Metering Technologies

The meters used initially in electricity transmission, distribution, and supply were actually to allow means of knowing the amount of consumed electricity for billing purposes only. This type of meters is referred to as traditional meters, and the technologies used by such meters are called electromechanical technology. The need to provide more efficient and reliable electricity resulted in the development of smart meters, such as automatic meter reading (AMR) meters, and later advanced metering infrastructure (AMI) meters. The different types of meters from traditional AMR to AMI meters are shown in Figure 3.1. The AMR meters uses the electromechanical plus electronic technology that allows providers to read electricity consumption remotely using fixed network abilities such as hand-held/walk-by or drive-by devices. It still did not provide the much needed two-way advantage that allows consumers active participation, and this brought the advent of the AMI using the newest technology in metering referred to as hybrid technology.

Gain of Smart Meters vs. the Conventional Meter

• • The conventional meter can only provide usage data to service provider, in most cases, collected manually for monthly billing.
• • On the other hand, smart meter provides what is referred to as two-way information that helps the utility provider and the end user.
• • It informs both parties of any power outage and possible theft.

FIGURE 3.1 Different types of meters.

• • It also improves power quality, gives more efficient and secure power delivery, enhances electricity reliability, and allows for prepayment options and more accurate billing.
• • In short it brings the end of estimated bills and over paying/underpaying.

Communications Used in Smart Grid

The smart meter is connected in two ways using wide area network (WAN) and home area network (HAN). WAN is used to connect smart mater, supplier, and utility server, whereas HAN is used for connecting smart meter with home appliances. The different technologies used by WAN for communications are fiber optics and 3G/GSM, whereas technologies used by HAN are Bluetooth, Zigbee, and wireless Ethernet or wired Ethernet.

Zigbee

In wireless communication technologies, National Institute for Standards and Technology (NIST) confirmed Zigbee Smart Energy Profile as the most applicable communication infrastructure for smart grid network due to its advantages such as low cost, comparatively low-power consumption, less complexity, and fast data rate transfer. Zigbee is used in smart grid for automatics meter reading, energy monitoring, and home automation. It has a bandwidth of 2.4GHz plus 16 channels, and every channel uses 5 MHz bandwidth and a maximum output power of 0 dBM including transmission range between 1 and 100 m with a data rate of 250 kb/s [1].

Wireless Mesh

A wireless mesh network is a combination of nodes that are joined in groups and working as a self-reliant router. Self-healing property of these nodes helps communication signal find a route through active nodes. Infrastructures of mesh network are decentralized because each node sends information to the next node. Wireless mesh is used in small business operation and remote areas for affordable connections [1,10,11].

GSM

GSM is Global System for Mobile communication used to transfer data and voice services in communication technology. It is a cellular technology that connects mobile phone with the cellular network [1].

Cellular Network

Cellular networks can be another excellent option for communication between far nodes for utility purpose. They are used to build a dedicated path for communication infrastructure to enable smart meter deployment over a WAN [1].

Billing Methods

Majorly, there are three different types of billing in the smart grid system: net metering, feed-in tariff, or time of use (Toll). These are discussed next.

Net Metering

This is a mean of measuring the amount of excess energy a homeowner was able to produce to the smart grid which is returned back to the homeowner at the same tariff rate during night or when there is less sunlight for him to produce enough energy.

Feed-In Tariff

In this situation, a home owner is paid a rate which is usually calculated using the ToU. Should he need energy back, it will be as well sold to him at similar rate.

Time of Use

This is a billing plan in which the electricity consumption is calculated based on the real time in which such energy is utilized. The pricing of electricity usage is significantly low when used at time that the demand for power supply is low and high when used at time or period of high power demand. When a homeowner shifts his large electricity consumption to period of low demand, he capitalizes on paying low energy bill [12].

The time of the day when energy demand is high is called on-peak, and time of the day when the demand is low is referred to as off-peak, while in-between these periods is the mid-peak. There are variations in timing for different seasons: for summer, peak time is 3 pm-8 pm and mid-peak time is 6 am-3 pm, whereas for winter, peak time is 6 am-10 am and mid-peak time is 10 am-5 pm. The best plan is usually to move more electricity usage to off-peak which is more preferable between

11.30 am and 2.30 am [13].

