How Voltage Optimisers Reduce Energy Bills

Voltage optimisation is the process of lowering the incoming mains power supply voltage, in areas with a high mains power supply voltage, to reduce the energy used by devices on a site. Voltage optimisation is a voltage reduction technique used in countries including the UK (and Japan) whose traditional mains power supply voltage was 240Vac before being harmonised within the European Union to 230Vac

UK Electricity Supplies

In the UK, our electrical infrastructure consists of HV (high voltage) and MV (medium voltage) generating stations with electricity distributed down to LV (low voltage). The UK electrical supply voltage used to be 240Vac and 220Vac in Western European countries, but this was harmonised down to 230Vac. The 230Vac level was achieved in the UK by amending the acceptable operating window from +6 to -10% to +10 to -6%.

Most loads, whether inductive or capacitive, have a wide input voltage window. This benefits product manufacturers (in terms of scale economies) who can manufacturer one product for the whole of the EU market / 230Vac region. Plug a device into a UK socket or a European socket with an adapter and the device will work without modification to the internal power supply itself.

In the UK the traditional supply voltage was 240Vac and in some parts of the country a far higher mains power supply voltage can be recorded. Sometimes this can be above 250Vac for a single-phase supply and approaching as high as 260Vac or more. Whilst the traditional 240Vac supply voltage is one reason for this, another is the dramatic increase in the last 10 years of renewable power generation systems (on-shore and off-shore wind and solar PV) and an increasing number of injection (export) connections into the National Grid.

As the mains voltage rises, there is increased wear and tear on power supplies and the risk of shutdown to prevent overvoltage damage. Lowering the voltage from 250Vac to around 220Vac removes the risk of accidental shutdown from a high mains voltage and reduces energy consumption. Care must be taken now to go too low below 220Vac as some systems may see a low voltage as outside their input voltage window and shutdown.

The Voltage Optimisation Process

Voltage optimisers typically provide their best energy savings when used in areas with a mains power supply voltage above 254Vac. The process relies on Ohm’s Law (Power=IV Watts) to generate an energy saving. For a device drawing 3Amps at 220Vac the power drawn is 660Watts. At 250Vac the power drawn is 750Watts. Lowing the supply voltage produces a power saving of 110W (750-660Watts) which in turn reduces the energy drawn from the mains power supply (Watthours, Who).

Voltage Optimiser Installation

Most UK buildings can benefit from voltage optimisation. The most important step for any installation is a desktop survey to analyse electricity bills and the loads being used on site. If the desktop survey results in a ‘green light’ the next stage of the process is a site survey.

The site survey includes an audit of the systems to be protected on site and their distance from where the voltage optimiser will be installed. Care must be taken when sizing a voltage optimiser and decided on the electrical specifics of the installation. The voltage the optimiser is set to reduce to has to be at a level that considers the input voltage window of each of the loads and cable run losses. The survey also must take into consideration 24hour 7day working practices and changes in load, as well as seasonal variations. It may be necessary to install data loggers and mains monitoring systems to provide a complete dataset for the site.

Once all the data is accumulated the right voltage optimisation technology must be selected and a cost: benefit analysis provided showing the energy savings, Return on Investment (ROI) and Net Present Value (NPV) calculations that may be used to justify the installation. Regular inspection and maintenance contract costs should be built into the calculations. A voltage optimiser should typically be inspected annually and to ensure it is operating correctly and to allow for any changes to the site loads and conditions. A typical voltage optimiser installation will achieve a cost recovery within 3-5 years with some VO manufacturers providing guaranteed energy savings.

Voltage Optimiser Technologies

Voltage optimisers can be based on dynamic electro-mechanical or static transformer (toroid or auto) designs. Static designs tend to require less maintenance than dynamic ones due to the lack of moving parts and care should be taken with both types in terms of consumable items including fans and capacitors.

For solar PV installations, voltage optimisers can also lead to improve power generation in areas with a high mains power supply voltage. This is down to the fact that solar PV inverters must generate their AC power at a higher level than the mains power supply. If the mains power supply voltage is high, then the solar inverter could trip-out to protect itself at peak generation losing any potential feed-in tariff for the solar PV installation owner.

The Carbon Trust lists voltage optimisation as a proven energy saving and voltage management technology – https://www.carbontrust.com/media/77191/ctg045.pdf and one suitable for a wide range of buildings, companies and organisations. For Renewable Energy Supplies, voltage optimisation is one of the energy saving solutions we can supply to organisations with products including both single and three phase options up to 1MVA.