Sarulla Operations Ltd (SOL) is sponsored by a consortium of Medco, Itochu, Kyushu, Inpex and Ormat. The total investment of the project is USD 1.7 billion. The second amendment of the ESC (Energy Sales Contract) and JOC (Joint Operation Contract) between SOL, PLN and PGE was signed on April 4 2013. SOL has built the world's largest Geothermal Power Plant in a single contract, with a capacity of 3 x 110 MW to contribute the electricity needs in North Sumatra. The Sarulla project is located in Pahae Julu and Pahae Jae Districts, North Tapanuli Regency, North Sumatra Province. The first unit was operated commercially in March 2017, the second unit was operated in October 2017 and the third unit was started to operate in May 2018. The geothermal power plants are fueled by steam and brine from production and injection facilities at Silangkitang and Namora-I-Langit reservoirs. The power plants utilize geothermal combined cycle units which are more efficient than conventional flash type geothermal power plants. The plants capture the steam and brine from the wells and produce energy throughout the day which are intended for base load operation. The condensate steam and the brine water are re-injected to underground via wells to maintain sustainable geothermal resources.