Indoor Light and Organic Solar Cells - Energy Without Sunlight

Image Credit: Thor Balkhed - Wuming Wang, PhD Student, and Jonas Bergqvist, Principal Research Engineer in the solar cell laboratory

The new organic solar cell, optimized to convert ambient indoor light to electricity, is being developed by scientists at Sweden's Linköping University, the Chinese Academy of Sciences, and the University of Science and Technology Beijing.

Although the power produced by it is low, the scientists believe it could be enough power to support the many products that the Internet of Things will bring online. 

Low energy consuming devices sensors that detect and measure moisture, particle concentrations, temperature, and other parameters will require small and cheap sources of renewable energy.

The researchers developed an active layer made up of donor and acceptor materials. The new combination - a non-fullerene acceptor blended with a polymer donor - supported the development of a photoactive layer allowing it to absorb the exact wavelengths of light that are typically found in most indoor environments. In a nutshell, donor materials absorb photons, while acceptors acquire electrons. Photovoltaic characterizations of the new solar cell revealed a low energy loss below 0.60 eV.

Two prototypes have been created so far, one measuring 1 square centimeter (0.2 sq in) and the other measuring 4 sq cm (0.6 sq in).

The optimized organic photovoltaic cell, with an area of 1 cm2, showed a power conversion efficiency of 26.1% with an open-circuit voltage of 1.10  V under an LED illumination of 1000 lux (2700 K).

“We are confident that the efficiency of organic solar cells will be further improved for ambient light applications in coming years, because there is still a large room for optimization of the materials used in this work,” said professor Jianhui Hou from the Chinese Academy of Sciences.

The technology is now being commercialized by a Linköping spin-off company. A paper on the research, which was led by the university's Assoc. Prof. Feng Gao, was recently published in the journal Nature Energy.

Sources: Linköping University & Newatlas

Organic Solar Cells Break New Efficiency Record: 17.3%

In recent years, scientists have been trying to find a way to improve the efficiency of organic photovoltaic cells. Some researchers have even thought that organic solar cells may never improve beyond 15 percent. Solar cells based on silicon, by comparison, are in the 18 to 22 percent range.

But in a new effort, the researchers in China have developed an organic photovoltaic cell that converts 17.3% of the energy in sunlight into electricity. 

“Organic solar cells have been studied for many years, but they’re still relatively young compared to silicon,” said Chen Yongsheng, a chemist at Nankai University in North China's Tianjin. “We still don’t understand their device performance very well.” 

Chen's group used tandem cells, which are put together by different layers of organic materials. Previous designs for tandem organic cells have failed to tap into the abundant solar energy of the near-infrared range, but Chen’s team addressed this issue. 

They used a non-fullerene acceptor molecule known as O6T-4F, which was able to work better at this wavelength. They then combined that with a layer containing a relatively new electron acceptor, called F-M for short, which the team had earlier developed. This material was shown to be an excellent match for its electrical properties and could absorb visible light.

"Different layers of the tandem cells can absorb different wavelengths of light. That means you can use sunlight in the wider wavelengths more efficiently and achieve a higher power conversion rate," Dr. Chen Yongsheng said.

"There’s no reason why an organic solar cell can’t have a similar or higher performance to silicon or perovskites,” according to Chen.

Sources:

https://physicsworld.com/a/organic-solar-cells-break-new-efficiency-record/

https://www.futuretimeline.net/blog/2018/08/15.htm

https://cen.acs.org/energy/solar-power/Organic-solar-cell-smashes-performance/96/web/2018/08

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The breakthrough is published in the journal Science

China's Solar-Powered City Rizhao

Since I found this information interesting and inspiring I decided to publish one more post about China and solar energy, this time featuring China's solar-powered city Rizhao. China has a major problem with pollution, largely as a result of the country's rapid industrial growth and a large increase in energy consumption, which is primarily provided by coal power plants. So, I think that projects and strategies like this one in Rizhao deserve admiration and popularization.

Rizhao is a "small" coastal Chinese city of nearly three million, located at the southern end of Shandong Peninsula and bordering on the Yellow Sea. It is a rising seaport and tourist city, with golden beaches, mild climate and lots of sunshine - Rizhao receives an average of 270 days of sunlight every year. Recently, Rizhao has gained much popularity because of using sun's light and heat to provide energy, thus limiting the city’s carbon emissions and urban pollution. By using the simple, cheap solar devices that sit on the almost all of Rizhao's rooftops, the city has cut its yearly carbon dioxide emissions by about 53,000 tons. The features of a coastal city with “large green space, gardenable, open and ecological” are also obvious. The public green space per capita is up to 16 m3.

