ENERGY


The enduring role of standby diesel generation


Geoff Halliday, business consultant at Rehlko (formerly WB Power Services Ltd), discusses the continuing role of diesel generators, the challenges that stem from an ever-evolving regulatory environment, and how modular critical power trains can help optimise performance, reduce risk, and align with decarbonisation goals.


Hospitals and other healthcare facilities are among the most demanding consumers of power, requiring reliable continuous power especially for life support systems, theatre lighting, medical IT equipment, HVAC, sterilisation, and diagnostics, along with other mission critical infrastructure. A failure of mains supply is not simply inconvenient – it threatens life and can be catastrophic. Standby diesel generation has, for many decades, been


the backbone of healthcare facilities’ resilience strategy in the UK. Despite growing concerns over carbon emissions, rising interest in alternative technologies, and regulatory pressure, there remains a compelling case for the ongoing role of diesel generators. What is changing, however, is how they integrate into the broader critical power train: modularity, hybridisation (which includes battery energy storage (BESS)), Combined Heat and Power (CHP), and more flexible plant architectures.


The risks of over-prioritising CO2 in


hospital power infrastructure planning Hospitals are under growing pressure to demonstrate progress towards Net Zero, with many NHS Trusts now reporting against the ISO 14064 standard for greenhouse gas accounting. While this provides a valuable framework for transparent measurement and reporting across Scope 1, 2, and 3 emissions, there is a danger in focusing too narrowly on carbon dioxide reduction as the sole driver of infrastructure decision making. In the context of hospital electrical systems – and particularly the critical power train – this approach can introduce unintended risks and hence consequences.


A singular focus on CO₂ might, for example,


encourage premature displacement of proven standby diesel generation or CHP systems in favour of lower carbon but less mature technologies and an increased dependence on the grid. While alternative fuels, battery energy storage, and hydrogen engines are available and developing rapidly, they do not yet consistently meet the resilience requirements of HTM 06-01. If carbon reduction


targets are prioritised without equal consideration for performance and reliability, the result could be a power strategy that satisfies an emissions agenda but compromises patient safety during grid failure. The same tension is seen with Scope 2 emissions. A


trust that concentrates only on reducing grid purchased electricity may be incentivised to maximise on site renewables or CHP plant. While this improves reported CO₂ intensity, it alters fault levels, transient load behaviour, and synchronisation dynamics with standby systems. Without careful electrical studies, embedded renewables can introduce harmonics, complicate protection schemes, and expose critical loads such as theatres and ICUs to instability. Striking a balance though can difficult. When assessing a fully integrated CHP in the context of ISO 14064, it is important to recognise the shifting balance between Scope 2 and Scope 3 emissions. A fully integrated CHP system within a hospital microgrid will increase reported


A Combined Heat and Power (CHP) system.


Removing or marginalising diesel generating sets entirely would require a significant design rethink and infrastructure rework of all major critical power system plant and how it operates.


September 2026 Health Estate Journal 55


Clarke Energy – a Rehlko Company


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