Four-year-old local fuel-cell membrane maker Hoku Scientific Inc. yesterday celebrated the grand opening of its new $6 million headquarters in Kapolei.

The 14,000-square-foot office, manufacturing and research and development facility at 1075 Opakapaka St. represents a doubling of the company's former digs, a 7,000-square-foot facility in Honolulu.

Hoku largely completed the move to the Kapolei site in August, the same month it first sold shares in the company to investors on the Nasdaq stock market.

The initial public offering raised roughly $18 million for the high-tech firm. Hoku also is authorized to sell $10 million in tax-free revenue bonds under state legislation signed into law in May, but has not yet sold such bonds.

Hoku, which has about 20 employees, develops the membrane, or engine, that drives fuel cells. Its products are geared toward markets such as energy production for homes and autos, and its customers include Sanyo Electric Co., Nissan Motor Co. and the U.S. Navy.