Robust design principles for home smart grid metering
While the AMI meters are a major step forward for utilities, a new generation of advanced smart meter designs will be needed for the smart grid to achieve its full potential. These advanced smart meters (ASM) will provide two additional capabilities that AMI meters lack.
One is to give consumers real-time billing information that can help guide them to moderate peak demand as well as reduce their overall energy usage. The other is to give utilities access into home networking systems for more direct control of consumer energy usage.
The key to both of these capabilities is giving the meter access to home area networking (HAN). Such networks have already begun to appear in new residential and commercial construction in appliances, heating and air conditioning (HAC) systems, and lighting.
The network provides intelligent monitoring and control for these elements, allowing a PC or other central controller to turn nodes on and off, adjust settings, and gather status information. The network links may use building wiring, such as powerline signaling, or may be wireless as with the ZigBee protocol.
The advanced smart meter links the utility to the HAN through the smart grid. The meter serves as a communications hub, providing bidirectional communications between the utility and the building. This allows the utility to monitor individual systems within the building, such as reading thermostat settings, and offers an avenue for control, as well.
The value of this link between the utility and the HAN is a significant increase in the flexibility of demand response systems. The meter can, for instance, provide the HAN with real-time energy usage and cost information for display to the residents. Armed with such information, consumers can make real-time choices on what systems to use or turn off, adjust HAC settings to optimize cost and comfort, and track down “vampire” appliances such as printers, computers, and entertainment systems that are in standby mode rather than being completely shut down.
The link can also allow the utility to take control of some home systems as the need arises. During a heat wave when air conditioning usage skyrockets, for instance, the utility could change thermostat settings through the HANs to keep power demand from triggering a brownout or blackout condition. Under more typical conditions the utility could similarly take action to help reduce residential energy consumption during periods of peak demand.
Advanced Smart Meter Requirements
The design of such an advanced smart meter must meet many functional requirements. The prime function, of course, is to provide energy metrology. This metrology requires that the meter know the time (for billing) as well as current power utilization. Further, the implementation must be flexible to accommodate differences between the ways utility service providers measure and track such utilization. The energy meter may also offer the ability to integrate with other utilities such as gas and water to eliminate multiple meters (Figure 1 below).
Figure 1. The advanced smart meter will do more than measure energy; it will link the utility to the consumer for detailed monitoring and control of energy consumption and coordination with energy generation.
In addition to measuring current power utilization, the meter must be able to record cumulative power utilization. For time-of-use billing, this requires that the meter offer multiple “bins” for tracking power consumed at the different rates. These bins must be configurable in order to provide the utility with a mechanism for making changes to times and rates.
A second design requirement for the advanced smart meter is an ability to communicate with both the smart grid and the home network. There is little consensus, however, on what those communications channels are to be.
Depending on the provider, communications with the utility network may use mesh RF, powerline signaling, WiMAX, or even the cellular network. Similarly, regional and individual preferences may call for the HAN to use ZigBee, powerline, WiFi, or some other protocol. Ideally, then, the meter design would be flexible enough to accommodate easy configuration of its communications channels to meet specific installation requirements.
The meter must provide hub functionality in order to be effective, including address translation for the utility to be able to control appliances on the home network. But the meter is not simply a translation device between the two networks. It must be able to provide security in order to prevent malicious intrusion as well as drive the user interface within the residence.
Security functions are essential safeguards for both the consumer and the smart grid with three key components: authentication, validation, and authorization. Authentication is needed in order to ensure that messages to the utility or the meter have the proper origin.
This prevents a system errors and third parties from introducing false messages that can interfere with billing or hijack control through the network. Validation ensures that a received message has the right form and content, helping prevent errors from causing unexpected or undesirable results.
This may include making certain that a command does not violate safety restrictions, such as turning a water heater up beyond a pre-set limit. Authorization ensures that the message sender has the right to issue commands in the first place.
The user interface is key toward making the consumer an active element in demand response systems. Without some way of seeing in real-time the effects of their energy usage decisions, and some way of implementing their decisions, consumers cannot respond effectively. Thus the meter needs to provide a means of controlling energy usage at the unit level as well as monitoring energy consumption of the house as a whole.
One effective way to provide these monitoring and control capabilities is for the meter to include a link to a control and display panel mounted inside the structure for convenient user access. The panel would show energy usage and cost in real-time to prompt action from the consumer as well as indicate the outcome of that action.
Ideally, the panel would also be the user interface for taking action through the HAN such as disabling energy consumers or adjusting settings, to make the process more convenient for the consumer and thus more likely to occur. For the same reason, the interface must be easy to understand and use.
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