evaluating environmental monitoring applications of low

A look at the potential applications for new low-cost sensors in industrial

environmental monitoring.

Evaluating Environmental Monitoring Applications of Low-Cost Sensors for

Electric Utilities

Evaluating Low-Cost Sensors for Electric Utilities by Stephanie Shaw and Bruce Hensel

em • The Magazine for Environmental Managers • A&WMA • November 2017

A variety of novel environmental monitoring technologies,such as small low-cost air quality sensors, have been on therise for the past several years, fueled in part by advances inmanufacturing technologies that have eased miniaturizationof electronics. These devices are often quite inexpensive andaccessible to potential users, while still providing real-time information on environmental metrics. Sensor tools have thepotential to provide screening-level data in currently unmoni-tored areas, or to supplement more complex existing moni-toring programs. However, their applicability for environmentalmonitoring performed by electrical utilities has yet to be vetted. This article considers potential applications of sensorsto a subset of industrial facility monitoring that is occurring at electric utility sites.

Potential for Sensors in Industrial Environmental MonitoringScientists and engineers at our organization, the ElectricPower Research Institute (EPRI), are always looking for newtools and processes that may help electric utilities operate theirfacilities more efficiently, with more flexibility, and at lowercost. Over the past several years, EPRI has engaged in a cross-disciplinary research program on intelligent sensor systemsand associated data analytics that is investigating sensor performance and data acquisition, data communications andmanipulations, and final use of sensor data in facility opera-tions (see Figure 1). Sensor applications are considered withrelevance to the various electricity research sectors: generation,



nuclear power, transmission and distribution, and energy and environment.

Intelligent sensors are needed throughout the power systemto transform raw data into actionable information. For example,EPRI has developed its own sensor packages for equipmentmonitoring and condition-based maintenance. These devicesare being tested on the transmission grid and at substationsto demonstrate the technology’s potential to reduce or extendintervals between preventive maintenance and surveillancetasks. Development and in-plant testing has been conductedof novel systems that can continually sense torsional vibrationat turbine shafts. This enables early detection of conditionsthat cause turbine blades and other rotor elements to fail.

Similarly, chemical or physical sensors might be relevant toolsfor environmental monitoring at power system facilities. Inaddition to their relatively low cost, the ability to deploy sensorsystems in complex environments and without line powermake them attractive for locations that cannot accommodatetraditional instruments due to space or infrastructure limitations,such as on the grounds of working industrial facilities. Ideally,real-time information about electric power system assets provided by sensors would be secure, and incorporated tooperate the system efficiently and effectively while managingenvironmental impacts.

EPRI scientists have brainstormed a variety of potential

Figure 1. EPRI’s approach to electric utility sensor systems.



environmental applications relevant to electric utilities for whichthey would like to see viable sensor options exist. Some examples include:

1. Use of sensors to help site permanent monitoring instruments;

2. Measurement of emissions sources at power generationfacilities (e.g., fugitive dust or methane);

3. Creation of early warning or detection systems, such asfor geotechnical parameters (e.g., berm stability) orleaks of materials in confined spaces;

4. Worker personal exposure monitoring; and5. Interaction with local communities or other stakeholders

for education.

Listing of these example applications does not necessarilymean that the technologies are currently commercially availableand appropriate for deployment now, rather they are aspira-tional applications if sensors of appropriate performance are identified.

Real-World Testing Is Vital for Sensor EvaluationAs with any new and emerging technology, it is crucial to ensure that the performance capabilities and limitations ofsensors are adequately understood before they are applied.These complexities can then be communicated to stakehold-ers. Despite a marked increase in recent reports summarizingresults from field studies testing environmental sensors, a lackof evaluation data still exists for many potential applications.Additionally, the fundamental designs of low-cost sensorsmake it difficult to extrapolate performance from one site,metric or sensor model to other situations, even if they aregenerally similar in design.

Prior research studies have repeatedly shown that while sensor components themselves can often have high precision,many of the detection techniques used can be subject tochemical interferences (cross-sensitivities), drift, and other factors that affect data quality to a greater degree than traditional instrumentation. Even if these concerns may beanticipated due to manufacturers’ specifications and prior laboratory analysis, they do not always present in expectedways due to the complex real-world ambient air matrix inwhich they are deployed. Therefore, comprehensive site-specific performance testing can be used to determine suitability of sensors for electric utility applications.

