Sensors put intelligence in the smart grid

Sensors put intelligence in the smart grid

An energy grid that can adjust itself doesn’t work well without transducers that can monitor conditions in real time.

The road to the smart grid is paved with sensors. Or at least that is the impression you might get if you listen to the American Council for an Energy-Efficient Economy (ACEEE). A smart grid isn’t much good unless it knows a lot about real-time conditions in homes, offices, and manufacturing plants. So ACEEE thinks a systems level approach using innovative sensors and controls is the way to go. In manufacturing plants alone, it figures such measures can save some 2 to 14% of energy used.

All in all, taking advantage of currently available information and communications technologies would let the U.S. reduce its energy use by about 12 to 22%, says ACEEE. But the kind of approach the organization envisions “is not your father’s device-driven approach to energy efficiency,” says R. Neal Elliot, ACEEE associate director for research. “System efficiency opportunities produce energy savings that dwarf component-based efficiency improvements by an order of magnitude,” he adds.

What Elliot means is that optimizing the efficiency of, say, your water heater, refrigerator, and other appliances can only advance the energy equation so far. Knowing how to orchestrate the operation of energy consuming devices is where the big gains are likely to come from. And the only way to get the information necessary for making informed decisions is through more sophisticated sensors.

Motors are just one example. They consume half the electricity in the U.S. Efficiency standards for integral horsepower induction motors in the past few years have pushed their mandated efficiency levels to the 95% range and higher. There have also been improvements in the smaller motors powering pumps, compressors, and household appliances. But the cost of drive circuits able to run motors in energy efficient ways has been high because the necessary electronic devices have been costly. This situation has begun to change. For example, Semiconductor IC manufacturers like STMicroelectronics have targeted motor control with drive electronics such as the SLIMM-nano (small low-loss intelligent module). It is basically a 3-A 600-V three-phase insulated-gate bipolar transistor (IGBT) inverter bridge driver for ac motors. It is said to improve efficiency by reducing power losses through an optimal layout and through the inclusion of such functions as a bootstrap diode, smart-shutdown capability, and sensing and protection circuitry.

Better sensors will give efficiency movements such as the Green Button Initiative an improved chance of success. Green Button promotes the idea that electricity customers should be able to securely download their own detailed household or building energy usage information from their utility website. The initiative is so-named because it allows people to see this information simply by clicking a green button on the utilities’ websites.

Ideally, consumers would be able to see how much electricity or energy they used every 15 minutes, every day, or every month depending on what their utility is able to make available. Other information Green Button foresees providing includes an hourly load profile for past billing periods plus current period to date, a fifteen minute load profile for the most recent 15 days, a daily load profile for the past month or year, gas and water usage profiles, and several other factors. Data would be made available in a common XML format.

Green Button also foresees this facility as promoting the rise of new energy efficiency industries such as entrepreneur-created web portals to analyze energy use and provide actionable tips. It as well may give rise to improved decision-support tools that facilitate energy efficiency retrofits and up-to-date measurement of energy efficiency investments. Other possibilities: services that provide energy costs for tenants and/or new home purchasers and show how to optimize renewable installations by, say, calculating the optimal size and pay-back for rooftop solar panels.

“The convergence of energy management and communication is letting companies get energy savings of 30% or more,” says Schneider Electric Vice President of Government Affairs Paul Hamilton. An example of the communication facilities that lead to such savings is that from AtSite Inc. The firm has hooked up with Panoramic Power in Israel to use the latter’s P3E energy management system. The system combines self-powered wireless sensors with a cloud-computing-based analytic platform. Key to the system are noninvasive, self-powered, miniature wireless current sensors. The sensors clamp on the electrical outgoing wire from the circuit breaker, harvesting the magnetic field as a power source for monitoring the flow of electricity and sending information about power use back to a computer. Panoramic Power says hundreds of sensors can be installed in a few hours with no disturbance of daily operations. Once installed, the sensors become part of the building infrastructure and never need maintenance, service, or battery replacement. Two sensor models can monitor ac current ranging from 0 to 63 A and 0 to 225 A.

AtSite finished testing the Panoramic power system earlier this year and has deployed it in numerous facilities including restaurants, supermarkets and retailers. Most recently, it began operation in the headquarters of the U.S. Green Building Council (USGBC) in Washington, D.C.

The sensors in the Panoramic Power system are industrial grade. Residential consumers would likely benefit from scaled-down versions as an advanced metering infrastructure (AMI) goes into place. Planners envision AMI empowering energy savings by measuring, collecting, and analyzing energy use through and communication with metering devices. But only if consumers get motivated to save energy by seeing real-time feedback, as provided by judiciously placed sensors. ACEEE estimates well-designed and implemented feedback programs for the U.S. residential sector might generate savings ranging from 0.4% to more than 8.4%.

