began to develop in the early 1960s with India's assistance. During Bhutan's Third Five-Year Plan, public works, still primarily roads, continued to take a significant share of the Nu475.2 million development budget (17.8 percent). Despite amounts budgeted for planned development, there were additional capital expenditures outside the formal development plan, including road construction and hydroelectric plants. The Sixth Five Year Plan (1987–92) was the first to allot power generation projects a significant portion of the national budget (13.1 percent). At Nu9.5 billion, the sixth plan was considerably more expensive than its predecessors. The goals included strengthening Bhutan's self-reliance, as it was hoped that Bhutan would begin exploiting markets in neighboring countries with manufacturing, mining, and hydroelectric projects. Faced with rising costs, Bhutan postponed some projects requiring large inputs of capital until the Seventh Development Plan (1992–96), which presented no major changes in overall sectoral development. The first major expansion of hydroelectric facilities started in 1975 on the Wang Chhu between Thimphu and Phuntsholing. Known as the Chukha Hydel Project, it helped boost the nation's fledgling industrial development. The 336-megawatt Chukha Hydropower Station came on line in 1986 and was synchronized with the Indian grid that same year, and additional capacity became available in 1988. The Nu2.44 billion Chukha project was 60 percent paid for by India and budgeted outside the normal development plan process. It was planned that Bhutan would sell at low cost all excess power to West Bengal. At the same cost, Bhutan also hoped to reimport some of that power through the Indian power grid into southern districts. The Chukha project was important not only because it supplied electric power to western and southern districts but also because it provided a major source of income for the government. In 1981 Bhutan generated 22 million kilowatt-hours of energy from hydroelectric sources. The project's gross annual income was projected at Nu380 million in 1989. Another major plant in southwest Bhutan — the 18,000-kilowatt Jaldhaka hydroelectric plant — furnished electricity locally and exported the balance to India's West Bengal. In 1989 nearly 95 percent of Bhutan's government-installed power generation — a total of 355 megawatts — was supplied by Chukha, and a total of some 20 principal towns and 170 villages had been electrified. By 1990 Thimphu's commercial district had an underground cable system for its power supply. By 1991, besides the Chukha project, government installations included seven mini hydroelectric