-
Get a structural engineer to verify weight capacity of the roof.
Current panels are 450W so 40 panels would be 18kW. Will generate around 15,000kWh per year if south-facing.
You will need DNO permission for an inverter (either 15kW on one phase or 3x6kW spread across 3 phases, or one 3-phase inverter).
So check out what the roof can bear and what inverter capacity you can connect. Your current proposed array is larger than you need for the business so make sure it makes sense to tie up the money and get it back through export payments.