Solar Consultancy service.

I do (non-solar) consulting work, and I can tell you it is a low bar to start a consulting practice.

The most important skill for being a successful consultant is to be able to personally connect and communicate with potential clients. Clear communication is key, both orally and in writing; it's probably the most important skill a successful consultant can master. Consulting is first and foremost a people business, and the most successful consultants have the ability to effectively communicate with their clients and make them feel comfortable with the person and services they are purchasing.

Having licenses and/or certifications is very important. Review what you need to practice in your field of expertise and obtain them.

Being really good at what you do is a definite plus, but not an absolute requirement like communication skills. Also, being really cheap at what you do is also a plus, but again, it's not a requirement.

In much if not all of the US you need a Professional Engineers (PE) license in order to provide design services that involve engineering. Designing solar systems require engineering and therefore a PE license is required. Each state has specific requirements to obtain a PE , but in general the requirements are a 4 year engineering degree from an accredited institution, passing an 8 hour Engineering fundamentals exam, several years of apprenticeship under a PE and then passing an 8 hour exam. Many states also require a license for your firm and in many cases its more difficult to obtain the firm license than it is to obtain the PE license. Some states allow limited engineering work to be done under another states license but generally it requires permission in advance. Each state usually has a petition process to waive parts if not all of the licensing requirements but that process is generally quite difficult and its not guaranteed. It is also costly, I maintain a couple of state licenses and generally a fee of $100 to $200 is expected per state plus many states have continuing education requirements that can cost additional dollars. You also need professional references, generally they have to be other licensed professional engineers willing to vouch for your abilities.

Most engineering consultants also obtain professional liability insurance as they may get sued for either their faulty design or far more likely just included in lawsuit by a lawyer out for money. The last time I looked into it several years ago was about $16,000 a year.

There are some workarounds. Master electricians apparently can design a specific system that they are installing. Manufacturers can supply a kit of materials sold as pre-engineered package which may or may not meet the requirements of the local permitting officials.

In addition to an electrical design many jurisdictions require a structural engineer to review the structure to determine if it is adequate for the additional loads.

If you have read this far, it should be obvious that providing engineering services in the US is mostly likely not going to be something you can do from India.