Voltage optimisation: where it shines and where it doesn’t

Voltage optimisation can deliver measurable savings, but only when the electrical load profile and plant age align with its strengths. This article separates the sites where the technology pays for itself quickly from those where it merely adds cost, and provides a practical framework for evaluating the business case.

Understanding voltage optimisation

Voltage optimisation (VO) is a power‑quality service that trims the supply voltage to a level just above the minimum required for reliable operation. By reducing the RMS voltage by 5‑10 % on a typical UK 230 V supply, the current drawn by resistive loads falls proportionally, cutting I²R losses in wiring, transformers and motor windings. The result is a lower kWh reading on the meter and, consequently, a reduced electricity bill.

The technology is usually delivered via a solid‑state regulator installed at the mains board. Modern VO units are programmable, can be remotely monitored, and integrate with TUS’s Yolk portal for real‑time performance data. The regulator does not alter the frequency or phase, so it does not interfere with protection devices.

Where it delivers fast payback

Motor‑intensive sites

Industrial or distribution centres that run large numbers of induction motors (e.g., refrigeration, material handling, HVAC fans) see the greatest benefit. Motors are typically designed to operate up to 230 V but run efficiently at 215‑220 V. A 7 % voltage reduction can lower motor current by roughly the same proportion, translating into a 5‑10 % reduction in overall site electricity consumption.

Example: A 2 MW motor‑driven warehouse consumes 12 GWh per year. A 6 % saving equals 720 MWh, worth about £50,400 at the current £70 /MWh market rate. With a typical VO installation cost of £12‑15 k, the payback period is under two years.

Sites with fluorescent or legacy lighting

Older commercial premises often retain fluorescent tubes and magnetic ballasts that are voltage‑sensitive. Reducing the supply voltage reduces the lamp current without noticeably dimming the light output, delivering 5‑12 % savings on lighting electricity, which can be a sizeable share of the total load in retail or office blocks built before 2010.

Older electrical plant

Buildings with dated wiring, undersized distribution transformers or legacy switchgear experience higher I²R losses. VO directly cuts these losses, and the effect compounds when the plant is also motor‑heavy. TUS’s own data shows that sites with a mix of legacy plant and heavy loads have realised up to 15 % total site savings, beating supplier projections by 20 % in the last 12 months.

Where it falls short

Modern LED‑dominant sites

LED luminaires draw far less current and are less voltage‑sensitive than fluorescent fixtures. In a newly fitted office with 90 % LED lighting, VO may only affect a small fraction of the total load, delivering savings below 2 % – insufficient to justify the capital outlay.

Low‑load or already optimised sites

A small boutique shop or a data centre that already operates at the lower end of the statutory voltage range (≈ 216 V) will see negligible additional savings. In such cases, the regulator may even cause equipment to operate below its design voltage, risking premature failure.

High‑voltage equipment sensitive to voltage reduction

Some process control gear, variable‑frequency drives (VFDs) and sensitive electronics require a tight voltage tolerance. Reducing the supply can cause tripping or reduced performance, negating any energy benefit.

Calculating the economics

A pragmatic approach is to start with the site’s annual electricity consumption (kWh) and the proportion of that consumption that is voltage‑sensitive. The following simplified formula can be used:

Estimated saving (kWh) = Total kWh × % voltage‑sensitive load × 5‑15 %
Annual monetary saving (£) = Saving (kWh) × £70/MWh
Payback (years) = Installation cost (£) / Annual monetary saving (£)

Illustrative case: A 500 kW distribution centre uses 3 GWh per year. Assume 60 % of the load is voltage‑sensitive (motors, legacy lighting). Using a conservative 6 % reduction:

• Saving = 3 GWh × 0.60 × 0.06 = 108 MWh
• Monetary saving = 108 MWh × £70 = £7,560 per year
• Installation cost (typical VO package) = £12,000
• Payback = 12,000 / 7,560 ≈ 1.6 years

Even at the lower end of the 5‑15 % range, the payback stays within the 2‑3 year window that TUS promotes for its optimisation solutions.

Regulatory context

SECR (Streamlined Energy and Carbon Reporting)

From April 2023, large UK companies must disclose energy use and carbon intensity. Demonstrating a verifiable reduction through VO can improve SECR scores and reduce the risk of reputational penalties.

CCL (Climate Change Levy)

The CCL is levied on electricity consumption for non‑domestic users. A 5‑15 % reduction directly lowers the levy payable, enhancing the net financial benefit.

Ofgem and DESNZ guidance

Ofgem’s “Energy Efficiency Best Practice” notes that voltage optimisation is an acceptable low‑cost measure when the site’s load profile justifies it. DESNZ’s recent focus on demand‑side flexibility encourages the use of technologies that can be combined with flex‑management – an area where TUS already manages over 150 GWh.

NESO and capacity market considerations

While VO does not directly affect capacity market obligations, the reduced demand can improve a site’s performance against the Capacity Market “availability” metric, potentially lowering any associated charges.

Implementation considerations

1. Site audit – A qualified electrical engineer should map the load profile, identify voltage‑sensitive assets and confirm that the supply voltage can be safely reduced.
2. Regulator selection – Choose a unit with remote monitoring capability. TUS’s preferred suppliers offer a 30‑plus panel of vetted manufacturers, ensuring reliability and warranty support.
3. Performance verification – Use the Yolk portal to capture pre‑ and post‑installation kWh data. TUS typically validates savings against a 20 % improvement over supplier forecasts.
4. Maintenance – VO units require minimal upkeep, but periodic checks (annual) ensure the set‑point remains optimal as plant ages or load patterns change.
5. Risk mitigation – For sites with mixed modern and legacy equipment, a staged rollout – starting with motor‑intensive zones – can isolate any adverse effects.

Bottom line

Voltage optimisation is a low‑cost, low‑maintenance technology that can deliver 5‑15 % electricity savings and a 2‑3 year payback on sites with heavy motors, fluorescent lighting or ageing plant. It adds little value to modern LED‑only premises or low‑load buildings, and can even be counter‑productive where equipment requires tight voltage tolerances. A disciplined audit, combined with TUS’s proven supplier network and performance monitoring, ensures that the investment is justified and aligns with UK regulatory drivers such as SECR and the CCL.