a smart power outlet for electric devices that can benefit...

A Smart Power Outlet for Electric Devices that canBenefit from Real-Time Pricing

V.P. Ramavarapu⇤, R. Sowers†, and R.S. Sreenivas‡⇤ Centennial High School, Champaign, IL 61821 (Summer Intern, RIoT Lab, UIUC)

† Co-Director, Rapid IoT (RIoT) Laboratory, ISE & Mathematics‡ Senior Member, IEEE, Co-Director, Rapid IoT (RIoT) Laboratory, ISE, CSL & ITI

University of Illinois at Urbana-Champaign, Urbana, IL 61820.

Abstract—Under Real-Time Pricing (RTP) the cost perkWh varies with time as a consequence of the changingsupply and demand conditions in the market. Customersthat are able to shift their electricity consumption patternscan reduce their costs by using their devices when priceis low. This requires a smart power outlet that can turnitself on/o↵ based on price, and customer preferences.

This paper is about a smart power outlet that uses aBelkin WeMo Mini Smart Plug (WeMo) [1], which can beautonomously turned on/o↵ using an Intel Edison (Edison)[2] through a WiFi connection. The JavaScript code, whichruns on the Intel Edison, currently turns on (resp. o↵)the electric device that is connected to the WeMo if thecurrent price is negative (resp. positive). This code canbe modified to incorporate other criteria like customerpreferences if necessary. Our ongoing work involves thedesign and validation of a suite of switching-algorithmsfor this platform.

I. IntroductionTesla’s Charge-at-Home [3] recommends an hour

of charge every 29 miles of range. It is estimatedthat a Tesla user would require about four hours ofcharge daily, which is usually done at night at thecustomer’s home. It is important to note that thecharging-times do not have to be contiguous. Thecharging cost to the user would be determined bythe price o↵ered by the electricity provider duringthe charging-periods.

The electricity provider uses the supply and de-mand of the market, along with other considera-tions, to set the price. Traditionally, this used tobe a fixed/flat price. Nowadays, providers o↵er adynamic price to the consumer, who can makeinformed energy choices that are tailored to the indi-vidual. This promotes smarter energy use, which canimprove e�ciency, lower costs, and has a positiveimpact on the environment.

Commonwealth Edison (ComEd) is the largestelectric utility in Illinois, serving the Chicagoand Northern Illinois area. ComEd o↵ers a 5-minute price (cf. https://hourlypricing.comed.com/live-prices/five-minute-prices/), and an hourly-price(cf. https://hourlypricing.comed.com/live-prices/),which is the real-time average of the current hour’stwelve 5-minute prices. Figure 1 shows ComEd’sReal-Time Hourly Price (RTHP) on May 14th,2017. On this date, there was a period of 6.5hours where the RTHP was negative. A Teslauser, whose charging adapter was connected to asmart outlet that turned itself only during periodswhen the price was negative, would have chargedhis vehicle for minimal cost on this day. Theremight be other days where a full-complement ofsix hours of negative price might not be realized.Under this circumstance, the user would needa charging-strategy that ensures a full-charge atminimal cost. Our current research is focused onthe design and back testing of these strategies.Before any of these strategies can be implementedin practice, it is critical to have a smart electricoutlet that can be remotely turned on/o↵ basedas per the direction of the implemented strategy.Stated di↵erently, an end-user device that decidesthe appropriate times to turn itself “on” or “o↵”based on price is the mandatory first-step beforeany high-granularity, smart-energy managementmethods (eg. [4], [5]) can be implemented inpractice.

This paper is about the construction of such asmart outlet using an Intel Edison (Edison) [2],Belkin WeMo Mini Smart Plug (WeMo) [1], andsome (easily extended) JavaScript programming.The example of charging an electric vehicle is used

The 2017 International Conference on Control, Electronics, Renewable Energy and Communications (ICCEREC)

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Fig. 1. ComEd’s Real-Time Hourly Prices (RTHP) for May 14th, 2017 (cf. https://hourlypricing.comed.com/live-prices/). The RTHP (shownin blue) was negative from Midnight to 6:30AM. This plot has been clipped to highlight the RTHP-trajectory during the early hours of May14th, 2017. The entire RTHP-trajectory for this date can be found here – https://hourlypricing.comed.com/live-prices/?date=20170514.

in this paper for illustrative purposes. This smartelectric outlet can be used in conjunction with anyelectric device that benefit from the real-time priceo↵ered by a provider.