A further need in the design of sensor performance testing is a robust assessment of the full sensor system cost. For example, the capital cost for the sensor component and thepackage into which the sensor is incorporated, including electronic control boards, power systems, wireless communi-cation systems, and data handling infrastructure, all need

careful evaluation. Additionally, operations and maintenancecosts for sensor deployments are often expected to be relativelylow, due to the relative ease-of-use of sensors compared totraditional reference instrumentation. However, the labor costof any need for frequent maintenance (e.g., online or offlinecalibrations or cleaning activities) should be a consideration.

Management of the challenging “big data” files resulting fromthe real-time measurements can also be substantial. Any evaluation of whether low-cost sensor technologies are an appropriate opportunity to pursue for a given applicationshould, at minimum, consider these issues that contribute to their classification as a help or a hindrance to facility monitoring.

Lessons Learned from Test ApplicationsSeveral EPRI pilot projects have begun to test the capabilities ofindividual environmental sensors, as well as logistics concerningtheir usage, such as power supply (often off the grid) andwireless data transmission. One pilot project involved a deployment of particulate matter sensors for fugitive dustmeasurement at a power generation facility. Dust sources at these facilities can include material handling processes forcoal and ash, which can include bulldozing, rail delivery, and wind-driven lofting and advection. Road dust can also be present.

Three sensor systems from different manufacturers weretested to see if they could detect dust plumes. All systems incorporated sensors using optical techniques to count particlenumber, with conversions required to produce results inunits of particle mass. Two of the systems were powered withsmall solar panels and batteries, rather than through connectionto grid power (see Figure 2). The sensor results will be com-pared against reference instruments, including hourly FederalEquivalent Method data, sub-hourly data, and particle sizedistribution data.

This deployment was only recently completed, and analysis isongoing, but early results suggest that some of the deployedsensors did capture many of the dust plumes of interest.Good precision was observed between duplicate sensors ofthe same manufacturer and model (see Figure 3). Accuracy is still to be determined. As the field study lasted for ninemonths, an initial consideration of the sensor lifespan and long-term replacement frequency is possible. Impacts of seasonalmeteorology on sensor performance will also be investigated.

EPRI is also testing sensors in a groundwater monitoring deployment using down-hole multi-sound sensors equippedwith probes for pH, electrical conductance, chloride, tempera-ture, and groundwater elevation. There is currently no sensorthat can completely replace a traditional groundwater monitoring program, particularly for inorganic applications,



because probes are not commercially available for constituentssuch as boron and sulfate dissolved in groundwater. However,there may be applications where sensor information can supplement traditional monitoring using surrogate constituentssuch as electrical conductance and chloride. For example,providing higher time resolution information between samplingevents may be of value in groundwater environments withrapid flow, such as karstic groundwater systems.

Another potential use is monitoring of indicator constituentsduring remediation. For example, one use could be to optimizeoperation of an enhanced groundwater flushing system, whereclean groundwater is injected at some wells and impactedgroundwater is extracted at other wells, and where injectionand pumping rates can be modified in response to systemeffectiveness as indicated by the sensor array.1 Results ofEPRI testing to date have demonstrated the ability of theseinstruments to achieve the objective of monitoring short-termfluctuations in groundwater quality. The results have also suggested that maintenance requirements for these devices,in their current stage of development, makes them bestsuited to specialized applications.

Other innovative environmental sensor applications have also been tested. One utility member of EPRI has set up anextensive array of geotechnical sensors that provide real-timedata to monitor dike stability at impoundments using vibratingwire transducers to monitor pore water pressure, inclinometersto measure lateral movement, and borehole extensometer tomonitor settlement/vertical movement. EPRI is documentingthis successful application so that other companies can consider similar deployments.2

Both expected and unexpected challenges were encounteredduring these pilot deployments. For example, complicationswith the air particulate matter sensors were expected at highrelative humidity levels, and were indeed observed. However,prior deployments and manufacturer specifications did notprovide prior indication of the number of large false positivesignals that were observed at temperatures below zero degrees Celsius. Additionally, an unexpected failure of electromagnetic compatibility was found during a deploymentat a power generation facility, which was associated with asingle component in a sensor system package. This samepackage design was deployed at a variety of other types ofsites (e.g., rural, urban) with no indication of any issue.

