What to look for when making a purchase…
This guide explains how to choose the right generator for your site by looking at cost, reliability, load requirements, generator size, noise control and sector-specific needs. It is designed to help commercial, industrial and critical-service organisations make a confident decision before requesting quotes or committing to hire or purchase.
We focus on the three questions that make the biggest difference when choosing a generator for a commercial or critical site:
· Cost: what you pay upfront and what you pay over the machine’s lifetime
· Reliability: whether it will start and run when you need it to
· Adaptability: whether it is genuinely suited to your industry, site and load.
Answer these three questions well and the rest of the decision, including brand, finance and delivery timescales, becomes much easier. Here is how to think through each one.
Cost: value versus premium pricing
Generators span a huge price range depending on make and model. A cheaper unit that’s underspecified for your load, or that lacks proper after-sales support, can end up costing far more once you factor in breakdowns, emergency callouts and shortened service life.
When weighing up cost, it’s worth separating the decision into these questions:
What is the total cost of ownership, not just the purchase price?
Fuel efficiency, service intervals, parts availability and expected lifespan all affect what a generator costs you over 10 to 15 years of use.
Is buying the best option, or would hiring make more financial sense?
For short-term projects, planned works or bridging cover while a permanent installation is commissioned, hiring a generator avoids tying up capital in a machine you may only need for weeks or months.
Hire generators can typically be delivered and running within hours of a confirmed order.
Is a premium-brand engine worth the difference for your needs?
For critical infrastructure, the reliability premium of a well-supported, industry-standard engine is easy to justify. For lower-risk, ad hoc backup, a value-tier unit may do the job perfectly well.
The right answer is not always the cheapest generator, and it is not always the most expensive one. It is the one sized and specified correctly for the job.
Reliability
A generator that does not start during a power cut has failed at the one thing it exists to do. Reliability comes from two places: the build quality of the machine and the capability of the installer or service provider, such as Pharos Generator Services, to maintain it and provide ongoing support.
When assessing a supplier’s reliability, look for independently audited accreditations. ISO 9001 for quality management, ISO 14001 for environmental management and ISO 45001 for health and safety management are a reasonable baseline for any contractor working on critical power infrastructure. Membership schemes such as Constructionline Gold, CHAS and SafeContractor add a further layer of independently checked due diligence.
Also look for a genuine service and maintenance track record, not just a sales relationship. A supplier who offers weekly, monthly or quarterly planned maintenance, tailored to how hard the generator works and the environment it sits in, is planning for the long term, not just the sale.
A reliable supplier should offer 24/7 emergency response with a realistic call-out time. Ask what happens at 2am on a bank holiday, not just during office hours.
Look for sector experience with organisations that cannot afford downtime. Suppliers trusted by the Ministry of Defence, the NHS, telecoms providers or blue-light services have been through procurement processes that scrutinise reliability closely.
If a supplier can’t point to independently audited accreditations, a maintained fleet of long-standing clients, and clear evidence of how they respond when something goes wrong, that’s worth treating as a warning sign, regardless of how competitive the initial quote looks.
Adaptability: why industry-specific matters more than raw power
Adaptability comes down to three practical questions.
Size: based on the output you require
Generator capacity is measured in kVA (kilovolt-amperes), and getting this number wrong is one of the most common mistakes in generator buying. Two things drive the correct size: running load and starting load.
Running load is the total power your equipment draws once everything is operating normally. Starting, or surge, load is the extra power some equipment needs during the first few seconds of starting.
Many types of equipment, particularly anything with an electric motor, draw significantly more power in the first few seconds of starting than they do once running. A generator sized only for running load can fail the moment equipment switches on.
As a rough sense of range, standby generators for small commercial premises might sit around 20–100 kVA, mid-sized commercial and industrial sites often need 100–500 kVA, and large sites such as hospitals, data centres, manufacturing plants, can require 500 kVA up to 2 MVA or more, sometimes across multiple units working together. The only reliable way to land on the right figure is a proper load survey of your site, not a guess based on floor area or headcount.
Type of load required
Not all power demand looks the same. Whether you need standby power, prime power or continuous power changes both the generator specification and the maintenance regime it needs.
Equally, a load that is mostly resistive, such as heating or lighting, behaves very differently from one with heavy inductive or motor-driven demand, such as pumps, compressors or lifts. The latter needs more surge capacity headroom built in.
Industry-specific requirements
Different sectors bring different non-negotiables:
· Healthcare and data centres: typically need automatic transfer switching with near-instant changeover, N+1 or N+2 redundancy, and rigorous testing
regimes. In healthcare, downtime can put safety at risk; in data centres, it can threaten uptime, service continuity and stored data.
· Construction and events: usually prioritise portability, fast deployment and flexible hire terms over long-term ownership.
· Telecoms and infrastructure: sites are often remote and unmanned, so remote monitoring and extended fuel autonomy matter more than they would on a staffed site.
· Manufacturing: frequently needs to handle heavy motor-start loads and may run generators as part of a combined heat and power strategy to improve overall energy efficiency.
Canopies and noise control are important when a generator will sit next to an office window, on a residential-adjacent site, or in an open industrial yard.
Where a generator will sit determines how much you need to think about noise. Canopied generators house the engine in an acoustic enclosure that significantly reduces operating noise, making them the right choice for sites near housing, hospitals, offices or anywhere local noise regulations apply.
Containerised units go a step further, housing larger generators in a fully enclosed, weatherproofed structure. This is useful for larger installations or where the generator needs to be more discreet and better protected from the elements.
Open-type generators, without acoustic housing, are usually reserved for locations where noise genuinely is not a constraint, such as some remote industrial or construction sites.
Finding the right power solution for you
Our team of engineers are here to answer your questions, provide advice and help you make the right decision for your requirements.
Talk to an expert