How Smart Meters work
A Smart Meter works by measuring the electrical current flow and voltage at regular intervals and then adding this up to calculate the power used in a half-hour period. Similarly, for gas the flow is measured at regular intervals. This information can be sent to your In Home Display and to your supplier. Different communications technologies may be used in different kinds of premises for the Home Area Network to communicate with your In Home Display, and different technologies will be used in different parts of the country to allow the Wide Area Network to send data to and from the company providing the communications.
As well as measuring energy, meters are constantly monitoring their own performance and environment. For example, they will report if they have an internal memory problem and report if the terminal cover is removed. In these cases your supplier may send someone to your home after contacting you.
End to End
The information from your meter goes first into a communications hub that is usually built into the electricity meter, and then through radio waves to the communications company. In the case of the SMETS 2 meters, it is the Data and Communications Company (DCC). From there it is sent on to the various DCC Services users who have a need for the data.
We will now explain each leg of the end to end journey shown in the diagram above.
In your home as an energy customer, you will have a smart meter for electricity and a smart meter for gas (if you're dual fuel). Both meters communicate with a communications hub which is normally a part of the electricity meter however, it could be separate if your gas smart meter is installed first. To power the communications in the gas meter a battery is used as it would be dangerous to use mains electricity.
In addition, you will have an In Home Display which is powered though the mains and communicates with the meters through the same communications hub. In the future, more gadgets could use the communications hub, provided they have the right security credentials.
Data and Communications Company (DCC)
To minimise costs for the long term use of SMETS 2 meters the DCC went out to tender for the communications network having split the country into regions for this purpose. So depending on where you are you could have one of two companies communicating with your meter, Arqiva Limited in the north and Telefónica (better known to us as O2) in the central and southern regions.
DCC Service Users
From the DCC, the Smart Meter messages can be sent to various Service Users depending on the messages content. Electricity and gas suppliers and distribution network operators will all have a keen interest in the data from Smart Meters. They will use it for the following reasons:
- Meter readings - for billing purposes
- Half Hourly readings - for additional services or sophisticated products
- Maintenance messages about the health of the meter - such as memory problems
- Firmware messages - to update the software in the meter
- Configuration messages - to set up new products
- Pay As You Go messages - to top up PAYG credit
- Tamper messages - to detect theft and security attacks
- Export meter readings - to measure how much electricity your solar cells or wind turbine is passing back to the network for load management and to credit the customer, depending on the commercial arrangement.
- Distribution Network Operators
- Power outage messages - to know when and where outages occur
- Meter readings - for network billing to suppliers
- Half Hourly readings - for network load planning
- Voltage, Current and Power Factor readings - for network operation and planning.
- Export meter readings - for network operation and planning.
- Other Authorised Parties
- Meters readings - to analyse and show you your energy usage
- Half Hourly readings - to analyse and show you your particular energy profile shape.
You may have wondered how your energy bill is calculated, especially for gas, which is more complicated. Both electricity and gas are priced in pence per kilowatt-hour (kWh), so one multiplies the kWh by the price, dividing by 100 to get from pence to pounds.
But how do meters measure the kWh used, and what are the basic calculations that the meters carry out to determine the quantity of energy used?
The meter is constantly measuring the voltage and the current passing through the meter. It multiplies voltage measured in Volts by current measured in Amps to get power measured in Watts.
The above calculation takes no account of time, so it is an instantaneous measure of power. To get a measure of energy used we need to introduce time, in the case of electricity, domestic pricing is at the hourly level, so we use time measured in hours to get kilowatt-hours or kWh.
It is kilowatt-hours that your meter displays as Active Energy or Active Power. A kilowatt-hour is also known as a Unit. Because a Smart Meter can measure power in both directions, it may also indicate IMP or IMPORT to show the power consumed as opposed to the power exported.
A gas meter simply measures the volume of gas that passes through it. Older gas meters measure the volume in units of 100 cubic feet (ft3) and newer meters in cubic metres (m3). The suppliers systems hold the meter details and so can accurately calculate the volume of gas used.
Suppliers then have to convert the volume of gas used into kWh for billing. The following equation is used:
What do these terms mean, and why are they necessary?
- The volume of gas used; measured in cubic metres or hundreds of cubic feet.
- Metric Conversion
- If you've got a metric meter, you can ignore this step. If your reading is in cubic feet, then a conversion factor of 2.83 must be applied to convert to cubic metres.
- Calorific Value
- Calorific Value (CV) describes how much heat is generated when a known volume of gas is burned. Suppliers' bills show the value of CV used, which is typically between 37.5 and 43.0 MJ/m3 (Mega Joules per metre cubed).
The CV of the gas at each Local Distribution Zone is continually measured by the National Grid who sends this figure to your gas supplier, who then uses it for their calculations.
- Volume Correction
- The volume correction factor is used to take into account the temperature, pressure and atmospheric conditions at a property. This factor is typically 1.02264 unless your household has unusual atmospheric conditions. You can usually find this number on your gas bill.
- Joules to kWh
- We have ended up with Mega Joules from the above calculations. One kWh equals 3.6 million Joules, so we finally divide by 3.6 to get the energy used in kWh.
Questions & Answers
- We suggest you wait 24 hours to see if the device reconnects.
- If not move the IHD close to the electricity meter and wait another 24 hours for reconnection.
