Non-Toxic and Cheap Thin-Film Solar Cells for ‘Zero-Energy’ Buildings

World’s highest efficiency rating achieved for CZTS thin-film solar cells

Dr Xiaojing Hao of UNSW’s Australian Centre for Advanced Photovoltaics holding the new CZTS solar cells. Credit: Quentin Jones/UNSW

‘Zero-energy’ buildings — which generate as much power as they consume — are now much closer after a team at Australia’s University of New South Wales achieved the world’s highest efficiency using flexible solar cells that are non-toxic and cheap to make.

Until now, the promise of ‘zero-energy’ buildings been held back by two hurdles: the cost of the thin-film solar cells (used in façades, roofs and windows), and the fact they’re made from scarce, and highly toxic, materials.

That’s about to change: the UNSW team, led by Dr Xiaojing Hao of the Australian Centre for Advanced Photovoltaics at the UNSW School of Photovoltaic and Renewable Energy Engineering, have achieved the world’s highest efficiency rating for a full-sized thin-film solar cell using a competing thin-film technology, known as CZTS.

NREL, the USA’s National Renewable Energy Laboratory, confirmed this world leading 7.6% efficiency in a 1cm2 area CZTS cell this month.

Unlike its thin-film competitors, CZTS cells are made from abundant materials: copper, zinc, tin and sulphur.

And CZTS has none of the toxicity problems of its two thin-film rivals, known as CdTe (cadmium-telluride) and CIGS (copper-indium-gallium-selenide). Cadmium and selenium are toxic at even tiny doses, while tellurium and indium are extremely rare.

“This is the first step on CZTS’s road to beyond 20% efficiency, and marks a milestone in its journey from the lab to commercial product,” said Hao, named one of UNSW’s 20 rising stars last year. “There is still a lot of work needed to catch up with CdTe and CIGS, in both efficiency and cell size, but we are well on the way.”

“In addition to its elements being more commonplace and environmentally benign, we’re interested in these higher bandgap CZTS cells for two reasons,” said Professor Martin Green, a mentor of Dr Hao and a global pioneer of photovoltaic research stretching back 40 years.

“They can be deposited directly onto materials as thin layers that are 50 times thinner than a human hair, so there’s no need to manufacture silicon ‘wafer’ cells and interconnect them separately,” he added. “They also respond better than silicon to blue wavelengths of light, and can be stacked as a thin-film on top of silicon cells to ultimately improve the overall performance.”

By being able to deposit CZTS solar cells on various surfaces, Hao’s team believe this puts them firmly on the road to making thin-film photovoltaic cells that can be rigid or flexible, and durable and cheap enough to be widely integrated into buildings to generate electricity from the sunlight that strikes structures such as glazing, façades, roof tiles and windows.

However, because CZTS is cheaper — and easier to bring from lab to commercialisation than other thin-film solar cells, given already available commercialised manufacturing method — applications are likely even sooner. UNSW is collaborating with a number of large companies keen to develop applications well before it reaches 20% efficiency — probably, Hao says, within the next few years.

“I’m quietly confident we can overcome the technical challenges to further boosting the efficiency of CZTS cells, because there are a lot of tricks we’ve learned over the past 30 years in boosting CdTe and CIGS and even silicon cells, but which haven’t been applied to CZTS,” said Hao.

Currently, thin-film photovoltaic cells like CdTe are used mainly in large solar power farms, as the cadmium toxicity makes them unsuitable for residential systems, while CIGS cells is more commonly used in Japan on rooftops.

First Solar, a US$5 billion behemoth that specialises in large-scale photovoltaic systems, relies entirely on CdTe; while CIGS is the preferred technology of China’s Hanergy, the world’s largest thin-film solar power company.

Thin-film technologies such as CdTe and CIGS are also attractive because they are physically flexible, which increases the number of potential applications, such as curved surfaces, roofing membranes, or transparent and translucent structures like windows and skylights.

But their toxicity has made the construction industry — mindful of its history with asbestos — wary of using them. Scarcity of the elements also renders them unattractive, as price spikes are likely as demand rises. Despite this, the global market for so-called Building-Integrated Photovoltaics (BIPV) is already valued at US$1.6 billion.

Hao believes CZTS’s cheapness, benign environmental profile and abundant elements may be the trigger that finally brings architects and builders onboard to using thin-film solar panels more widely in buildings.

Until now, most architects have used conventional solar panels made from crystalline silicon. While these are even cheaper than CZTS cells, they don’t offer the same flexibility for curved surfaces and other awkward geometries needed to easily integrate into building designs.



Energy Efficient Home Tips

Here are easy pointers to make your home affordable and comfortable.

Each year homeowners spend millions of dollars heating and cooling inefficient homes. Here are a few energy-saving tips to make your home more efficient.

