The ISA will "become a treaty-based international intergovernmental organization on December 6, 2017," said Power and New & Renewable Energy Minister RK Singh.
The ISA was launched jointly by India and France on November 30, 2015.
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Modi floated ISA as an Indian initiative to spearhead a massive shift to renewable energy at the Paris climate change conference in 2015.
It is a treaty-based multi-lateral organization with 121 prospective member countries located between the Tropic of Cancer and Tropic of Capricorn, which receive abundant sunlight.
The alliance aims to efficiently harness solar energy to reduce dependence on fossil fuels.
45 members have signed the ISA treaty, 15 have ratified
"As many as 45 countries had already signed the ISA treaty and 15 have ratified it till November 30, 2017, and many more are set to join," he added.
Singh said the ISA is crucial for India's energy security, given its dependence on fossil fuel imports.
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Non-tropical countries express interest in joining ISA
Meanwhile, countries such as Germany, Nepal, Korea, Mongolia, and others, who don't fall between the two tropics, have approached the ISA for membership and voting rights.
The first director general of the ISA, Upendra Tripathy, has said the organization's steering committee will discuss this during its next meeting.
The committee is chaired by India while France is the co-chair.
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