Fortunately for the locals, Zhang soon discovered that Panam's soil was actually suitable for growing vegetables, even at such high altitude. He could envisage his greenhouse techniques working in the area.

But many locals initially could not get used to planting in the greenhouses because it was "wet and hot inside", he says.

Language was also a major obstacle when he started to teach the Tibetans his farming skills.

"I barely understood a word of Tibetan. The locals also did not understand me when I spoke Mandarin," says Zhang. "But I still managed to teach them very successfully, through a combination of body language and eye contact. The locals were warmhearted people and they were very eager to learn."

Three months after Zhang's lessons, Panam's residents started to reap the rewards of their hard work. The first batch of farmers who planted tomatoes in greenhouses managed to earn more than 10,000 yuan each from their crops.

There are now 5,428 greenhouses in the county, with more than 100 types of vegetables growing in them. The local government built most of the facilities in the past 17 years, with the help of hundreds of farmers from Shandong like Zhang.

Zhang himself has taught at least 5,000 farmers how to plant crops in greenhouses. He has trained more than 70 local farmers to become specialists in the technique.

Among the seven couples who arrived in Panam in 2000 to help the locals, only Zhang and his wife stayed on for so many years.

"At the beginning, I thought life in this place was tough. But then I thought, 'if I left, who would teach the local farmers? They have not fully grasped the skills needed for greenhouse planting'. So we stayed. And we stayed year after year. Now we do not see our lives in Panam being any different from back home," Zhang says with a laugh.

The only regret he has for spending all this time in Tibet is that he was not able to see his son growing up. The boy was only 10 when his parents left Shandong. He is now working at an iron and steel company in Jinan.

Zhang says he will definitely be in Panam for a few more years. "I want to continue working here, to help upgrade local agricultural practices."