Xu Xinjian,  chairman of Jiangsu Sunrain Solar Energy, has joined the ranks of the world’s billionaires following record gains in the share price of the Shanghai-listed supplier of solar water heaters.

Xu, 50, together with his father Zhengran and wife Wu Dianhua own 62% of the listed company, a stake worth $1 billion at today’s record closing price of 24.76 yuan. Shares have nearly doubled on the past year on optimism about the company’s new water purification business.  Our estimate of the fortune includes dividends received.

Xu cofounded the predecessor of Jiangsu Sunrain Solar Energy in 1997. Earlier, he worked as a power supply technician at a state-owned organization and as a technician at a pharmaceuticals factory in Jiangsu Province

Sunrain’s revenue in first nine months of 2014 was 2.1 billion yuan, or $338 million, a decline of 11% from a year earlier.

Xu’s wife and father have no position in the listed company.

–with Maggie Chen

–Follow me on Twitter @rflannerychina