Interoperability is the measure of ease of integration between two systems or software components to achieve a functional goal. It can be achieved at the device level or the system level. Device-level interoperability is the ability to replace one device with another without reducing the original functionality while system-level interoperability is the ability of a system to exchange data with other types of systems. In power utilities, device-level interoperability enables smart meters manufactured by different manufacturers to communicate with each other and replace each other without altering the consumer experience. Meanwhile, system-level interoperability enables different head-end systems (HES) to communicate with the meter data management system (MDMS).
Interoperability is crucial to prevent vendor lock-in. Meanwhile, the lack of interoperability could impact investments and synergies, and lead to additional costs for redesign. In India, end-to-end interoperability has been one of the key missing features of automatic metering infrastructure (AMI) projects.
To achieve interoperability, utilities need to develop in-house standards and create an ecosystem of manufacturers that conform to the standards. Alternatively, a central organisation can develop a framework, which includes protocols and model standards, to achieve interoperability of smart grid devices including meters and communication systems. To address the issue of interoperability in smart meters, the India Smart Grid Forum (ISGF) has suggested the following measures in its Smart Grid Handbook for Regulators and Policy Makers prepared by ISGF:
- Long-term rate contract: While procuring smart meters (and associated hardware and software for AMI), a rate contract of 7-10 years with select meter vendors, which provide interoperable meters, may be considered. Hence, when new customers are to be added to the AMI network, these meter manufacturers can provide the existing solution to the utility at the previously agreed rates. This will enable the seamless integration of new smart meters.
- Choose communications technology first: Another approach is to first choose the communication technology and then select the meter manufacturer(s). In this case, all potential meter manufacturers will have to integrate this communication technology into their meters. Hence, device-level interoperability will be easily achieved. The communication solutions provider needs to certify that its network interface card is integrated with the meters that will connect with the HES.
- Third-party certification: A utility can also opt for third-party certification for ensuring device-level interoperability. In this case, the utility will ask the meter manufacturers to present an interoperability certificate acquired from the certification agency.
- Wi-Fi for last-mile connectivity: Smart meters can connect to the utility servers using Wi-Fi in the building. Moreover, providing last-mile connectivity through Wi-Fi can solve issues of interoperability, scalability, maturity, reliability and cost effectiveness.
- Multiple HES with one MDMS: If multiple communication technologies (each having its own HES) are selected by a utility over successive tenders, a common MDMS may be chosen that can interface with multiple HES. In such a case, all communication interfaces will have to be standardised as per the IEC 61968: Application integration at electric utilities – system interfaces for distribution management. This is a series of standards that define the key elements of interface architecture for distribution management systems in utilities.
The utility may choose the appropriate option to achieve interoperability in smart metering. However, as per the ISGF, selecting Wi-Fi for providing last-mile connectivity proves to be the best solution as it is mature, scalable, reliable and cost effective. Moreover, a common MDMS with multiple interfaces should be the last resort, to be used if the above options are not available.
Standards and testing
In India, the Department of Electronics and IT under the Bureau of Indian Standards formulates the standards for smart grids. It has issued IS 16334:2015, the standard on “Power System Communications – Interoperability Guidelines”. It covers the traditional value chain (generation, transmission and distribution), the newer elements (trading, risk-management, renewable generation, etc.), information and communication technologies and other automation-related technologies. For testing interoperability, device language message specification (DLMS) is a globally recognised protocol for data exchange with smart devices. DLMS helps avoid the risks associated with large-scale roll-outs such as vendor lock-in and volatility of the technology, and can provide predictability for such roll-outs over the lifetime of the asset.
In sum, it is very important to ensure interoperability while implementing a smart meter project. It is advisable to implement system-level interoperability and not just device-level interoperability. In India, system-level interoperability has been adopted wherein smart meter data can be transported using any communication protocol.