- Try resetting your IHD and wait another 24 hours. There are various methods to reset an IHD depending on the model. Find a guide for your device at www.smartme.co.uk/documents.html.
- If this does not work then contact your energy supplier who will have to send commands to the devices to re-run the connection process.
This does not mean it will cost people more as, firstly you would have to agree to be on such a tariff, and secondly if you do not change your pattern of use it is likely to cost you the same as a simple tariff. The advantage is that if you reduce your demand at the times of high prices you will save money.
Smart meters make it easier to provide time banded rates as they can provide time bands at 30 minute intervals if required. (Updated: 2022-04-18)
Once you have the electricity meter model number you could look it up on our SMETS 1 or SMETS 2 Meter pages in order to work out if it is SMETS1 or SMETS2.
For further details on how to operate your meter see our manuals on our Documents page. (Updated: 2020-02-07)
Ultimately all customers pay for this as a percentage increase which is applied by area. For a technical explanation see Electricity Distribution System Losses. (Updated: 2020-08-19)
- This shows the status of the hub's software. You should see a green light flashing every five seconds.
- Shows your communication hub's ability to communicate with your supplier. If your meter is connected, you'll see a green light flashing every five seconds. This light may be off if your meter is using the MESH network to communicate.
- This light may be on if your meter is connected and communicating through another network (this network has been built to allow more meters to communicate in areas with poor or no signal).
- This light shows the connection status of your electricity meter, gas meter and/or IHD with your communications hub on the HAN (Home Area Network). If connected, you'll see a green light that flashes every five seconds.
- This light tells you if a gas meter is connected; you should see a green light flashing every five seconds. If you don't have a gas meter installed, this light will be off.
Currently domestic and small business electricity use is modelled on a small number of average usage profiles. Obviously when you add up what was supplied and what was used they are not the same because of the use of average profiles. So the use of half hourly data will improve this and means that suppliers will have a more accurate wholesale energy bill.
This could improve customers' bills as the commercial risk for suppliers is slightly reduced.
This does not change tariffs for customers or what data domestic customers allow their smart meters to send unless they agree. (Updated: 2021-06-17)
Firstly you can use the emergency credit that most suppliers offer. If that runs out you can enter the long authorisation number that you received when you paid for the credit into the meter or IHD (In Home Display) to apply your credit. This very difficult to do on the meter so use the IHD if you can. (Updated: 2019-10-21)
The EXP KWH is for how many kWhs you've pumped out to the National Grid, which is only relevant if you've got something generating electricity such as solar panels.
IMP KVARH is only used by distribution companies as it helps understand the current flowing in the supply cables. (Updated: 2021-04-09)
The security system consists of many layers and has been design by Government Communications Headquarters (GCHQ). The National Cyber Security Centre (NCSC) is involved in ongoing reviews.
Smart meters use their own bespoke wireless connection to communicate with suppliers. This wireless connection has been built to be extremely secure, and is encrypted to prevent hackers being able to attack electricity supplies.
There are also monitoring systems in the background known as "Anomaly Detection" which look for unusual patterns of data across the communications network.
So they're not connected to the internet and only hold information on your energy consumption. Not only are smart meters hard to hack, there would be no point doing it anyway. (Updated: 2021-04-23)
The comms hub uses the Home Area Network (HAN) to talk to the electricity, gas and IHD (In Home Display) devices. To save battery power the gas meter communicates only every half-hour and so the comms hub stores a copy of the gas meter data for querying when required. This copy is known as the gas mirror or Gas Proxy (GPF).
The comms hub uses the Wide Area Network (WAN) to talk to the company responsible for collecting the data and passing it on to other businesses such as suppliers; for the latest SMETS2 meters this company will be the DCC (Data Communications Company) which the government has set up especially for this role.
Depending on the Communications Service Provider, which varies by areas of the UK, the radio technology can change depending on what works best in a local area. Sometimes your comms hub will communicate directly with DCC and sometimes it will talk through other comms hubs around you to reach a particular comms hub which has direct communications with DCC. This form of communications looks like a mesh when you draw out the possible links between meters and is therefore known as a Mesh network. (Updated: 2020-11-07)
A different communications method (Zigbee 868MHz) available from mid 2020 will improve this for about 3.5% of properties but that still leaves a large number for whom Smart Meters won't work.
For these final properties, for example where meters are in a basement a long way from the customer's IHD, a separate company has been set up to investigate solutions, prepare contracts and procure the equipment. The company is the Alt HAN Co Ltd and solutions are expected in 2021. (Updated: 2021-10-03)
If you are on a tariff switched by RTS we recommend you speak to your supplier to get a Smart Meter and ask what tariff you can move to. The RTS service uses the BBC Radio 4 long wave signal and is planned to end in March 2023. (Updated: 2021-04-25)
Arqiva Limited for CSP North region with a 15-year contract worth £625M using Long-Range Radio communications.
Telefónica (O2) for the CSP Centre (Midlands, East Anglia and Wales) and South (south of England) regions using the 2G/3G cellular radio communications network. The two Telefonica contracts over 15 years are worth £1500M.
The contracts were awarded in 2013. (Updated: 2021-11-15)
See Wikipedia for an explanation of Three-phase power. (Updated: 2021-02-12)
However, as this is not a common requirement suppliers have been slow in implementing systems to support it - you will have to shop around for the supplier which can support your requirements. (Updated: 2019-10-21)