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:
- 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.
- 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).
- Check that the customer’s electricity usage is sufficiently high to justify the cost of installing a voltage optimiser with reasonable payback time (ROI).
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
Electrical equipment will operate adequately, even at this low level.
The ideal voltage to maximise equipment efficiency and prolong lifespan.
The average level at which voltage is supplied in the UK.
The maximum level that electricity should be supplied.
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 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 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.
Harmonics are current and voltage waveforms at multiples of the fundamental frequency of the 50 Hz UK mains electricity supply. Harmonics are caused by non-linear loads (power supplies for computers, variable speed drives, discharge lighting etc).
Reactive power is the name given to unusable power. It does no work in the electrical system, but is used to charge capacitors or produce a magnetic field around the field of an inductor. Reactive power needs to be generated and distributed through a circuit to provide sufficient real power to enable processes to run. Reactive power increases significantly with increasing voltage as the reactance of equipment increases. Correcting this with voltage optimisation will therefore lead to a reduction in reactive power and improvement in power factor.
When lighting loads are in use for a high proportion of the time, energy savings on lighting equipment are extremely valuable. When voltage is reduced, incandescent lighting will see a large decrease in power drawn, a large decrease in light output and an increase in lifetime.
However, other types of lighting can also benefit from improved power quality, including systems with resistive or reactive ballasts. Fluorescent & discharge lighting is more efficient than incandescent lighting. Fluorescent lighting with conventional magnetic ballasts will see a reduced power consumption, but also a reduced lumen output (brightness) from the lamp. Fluorescent lamps on modern electronic ballasts will use approximately the same power and give the same light.
To provide the same wattage at the reduced voltage will require a greater current and increase cable losses. However, lighting controllers and ballasts are responsible for generating high levels of harmonic distortion, which can be filtered with some types of voltage optimiser, in addition reducing the need for lighting controllers.
Heaters will consume less power, but give less heat. Thermostatically controlled space or water heaters will consume less power while running, but will have to run for longer in to produce the required output, resulting in no saving.
Assuming a mixture of loads including 7% fluorescent lighting, 0.5% incandescent lighting, 12.5% three phase air conditioners, 5% motors, 22.5% small 3-phase motors, 52.5% large 3-phase motors.
It is likely that a modern installation would have less opportunity for savings: almost no incandescent lighting, partly high-frequency fluorescent lighting (no saving), some variable speed drives (no saving), higher motor efficiencies (therefore less waste to save).
The best potential for saving is probably with older lighting (incandescent or fluorescent and discharge lighting with conventional control gear. Therefore, older commercial and office premises are likely to have a better saving potential than modern buildings or industrial sites.
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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