The enduring role of standby diesel generation

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 Scope 2 emissions, as the Trust is directly responsible for consuming the electricity and heat generated on site, usually from natural gas. This, however, needs to be set against the alternative of importing electricity from the national grid.

Grid supplied electricity in the UK is produced from a diverse mix of gas, nuclear, and renewables, but once transmission and distribution losses of around 7—8 per cent are factored in, its effective carbon intensity at the point of use rises. Under ISO 14064, those upstream generation and distribution losses are reported as Scope 3 emissions for the consuming trust. By generating power locally and using waste heat, a fully integrated CHP system can achieve overall efficiencies of over 80 per cent, significantly higher than the 35—45 per cent net efficiency typically realised by grid electricity delivered to site. The result is that, while Scope 2 emissions may appear higher for the trust operating a CHP, the system wide emissions footprint (Scopes 1—3 combined) is often materially lower than relying solely on grid imports. This distinction is crucial for healthcare estates teams: carbon accounting must not only focus on how emissions are categorised, but also on the true whole system efficiency that underpins resilience and sustainability.

The regulatory / standards landscape:

HTM, BS, and NHS requirements

We have been providing standby generator solutions to the healthcare sector for over forty years. Our team is clear that the starting point for design, installation, and operation in healthcare is HTM-06, with some of the key expectations including:

• Standby generators must be able to pick up load within a defined timescale after mains failure, with UPS or other secondary power sources covering the very short interval.
• Single or multiple generating sets can be configured in various configurations, augmented by a fuel system, control system, exhaust system, appropriate levels of attenuation, and — above all — must be reliable, supported with rigorous maintenance regimes.
• Generators must be capable of handling the required load, achieve prescribed first level load step acceptance and large surge loads such as motor starts, HVAC, etc. while maintaining voltage/frequency within prescribed limits.
• Many manufacturers and specifiers often find that some HTM requirements do not align exactly with how commercial diesel generating sets are designed or tested.

The regulatory environment is tightening: environmental legislation, emissions standards (Medium Combustion Plant Directive MCPD), and carbon reporting, plus the NHS has its own Net Zero commitments, and public expectations are becoming increasingly influential. These things themselves do not render diesel standby generation obsolete, but they do influence how it is considered internally, how it is specified, deployed, and operated.

Why standby diesel generation remains crucial

The journey to Net Zero is forcing a fundamental rethink of how energy is generated, distributed, and consumed. As we move closer to a Net Zero future, government policy remains focused on:

• Reducing fossil fuel use across the economy.
• Scaling up renewable energy sources such as wind, solar (PV), and nuclear — diversifying our energy mix.
• Electrification of transport, domestic, and industrial heating.
• Electrification of energy hungry processes such as steel and concrete production.

All of these will add massively to electrical demand while altering the way in which that additional energy is both produced and distributed.

Speaking in 2024 about the growing power demand, National Grid chief executive John Pettigrew spoke about:

• The potential for a six-fold increase in data centre energy consumption in the coming decade, which poses a real threat to network stability.
• That the grid was becoming “constrained” and “bold action” was required to create a network able to cope with “dramatically” growing demand.
• That “future growth in foundational technologies like AI and quantum computing will mean larger scale, energy-intensive computing infrastructure”.

He also noted that much of the UK’s high voltage ‘super grid’ is over 70 years old, and that to reach Net Zero by 2050, the operator must:

• Upgrade infrastructure to meet higher consumer demand.
• Do so sustainably by connecting the growing number of renewable energy sources and maintaining grid stability.

For hospitals, failure of the utility supply is not theoretical, and diesel standby generators provide a proven, well understood critical last line of defence.

Guaranteed resilience against mains failure

Taking full advantage of decades of engineering maturity, most diesel generating sets are able to achieve the rapid start, run up, and load acceptance requirements of 
HTM-06. Correctly installed, well maintained, and regularly tested (including load bank tests) a diesel generating set will provide years of reliable service.

For large hospitals, multiple theatres, labs, sterilisation suites, cooling, etc., the peak load is significant. Diesel generators scale well (multi-megawatt systems) and for standby duty can have favourable life cycle cost profiles — especially when amortised over many years.

Today, there is regulatory and procurement certainty surrounding diesel generation, and the scope of performance and deployment is well defined under HTMs and BS/EN standards, and familiar to NHS procurement frameworks. HTM-06 also provides clarity on maintenance and testing. The introduction of new technologies will bring with it the requirement for additional validation or proof of performance in the healthcare context, which adds time and risk to any installation.

As the go-to technology of choice, all hospitals already have diesel standby generation assets installed, whether in plant rooms or containers. All of these installations are fully integrated into the hospital electrical distribution system, supported with all the necessary ancillary elements and maintained by trained staff. Replacement or augmentation must build on this legacy. 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.