Table 3.2 shows how price of electricity can be reduced by moving most electricity consumption to off-peak periods by computing ToU pricing for 1000 kWh used per

TABLE 3.2

Portland General Electric ToU Price Compared with Standard Rate

month at different periods with a table showing variation in the seasonal pricing periods.

Pricing for each time of the day is as follows:

• • On-peak 13.197 cent per kWh
• • Mid-peak 7.572 cent per kWh
• • Off-peak 4.399 cent per kWh

This will bring to an end the usual fixed monthly charge plan where electricity will be charged based on its usage.

Solar Energy

The energy from the sun is certainly enormous and will of course remain forever, the process of collecting the energy for use as electricity varies, and it is such type of generated energy that is referred to as solar energy or solar electricity. The major ways of utilizing sun radiations to generate electricity are discussed next.

Solar Panels (Photovoltaic Modules, PV)

This is the most common method of generating electricity from the sun. It is mainly the use of materials that are semiconductors that easily give out electrons when it absorbs heat from the sun, to produce what is called a solar panel. This has been used in power houses, industries, and the largest PV generating plant (290 MW plant) in Arizona [14].

Solar Thermal (Concentrated Solar Power, CSP)

This technology used to generate electricity from the sun is not very popular and will produce far more electricity than the PV; thus, it cannot be utilized for residential purposes but for large-scale purposes, i.e., in utility plants. The largest facility using this technology to generate electricity is the 377 MW plant in a desert in California The concentrated solar power (CSP) is categorized into different known technologies based on the collection of energy from the sun, which are discussed next.

Dish Engine Technology

In this method, power is produced from the use of dish-shaped parabolic mirrors where gas is heated in a chamber with collected energy from the sun and the heated gas drives a piston of a generator, thereby producing electricity. For more efficiency, the dish is mostly attached to a tracking system that maximizes sun radiation [13].

Parabolic Trough

This method uses trough-shaped mirrors which are long enough to reflect solar energy into a tube filled with liquid which collects heat as it focuses on the sun, thereby heating the liquid in the tube connected to heat exchange system where water is heated to steam that is used in a steam turbine generator to generate electricity.

This operates in a continuous recycling process: as the heated fluid transfers its heat, the steam cools and condenses; then, the same process is continuously repeated over and over. Heated fluid can also be stored for a long period and then be reused when the sun is down [9,13].

Tower Focal Point-Concentrated Solar Power

In the focal point CSP technology, a large number of flat computer-controlled mirrors constantly move to get maximum sun reflection all through the day onto a tower that has a collecting tank on it. Molten salt moves in and out of the tank and as a result are heated to a very high temperature of 537.8°C (1000°F); the heated fluid is sent to a steam boiler where it uses the inherent heat in the fluid to propel a steam turbine to produce electricity [13].

Storage Facilities

The usage of energy from the sun gained significant importance with improved storage facilities such as batteries (e.g., sodium sulfur, lithium ion, lead-acid, metal-air), compressed air energy storage (CAES), pumped hydro, flywheels, fuel cells, and super capacitors [15].

Sodium Sulfur (NaS) Batteries

This is manufactured from a combination of two salts: sodium and sulfur. Excellent energy density, very good charge and discharge efficiency, and low cost make it advantageous for use as storage facility in smart grid.

Sodium sulfur batteries are also used as utility-scaled energy storage in Japan, with hundreds of MW as shown in Figure 3.2. NaS batteries were first hosted as demonstration project in 1992 which become available commercially in 2002 [16].

Flywheel Storage Device

This revolution in technology of storage facility is regarded as the most used for smart grid storage infrastructure at both transmission and distribution stages. This could

FIGURE 3.3 Rotating flywheel storing energy mode [17].

be a result of its rapid response time in discharging stored electricity, high efficiency, long life and the quite insignificant maintenance. It is cylindrically shaped, having large rotor contained in a vacuum. Flywheel storage device stores electricity in the form of rotational energy, which can also be referred to as spinning mass.

It can store electricity for a smart grid by drawing energy from it as the rotor rotates at a very high speed, as shown in Figure 3.3. To discharge the electricity, it slows down by switching to generation mode, thus returning electricity back to the grid for onward distribution [17].