The old electromechanical electric utility meter changed little in principle over the last hundred years. In the next coming decades the smart meter will progress as much over this meter as the PC has over the typewriter. It will utilize a microcontroller as sophisticated as any PC. It will have its own web page that can be part of your home page and your social network. It can evolve to best serve the most efficient use of renewable energy.
The present meters are also called “Thomson” meters after the supposed inventor Elihu Thomson the first CEO of General Electric (after restructuring of Edison General Electric). Thomson’s meter was like a clock with a torsion pendulum. Instead of a spring, the force between two magnets governed the speed of the pendulum.
The force of one magnet was proportional to voltage, the other to the current drawn by the load. The frequency of the pendulum was proportional to power (voltage time current). The clock-like mechanism summed power over time to find energy that was displayed on a series of dials.
GE purchased the “Thomson” meter from an independent inventor. Thomson’s ability to immediately yield to superior ideas made him an effective manager and certainly contributed to GE’s success.
The improved Thomson meter uses a motor in place of a pendulum. The speed of this motor is proportional to voltage time current. Since this motor “spins backward” if the power travels back through the meter, this meter was instrumental in the development of photovoltaic. It permitted the solar panel owner to sell surplus power back to the utility.
The experts at SmartlyHeated say the major disadvantage of the old meter is that it doesn’t record when the energy is consumed. Electricity is an extremely perishable commodity. Sometimes electricity is abundant and cheap. Often this is renewable energy such as wind. Other times it’s scares and expensive. Typically, this is during heat waves and peaker plants, usually fuelled by natural gas, must fire up to supply power for air conditioning.
Another disadvantage is that the old meters measure real rather than apparent power. At first this is an advantage to the customer since real power is usually smaller than apparent. It’s a disadvantage to the utility since their costs are for delivering apparent power. What’s the difference?
Years ago when most residential loads consisted of mostly incandescent lighting and heaters with a few electric motors, apparent power was only slightly greater that real. Such a residence had a Power Factor (ratio of real to apparent power) near 1.0. In this example only the motors have a PF less than 1.0.
Today, a compact florescent rated at 23-watts (real power) delivers light equivalent to a 100-watt incandescent, but presents a 40-watt apparent load. It has a PF = 0.57.
Since the Thomson meter measures real power, the utilities are effectively subsidizing the use of these lamps, which is good since it encourages their use. Smart meters can be designed to measure apparent power just as easily as real. Microcontrollers and solid-state sensors are extremely versatile.
Eventually, we need to measure accurately the resource demands of customers so that they can be accurately accounted. Smart meters will be able to work with smart appliances that have their own microcontrollers. Smart meters will be able to identify these appliances and make adjustments for them.
For example, switching capacitor into the line at the customer or utility site can compensate for appliances with low PF. The coming LED lamps are non-linear and produce harmonics online. Placing filters online can compensate them.
Smart meters can switch on deferrable appliances such as dish and laundry washers to run on cheap renewable energy. In an insulated energy efficient house, air conditioning can be postponed and operated “off peak.”
Logs produced by smart meter can appear on web pages. If these logs are time stamped and authenticated (tamper proof) they can be used as a proof of energy efficiency of a house. (To see a smart meter web page sample suggested by Google click here.)
Smart meter logs can be shown on social networks and compared with friends who can give and accept suggestions for more efficient energy use. Logs taken over a year will demonstrate the economics of house energy improvements.
Photo Credits: Thomson Meter with case removed, c. 1900/Elsa Etcheverry: Thomson Meter, c. 1990/Elsa Etcheverry: Georgia Power Smart Meter, c. 2008/flicker.com/Adrian P