Residents take photos of the Solar Impulse 2 in Chongqing on March 30. Photo: CFP

It is a quiet windless night on Monday March 30, and Chongqing's Jiangbei Airport has detected an aircraft entering municipal airspace. This is not a normal civil airplane, but a revolutionary manned airplane powered purely by solar energy and eagerly awaited by crowds of airport staff, media and aircraft lovers.

The groups have been waiting for more than two hours. At around midnight, the lights of the plane finally appear as it starts its slow approach. The aircraft's fuselage is slim and it has a very wide wingspan larger than that of a jumbo jet. After another hour of waiting, the plane suddenly increases its speed, and at 1:35 am on March 31, it touches down on the airport's runway.

Big and light

The aircraft is named Solar Impulse 2. It represents the first attempt to make a round-the-world flight powered solely by solar energy. The team hopes to raise awareness of the use of renewable energy and clean technology through their journey in their zero-emission plane.

Chongqing is the journey's fifth leg, following stops in Abu Dhabi, Oman and Myanmar, while the team plans to fly to Nanjing, Jiangsu Province next. The itinerary includes speeches and science exchange activities with schools and experts.

"Chongqing and Nanjing are both good in terms of weather, airport size and distance," Bertrand Piccard, one of the two pilots of Solar Impulse 2, told the Global Times.

Solar Impulse 2 is different from other airplanes in terms of its structure. The aircraft is made of carbon fiber. It has a 72-meter wingspan but weighs just 2,300 kilograms, about the same as a typical family sedan. It can reach a maximum speed of 140 kilometers per hour.

The plane has more than 17,000 solar cells built into its wings and cruises at an altitude of around 8,500 meters during the day to catch the sun's rays, dropping at night to around 1,500 meters when flying over the ocean. The aircraft flies during the evening using energy stored in its batteries during the day.

However, It cannot fly in rainy weather. Weathermen must trail the plane to help predict the weather along its flight path. Also, the plane does not have a pressurized cockpit, so pilots can feel changes in temperature. As a result, their blood oxygen levels are constantly monitored.

Negotiations underway

Piccard explained that negotiations with the Chinese government are one of the most important parts of the project.

"Before we confirmed we would come to China, we had to deal with the Chinese Ministry of Foreign Affairs, civil aviation authorities, the China Association for Science and Technology, airport authorities as well as the governor of Chongqing [and the mayor of] Nanjing," he said.

"It is a special aircraft so we need special permission. We need to explain what we are going to do and find a solution to get to the airport. Also, we have to wait until midnight to land, as that is when there's not much traffic, so we won't disturb anyone," he noted.

In order to ensure a safe landing for Solar Impulse 2, Nanjing Lukou International Airport told the Global Times that airport staff made extensive preparations, including designing a detailed landing plan, arranging a landing area and additional airport staff.

"We hope we can arrange for it to land after midnight to minimize its impact on other flights," Xu Bin, a deputy director of the operations command center of the airport, said, adding that one of the two runways will be cleared beforehand for Solar Impulse 2. Xu said he expects less than 10 regular flights to be affected by the landing.

"We think that Solar Impulse 2 and the environmental protection it represents are meaningful. That's why we're supporting the landing despite the extra work," Xu stressed.

More research, more awareness

The landing of Solar Impulse 2 attracted attention from citizens and renewable energy scientists, since its round-the-world journey has proved that solar airplanes can fly long distances.

In fact, solar energy is nothing new to China, as the country is one of the world's largest producers of photovoltaic (PV) cells.

"Over 60 percent of the PV cells in the world are made by China," Hong Wei, a research fellow at China Institute of Energy Economics, told the Global Times.

"China has enough resources and we have the skills required for manufacturing solar-powered products, which means that China is capable of producing a solar airplane that may even better than Solar Impulse 2," Li Changming, head of the Institute for Clean Energy and Advanced Materials of Southwest University, told the Global Times, listing Chinese spacecraft as an example where Chinese solar energy technology has already been applied.

So why are solar-powered aircraft not in wide use? Analysts say that the high cost of PV cells and insufficient performance are the main reasons.

"There are different PV cells in the market and they are expensive. If we can produce more PV cells and lower prices, the cells made with more advanced techniques could become more affordable," Li said

"Solar aircraft normally fly slower than other airplanes. If that can be tackled, it is completely possible that solar airplanes could be used as civil aircraft," he added.

Hong however argues that public knowledge of and support for renewable energy is still not strong enough, resulting in a lack of investment in manufacturing such aircraft. But both Hong and Li expressed optimism that Solar Impulse 2 and its team could help boost renewable energy industry in China. 

Solar Impulse 2 will leave Chongqing whenever weather along its flight path to Nanjing improves. In the meantime the team will continue to visit universities and schools to promote renewable energy.

"We want to demonstrate which technology has the best future," Piccard said.   
Newspaper headline: Chasing the sun