  • Turning back your thermostat by just 10 to 15 percent for eight hours a day can trim your annual heating bills by up to 10 percent.
  • A programmable thermostat can do this automatically, helping to minimize unnecessary heating and cooling when not at home.
  • Stop drafts by caulking and weather stripping doors and windows, and close vents and doors to unused rooms.
  • Have your home’s heating and cooling systems serviced before peak seasons and change filters monthly to allow for better air flow.
  • If you rely on propane to heat your home, fill your tank before cold weather hits, and talk with your propane dealer about spreading out costs to keep your winter bills more manageable. Note: Know what propane smells like. There are propane leak detectors and pamphlets with scratch-and-sniff spots.
  • Reduce the cost of hot water by setting your water heater to 130 degrees instead of the standard 140 degrees. Note: Propane water heaters can cost one-third less to operate than electric water heaters. They recover hot water twice as fast as electric water heaters. You can increase your water heater’s efficiency by draining it every six months to remove lime deposits and sediment.
  • You can further reduce hot water use by installing a flow-restricting showerhead and by filling your washing machine and clothes dryer with full loads.
  • To get the most out of your gas stove, select one with an electric ignition so the pilot light isn’t always on. An electronic ignition uses 40 percent less energy than a standard pilot light.
  • Make sure the burners on your stove are burning with blue cone-shaped flame. A yellow flames means air inlets or burners need repair.
  • Finally, check the seal on your oven door regularly for gaps or tears that let heat escape.Remember, an energy-efficient home is not only more affordable; it’s also more comfortable.Courtesy:

The House of the Future: It’s Heated by Sand and Being Tested on Carleton’s Campus


Urbandale will keep a close eye on testing in the home, says general manager Peter Weiss, then ‘figure out how to take it to market. Bruno Schlumberger/Postmedia News

A home heated by sand? It’s just one of the enticing technologies being tested at the Urbandale Centre for Home Energy Research, a glossy name for a very ordinary-looking home perched on a sunny rise at the north end of Carleton University’s campus.

Visible from Bronson Avenue, the recently completed two-storey, wood-clad house is the result of a long-running collaboration between Urbandale Construction and Carleton University with an eye to enhancing energy efficiency, maximizing solar energy and reducing greenhouse gas emissions.

Ian Beausoleil-Morrison, a professor in Carleton’s department of mechanical and aerospace engineering, came up with the idea for the research facility. Urbandale, a leader in green building, kicked in $200,000 and helped with design and construction. Fourth-year Carleton engineering students also contributed energy-generating and other ideas, and the Ontario Research Fund and the Canada Foundation for Innovation helped fund the $1.5 million project.

The 1,600-square-foot house — which inside is left at the drywall stage but divvied up into a main living area, three bedrooms, and a basement bristling with pipes and instrumentation and hulking mechanical systems — will officially open in 2016.

Back to the sand. Saturated with water to enhance heat retention capacity, the sand is in a heavily insulated, six-by-six-by-three-metre box buried beside the house. A rooftop solar array heats the soggy sand during the summer, and in the winter the stored heat warms both the house via a radiant floor system and services the domestic water supply.

“We calculate 90 per cent of space and hot-water heating needs will be met with the system,” says Beausoleil-Morrison. “We wanted to make (the box) a practical size,” he adds, the kind of thing that could conceivably fit in a suburban backyard.

We calculate 90 per cent of space and hot-water heating needs will be met with the system

Beausoleil-Morrison and company are also testing other heating systems, including a cold-climate air-source heat pump from Ecologix. Air-source systems, which use refrigeration technology to extract heat from outside air to warm buildings, can deliver one-and-a-half to three times more heat energy to a home than the electrical energy they consume, according to the U.S. Department of Energy.

Problem is, they’re usually effective only to around -15 C. The set-up at Carleton pre-warms the air by passing it through buried stone (it’s warmer below grade than above) before it enters the system. That should make the heat pump effective to about -30 C, says Beausoleil-Morrison.

“We don’t know if they’re going to work,” he says disarmingly of the multiple technologies in the home. “But it’s low-risk because there’s no one living here … We’ve used lots of assumptions and models, and we’ll find out if they all work when we do the testing.”

Initial testing of some mechanical systems has already begun.

The house also employs more standard energy-efficiency strategies. For example, windows on the heavily glazed south side will help provide winter heat via solar gain. But because they are triple-paned and argon-filled with double low-E coatings, heat loss at night will be minimized.

As well, one of Beausoleil-Morrison’s students has developed software to control south-side window blinds based on how the house will respond to forecasted weather. When the summer sun threatens to overheat the home, the blinds roll down.

To reduce heat loss, there are no windows on the north side. However, there are removable panels in the cladding to allow monitoring of building performance or changes to technology.

Urbandale has also integrated some of its standard specifications into the design. To help keep basements in its homes dry and mould-free, for instance, the company uses a “proud” foundation that’s heavily insulated from the outside to reduce moisture penetration. That design has been incorporated into the research facility.

