Yeah! IISE is a legitimate institution which offers industry level training to candidates for the Solar Energy Technology. It offers online courses which are interactive and obviously paid.

In reality you know a certification course for 1 month will not lead you to a great level such that you can apply for jobs or anything like that in the sector. Thus I would suggest you that you don't just think that certification course will lead you to a separate level of employability. So if you want you should try to go for Diploma Courses at least in order to ensure your credibility in the field and to increase your employability. Now if you just want learn then you can do a certification course but it will not be that much useful for your future.

To know more about the course then you should visit the link below:

https://indianinstituteofsolarenergy.com/courses/

I hope this answer helps. All the very best for your future endeavors!