Voltage Optimisation

A voltage optimiser can help reduce energy consumption – which is vital to lowering energy bills

Voltage optimisation is a well established energy saving technology which can help reduce electricity bills by lowering the voltage of incoming electricity to a property down to 220 volts, which can allow devices to draw less power, or prolong the lifespan of some devices.

Many electrical appliances can function more efficiently at a lower voltage by using less power and producing less waste heat. Some voltage optimiser manufacturers suggest average energy saving of around 13%. However, not all electronic devices will benefit to the same degree, so the decision whether or not a voltage optimiser is a sensible choice for you depends on the types of electrical appliances you use, the size of your electricity bill, and the time it will take for your investment in a voltage optimiser to pay for itself through electricity savings.


Overvoltage refers to voltage higher than that which the equipment is designed to operate most effectively. Electrical devices running on a higher voltage than 220 V will use more power in the form of excess heat, increased brightness, noise or other inefficiencies which can also act to reduce the lifespan of the device, with no improvement in performance.

The Wiring Regulations BS7671 makes the following statements in relation to overvoltage:

“A 230V rated lamp used at 240 will achieve only 55% of its rated life” (referring to incandescent lamps) and “A 230V linear appliance used on a 240 V supply will take 4.3% more current and will consume almost 9% more energy.”

Is Voltage Optimisation suitable for my home?

Any building that uses electrical appliances or lighting should be considered for voltage optimisation.

Before a voltage optimiser is installed, a qualified electrician should first:

  1. Test the existing mains voltage supply to access the voltage level. If the mains supply to the building is lower than 240v, energy savings may not be sufficient to merit the cost of installing a voltage optimiser – or payback time may be deemed too long to be financially viable.
  2. Assess what electrical products make up the normal “electrical load” to ensure that sufficient appliances will actually benefit from voltage optimisation (for example, heat producing electrics will not save money with a voltage optimiser).
  3. Check that the customer’s electricity usage is sufficiently high to justify the cost of installing a voltage optimiser with reasonable payback time (ROI).
Different types of electrical devices vary in the amount of energy they can save through voltage optimisation. Heat producing devices such as heaters, or kettles, will take a little longer to heat up, but the same amount of energy is required to make the room or cup hot, so no saving is made. Other devices such as fridges, freezers, televisions etc will save money.

How do Voltage Optimisers work?

The average UK mains electricity supply is 230 volts with a tolerance of +10% to -6% (depending on the the National Grid’s ability to maintain a consistant voltage across its network), so can actually fluctuate between 216 – 253 volts. European mains electricity operates at a lower voltage of around 225 V, therefore, all electrical appliances sold across Europe, including electrical products sold in the UK (with a CE mark) have to work safely between 207-253 V.

UK Mains Voltage

207 V

Electrical equipment will operate adequately, even at this low level.

216-220 V

The ideal voltage to maximise equipment efficiency and prolong lifespan.

242 V

The average level at which voltage is supplied in the UK.

253 V

The maximum level that electricity should be supplied.

Since 1993, electrical appliances must carry a CE mark to prove they have been tested and comply with all relevant standards, making them capable of working across a wide range of voltages between 207v-253v.

The higher the voltage – the higher the power consumption, in the case of a pure resistance load. A reduction in voltage does not affect the energy used by domestic appliances using resistive loads, with the exception of heat producing devices such as kettles, toasters and electric heaters – which will take longer to do their job.

What is the difference between inductive and resistive loads?

A load is any device that absorbs energy in a power system. Domestic appliances generally fall into two broad groups of loads: resistive and inductive.

Resistive Loads

Resistive loads are components or devices which convert electricity into heat and motion. Examples of products which are resistive loads are incandescent lamps or electric heaters.

Inductive Loads

Inductive loads are devices in which the electricity flows through the coils, producing an electric field. Examples of inductive load devices are motors, fans or refrigerators, or transformers (which are found in most electronic devices), such as televisions, computers or fluorescent lamps.

In the home, the potential electrical energy saving can be up to 12%. A voltage optimiser will lower the voltage to around 220V, the most efficient level which will maximise savings on electricity, but you may notice heat producing appliances which have a resistive load such as kettles and toasters, take a little longer to heat up and do their job.

It is a common misconception that fridges and freezers do not provide savings through voltage optimisation because they are fitted with a thermostat. Fridges and freezers operate completely differently from resistive heating devices. If a resistive heating device is driven from a higher voltage, the result is heat which is helpful in its intended purpose (heating). If a fridge or freezer is driven from a higher voltage the result is also heat however this is not helpful in its intended purpose (cooling). The compressor motor power output is reduced slightly by voltage optimisation so the fridge/freezer thermostat will keep the motor on a little longer however overall the effect is for the motor to run slightly longer at much lower losses.

Tests at Manchester university showed a 10 °C reduction in motor temperature under voltage optimisation due to the reduced losses in the motor.

Voltage Optimisation and Solar PV

In order to feed electricity generated back to the grid, a solar PV inverter must step up the voltage delivered by the solar panels to be higher than the existing mains voltage (216 – 253 volts). This means that electrical appliances might be subjected to a higher voltage than the regular mains would supply.

Installing a voltage optimiser alongside a solar PV system can reduce the voltage of the house, and therefore lower the voltage that the solar inverter is required to produce in order to feed the electricity into your home. This can help to achieve a greater reduction in energy consumption and carbon emissions, resulting in faster payback periods and a greater return on investments.

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