A substantial upfront labor investment was required for thepilot deployments to understand drivers of sensor performanceand to determine likely maintenance needs. These labor costscould likely be reduced with future deployments, when asensor network is beyond the pilot stage. In addition to upfrontlabor, resources are needed on an ongoing basis to checksensor readings for evidence of drift or malfunction, and to

make necessary adjustments in the field. This requires train-ing of individuals to understand how to calibrate sensors andotherwise maintain the equipment.

Important Study Design FeaturesBest practices for study design and implementation learnedfrom the EPRI deployments are evolving. Most practices rele-vant at utility sites were like those previously recommendedfor ambient sites. For example, it was important to test multiplesensor devices of same manufacturer and model, as well asmultiple different models. This helped to detect and address

Figure 2. Example of an air sensor node on a tripodstand, with solar panel and battery for power provision.



Stephanie Shaw and Bruce Hensel are Principal Technical Leaders at the Electric Power Research Institute in Palo Alto, CA.

References1. Corrective Action Technology Profile: Groundwater Extraction and Treatment at Coal Combustion Residual Facilities; Technical Report 3002010945; EPRI, Palo

Alto, CA: 2017.2. SENTINEL: Geotechnical Instrumentation Overview—Example Application and Cost. EPRI, Palo Alto, CA: in-press.3. Dye, T.; Graham, A.; Hafner, H. Air Sensor Study Design—Details Matter; EM November 2016.http://pubs.awma.org/flip/EM-Nov-2016/dye.pdf

the same, slow-flowing, mass of groundwater. Therefore,chemical measurements are not independent and are notuseful, which makes moot one of the advantages of usingsensors, which is collecting many readings over a short period. This suite of details to consider during sensor deployments highlights the importance of incorporating a site-specific approach to project design.

Another important component of any eventual sensor monitoring program determined to be suitable for real-worlduse at utilities is an alerting system. For such an application,data are accumulated, statistically evaluated or compared tometrics, and alerts sent when readings are out-of-bounds ofexpected values. Alerting facilitates the ability to take operationalaction to respond to the observations.

Future ValueAll signs point to a continuation of research on environmentalsensor applications and performance evaluations. EPRI willalso continue to review new sensor developments and potentialapplications for opportunities and partnerships that may berelevant to electric utilities. These include applications relevantto ambient environments and traditional environmental monitoring networks, as well as facility monitoring. EPRI’sfocus is on technologies that provide high data quality whilehelping electric utilities to lower their monitoring costs, provideincreased spatial or temporal density of measurements, orotherwise provide new insights to assist with managing facility operations. em

Figure 3. Example field measurements in particles per cc of air for duplicate sensor systems of the same manufacturerand model (x- and y-axes) for (a) PM1, (b) PM2.5, and (c) PM10 size fractions.

issues with sensor stability, precision, and usefulness thatwould adversely affect results. Advance review of the technologyspecifications and laboratory testing cannot replace testingthe devices of interest at the site of interest. It is crucial to include a collocated certified monitor (e.g., Federal Referenceor Equivalent Method) or similarly vetted sampling andanalysis protocols, as the best reference for comparison tosensor performance. This will help ensure accurate sensorreadings and provide early indications of drift, confounding,or other issues. The reference instrument that provides data on a similar time interval as the sensor (i.e., typically lessthan 1 hour for air) enables the most robust comparison.

Development of relevant data quality control and quality assurance approaches for long-term sensor operations anddata management is also important. Ongoing intermittentcomparison of sensor data against data from more traditionalmethods can be done on time periods suitable for the equip-ment and metrics being measured. Other details importantto consider, from the perspective of an air sensor deployment,are summarized in a prior issue of EM.3

For groundwater, another important consideration is whetherthe cost of installing and maintaining the sensor is lower thanthe cost of sending a person to collect and a laboratory to analyze the samples. Another consideration for groundwaterapplications is sample independence. In many non-karsticgroundwater environments, multiple sampling events on thesame day, or even same week, are essentially drawing from

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