One complicating factor is that neither the communication schemes between smart meters and utilities nor those between the sensor and the smart meter have been standardized. Utilities in different parts of the world are taking different approaches. For example, power line communication (PLC) is one communication method. It impresses data onto ac lines at frequencies designed not to interfere with radio communications. The technique is controversial in the U.S. because of claims it interferes with amateur radio, but is less so outside North America. An example of products in that area is the STMicroelectronics ST75xx STarGRID series of PLC silicon-on-chip (SoC) ICs. Made using the company’s bipolar-CMOS-DMOS (BCD) process, it allows analog, digital and power circuits to reside on the same chip. The devices are being used in smart meters installed in Italy and Spain.

Smart meters may be able to communicate with utilities, but today, there is precious little information provided between the utility and the residential consumer. This is despite the availability of Internet tools like Google’s PowerMeter (now retired) and feedback programs from companies like Opower, which uses a web portal to supply home energy reports, and Efficiency 2.0 (recently acquired by energy software firm C3) which lets neighbors compare and kibitz about their energy consumption.

One way to save energy is to use less of it to begin with. In that regard, occupancy sensors are taking a more prominent role, though no one yet seems to be promoting the idea of hooking them into smart grid facilities. Already required by building codes in states that include California, these sensors turn off lights when no one is in a room or a defined area. They can mount on walls or ceilings.

Look for occupancy sensors to begin controlling more than just room lighting. Residential thermostats, most notably the Nest Learning thermostat, now incorporate occupancy sensors as a way of deciding when to adjust temperature up or down. So it is conceivable that other appliances or energy users could deploy them to implement low-energy operation modes.

And it seems likely the EPA may build use of power management functions -- such as occupancy sensors, proximity sensors, and timer functions -- into future versions of Energy Star TV specs. It specifically says, “EPA understands that manufacturers are developing and implementing innovative power management functions for televisions such as occupancy sensors, proximity sensors or timer functions. As additional information about these technologies becomes available, EPA is exploring ways to encourage use of such measures in Energy Star televisions. Therefore, EPA seeks additional information about these functions, their savings, and projected market presence.”

A typical occupancy sensor unit consists of a motion transducer, electronic control circuitry, and a controllable switch/relay. A built-in timer signals when to shut down after a set period of inactivity. Some units also incorporate a light sensor for cutting back power during daylight hours.

Typical occupancy sensors can use several technologies. Infrared (IR) sensors may switch off after some time period of no activity in their IR beam; passive IR devices look for a difference between the IR signature of the room floor and a human. Ultrasonic sensors look for echoes; microwave sensors are handy for detecting movement outside a window as when occupants approach a building. And audio sensor types, as their name implies, note audible noise as an indication of an occupied room. Some of these sensors are specialized for specific room types such as bathrooms, hallways and stairwells.

Thermostats, of course, are the means of choice for controlling room temperature. Advanced thermostats with programmable heating and cooling are a disappointment from the standpoint of energy efficiency, however. The U.S. Dept. of Energy’s Lawrence Berkeley National Laboratory looked at how people use programmable thermostats. LBNL found few people actually bother to program them though they have been around since the 1970s. In fact, programmable thermostats are so ineffective at reducing energy bills that EPA’s Energy Star program revoked the certification of all thermostats in 2009.

No one yet has floated the idea of hooking residential thermostats to the smart grid. The concept conjures up images of a “big brother” utility turning off the A/C on sweltering days. The closest modern thermostats come to being controlled from a remote facility is through Wi-Fi connections. Thermostats on store shelves today can include connections to home Wi-Fi that typically let the user get access to thermostat controls through a smart phone or similar mobile device.

It looks as though the more acceptable route to the control of heating and cooling for energy efficiency is to improve the thermostats themselves. On that score, recently developed thermostats try to make it easier to implement heating and cooling schedules that save energy by making these functions automatic. The prime example of the trend is the Nest Learning Thermostat. This device has built-in software that lets it learn from the occupants’ behavior patterns, preferences and surroundings to create a custom heating and cooling schedule.

The thermostat control routine is based on the temperatures the occupant sets. It learns the personal schedule of house occupants in about a week. At that point, users see a message informing them that no further tweaks are needed. The Nest device then starts automatically turning down heating or cooling when such measures seem to be acceptable. Users can of course override these decisions.

The occupancy sensor in the Nest is a part of an Auto-Away feature that detects when occupants have left. The Nest also provides an energy history available over its built-in Wi-Fi connection.


Annual Energy Outlook 2012 With Projections to 2035, U.S. Energy Information Administration,
A Defining Framework for Intelligent Efficiency, American Council for an Energy-Efficient Economy, June 2012, Report E125,
Advanced Metering Initiatives and Residential Feedback Programs: A Meta-Review for household Electricity Saving Opportunities, American Council for an Energy-Efficient Economy, June 2012, Report E105, http:
Green Button Data: More Power To You, U.S. Dept. of Energy,
Improving Building Performance. Reduce Energy Consumption By 20% With Little Or No Cost: A Guide to Energy Efficient Technologies, June 2012,
Greening The Dept. of the Interior,

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