Solar PV Panels:
Solar PV Panels are the most important part of any rooftop solar system. As there are many variations in technology and make of the panels, it is very important to choose them wisely. You can go through this link here to help you choose them for your plant. These are mostly warrantied for 25 years (performance warranty) and have a life of about 30 years.
Panasonic, Trina, Canadian Solar are a few very excellent brands you can opt for.
Solar inverters are the heart of the system. They basically convert the DC power generated by the solar panels and give AC output which is used for running our loads. Another most important function they have is anti-islanding. That is, whenever there is a power cut, they stop the output from solar panels as per the MNRE guidelines. They also have internet connectivity to help you understand the solar plants generation pattern. You can learn a bit more about them on the link here.
Lightning Arrestors and Earthings:
Every rooftop plant needs a separate lightening arrestor and three earthing to safeguard the system from leakage currents and lightnings. DC side and AC side both can have separate earthing for better dispose strength. Preferably they should be chemical type and made of copper. It is important to keep a check on their resistance levels (their health levels you may say) to ensure they earth the current properly.
Cables and safety devices:
Cables and connectors (MC4, thimbles, etc) are often the most ignored part of the Solar pv plant. Cables with appropriate core diameter for the size of the system and thimbels which can transmit the current without over heating should be used. Some precious calculation is needed to determine the size of these components. Along with this, ACDB and DCDB (Safety devices on AC side and DC side) must have accurately calculated components. They protect the plant and the user in case of there is any surge in the current
Learn more about the safety devices used in solar systems on the link here.