Tourism is the primary economic activity. The islands host 2 million visitors a year, many of whom visit on cruise Ships. The manufacturing sector consists of mainly rum distilling. The agricultural sector is small, with most food being imported. International business and financial services are a small but growing component of the economy. Most energy is also generated from imported oil, leading to electricity costs four to five times higher than the U.S. mainland. The Virgin Islands Water and Power Authority also uses imported energy to operate its desalination facilities to provide fresh water. Until February 2012, the Hovensa plant located on St. Croix was one of the world’s largest petroleum refineries and contributed about 20% of the territory’s GDP. It has since been largely shut down and is now operating as no more than an oil storage facility, provoking a local economic crisis. The U.S. Virgin Islands are located in the Atlantic Standard Time zone and do not participate in daylight saving time. When the mainland United States is on Standard Time, the U.S. Virgin Islands are one hour ahead of Eastern Standard Time. When the mainland United States is on daylight saving time, Eastern Daylight Time is the same as Atlantic Standard Time. To draw more technology-focused companies and expand this segment of the economy, the government founded and launched University of the Virgin Islands Research and Technology Park in conjunction with private businesses and the University of the Virgin Islands. The U.S. Virgin Islands are an independent customs territory from the mainland United States, but operate largely as a free port. U.S. citizens thus do not have to clear customs when arriving in the U.S. Virgin Islands, but do when traveling to the mainland. Local residents are not subject to U.S. federal income taxes on U.S. Virgin Islands source income; they pay taxes to the territory equal to what their federal taxes would be if they lived in a state.