SPSolutionCollection Class

Use the Solutions property of the SPFarm class to get the collection of solutions installed in the server farm. To add a solution to the collection, use the Add method.

Important:
Using the SPSolution constructor to create a solution object is not supported and returns a NullReferenceException if you attempt to implement members of an object created through the constructor.

Use an indexer to return a single solution from the collection. For example, if the collection is assigned to a variable named myDefinitions, use myDefinitions[index] in C#, or myDefinitions(index) in Visual Basic, where index is the GUID of the Solution.