The rest of the paper is organized as follows. Inthe next section we present a brief review of real-time pricing and its influence in the power-market.Section III describes the smart power outlet, andpresents a verification of its functionality. The paperconcludes with a review of our ongoing work.

II. A Review of Real-Time Pricing in the PowerMarket

The U.S. Energy Information Administration(USEIA) reports that in 2016, the annual averageprice of electricity in the United States was 10.28cper kilowatt-hour (kWh). Residential customers paid12.55c per kWh; commercial customers paid 10.37cper kWh; Industrial customers paid 6.75c per kWh;and Transportation customers paid 9.48c per kWh,respectively [6].

Dynamic pricing o↵ers a price that depends onwhen electricity is used. The customer can consumeenergy when it is cheaper, and chose to conserveenergy when the price is expensive. This resultsin better utilization of generated-power, lower-coststo the customer, and is said to have a positiveimpact on the environment. It was thought that whiledynamic pricing will promote the judicious shiftingof energy use, it would not reduce the total energyuse in any way. However, the data shown in Table

3 of reference [7] shows that dynamic pricing hasresulted in a 4% annual reduction in kWh usage perhousehold.

Section 3.4 of reference [7] notes that in 2010ComEd’s Residential Real-Time Pricing had gen-erated bill savings of $3,954,882, and the average2010 bill savings among customers who were in theRRTP program for all of 2010 was $177.

The above mentioned reference also notes thatthe RRTP program had some unintended benefitsas well, in that the RRTP program reduced SO2,NOx and CO2 emissions, which is estimated to beabout $185,000 per year. That is, dynamic pricingis environmentally friendly, as well.

ComEd’s hourly price [8] is the average of twelve5-minute prices for that hour, and the real-timehourly price is only known after the hour has passed(cf. figure 2). The current hour average price, whichis posted on the web, is the real-time average of thecurrent hour’s 5-minute prices (cf. figure 3).

It is possible for the price of electricity to benegative for short periods of time. This happenswhenever the supply of electricity exceeds the de-mand. When demand is short of supply, due tophysical-considerations, many electricity generatorscannot reduce output to match demand. If the pricegoes negative for a period, the consumer is paidto consume electricity. A nominal delivery chargemight apply in some cases. As shown in figure 1,the real-time price was negative for 6.5 hours onMay 14, 2017.


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ComEd provides an API that provides theCurrent-Hour 5-Minute Price via an API [9], whichcan provide its output in JSON- [10], RSS- [11], ortext-format. The default output format is JSON.

For the remainder of this paper we will workunder the assumption that the strategy of consumingpower (for the present 5-minute period) only whenthe Current-Hour 5-Minute Price (cf. figure 3) isnegative is desirable. The rest of the paper is aboutthe construction of such a device using an IntelEdison and a WeMo switch.

III. The Smart Power Outlet

The Intel Edison (cf. figure 7) is a 22 nm IntelSystem on Chip (SoC) that includes a 500 MHzdual core, dual threaded Intel Atom CPU with 4GB of flash memory with pre-installed Yocto Linux[12]. It also has a 100 MHz 32-bit Intel Quarkmicro-controller, and a Broadcom BCM43340 chipthat provides standard dual-band 2.4 GHz and 5GHz IEEE 802.11 a/b/h/n connectivity. The WiFiconnection can be protected using WPA and WPA2authentication. The Edison can connect via Blue-tooth to other devices like smart-phones. It support40 General-Purpose I/O (GPIO) connections. It iscan be programmed using Intel’s Integrated Devel-opment Environment (IDE) – Intel XDK – whichcan be used develop JavaScript-based Node.js [13]applications for the Edison.

The Belkin WeMo Mini Smart Plug (WeMo) (cf.figure 5) is a switched-outlet that can be controlledvia IP networks. It comes with an iOS/Android Appthat can turn on/o↵ the plug (and any device that isconnected to it) remotely.

The wemo-client is a low-level client librarythat can be used to control WeMo devices withinNode.js applications. The details of the wemo-clientAPI can be found in reference [14]. It can beinstalled on the Edison using the npm install wemo-client command via the SSH Terminal on the IntelXDK (cf. figure 6).

