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Flexible multiport power conversion systems deliver resilient hybrid microgrids

By John Merritt
Recently commissioned Ideal Power project with JLM Energy at Carilion Roanoke Memorial Hospital. Image: Ideal Power.

The unprecedented natural disasters that took place in 2017 are bringing greater attention to the importance of resilient energy systems. Disasters cost the United States a record-breaking US$306 billion in damages last year alone, according to recent figures from the National Oceanic and Atmospheric Administration. While these disasters did not discriminate by geography, and many parts of the country and the world were impacted, island nations such as Puerto Rico were hit especially hard and are still in need of power for basic and critical services many months later. 

Hybrid microgrids connecting renewable energy and distributed energy resources such as diesel generators are a cost-effective and adaptable option for providing power in these extreme-weather prone, remote areas. While conventional equipment is cumbersome, complex and inefficient with high upfront costs, advanced multiport power conversion systems provide unprecedented flexibility and adaptability, overcoming barriers to meet unique island energy needs. Most importantly, when critical facilities – such as schools, hospitals and municipal buildings – are offline and in need of power quickly, hybrid microgrids with seamless multiport power conversion can effectively deliver or return power to communities following a storm or another type of power disruption. 

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Challenges with traditional integration

System integrators and project developers have historically faced the challenge of power conversion technologies that fall short when it comes to stability, efficiency and flexibility. Bulky and inefficient components have been the mainstay of power conversion for decades. A conventional converter can weigh upwards of 700 pounds, with limited compatibility for outdoor installation – the significant size and weight of that type of equipment makes installation costs very high and laborious. 

Cost is a significant barrier for islands in particular, as they already experience disparately high energy costs. The cost of electricity on the Caribbean islands averages about 50 cents per kilowatt-hour (kWh) – about three to five times that of the mainland US. If a project developer isn’t aware that cost-effective solutions are available and can be adapted for island needs, this is the most significant hindrance to implementing microgrid projects. 

Cumbersome and complex equipment can also be a major hurdle. Traditional solar-plus-storage microgrids require two separate power converters, making the management and integration of the hardware and software much more difficult. Connecting multiple resources can involve devices that are large in size and difficult to place, which is especially challenging for island communities with space limitations. Systems that require multiple power conversion boxes required complex and real-time embedded controls, complicating ongoing management. Additionally, it can be difficult to identify integrators and project managers with the technical abilities to develop, deploy, commission and manage such control systems. 

For any system that includes storage, power converters without proper operational control systems can cause significant wear and tear on batteries. Putting stress on a battery is not only inefficient, but it also shortens the lifespan of a system. Storage efficiency is essential because solar energy is an intermittent resource and on its own cannot be relied upon as a resilient power supply.

Finding the right technology

Emerging power conversion technologies allow for direct current (DC), alternating current (AC) and hybrid microgrid solar-plus-storage systems, with options to integrate solar photovoltaics (PV), diesel, energy storage and other distributed energy resources into a single hybrid microgrid project. Each system has benefits for various project types, but hybrid multiport power conversion systems are the clear solution for providing off-grid backup power. While hybrid microgrids come in different shapes and sizes, they have a few defining features. 

A hybrid microgrid includes solar-plus- energy storage, coupled with diesel generator sets that are strategically controlled and can operate in both “islanded” and/or grid connected mode when a grid connection is available. 

Multiport power conversion allows multiple power inputs to be integrated through a single power processing stage to remove redundancies that exist with conventional single-port converters. Compact hybrid multiport converters save space, weight and dramatically simplify wiring interconnection and installation. The most effective multiport solutions also include embedded key control functions, which further simplify management.

Ideal Power Stabiliti 30C unit. Image: Ideal Power.

US Virgin Islands: putting concepts into practice

Ideal Power and its integration partners deployed a hybrid microgrid system in Saint Croix in the US Virgin Islands in June 2017. On this site, six Stabiliti 30C3 multiport power conversion systems operate in parallel to integrate solar, storage and diesel into a hybrid 180kW microgrid powering a local entertainment facility. Similar to many commercial sites in the Caribbean, the facility was never connected to the central power grid and prior to the solar-plus-storage microgrid implementation, the site relied entirely on diesel generators for its power needs 24/7. Diesel generators are common in island nations with unpredictable and costly grid-supplied power, but these generators can be paired with solar-plus-storage to create a more affordable – and green – microgrid solution. 

The facility experiences peak load – its greatest energy use – during the late afternoon and early evening when customer traffic and air conditioning demands are highest. Solar on its own could not be relied upon to deliver enough power during peak hours and moving the site from a 24/7 diesel-powered microgrid to a 24/7 solar-plus-storage microgrid was cost prohibitive for the site owners. Ideal Power’s project team determined that integrating solar-plus-storage alongside diesel would slash operating costs and pollution by reducing annual diesel fuel consumption by 30%. The right multiport power conversion system made this possible by connecting diesel, solar and storage in a compact and modular solution. Lastly, the six-converter configuration provides a robust level of redundancy. If a single converter faults and trips offline, the remaining five systems will support the building in a seamless manner – resulting in lights that never flicker. 

Unfortunately, shortly after the Saint Croix project was deployed, the project site was impacted by Hurricane Maria. The storm’s high winds ripped o most of the rooftop solar panels, but the batteries, control equipment, generators and converters remained intact. The team will restore and rebuild the rooftop solar array using new mounting hardware designed to better withstand high winds. In the interim, the power converters will continue to o set fuel use by paralleling the batteries with generators. Eventually, the goal is for the facility to run on batteries alone from late night until early morning. This capability will require intelligent load management equipment, such as HVAC and lighting controls, to ensure building loads are minimised during unoccupied periods. When considering opportunities for future project sites that rely on diesel generators, even greater fuel savings of 60% or more could be achieved by increasing battery capacity. 

The existing system will reduce emissions and energy costs while post- hurricane repairs take place. The Saint Croix site has the potential to achieve greater efficiencies once solar panels are replaced and integrated back into the system. Through effective technologies that meet unique island community challenges and needs, the Saint Croix project site has proven that multiport power conversion capabilities that support a hybrid microgrid are an effective solution for day-to-day operations and also in the face of a devastating storm. 

Key factors for resilience

The flexibility and adaptability of multiport conversion technology supports effective hybrid microgrid sites, which in turn o er island nations, isolated communities and any area vulnerable to natural disasters with resilient, cost-effective and green power generation. As a changing climate means years like 2017 become more of the norm rather than the exception, hybrid microgrids will play a growing role in the future of energy use for island nations, rural areas and beyond. 

This article originally appeared in 'Storage & Smart Power', presented by Energy-Storage.News as a section of PV Tech Power Vol.14, our publisher Solar Media's technical journal for the downstream global solar PV industry. You can download the entire journal, including a special focus on floating solar, here, while individual Storage & Smart Power papers and articles from the journal will be archived on the Resources page of this website, here. This article was a companion piece to 'From ‘squishy batteries’ to pre-packaged systems – how the times are changing', an interview with Jason Petermeier of ELM Fieldsight, which has worked with Ideal Power on several relevant projects. 

Ideal Power military microgrid project. Image: Ideal Power.

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