuttering start in power since the party’s election win in July.

Labour, in opposition for 14 years, has vowed to revitalise the UK economy, which it claims faltered badly during successive Conservative administrations since 2010.

Central to its plans is green energy, to transition the country away from polluting fossil fuels towards renewables such as wind, wave and solar, to meet net-zero targets.

But Starmer and his finance minister Rachel Reeves have been accused of scaring off investors by relentless talk of a dire economic inheritance from the Tories and warnings about tough remedial measures to come.

Spain’s Iberdrola, which owns UK energy provider Scottish Power, said it was doubling its investment in the UK over the next four years to �24 billion.

Denmark’s Orsted is investing �8 billion and Portugal’s Greenvolt �2.5 billion, Downing Street said in a statement.

The announcements come after a record 131 new green infrastructure projects were awarded at auction last month, including plans for Europe’s two biggest offshore windfarms.

Starmer said creating the right conditions was key to boosting growth and that the International Investment Summit on Monday would be a “springboard” to do so.

The UK premier and Reeves are both slated to speak at the meeting in central London.

Labour announced its green energy strategy in July, including Great British Energy, a public-owned body that intends to spur investment in domestic renewable projects.

Great British Energy will receive �8.3 billion over the next five years.

Last week, the government announced nearly �22 billion of investment over 25 years to support three carbon capture projects in northeast and northwest England.

It has also lifted a ban on onshore wind projects in England, introduced after opposition from local residents.

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Solar Energy

Streamlined perovskite solar cells offer path to cheaper, more efficient energy

Published

24 hours ago

October 11, 2024

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Streamlined perovskite solar cells offer path to cheaper, more efficient energy

by Simon Mansfield

Sydney, Australia (SPX) Oct 11, 2024

Researchers at City University of Hong Kong (CityUHK) have developed a new fabrication method that enhances the efficiency, stability, and affordability of perovskite solar cells, bringing them closer to commercial viability.

Published in ‘Science’, this study highlights how a simplified device structure designed by the CityUHK team could pave the way for future industrial-scale production of perovskite solar cells, improving their reliability and reducing costs.

“The improvements in stability and the simplification of the production process of perovskite solar cells represent a significant step forward in making solar energy more accessible and affordable,” said Professor Zhu Zonglong from the Department of Chemistry at CityUHK. Perovskite, the key material in these solar cells, effectively converts sunlight into electricity.

The team’s advancements focus on two innovations. First, they integrated hole-selective materials with the perovskite layers, streamlining the manufacturing process. Second, they replaced traditional organic materials with an inorganic electron transport layer, tin oxide, which significantly improves the solar cells’ operational stability. “The device structure reported in this study represents the most simplified architecture in the current field of perovskite solar cells,” explained Dr. Gao Danpeng, a co-author and postdoctoral researcher at CityUHK. This innovation reduces production costs by eliminating the need for an organic transfer layer, simplifying manufacturing.

These developments have resulted in power conversion efficiencies exceeding 25%, with the solar cells maintaining over 95% efficiency after 2,000 hours of continuous testing, according to Professor Zhu. This performance surpasses that of traditional perovskite solar cells, meeting key industry standards for longevity.

The findings offer new opportunities for researchers in materials science and renewable energy, with potential impacts for solar cell manufacturers and consumers alike. The study also emphasizes the environmental and policy implications, as this research could support the shift toward more sustainable energy sources, reducing fossil fuel reliance and promoting renewable energy.

In the next phase, the CityUHK team plans to scale up the technology by applying this structure to larger perovskite solar modules, aiming to enhance both efficiency and scalability.

This research was conducted in collaboration with the National Renewable Energy Laboratory and Imperial College London, reflecting the global effort toward sustainable energy solutions. “With the potential to be implemented in solar energy systems within the next 5 years, this research is a critical step towards achieving more sustainable and environmentally friendly energy production globally,” added Professor Zhu.

Research Report:Long-term stability in perovskite solar cells through atomic layer deposition of tin oxide

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Solar Energy

China’s solar goes from supremacy to oversupply

Published

2 days ago

October 10, 2024

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China’s solar goes from supremacy to oversupply

By Oliver HOTHAM

Beijing (AFP) Oct 10, 2024

Strong state support and huge private investment have made China’s solar industry a global powerhouse, but it faces new headwinds, from punitive tariffs abroad to a brutal price war at home.

