By Mike Yamamoto, managing editor of OptionMonsterNEW YORK -- Option traders are looking for more gains in Yingli Green Energy ( YGE), which spiked higher at the end of last week. OptionMonster's tracking systems detected heavy buying in the Chinese solar-technology company's Aug. 4 calls, where 5,558 contracts traded for $0.25 to $0.45 on Friday. The volume was 9 times higher than the strike's open interest of just 599 calls before the session began, indicating that this is fresh buying. Yingli Green Energy's shares surged 13.25% to close the session at $3.76. The beaten-down solar sector has cooled in the last month after a big run earlier this year, but Yingli had been trading toward the upper end of its recent range leading up to Friday's jump. Friday's calls lock in a $4 purchase price for the Yingli's stock no matter how far it might rise, but they will expire worthless if shares remain below that level through mid-August. The last time it closed above $4 was Feb. 17. Total option volume in the name topped 9,000 contracts in the session, more than 9 times its daily average for the last month, with overall calls outnumbering puts by a bullish 10-to-1 ratio. It also saw upside call buying on June 17. The company is scheduled to present at the Intersolar North America 2013 industry conference, which begins on Thursday. Yamamoto has no positions in YGE.