Despite major advances in air tightness and the efficiency of residential mechanical systems, there’s still lots of work to do be done in exploiting solar energy to displace natural gas and electricity, says Beausoleil-Morrison. That’s where much of the focus of this research facility lies, and he says that means the advanced technology being investigated needs to have potential application to the real world.

“Everything we’re looking at, we ask, ‘Is it practical?’ It can’t be too esoteric.”



San Francisco Adopts Law Requiring Solar Panels on all New Buildings

Tech capital is first major US city to require all new buildings of 10 storeys or under to have solar panels, reports BusinessGreen

The new legislation will help the city meet its goal of sourcing 100% of its electricity from renewable sources by 2020. Photograph: Alamy

San Francisco has this week passed landmark legislation requiring all new buildings under 10 storeys in height to be fitted with rooftop solar panels.

The city’s San Francisco Board of Supervisors unanimously passed the new rule on Tuesday, making the metropolis the largest in the US to mandate solar installations on new properties.

Smaller Californian cities such as Lancaster and Sebastopol already have similar laws in place, but San Francisco is the first large city to adopt the new standard.

From January 2017 all new buildings in the city with 10 floors or fewer must have either solar PV or solar thermal panels installed. The measure builds on existing Californian state law which requires all new buildings to have at least 15% of their roof space exposed to sunshine, in order to allow for future solar panel use.

Supervisor Scott Wiener, who introduced the legislation, said the new measure would put San Francisco at the forefront of the US fight against climate change.

“In a dense, urban environment, we need to be smart and efficient about how we maximise the use of our space to achieve goals such as promoting renewable energy and improving our environment,” he said in a statement.

Wiener is also working on legislation that will allow “living roofs” – which provide low-cost insulation, minimise storm flooding issues and provide new wildlife habitats – to also be eligible to meet the new requirements. The proposals are expected to be introduced in the coming weeks.

“This legislation will activate our roofs, which are an under-utilised urban resource, to make our city more sustainable and our air cleaner,” Wiener added.

San Francisco has a target to source 100% of its electricity from renewable sources by 2020 and has emerged as one of the US’s leading clean tech hubs with a raft of Silicon Valley investors and entrepreneurs backing a host of green technology start-ups in the region.



Solar Impulse 2 Lands Safely in San Francisco after Historic Flight over Pacific

Plane powered only by sun flies over Golden Gate Bridge after spending 56 hours coming from Hawaii on riskiest leg of its journey around the world

Solar Impulse 2 flies over San Francisco’s Golden Gate bridge after coming across the Pacific from Hawaii. Photograph: Jean Revillard/AFP/Getty Images

A solar-powered plane accomplished a 56-hour, record-setting flight over the Pacific Ocean, flying by San Francisco’s Golden Gate Bridge and landing in Mountain View, California late Saturday night.

“I crossed the bridge. I am officially in America,” said pilot Bertrand Piccard, as he guided the Solar Impulse 2 toward its landing after an extended journey around the world.

“Can you imagine crossing the Golden Gate Bridge on a solar-powered plane just like ships did in past centuries? But the plane doesn’t make noise and doesn’t pollute,” Piccard said a live video feed on the website documenting the journey.

“It’s a priority to link the project we have with the pioneering spirit in Silicon Valley,” he added.

The aircraft started its around-the-world journey in March 2015 from Abu Dhabi, the capital of the United Arab Emirates, and made stops in Oman, Myanmar, China and Japan. This is the ninth leg of the circumnavigation.

The trans-Pacific leg of its journey was the riskiest part of the solar plane’s global travels because there were so few places where the plane could make an emergency landing.

“It is more than an airplane,” Piccard later said in a celebratory statement. “It is a concentration of clean technologies, a genuine flying laboratory, and illustrates that solutions exist today to meet the major challenges facing our society.”

His partner, the company’s CEO André Borschberg, added: “Just imagine your energy reserves increasing during flight and available day after day! This is what we may be doing in our communities, our cities and our countries.”

After uncertainty about winds, the plane took off from Hawaii on Thursday morning and at one point passengers on a Hawaiian Air jet caught a glimpse of it, before speeding past.

Solar Impulse 2 had landed in Hawaii in July and was forced to stay in the islands after the plane’s battery system sustained heat damage on its trip from Japan.

The team was delayed in Asia as well. When first attempting to fly from Nanjing, in China, to Hawaii, the crew had to divert to Japan because of unfavourable weather and a damaged wing. A month later, when weather conditions were right, the plane departed from Nagoya in central Japan for Hawaii.

The plane’s ideal flight speed is about 28mph, though that can double during the day when the sun’s rays are strongest. The carbon-fibre aircraft weighs about 2.3 tons.

The wings of Solar Impulse 2, which stretch wider than those of a Boeing 747, are equipped with 17,000 solar cells that power the propellers and charge batteries. The plane runs on stored energy at night.