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 decentralised, 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 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 mains power provided throughout our buildings consists of alternating current (AC). To convert this power from DC to AC, or vice-versa, it is necessary to use an inverter to feed into a centralised point (AC bus as shown in Figure 2), which can then supply final loads. A microgrid has different protection philosophies and techniques to conventional distribution systems, particularly during islanded operation. The level of fault current capacity available in a microgrid will be drastically lower than in interconnected systems. Further to this, due to a higher possibility of system transients and emergency response requirements, the range for voltage and frequency excursion during islanded operation can be much wider than typically considered permissible. Consequently, a microgrid needs to set voltage and frequency-based voltage protection schemes differently. With this in mind, the existing protective devices, for example circuit breakers, should be evaluated for their suitability to avoid unwanted tripping, and replaced with devices better suited to microgrids. This point is hugely important for the integration of microgrids within critical infrastructure. The risk of potentially creating additional weakness in a distribution system could lead to disastrous power failure, and subsequent losses – including both human and financial. For these reasons, regulatory standards, such as G99, have been introduced to account for this
What are the challenges?
Among the greatest challenges and possible limitations to widespread microgrid incorporation is the initial cost to design and install these systems. Solar PV, for example, can cost upwards of £1000 per m2 , 6 while tower-mounted wind turbines (100-2000 kW) can cost upwards of £700 per kW,6 and battery storage systems that use lead-acid and lithium batteries are now commercially available in Europe for about £900 per kilowatt (kW).7 Nevertheless, these technologies can significantly reduce operational energy costs over their lifecycle, and provide reasonable payback periods. For example, Castle Hill Hospital, Cottingham has recently installed 11,000 solar panels at a cost of £4.2 m, which provide monthly savings of up to £300,000 on energy bills, and cut Hull University Teaching Hospitals NHS Trust’s carbon footprint, while reducing the demand on the energy grid. Incorporating battery energy storage alongside renewable sources makes it possible to further reduce operational energy costs, while also providing increased resilience with back-up energy storage.
A lack of space
Space is also somewhat problematic when it comes to healthcare sites and siting of renewable sources and battery energy storage. For instance, the installation of a solar PV array such as the one at Castle Hill requires vast expanses of open space, which is rarely available in more urban healthcare sites. On the other hand, more effective use of rooftop areas, and allocation of space to site these technologies, are necessary to ensure more widespread implementation. Planning during the early stages of consultation and design of extension works or new-builds can ensure that consideration is made for allocating sufficient space to accommodate these technologies. For instance, in France specific legislation on this has been approved, and will see car parks with over 80 spaces require the installation of a solar array.
Looking forward
Microgrids are still in their infancy, and will likely see more research, and become increasingly widespread, as our cities and energy grids become more ‘connected and intelligent’ to achieve Net Zero targets. As our cities and energy grid become ‘smarter’, we will see greater use of information communication technology (ICT) to ensure flexible, reliable, and resilient delivery of energy and related services. Considering that many healthcare sites have an internet protocol (IP)-based communication network and building energy management system (BEMS), they are already well placed to be incorporated into the ‘smart grid’. In addition, battery energy storage is expected to undergo significant development and advances in the future, especially given that, currently, the raw materials used in lithium-ion batteries are costly and difficult to extract, while the material is also costly to manufacture and recycle. Recent experiments8 carried out on sulphur-sodium-based batteries to improve the reactivity of sulphur, and the reversibility of reactions between the two elements, have exhibited much higher capacity and life in comparison with lithium-ion batteries. Although this is at an early stage of research, the results are promising, and may eventually offer a cheaper and more environmentally-friendly alternative for battery energy storage.
Electric vehicles
While there has also been significant research dedicated to the utilisation of energy stored within electric vehicles (EVs) during a grid outage, known as vehicle-to-grid (V2G), there are numerous technical and social issues surrounding this topic, which will see substantial changes in the future. Firstly, the installation of EV charging points would be required, which is lagging significantly behind the number of EVs currently on the road; secondly, V2G requires bidirectional power flow, which entails new wiring, metering, and a communication network,9 and thirdly, the adoption of V2G faces social challenges which include customer attitude, driving patterns, and sensitivity to incentives.10
Time will tell as to which technologies become commonplace among microgrids. However, the current trends suggest that battery energy storage is essential, but that cost and space availability remain a notable obstacle toward widespread implementation throughout the NHS. My research hopes to further understand these issues, and to provide potential solutions to continue to decarbonise the NHS.
Jonathan Dobing
Jonathan Dobing is currently employed at Mott MacDonald, Leeds, as an Electrical Design engineer, where he primarily focuses on providing all aspects of electrical design within the public sector of the built environment. He has three years’ experience as a design engineer, and previously worked for two years as a trainee electrician. Looking to specialise in Net Zero and energy security strategies in the built environment, he is currently undertaking a Master’s degree in Building Services Engineering at Leeds Beckett University, having completed a Bachelor’s degree in Electrical and Electronic Engineering at Newcastle College through Teesside University in 2015. He is planning to submit his application for Professional Registration with the Chartered Institute of Building Services Engineers (CIBSE) in February 2024, upon graduating from his studies in September 2023.
References
1 Hervás-Zaragoza J, Colmenar-Santos A, Rosales-Asensio E, Colmenar-Fernández L. Microgrids as a mechanism for improving energy resilience during grid outages: A post covid-19 case study for Hospitals. Renewable Energy 2022; 199: 308–19.
2 Marqusee J, Jenket D. Reliability of emergency and standby diesel generators: Impact on energy resiliency solutions. Applied Energy 2020 Jun15; 268: 114918.
3 Lawrence B, Hancock M, Stieva G. How unreliable power affects the business value of a hospital. Schneider Electric [Internet]. White paper 2010 (cited 2 January 2023). https://tinyurl. com/2s4cv6zf
4 Marnay C, Chatzivasileiadis S, Abbey C, Iravani R, Joos G, Lombardi P et al. Microgrid evolution roadmap. 2015 International Symposium on Smart Electric Distribution Systems and Technologies (EDST) 5 Nov 2015.
5 Jenkins N, Ekanayake J, Strbac G. Microgrids. In: Distributed generation. London, UK – The Institution of Engineering and Technology, 2010; 175–82.
6 Hawkins G. Costs. In: Rules of Thumb: Guidelines for building services; 82–83. BSRIA, March 2011.
7 Towler J. [Internet]. Energy storage – the missing piece? BSRIA; 2016 (cited 2 January 2023). https://tinyurl. com/3svdnpt6
8 Zhang BW, Cao L, Tang C, Tan C, Cheng N, Lai WH et al. Atomically dispersed dual-site cathode with a record high sulfur mass loading for high-performance roomtemperature sodium–sulfur batteries. Advanced Materials 29 October 2022: 2206828.
9 Noel L, Gerardo Z de R, Kester J, Sovacool BK. Vehicle-to-grid: A Sociotechnical Transition Beyond Electric Mobility. 1st ed. Cham, Switzerland: Palgrave Macmillan, 2019. 10 Hussain A, Musilek P. Resilienceenhancement strategies for and through electric vehicles. Sustainable Cities and Society May 2022; 80:103788.