The resilient microgrid –a new approach to viewing the grid and its intelligence

The resilient microgrid has become a key concept as it promises more support for the smart grid of tomorrow.
Published: Mon 12 Dec 2016

Up to now, the smart grid has always involved the placement of more intelligence and control at the high voltage grid, leaving the low voltage (consumer) level with much less intelligence in comparison. But, the shift away from a centralized one-way electricity system is demanding a new architecture to manage and balance the grid with distributed energy resources including intermittent renewables and storage.

As a result, the top-down approach is very quickly transforming into bottom-top processes involving small entities or ‘clusters’ on the grid.

This is where the resilient microgrid comes into play. We spoke to Cyril Carpentier, application engineer for PV and energy storage at Socomec, who explained the benefits of this new approach to grid intelligence.

New architecture for added grid resilience

With this resilient grid, intelligence is at a cluster level, starting from the bottom. A cluster can be a single building, or several actors (consumers, producers) connected together on a part of a grid, typically a LV grid. The resilient grid forms part of a grid with consumers, producers and energy storage that can work connected to the grid or disconnected from the grid, in autonomy.

The approach enables local intelligence to control the cluster working in stand alone, and to manage interactions with other adjacent clusters. Several clusters can form a bigger cluster, that can work with another big cluster. It is like “Matryoshka doll” with the advantage of resilience of Ethernet: If a part of an Ethernet network is down, the rest is still running. Once the part is back, it works again with the complete network. The transition from grid connected to islanding is automatic and transparent for the user, providing the same level of quality and safety when connected or disconnected.

According to Carpentier, the resilient microgrid is proving to be very valuable to countries that have poor to no central grid infrastructure and also in the US which faces a number of devastating storms as a result of climate change.  

Energy storage-the heart of the resilient microgrid

This type of grid has already proven useful in the Nice Grid project.[ERDF’s Nice Grid Advances Microgrid Energy Management.] [Engerati-Creating A More Open Interconnected Grid Architecture- NiceGrid’s Experiences].

For the project, Socomec developed a smart energy storage management solution because after all, energy storage is the heart of the microgrid. Energy storage can ensure the the optimum management of the energy locally when the main grid is present and to guarantee of supply of the customers during blackout. It also supports the integration of renewable energy into the microgrid.

Socomec’s solution for the Nice Grid project, SUNSYS PCS² power conversion and storage system, is scalable,  hot-swappable, works with nearly any battery and supercapacitor technology, and boasts a 97% efficiency rating. A built-in smart cooling system allows it to work at temperatures from -5°C to +60°C.The system controls each storage unit which houses a bank of Saft maintenance-free lithium-ion batteries.

In the event of a grid failure, the Nice microgrid can disconnect from the grid and keep electricity flowing to its customers through a combination of solar, storage and automatic switching. The islanding system is capable of maintaining power for up to five hours. This disconnection can be scheduled or is unexpected after the detection of an upstream grid failure. Once disconnected, the energy storage system is able to supply the microgrid with the support of the local renewable energies.

The duration of the islanding depends on the state of charge of the batteries and the local energy production such as Photovoltaic. This sequence ends with synchronization and reconnection of the microgrid to the upstream main grid without interruption for the consumers and energy producers. SOCOMEC has deployed four 66kW SUNSYS PCS² IM working in parallel as a voltage generator, connected to a 620kWh lithium ion battery container from SAFT.

The PCS is at the centre of the solution, making the link between the battery storing energy and the grid. It is used to charge/discharge the batteries and to manage the energy on the grid. In case of grid outage, the PCS will set the voltage and frequency within the microgrid using the energy in the battery and produced locally.

The excess energy which is captured enables greater grid flexibility and improves supply reliability. The storage converter enables islanding or the creation of a microgrid which helps Nice support the integration of renewable energy and it assists with grid balancing with the use of energy storage. The city, located on the periphery of the country’s transmission grid, often struggles with high peak demand for heating during the winter months. [Build your Microgrid learning from the NiceGrid experience.] Grid resiliency has been significantly improved as a result of the resilient microgrid.

Grid intelligence in action

Another project, the Paradise, rethinks the evolution of an electrical grid with a fully distributed approach: it gives the option of managing the intelligence of the grid at municipal and intermunicipal level with the idea of electricity clusters. The project is being carried out by the French local DSO and CEA the French Alternative Energies and Atomic Energy Commission.

Another,, the Veritas project in Italy, aims to analyze the performance of alternative energy storage technologies and to identify the optimum combination of energy production technologies and sources for a particular application. This microgrid can work connected or disconnected to the main grid, with or without a genset.

Resilient microgrid is also useful for smart buildings. For example, within the Solenbat project, Socomec is installing 50kW of PV and 66kW/70kWh of energy storage in a new office building. The building will be able to disconnect and reconnect to the grid without causing any interruptions.

The resilient microgrid is also proving to be useful in the US which faces extreme weather due to climate change. When storms hit the central grid and cause major blackouts, the resilient microgrids are relied upon to provide power. This added intelligence to the grid helps power distributors to get power to areas that have been left in the dark much quicker.

Finally, autonomous microgrid with PV, energy storage and genset are already today a reality, especially in remote locations. In this case, the main grid is replaced by the genset. Resilient microgrids can work with or without a genset thanks to the energy storage.

In conclusion, Carpentier adds: “The resilient microgrid enables grid operators to leave behind the centralised, one-way system and its production-heavy methods of load management in favour of an open, interconnected architecture-the way of the future.”