(Trina Solar earnings story updated with additional commentary and closing stock prices.)CHANGZHOU, China ( TheStreet) -- Trina Solar Limited ( TSL) beat quarterly earnings expectations and upped its forecast for solar shipment volume. Trina Solar said early Tuesday it more than doubled quarterly profits and revenue in its second quarter on record shipment volume, and expects strengthening demand for photovoltaic products to extend into 2011. "Trina had a good quarter," Wedbush Securities analyst Christine Hersey told TheStreet, commenting on the firm's increased shipment guidance for this year and capacity expansion outlook for next. Hersey expects a 15% decline in prices next year, which could pressure the margins of some sector players. But she added that Trina will sell more units as well as reduce its costs. "