, companies employed people (the so-called "meter readers") to read power meters on-site, such as here in
Glasgow during World War I. Even today, many power meters cannot be read remotely.
Commercial uses Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less. This is because most
electricity grids have demand surges throughout the day, and the power company may wish to give price incentives to large customers to reduce demand at these times. These demand surges often correspond to meal times or, famously, to advertisements interrupting popular
television programmes, such as the
TV pickup.
Home energy monitoring A potentially powerful means to
reduce household energy consumption is to provide convenient real-time feedback to users so they can change their energy using behaviour. Recently, low-cost energy feedback displays have become available, that may be able to measure energy (Watt-hours), momentary power (wattage), and may additionally be able to measure the MAINS voltage, current, uptime,
apparent power, capturing peak wattage and peak current, and have a manually set clock. The display may indicate the power consumption over the week graphically. A study using a consumer-readable meter in 500 Ontario homes by
Hydro One showed an average 6.5% drop in total electricity use when compared with a similarly sized control group.
Hydro One subsequently offered free power monitors to 30,000 customers based on the success of the pilot. Projects such as
Google PowerMeter, take information from a smart meter and make it more readily available to users to help encourage conservation. Plug-in electricity meters (or plug load meters) measure energy used by individual appliances. There are a variety of models available on the market today but they all work on the same basic principle. The meter is plugged into an outlet, and the appliance to be measured is plugged into the meter. Such meters can help in
energy conservation by identifying major energy users, or devices that consume excessive
standby power. Web resources can also be used, if an estimate of the power consumption is enough for the research purposes. A power meter can often be borrowed from the local power authorities or a local public library.
Multiple tariff Electricity retailers may wish to charge customers different tariffs at different times of the day to better reflect the costs of generation and transmission. Since it is typically not cost effective to store significant amounts of electricity during a period of low demand for use during a period of high demand, costs will vary significantly depending on the time of day. Low cost generation capacity (baseload) such as nuclear can take many hours to start, meaning a surplus in times of low demand, whereas high cost but flexible generating capacity (such as gas turbines) must be kept available to respond at a moment's notice (spinning reserve) to peak demand, perhaps being used for a few minutes per day, which is very expensive. Some multiple tariff meters use different tariffs for different amounts of demand. These are usually industrial meters. Domestic variable-rate meters generally permit two to three tariffs ("peak", "off-peak" and "shoulder") and in such installations a simple electromechanical time switch may be used. Historically, these have often been used in conjunction with electrical
storage heaters or
hot water storage systems. Multiple tariffs are made easier by time of use (TOU) meters which incorporate or are connected to a
time switch and which have multiple registers. Switching between the tariffs may happen via
ripple control, or via a radio-activated switch. In principle, a sealed time switch can also be used, but is considered more vulnerable to tampering to obtain cheaper electricity. meter and teleswitcher
Radio-activated switching is common in the UK, with a nightly data signal sent within the longwave carrier of
BBC Radio 4, 198 kHz. The time of off-peak charging is usually seven hours between midnight and 7:00am GMT/BST, and this is designed to power
storage heaters and
immersion heaters. In the UK, such tariffs are typically branded
Economy 7,
White Meter or
Dual-Rate. The popularity of such tariffs has declined in recent years, at least in the domestic market, because of the (perceived or real) deficiencies of storage heaters and the comparatively much lower cost of
natural gas per kWh (typically a factor of 3-5 times lower). Nevertheless, a sizeable number of properties do not have the option of gas, with many in rural areas being outside the gas supply network, and others being expensive upfront to upgrade to a radiator system. An
Economy 10 meter is also available, which gives 10 hours of cheap off-peak electricity spread out over three timeslots throughout a 24-hour period. This allows multiple top-up boosts to storage heaters, or a good spread of times to run a wet electric heating system on a cheaper electricity rate. Most meters using
Economy 7 switch the entire electricity supply to the cheaper rate during the 7 hour night time period, not just the storage heater circuit. The downside of this is that the daytime rate per kWh is significantly higher, and that standing charges are sometimes higher. For example, as of July 2017, normal ("single rate") electricity costs 17.14p per kWh in the London region on the standard default tariff for EDF Energy (the post-privatisation incumbent electricity supplier in London), with a standing charge of 18.90p per day. The equivalent
Economy 7 costs are 21.34p per kWh during the peak usage period with 7.83p per kWh during the off-peak usage period, and a standing charge of 18.90p per day. Timer switches installed on
washing machines,
tumble dryers,
dishwashers and
immersion heaters may be set so that they only switch on during the off-peak usage period.
Smart meters Smart meters go a step further than simple AMR (
automatic meter reading). They offer additional functionality including a real-time or near real-time reads,
power outage notification, and power quality monitoring. They allow price setting agencies to introduce different prices for consumption based on the time of day and the season. Another type of smart meter uses
nonintrusive load monitoring to automatically determine the number and type of appliances in a residence, how much energy each uses and when. This meter is used by electric utilities to do surveys of energy use. It eliminates the need to put timers on all of the appliances in a house to determine how much energy each uses.
