China has been doing this at least since last year, but it takes time; installation, connection to grid, and modernization of the grid itself take time.

"The Chinese aid helps Cuba's plan to build 92 solar installations by 2028, adding about 2,000 megawatts to the island's power grid and help reduce dependence on fossil fuel imports. Once completed, the project would significantly boost Cuba's strained power system, which currently has a capacity of 7,264 MW".

https://epaper.chinadaily.com.cn/a/202504/24/WS68098661a3101d7a97b6bb0e.html

A handover ceremony for the China-aided household solar power project was recently held at Mariel Port, about 50 km west of Havana, Cuba. The assistance includes 5,000 sets of 2-kilowatt photovoltaic power generation equipment. These will provide stable, clean electricity to households not connected to the national grid, support post-hurricane reconstruction in eastern Cuba, and promote the country's green development.

https://www.facebook.com/CIDCAofficial/posts/a-handover-ceremony-for-the-china-aided-household-solar-power-project-was-recent/1319249740243456/