Voltage optimisation
Many UK sites are supplied at a higher voltage than their equipment needs. Bringing it down wastes less.
What it actually is
A unit at the incoming supply holds site voltage closer to what the equipment is designed for. Nothing changes in how the site is used.
Motors, older lighting and resistive loads respond. Modern electronic equipment largely does not. Your voltage and load mix decide the answer.
Many UK sites are supplied at a voltage above what their equipment actually needs. A voltage optimisation unit sits at the incoming supply and holds the site voltage closer to the level the equipment is designed for, so less energy is wasted in the equipment itself.
Nothing changes in how the building is used. There is no behaviour change, no controls strategy and nothing for staff to operate. It is a single piece of equipment at the intake, and once it is commissioned it is invisible.
The catch is that not all loads respond. Motors, transformers, older discharge lighting and resistive loads use less when the voltage comes down. Modern electronic equipment with switched mode power supplies draws the power it needs regardless, so it saves nothing. Your load mix therefore decides the answer, and so does your actual measured voltage.
This is the measure most often sold on a headline percentage applied to a whole bill. That is the wrong way round. The right way is to measure the incoming voltage over a representative period, establish what proportion of the load is voltage sensitive, and apply the saving only to that part.
Which buildings it suits, and which it does not
It suits sites with a measured supply voltage at the top of the permitted range and a load mix weighted towards motors and older equipment.
It suits you less if the incoming voltage is already low, or the load is mostly modern electronics.
- Manufacturing with substantial motor loadGood fitPumps, fans, compressors and conveyors are the loads that respond most.
- Older buildings on legacy lightingGood fitDischarge and fluorescent lighting responds to voltage. Worth checking whether an LED retrofit would beat it outright.
- Sites with a measured high incoming voltageGood fitThe higher your supply sits within the permitted range, the more there is to recover.
- Cold storage and process coolingDependsLarge motor load is favourable, but modern inverter driven compressors respond much less than older fixed speed plant.
- Mixed use officesDependsDepends entirely on how much of the load is plant and how much is computing equipment.
- Modern buildings full of electronic equipmentRarelySwitched mode power supplies draw what they need regardless of supply voltage.
- Sites already measured at a low incoming voltageRarelyThere is no headroom to remove, and reducing further risks equipment operating below its tolerance.
- Data centres and critical loadsRarelyAlmost entirely electronic, and adding a device in series with a critical supply raises questions that outweigh the gain.
What it typically costs and saves
- Installed cost
- from £5,000 to £20,000 per site
- Reduction in consumption
- 7 to 12 per cent
What drives the variation
- •Site size and the rating of the unit required.
- •Whether it is fitted at a single intake or at multiple supply positions.
- •Switchgear works, bypass arrangements and protection.
- •Space at the intake, and any building or civils work to create it.
- •Whether monitoring is included so the saving can actually be verified afterwards.
- •Out of hours working for the shutdown.
How this appears on your building
What decides whether it works on your building
The measured incoming voltage
Over at least a week, capturing day and night and both weekdays and weekends, because supply voltage varies. A single spot reading is not a basis for a purchase.
The load mix
What proportion of your consumption is motors, resistive load and legacy lighting, and what proportion is electronic. The saving applies to the first group, not to the bill.
Whether variable speed drives are already fitted
Inverter driven motors respond far less than fixed speed ones, so a site that has already invested in drives has less left to recover.
Equipment tolerance
Some plant has a defined operating voltage range. Anything sensitive needs identifying before the target voltage is set.
Space and an outage window
The unit sits at the intake and installing it needs a planned shutdown of the whole site. On a continuous operation that window is the hardest part to arrange.
What else is planned
If a lighting retrofit or new drives are coming, the voltage sensitive share of your load is about to shrink. Assess in that order.
How long it takes and what it disrupts
Measurement first
Logging the incoming voltage and the load over a representative period. No credible proposal exists before this is done.
Design and shutdown planning
Agreeing the target voltage, the bypass arrangement and the outage window. On a continuous site the outage is usually the constraint on the programme.
Installation
The unit is installed at the intake during a planned shutdown, normally out of hours or over a weekend.
Verification
Metering before and after is the only way to know what you actually got. Insist on it, and agree in advance what will be compared against what.
What usually goes wrong or gets missed
Sold on a headline percentage
A number applied to the whole bill, without measuring the incoming voltage or examining the load mix, is a sales figure rather than an engineering one.
The saving claimed across the entire site
Only the voltage sensitive portion responds. Applying the percentage to everything can overstate the result several times over.
Fitted where lighting or controls would gain more for less
On many sites an LED retrofit removes both more energy and much of the voltage sensitive load, at a shorter payback.
No verification metering
Without a before and after measurement nobody can say whether it worked, and consumption moves for a dozen other reasons.
Losses in the unit itself not accounted for
The equipment consumes a little of what it saves. That belongs in the calculation.
No bypass arrangement
If the unit needs maintenance or fails, you want the site to keep running. Ask how that is handled.
- •It is sold on a headline percentage without measuring the incoming voltage first.
- •The saving is claimed across the whole site when only part of the load responds.
- •It is fitted where lighting or controls would have gained more for less.
What to ask an installer
- 01Have you logged my incoming voltage, over what period, and can I see the data?
- 02What proportion of my load have you treated as voltage sensitive, and how did you establish that?
- 03What target voltage are you setting, and is any of my equipment intolerant of it?
- 04How much energy does the unit itself consume?
- 05What verification metering is included, and what will you compare before and after?
- 06Is there a bypass, and what happens to the site if the unit fails?
- 07How long is the shutdown, and can it be done outside operating hours?
- 08What would an LED retrofit achieve on this site instead, and have you compared them?
- 09What maintenance does the unit need, and what is its expected life?
How it interacts with other measures
With LED lighting
Assess lighting first. LED fittings do not respond to reduced voltage, so a lighting retrofit shrinks the case for voltage optimisation. Doing them in the wrong order means paying for a saving that is about to disappear.
With variable speed drives
Drives and voltage optimisation act on the same motor load. Fitting both does not add the two savings together.
With solar
Reducing site consumption raises the share of generation you export, which is worth less. Model the two together rather than separately.
With an EPC rating
It is not a modelled input to a non domestic assessment, so it will not move a band.
Common questions
Does voltage optimisation actually work?
It works on the part of your load that is voltage sensitive, which means motors, resistive loads and older lighting. It does very little for modern electronic equipment. Whether it is worth it on your site depends on your measured incoming voltage and your load mix, not on a headline percentage.
How much can it save?
Providers converge on a reduction of 7 to 12 per cent of consumption on suitable sites. The important word is suitable. That range assumes a high measured supply voltage and a load mix weighted towards motors and older equipment.
How do I know if my site is suitable?
Log the incoming voltage for at least a week and look at what your load is made of. If the voltage sits near the top of the permitted range and much of your consumption is motors or legacy lighting, it is worth pricing.
Will it damage my equipment?
It should not, provided the target voltage keeps everything inside its operating range. Any plant with a narrow tolerance needs identifying during the survey.
Should I do LED lighting first?
Almost always. Lighting usually saves more, pays back faster, and it reduces the voltage sensitive load, so it changes the voltage optimisation case. Assess them in that order.
Related reading
Where these figures come from
Show the provenance
- Installed cost: from £5,000 to £20,000 per site
- UK commercial voltage optimisation market, 2026.
- Reduction in consumption: 7 to 12 per cent
- UK commercial voltage optimisation providers, converging estimates 2026.
The figures on this page are modelled ranges for UK commercial buildings, not a quote for yours. Add your building and we will model it on your own roof, load and rating.