We now present annotative description of theJavaScript code shown in figures 8 and 9, whiche↵ectively turns on (resp. o↵) the WeMo whenthe Current-hour-5-Minute-Price is negative (resp.positive). Before this code is run on the Edison,it is imperative that its clock is synchronized tolocal time. This was done by removing the exist-ing /etc/localtime file on the Edison, followed by

symbolically linking /etc/localtime to the appro-priate timezone file in /usr/share/zoneinfo/Amer-ica/. For our Edison, this was done by the ln -s /usr/share/zoneinfo/America/Chicago /etc/local-time command. The WeMo is assumed to be in the“o↵” position initially.

The function periodicActivity() is called every fiveminutes (starting as close as possible to the hour).This is done by the setTimeout(periodicActivity,300000); command at the end of the code shown infigure 8.

The http.get() command obtains the JSON-formatted output that would result soon afterComEd’s API1 is executed. The command varpriceResp = JSON.parse(body); stores the JSON-formatted response from the API. Consequently,each element of priceResp has two fields – “mil-lisUTC,” which is the UNIX-time [15]; and “price,”which is the price in cents per kWh at the timeindicated in the first-field. The price-field of thefirst-element of priceResp (i.e. priceResp[0].price)is the latest price. If this is is negative, the WeMohas to be turned on (if it is currently o↵).

Since WeMo devices can be temporarily lost– we include the WeMo device-discovery processwithin the periodicActivity() function. There wereother WeMo’s in the premises where this codewas tested, and the specific WeMo we wish tocontrol using the current-price had the name WemoMini 4. The wemo-client library provides a setBi-naryState(value) function, where value = 1 (resp.value = 0) turns the device on (resp. o↵). If theWeMo device was previously o↵, and the price wentnegative, it is turned on. Likewise, if the devicewas previously on, and the price went positive, thedevice is turned o↵. This device was tested between2:00PM and 3:30PM on May 21, 2017. Figure 7shows the RTHP-trajectory for that day. The deviceturned “on” between 2:10PM and 3:10PM whenthe price was negative. At 3:10PM the price wentpositive, and the device turned “o↵” for 5 minutes.Following this, at 3:15PM the price went negative,and the device turned “on,” and stayed on till3:30PM when the test was concluded.

IV. ConclusionThis paper describes a smart electric outlet that

can be turned on (resp. o↵) when the current (real-

1http://hourlypricing.comed.com/api?type=5minutefeed


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time) price of electricity is negative. The hardwarefor this device consisted of an Intel Edison anda Belkin WeMo Mini Smart Plug. The proposedfunctionality was achieved through the Node.jsJavaScript application that runs on the Edison. Thissoftware can be extended to include sophisticatedswitching-strategies that depend on the price-historyand user-preference. As an illustration, a Tesla userhas to charge his vehicle for six hours each day.This decision is not di�cult on a day like May 14,2017 (cf. figure 1). There will be days when theprice does not stay negative for a su�cient amountof time. This calls for the development of alternatestrategies that accomplishes the consumption-goalat minimal cost. This is a part of of our ongoingwork.

References[1] http://www.belkin.com/us/Products/home-automation/c/

wemo-home-automation/, Last Accessed: May 23, 2017.[2] https://software.intel.com/en-us/articles/

what-is-the-intel-edison-module, Last Accessed: May 23,2017.

[3] https://www.tesla.com/charge-at-home, Last Accessed: May 23,2017.

[4] R. Ahmad, A. Gani, S. Hamid, M. Shojafar, A. Ahmed,S. Madani, K. Saleem, and J. Rodrigues, “A survey on energyestimation and power modeling schemes for smartphone appli-cations,” Int J Commun Syst, vol. 30, 2017, https://doi.org/10.1002/dac.3234.

[5] Z. Pooranian, N. Nikmehr, S. Najafi-Ravadanegh, H. Mahdin,and J. Abawajy, “Economical and environmental operation ofsmart networked microgrids under uncertainties using nsga-ii,”in 2016 24th International Conference on Software, Telecom-munications and Computer Networks (SoftCOM), Split, Croatia,September 2016, pp. 35–40.

[6] https://www.eia.gov/energyexplained/index.cfm?page=electricity factors a↵ecting prices, Last Accessed: May23, 2017.

[7] Navigant Consulting Inc., “Evaluation of the residential realtime pricing program, 2007-2010,” June 2011, prepared forthe Commonwealth Edison Company, http://www.icc.illinois.gov/downloads/public/edocket/296671.pdf & http://www.icc.illinois.gov/downloads/public/edocket/296673.pdf.

[8] https://hourlypricing.comed.com/live-prices/, Last Accessed:May 23, 2017.

[9] https://hourlypricing.comed.com/api?type=5minutefeed, LastAccessed: May 23, 2017.

