The purpose of this thesis is to analyze the maturity and the performance of the currently available roaming solutions that provide interoperability and roaming services to Electrical Vehicle Charging Networks. At least three different entities are involved in an Electrical Vehicle (EV) charging roaming scenario, namely the EV, the home charging network and the visited charging network. All of these entities have to interface and interact with each other on the physical and the communication protocols level. The Open Clearing House Protocol (OCHP) roaming protocol is implemented and its performance is evaluated against the e-Clearing.net test platform. The protocol functionality for billing and its suitability for different scenarios is also evaluated. Furthermore, an extension to the protocol is proposed to support prepaid subscription, and its performance is also estimated. The findings of this study have verified the performance and the maturity of the OCHP protocol, and strongly recommends the implementation of roaming protocols and clearing houses. The estimated performance of the proposed extension confirmed that both prepaid and postpaid billing can be realized using the tested roaming protocol and clearing house implementations.