Passage: Portugal has considerable resources of wind and river power, the two most cost-effective renewable energy sources. Since the turn of the 21st century, there has been a trend towards the development of a renewable resource industry and reduction of both consumption and use of fossil fuels. In 2006, the world's largest solar power plant at that date, the Moura Photovoltaic Power Station, began operating near Moura, in the south, while the world's first commercial wave power farm, the Aguçadoura Wave Farm, opened in the Norte region (2008). By the end of 2006, 66% of the country's electrical production was from coal and fuel power plants, while 29% were derived from hydroelectric dams, and 6% by wind energy.In 2008, renewable energy resources were producing 43% of the nation's consumption of electricity, even as hydroelectric production decreased with severe droughts. As of June 2010, electricity exports had outnumbered imports. In the period between January and May 2010, 70% of the national production of energy came from renewable sources.Portugal's national energy transmission company, Redes Energéticas Nacionais (REN), uses sophisticated modeling to predict weather, especially wind patterns, and computer programs to calculate energy from the various renewable-energy plants.

Question: when did electricity exports surpass imports?
June 2010