Here is my situation:
We have a software that is used to monitor solar power plants developed. I have to introduce OPC as a new way to acquire data from the physical devi
You can download all OPC materials from OPC Foundation, specifically you are looking for the OPC .NET API 2.00 Source Code Download Link. It contains a solution that has the OPC dlls and sample clients (AE, DA, DX, HDA) to give you an idea of how OPC works. This source and DLLs are the basis for the OPC standards. Using these you can call to any proprietary OPC server that is compliant with the OPC standards.