In Rizhao City, which means "City of Sunshine" in Chinese, an incredible 99% of households in the central districts and more than 30% do so in the outlying villages use solar water heaters. Also, six thousand houses have solar cooking facilities and 60,000 greenhouses are heated by solar panels, reducing overhead costs for farmers in nearby areas. Almost all traffic lights, street lamps and park illuminations are powered by photovoltaic solar cells. In total, the city has over a half-million square meters of solar water heating panels, the equivalent of about 0.5 megawatts of electric water heaters.

Rizhao Municipality has made great efforts to build Rizhao into a modern coastal Ecocity. Mayor Li Zhaoqian explained: "It is not realistic to subsidize end users as we don't have sufficient financial capacity." Instead, the provincial government heavily invested in the local solar panel industries to achieve technological breakthroughs, which increased efficiency and lowered the unit cost.

Since 2001, Rizhao City officials have been educating people and implementing building regulations to promote the use of solar panels. A combination of investment in the industry, regulations and public education spurred the broad adoption of solar heaters. The city mandates all new buildings to incorporate solar panels, and it oversees the construction process to ensure proper installation. To raise awareness, the city also ran public advertising on television and held open seminars.

Rizhao has been granted many honorable titles, such as National Model City of Environmental Protection, China’s Outstanding Tourism City, Environmentally-friendly National Model City, and National Garden City.

Sources: Renewable Energy World, Worldwatch Institute

China - a World Leader in the Solar Water Heating Market

A roof-mounted solar water heater
Photo credit: www.bcsea.org

China is by far the world's largest producer and consumer of solar water heaters. A basic models of solar water heaters in China are very cheap, starting at around 1,500 yuan (US$190). By 2006, the cumulative installed area of water heating collectors in China hit 100 million square meters, and that is roughly 80 percent of the global solar thermal capacity installed worldwide. But this number corresponds only to 78 sqm of collector surface installed for every 1000 inhabitants, which implies a large margin of market potential. So, although China is the biggest solar thermal producer and market in the world, per capita installations of solar hot water systems are still quite low compared to countries like Israel, Greece, Cyprus, Germany and many others.

More than 30 million Chinese households now have one solar water heater installed, and the popularity is due to the efficient evacuated tubes which allow the heaters to function even under cloudy or smog-choked skies and at temperatures well below freezing. The evacuated tube technology was initially developed by Qing Hua University in Beijing in the early eighties, with pilot manufacturing in 1985.

A report from the China's top planning authority predicted that by 2010, the coverage of solar water heating systems in operation in China will reach 150 million square meters. It is also estimated, that by utilizing solar energy, China can save more than 50 million tons of coal in 2010.

"Green Olympics" - Beijing 2008

Beijing National Stadium - 'Bird's Nest'
Photo credit: Guo Lei/Xinhua

The 2008 Summer Olympics in China are in their apogee and they are drawing a lot of attention. Taking into account a massive global audience, the Beijing Olympic organizers are hoping to focus our attention to climate changes and popularize the idea of using eco-friendly technologies. The "Green Olympics" may help change peoples attitudes and set standards for future building projects in China and around the world.

The Olympic organizers are trying to make the Olympic Games environmentally friendly and Beijing a model city for using green technologies, zero net emissions and sustainable architecture. As a part of these efforts, more than a quarter of the energy used at Olympic venues is coming from renewable sources.

Beijing's Olympic Village is a great example of sustainable community development. All seven main Olympic stadiums are equipped with solar generators capable of outputting 480 kilowatts of energy at any given moment. The entire hot-water supply for the Olympic Village will be powered by solar energy. Photovoltaic panels are incorporated on the stadium walls and roofs for most of the outdoor lighting. Also, the main stadiums will receive power from Beijing's first wind farm.

Beijing National Stadium - 'Bird's Nest' includes a rainwater collection arrangement, a natural ventilation system and its upper surface is clad with Ethylene Tetrafluoroethylene (ETFE) roof panels, that let in natural light. The stadium is referred to as the ‘Bird’s Nest’ because of its saddle-shaped steel roof and interwoven façade

The spectacular-looking structure called "Water Cube" looks like a building made of bubble-wrap. It is officially known as the National Aquatics Center and is completely surrounded with ETFE pillows. It is expected to cut energy use by 30 percent and has been built so that after the Olympic Games to be converted easily to a shopping area and leisure center.

The idea for the Beijing's "Green Olympics" makes perfect sense because China sees its energy costs rising and energy sources dwindling, as well as significant damage to the environment. And the so-called "Green Olympics", although will not solve China's environmental issues, they could point the way to a more sustainable future, according to officials and experts.

China is already a world leader in many renewable energy technologies, but so far many of the green technologies have been for export only, because they are too expensive for the country to use itself. China, for example, led the world in manufacturing and utilisation of solar water heaters and energy efficient light bulbs. It is also on the way to becoming the world leader in wind turbine manufacturing and installation.