Prepayment meters tokens, from a rented accommodation in the UK. The button labelled
A displays information and statistics such as current tariff and remaining credit. The button labelled
B activates a small amount of emergency credit should the customer run out The standard business model of electricity retailing involves the electricity company billing the customer for the amount of energy used in the previous month or quarter. In some countries, if the retailer believes that the customer may not pay the bill, a prepayment meter may be installed. This requires the customer to make advance payment before electricity can be used. If the available credit is exhausted then the supply of electricity is cut off by a
relay. In the UK, mechanical prepayment coin meters used to be common, both in private rented accommodation and residential customers of the electricity boards, the nationalised electricity sector. Disadvantages of these included the need for regular visits to remove the cash, and risk of theft of the cash in the meters by both customers and burglars. The first automated pre-payment meters were introduced by London Electricity, in conjunction with the Schlumberger Metering based in Felixstowe, UK. They were initially called Key Meters and later renamed Budget Meters. They avoided the 60,000 disconnections for non-payment per annum and the many disadvantages of cash prepayment. They were also popular with customers who wanted a convenient payment method, especially in short term tenancies. Well over 1 million such meters were installed across the UK in the first few years after introduction. Modern solid-state electricity meters, in conjunction with
smart cards, have removed these disadvantages and such meters are commonly used for customers considered to be a poor
credit risk. In the UK, customers can use organisations such as the
Post Office Limited or
PayPoint network, where rechargeable tokens (Quantum cards for natural gas, or plastic "keys" for electricity) can be loaded with whatever money the customer has available. In
Indonesia,
Northern Ireland,
South Africa and
Sudan, prepaid meters are recharged by entering a unique, encoded twenty digit number using a keypad. This makes the tokens, which may be electronically delivered or printed on a slip of paper at point of purchase, very cheap to produce. Around the world, experiments are going on, especially in developing countries, to test pre-payment systems. In some cases, prepayment meters have not been accepted by customers. There are various groups, such as the Standard Transfer Specification (
STS) association, which promote common standards for prepayment metering systems across manufacturers. Prepaid meters using the STS standard are used in many countries.
Time of day metering Time of Day metering (TOD), also known as Time of Usage (TOU) or Seasonal Time of Day (SToD), metering involves dividing the day, month and year into tariff slots and with higher rates at peak load periods and low tariff rates at off-peak load periods. While this can be used to automatically control usage on the part of the customer (resulting in automatic load control), it is often simply the customer's responsibility to control his own usage or pay accordingly (voluntary load control). This also allows the
utilities to plan their transmission infrastructure appropriately. See also
Demand-side Management (DSM). TOD metering normally splits rates into an arrangement of multiple segments including on-peak, off-peak, mid-peak or shoulder, and critical peak. A typical arrangement is a peak occurring during the day (non-holiday days only), such as from 1 pm to 9 pm Monday through Friday during the summer and from 6:30 am to 12 noon and 5 pm to 9 pm during the winter. More complex arrangements include the use of critical peaks that occur during high demand periods. The times of peak demand/cost will vary in different markets around the world. Large commercial users can purchase power by the hour using either forecast pricing or real-time pricing. Some utilities allow residential customers to pay hourly rates, such as in Illinois, which uses day ahead pricing.
Power export metering Many electricity customers are installing their own electricity generating equipment, whether for reasons of economy,
redundancy or
environmental reasons. When a customer is generating more electricity than required for his own use, the surplus may be exported back to the
power grid. Customers that generate back into the "grid" usually must have special equipment and safety devices to protect the grid components (as well as the customer's own) in case of faults (electrical short circuits) or maintenance of the grid (say voltage on a downed line coming from an exporting customers facility). This exported energy may be accounted for in the simplest case by the meter running backwards during periods of
net export, thus reducing the customer's recorded energy usage by the amount exported. This in effect results in the customer being paid for his/her exports at the full retail price of electricity. Unless equipped with a ratchet or equivalent, a standard meter will accurately record power flow in each direction by simply running backwards when power is exported. Where allowed by law, utilities maintain a profitable margin between the price of energy delivered to the consumer and the rate credited for consumer-generated energy that flows back to the grid. Lately, upload sources typically originate from renewable sources (e.g.,
wind turbines,
photovoltaic cells), or
gas or steam
turbines, which are often found in
cogeneration systems. Another potential upload source that has been proposed is
plug-in hybrid car batteries (
vehicle-to-grid power systems). This requires a "
smart grid," which includes meters that measure electricity via communication networks that require remote control and give customers timing and pricing options. Vehicle-to-grid systems could be installed at workplace
parking lots and garages and at
park and rides and could help drivers charge their batteries at home at night when
off-peak power prices are cheaper, and receive bill crediting for selling excess electricity back to the grid during high-demand hours. == Location ==