The International Solar Alliance has its headquarters at Gurugram in Haryana, on the campus of the National Institute of Solar Energy at Gwal Pahari. India provided the land and building and met the running costs of the secretariat in its early years.

The alliance was launched jointly by India and France at COP21 in Paris in 2015, and it is a treaty-based intergovernmental organisation of countries seeking to expand solar deployment, cut technology costs and mobilise finance. Membership was first limited to states lying wholly or partly between the Tropics of Cancer and Capricorn, the solar-rich belt, and was later opened to all members of the United Nations.

Its significance for India is that it is the first international intergovernmental organisation to be headquartered in the country, which is the fact this question turns on.

Karnataka hosts Pavagada, among the largest solar parks in the country, but no organisation secretariat of this kind.

Dubai is the seat of the International Renewable Energy Agency, IRENA, which is a separate body with a broader mandate covering all renewables.

Colombo has no connection with the alliance's secretariat.

Hence the International Solar Alliance headquarters is located in Haryana, India.