will the power be fed to a meter point that is also supplying any of the farm buildings that have space heating (or technically air conditioning)?
If yes then it will need an EPC for that building.
If not,eg if it's connecting to a seperate metered supply to an unheated barn then I strongly suspect that it will need a statement from an EPC assessor to that affect, but am not sure on this point, as I don't really think there's any guidance on the level of evidence needed to support the case for an EPC not being required. I'd er on the side of caution though personally, particularly for a 50kWp install.
If it were having a separate new supply fitted just for this, then it wouldn't need an EPC, but would be at the standalone rate anyway, which is virtually the same thing anyway as the non EPC rate.
