ENERGY STORAGE AND GENERATION


Examining how microgrids can enhance resilience


Jonathan Dobing, an Electrical Design engineer at Mott MacDonald, discusses his research as part of a Master’s degree in Building Services Engineering to understand the challenges the NHS faces to improve its electrical resilience, and propose solutions to address loss of supply and ensure continuity of service, as well as reduced disruption. His main focus will be distributed energy resources – microgrids comprising renewable energy generation and storage. He is seeking HEJ readers’ views on, and attitudes to, this issue.


Critical infrastructures (e.g., healthcare, communications, and defence) are reliant on a constant, reliable source of energy to maintain the services they support. Pressures recently faced from the coronavirus pandemic and the war in Ukraine, alongside the most significant – climate change – have highlighted the need to ensure that power system resilience and tackling climate change are critical areas for hospitals and other healthcare facilities to address, often through improvement and upgrading.1 Moreover, the UK’s commitment to have the first Net Zero national health service provides a basis on which to investigate a range of options to ensure resilience. Among these, the potential use of de- centralised, locally sourced energy using microgrids that incorporate renewable energy generation and energy storage is an emerging option. Furthermore, the Net Zero targets set by the UK Government infer the need to introduce more sustainable sources of energy generation at a national and local level.


Limitations of solar PV Renewable generating sources are being increasingly deployed among existing and new buildings. However, solar photovoltaic (PV) will only generate energy when sufficient light is available, while wind turbines can only operate when it is sufficiently windy. In addition, the energy that is generated from these sources must either be used imminently, stored using appropriate technology, or lost. Previous research1


has highlighted the


benefits of using renewable microgrids to reduce reliance on the energy grid, while simultaneously providing cost savings through self-generation and storage.


What is a microgrid? The National Grid is a centralised energy distribution system, whereby several power plants provide most of the energy required for consumption, whereas a microgrid comprises locally sourced energy on a


Figure 1: A diesel generator in a hospital.


much smaller scale. A rudimentary form of microgrid can be understood via the secondary power supply throughout healthcare sites in the form of back-up diesel generators. These typically supply essential services within a hospital that would hinder operations for a period (as per HTM 06-01). Diesel generators have several known drawbacks: most notably, i) they are rarely used, and are known to be unreliable if poorly maintained;2 ii) they have a limited fuel supply, which in the instance of continued disruption, would require more fuel to be provided.3 In contrast, the equipment that makes up a hybrid microgrid can be used daily to provide energy savings while connected to the grid, and improve system redundancy, whereas diesel generators are solely used as a back-up supply.


The key components Fundamentally, a true microgrid incorporates generating sources (e.g., solar PV, small wind turbines, and mini-hydro),


and sinks (final loads and storage devices i.e., superconducting magnetic energy storage and batteries) under local control, and can be grid-connected or operated independently from the grid, or ‘islanded’.4 While operating independently, voltage and frequency are established in a microgrid, alongside maintaining acceptable power quality. Although it is difficult to maintain both voltage and frequency in a microgrid due to the varying loads and irregular output from the microgenerators, central microgrid controllers are used to maintain both elements. Frequency and voltage are regulated by using energy stores and demand-side management by controlling the output power of the microgenerators.5 The voltage can be regulated using a flywheel storage unit, which can counter the reactive and resistive loads found in microgrids.


Incorporating microgrid technology Renewable technologies such as solar PV generate direct current (DC), whereas the


February 2023 Health Estate Journal 41


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