Challenges and drivers for change

While diesel standby remains central, there are pressures and challenges that are pushing hospitals, their estates teams, consultants, and contractors to consider how diesel generating sets can evolve, be supplemented or replaced.

• Environmental / emissions legislation

Stricter limits on CO₂ in general, CO, Nitrous Oxide (NOx), Particulate Matter (PM), and other engine emissions, plus local air quality considerations.

• Carbon reduction / Net Zero targets

The NHS is under pressure to reduce its carbon footprint. Diesel generators, especially on test runs or inefficient duty cycles, contribute to CO₂ emissions, so there is a push for more efficient, lower carbon alternatives or hybrid systems.

• Fuel supply & security

Concerns around the availability, delivery, and cost of diesel, especially in more remote areas or during supply chain disruptions. Fuel storage risk (degradation, DIP etc.) also needs management.

• Operational costs & maintenance

Older generating sets are less efficient and more maintenance heavy; failure risk increases with age. Also, running costs, fuel, emissions compliance, and periodic load testing/maintenance are non-trivial.

• Space, noise, vibration, site constraints

Many healthcare sites are located in constrained urban areas; expansion or retro fitting of large generating sets may be spatially (roof, basement) or acoustically challenging.

Emerging alternatives and supplementary technologies

To reduce diesel dependency or augment generator standby systems, several technologies are gaining traction.

• Battery Energy Storage Systems (BESS)

Especially for bridging, peak shaving, and handling transient loads — all of which have the potential to reduce generating set running hours.

• Alternative fuels

Hydrotreated Vegetable Oil (HVO), possibly other biodiesel blends, low-carbon gaseous fuels; hydrogen in longer term (though availability, infrastructure, and safety must be addressed).

• Demand side management and load shedding

More fine-grained control of non-critical loads to reduce stress on standby systems or to prioritise critical loads in emergencies.

• Microgrids & local energy generation

On-site solar, wind, perhaps hydrogen, connected via control systems to feed critical loads or pre-charge battery systems; reduces dependency on grid and diesel. Space will likely be a limiting factor.

• Remote monitoring, predictive analytics, IoT

To detect anomalies, plan preventive maintenance, avoid failure during emergencies. However, none of these currently fully replace diesel standby sets, especially in terms of immediate, high current, large load capacity under failure conditions.

The future outlook: towards hybrid modular critical power

Given what we have seen, I believe that the coming decade will see increasing adoption of hybrid modular critical power systems in UK healthcare. Key trends likely to dominate are:

• Diesel + battery + smart control hybrids

Many hospitals will adopt battery storage not just for UPS / bridging, but to absorb load spikes, allow smaller engines to run more efficiently, reduce routine test run time where possible, and to reduce emissions from idling or low loads.

• Containerised / podded plant rooms

Off-site manufacturing of power pods combining diesel gensets, UPS, switchgear, controls, in environmental enclosures all tested, delivered, and commissioned rapidly. Particularly useful for retrofit, capacity expansion, and rural hospitals.

• Partial load emission controls

With more generators running in parallel, there will be increased use of load management to ensure each operates in its optimum band; plus after-treatment systems and cleaner engines (with after treatment fitted).

• Integration with heat / thermal demands

CHP or waste heat recovery especially in hospitals with significant heating, hot water, laundry, and sterilisation loads will become more common, perhaps with modular CHP blocks able to be switched in or out depending on heat demand.

• Regulatory evolution / incentives

Procurement frameworks (e.g. NHS frameworks) will increasingly take into account life cycle emissions, total cost of ownership (TCO), not just capital cost. Grants or incentives may be offered for lower carbon technologies or hybrid systems. HTM and aligned regulations may evolve to provide clearer guidance on hybrid and modular systems.

• Alternative fuel trials / biofuels

Use of HVO or other low-carbon diesels in standby roles, particularly for periodic test runs, could become more widespread. Hydrogen standby generation remains experimental but likely to grow as infrastructure catches up.

Conclusion

In summary, standby diesel generation remains an indispensable part of the UK healthcare critical power strategy. Its capability to deliver high reliability, meet regulatory demands, handle large transient loads, and integrate with legacy systems keeps it firmly at the centre. That said, the future for healthcare power will likely be hybrid, modular, and smarter. The inclusion of UPS, battery energy storage, modular plant rooms, and possibly CHP or alternative fuels will allow diesel to be used more efficiently, cleanly, and flexibly.

Experience shows that the optimal path is a carefully designed critical power train that includes modular standby diesel generation as a key component, augmented by other technologies, with robust controls, good maintenance, and clear attention to regulatory and environmental constraints.