Voltage Conservation Might Create More Problems Than It Solves
For decades, utilities, regulators and consumers have been intrigued by the concept of reducing electric consumption by lowering voltage levels on the electric grid. Theory and practice say that simply using 114 volts instead of 120 volts saves energy. However, in spite of a body of evidence favoring this little-analyzed concept, numerous recognized authorities suggest it should be relegated to the pile of good, but impractical, ideas.
Conservation Voltage Reduction (CVR) is the name given to the practice of reducing the voltage on the electric grid to save energy. And, what makes CVR so appealing is that it can be easily implemented at little cost while dramatically reducing energy consumption.
Advocates of CVR point to a number of studies showing that it meaningfully reduces electric consumption when applied at the utility level. The best-known research comes from the Snohomish County (Washington) Public Utility District (PUD), the second largest public utility in the Pacific Northwest and a long-time promoter of eco-friendly generation such as geothermal, tidal and hydro. Results from Snohomish PUD’s studies have shown that reducing the system voltage by 1% yields a very impressive 0.6% reduction in electricity consumption. An extrapolation of these results says that a mere 5% reduction in voltage, like 120 to 114 volts, could result in a whopping 3% reduction in energy consumption.
Applied nation-wide, CVR might save trillions of kilowatt-hours. However, not everyone is ready to embrace CVR despite such positive data.
The Edison Electric Institute and the Electric Power Research Institute (EPRI) have noted that there are practical issues related to CVR that require more investigation, such as the overall effect it might have on consumers. Even the Bonneville Power Authority in Washington, a CVR proponent, acknowledges that uncertainty about the cost and benefit to the end user is a barrier to its wide-scale adoption.
The primary concern with CVR is that too low of a voltage is a leading cause of problems for electric consumers and something that electric utilities work to avoid. With the existing technologies of the electric grid, utilities don’t have precise control of the voltage level for each customer and unilaterally lowering voltage levels could lead to a rash of unhappy consumers.
The voltage control problem is similar to what happens to water pressure on a hot summer day: with many people filling pools and watering lawns, the customers farthest from the water tower experience a drop in their water pressure. In electrical terms, the power used by other customers on the same distribution line reduces the voltage for the people farthest from the substation. To offset fluctuating voltage levels throughout the day, the utility uses voltage regulators to raise or lower voltage at the substation to ensure adequate voltage levels for users at the end of the distribution line.
While voltage level adequacy is a technical challenge with CVR, the real question is whether it is ultimately a benefit or a detriment to end users. Reduced consumption and lower electric bills must be weighed against the cost due to changes in operational reliability, electrical efficiencies and equipment life for each customer. There is no dispute that the performance of electrical devices changes when the voltage is reduced: determining whether such changes are beneficial and tolerable is challenge. And, there are good reasons to ask questions.
In a 2008 paper on energy efficiency, the Department of Energy (DOE) states, “The best motor performance occurs when power supplied to the motor terminals is close to the nominal utilization [rated] voltage.” They go on to say, “Full load efficiency is at maximum between nominal voltage and about 10% over-voltage [high voltage].”
Besides electric motors, transformers also operate more efficiently when run at nominal or higher voltage. Not all electric motors and transformers operate at full load all the time; so, reduced voltage could be an advantage in certain cases. However, recognizing that electric motors consume more than 50% of the electricity generated in the U.S. and 100% of all electricity passes through transformers, there is reason to be concerned about the large-scale implementation of CVR.
Furthermore, EPRI raises other concerns in a 2001 paper evaluating the power quality implications of CVR:
“For many types of load equipment, a CVR might not produce a reduction of power consumption and their sensitivity to power quality events occurring during the CVR can produce unexpected adverse side effects. A very significant negative impact of CVR is the resulting increase in the frequency of occurrence and severity of [voltage] sags that can disrupt manufacturing operations and information technology activities.”
Simply put, reduced voltage can cause some equipment to shut down or malfunction during electrical disturbances, without reducing power consumption. Such hiccups already cost U.S. businesses over $150 billion each year – reducing voltage levels could increase this figure.
Does all of this mean we should abandon conservation voltage reduction? Absolutely, not. What it means is that instead of considering voltage reduction as the only means to energy saving, we should look at optimizing voltage – using the voltage level for a given location or application that results in maximum energy efficiency.
The good news is that efforts in voltage optimization are already underway, as part of the smart grid development. EPRI characterizes it this way:
“This [voltage optimization] requires a new industry-wide initiative that addresses the modeling need from two different approaches:
Understanding the fundamentals of equipment response. Understanding the voltage response characteristics of particular types of loads – lighting, motors, power supplies and other power electronic-driven loads, heating, etc.
Understanding the aggregated response of loads. The important response at the feeder [distribution] level is the overall response of groups of customers - a combination of many types of loads.”
Just as the highly charged debate about global warming is morphing into a discussion about climate change, so too the CVR argument is developing into a thoughtfully considered effort to reduce energy consumption through voltage optimization. The energy savings potential from large-scale voltage optimization are substantial and benefit utilities and consumers, alike. Moreover, all of the technology is available today. It’s just a matter of time.
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