Officials meeting in Baku next month for the COP29 summit hope to agree on new finance targets to help developing countries respond to climate change, including ditching fossil fuels.

Last year, countries agreed to triple global installed renewable energy capacity by 2030.

China is installing almost twice as much solar and wind power as every other country combined.

And it dominates the market.

It makes eight out of every 10 solar panels and controls 80 percent of every stage of the manufacturing process.

It is also home to the world’s top 10 suppliers of solar panel manufacturing equipment, and its related exports hit a record $49 billion last year, according to Wood Mackenzie.

That supremacy is not accidental: Chinese state support has been key, analysts say.

Beijing invested over $50 billion in new solar supply capacity from 2011 to 2022, according to the International Energy Agency.

The industry has also benefited from access to cheap raw materials, readily available capital from state-owned banks, and huge engineering manpower.

“Chinese producers were ahead of everyone else on cost,” said Lauri Myllyvirta, co-founder of the Centre for Research on Energy and Clean Air, a climate think tank.

“That meant new investment takes place in China, because that’s where it’s most competitive,” he told AFP.

The focus has driven a “steep learning curve… both in solar cell technology and manufacturing know-how”, added Johannes Bernreuter, a longtime solar industry analyst.

That in turn has created “an efficient industry ecosystem”, he said.

– ‘Overcapacity’-

As countries around the world race to convert their power systems, China’s solar supremacy has become a growing concern.

The United States and other Western countries have accused Beijing of deliberate “overcapacity” and flooding global markets with cut-price solar exports intended to undercut competition.

Washington has doubled tariffs on Chinese panels to 50 percent, part of a broader package targeting $18 billion worth of Chinese imports in strategic sectors including electric vehicles, batteries, critical minerals and medical products.

The European Union is also probing Chinese-owned solar panel manufacturers for allegedly receiving unfair subsidies.

Most US solar panel imports now come from Southeast Asia, but Washington says Chinese manufacturers have relocated operations there to circumvent barriers.

China also accounts for almost all of Europe’s imports of solar panels from outside the bloc.

That means many markets will struggle to catch up “with two decades of very forceful and very successful industrial policy in China”, said Myllyvirta.

China’s solar industry faces its own struggles though, beyond trade barriers in the West.

The sector’s supersonic expansion has overleveraged the domestic industry, overloaded China’s grid and sparked a brutal price war, experts say.

Industry leaders have reportedly warned of an “ice age” and urged government intervention to stem slumping prices, but there has been little sign of relief.

This year saw a wave of bankruptcies, and new solar projects fell by over 75 percent in the first half of 2024, an industry group said in July.

– ‘Lots of companies will fail’ –

The price wars, which are so fierce that solar export earnings fell last year despite volumes hitting a new high, are like a “snake eating its own tail”, warned analyst David Fishman.

Companies get stuck “in this circle of competition where whoever is able to endure the pain for longest comes out as the victor,” said Fishman, a senior manager at the Lantau Group specialising in China’s power sector.

“Lots of companies will fail along the way.”

And while the manufacturing glut has helped China hit a wind and solar installation target nearly six years ahead of schedule, the country’s grid is struggling to keep up.

Increasingly, renewable supply is being blocked to prevent the grid from becoming overwhelmed, a process known as curtailment.

Solar curtailment rose four percent in the first quarter of 2024 from a year earlier, according to Fitch Ratings.

Authorities will soon be forced to “stop approving new projects or allowing projects to connect to the grid if it means curtailment rates are at risk of going higher”, Fishman said.

“They’ve got to build,” he added. “They have to catch up.”

Blocked in the West and running out of track at home, China’s solar is seeking new markets, and this year, Europe was overtaken by Asia as the biggest export market for solar products, according to an industry body.

Exports to Africa also soared 187 percent year-on-year in 2023, though the continent still buys a small fraction compared to Europe, according to energy think tank Ember.

The industry is now in a “restructuring and shakeout phase”, said Bernreuter.

After that, “the Chinese solar industry will march on with unperturbed pace and a more global manufacturing footprint”.

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