French power giant GDF Suez will buy a 50 percent stake in two power plants owned by Gek Terna Group as part of a joint venture to tap growing demand for power in Greece. Gek Terna and GDF Suez will each hold a 50 percent stake in the Heron I and Heron II power plants, according to a bourse filing. No financial details were released. Shares in Gek, the holding company, jumped 8.01 percent to 3.10 euros after news of the deal yesterday, while Terna stocks advanced 9.51 percent to 2.80 euros. The broader Athens bourse retreated 0.46 percent. Gek Terna has about 800 megawatts under operation and wants to boost that capacity to more than 2,000 megawatts in 2012. Foreign energy companies have been teaming up with local partners in a bid to tap strong growth in Greece’s energy market, which is opening up to competition. In July, refinery Hellenic Petroleum said it had set up a joint venture with Italy’s Edison and will aim at developing a 1,500-2,000 MW energy portfolio in five years as part of plans to become the country’s second-largest power company. Spain’s Endesa has also entered the local market by teaming up with local metals and engineering group Mytilineos in a similiar deal aimed at developing the country’s power supplies.