[10] https://www.w3schools.com/js/js json intro.asp, LastAccessed: May 23, 2017.

[11] https://validator.w3.org/feed/docs/rss2.html, Last Accessed:May 23, 2017.

[12] https://www.yoctoproject.org/about, Last Accessed: May 23,2017.

[13] https://en.wikipedia.org/wiki/Node.js, Last Accessed: May 23,2017.

[14] https://www.npmjs.com/package/wemo-client, Last Accessed:May 23, 2017.

[15] https://en.wikipedia.org/wiki/Unix time, Last Accessed: May23, 2017.

Fig. 4. The Intel Edison [2] with a Mini Breakout Board fromAdafruit.com.

Fig. 5. The Belkin WeMo Mini Smart Plug (WeMo).

Fig. 6. Installing the wemo-client on the Edison via the SSHTerminal on the Intel XDK.


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Fig. 2. ComEd’s Real-Time Hourly Prices (RTHP) for May 23, 2017. The price at 2:00PM was 3c per kWh.

Fig. 3. ComEd’s Current-Hour 5-Minute Price from 1:05PM to 1:55PM on May 23, 2107. The average of these eleven values was 3.06cper kWh.

Fig. 7. ComEd’s RTHP for May 21, 2017, which is close to the vicinity of 0c per kWh between 2:00 and 4:00PM.


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/ / V. P . Ramavarapu , R . Sowers and R . S . S r e e n i v a s , ”A Smart Power/ / O u t l e t f o r E l e c t r i c Dev ice s t h a t can B e n e f i t from Real�Time/ / P r i c i n g , ” In P r o c e e d i n g s o f t h e 3 rd I n t e r n a t i o n a l C o n f e r e n c e/ / on C o n t r o l , E l e c t r o n i c s , Renewable Energy , and Communicat ions/ / ( ICCEREC 2 0 1 7 ) , September 2017 , Yogyakar ta , I n d o n e s i a ./ // / I n t e l �Edison ’ s J a v a S c r i p t Code t h a t t u r n s �on ( r e s p . t u r n s �o f f )/ / t h e e l e c t r i c d e v i c e c o n n e c t e d t o t h e WeMo when t h e c u r r e n t/ / r e a l � t ime p r i c e i s n e g a t i v e ( r e s p . p o s i t i v e )/ /v a r h t t p = r e q u i r e ( ’ h t t p ’ ) ;v a r Wemo = r e q u i r e ( ’ wemo� c l i e n t ’ ) ;/ / h t t p s : / /www. npmjs . com / package /wemo� c l i e n t/ / Gl ob a l V a r i a b l e s a b o u t s w i t c h s t a t e & P r i c ev a r p r i c e I s N e g a t i v e = f a l s e ;v a r s w i t c h S t a t e = f a l s e ;

/ / C a l l t h e p e r i o d i c A c t i v i t y f u n c t i o np e r i o d i c A c t i v i t y ( ) ;

/ / Thi s f u n c t i o n i s c a l l e d f o r e v e r ( due t o t h e s e t T i m e o u t ( ) f u n c t i o n )f u n c t i o n p e r i o d i c A c t i v i t y ( ) {v a r ge tReq = ” h t t p : / / h o u r l y p r i c i n g . comed . com / a p i ? t y p e=5 m i n u t e f e e d ” ;/ / Make t h e r e q u e s tv a r r e q u e s t = h t t p . g e t ( getReq , f u n c t i o n ( r e s p o n s e ) {/ / Where we s t o r e t h e r e s p o n s e t e x tv a r body = ’ ’ ;

/ / Read t h e d a t ar e s p o n s e . on ( ’ da t a ’ , f u n c t i o n ( chunk ) { body += chunk ; } ) ;/ / P r i n t o u t t h e d a t a once we have r e c e i v e d a l l o f i tr e s p o n s e . on ( ’ end ’ , f u n c t i o n ( ) {

i f ( r e s p o n s e . s t a t u s C o d e === 200) {t r y {

/ / P a r s e t h e JSON t o g e t t h e p i e c e s we needv a r p r i c e R e s p = JSON . p a r s e ( body ) ;c o n s o l e . l o g ( ’ Spot P r i c e i s = %d ’ , p r i c e R e s p [ 0 ] . p r i c e ) ;p r i c e I s N e g a t i v e = ( p r i c e R e s p [ 0 ] . p r i c e <= 0) ? t r u e : f a l s e ;

} c a t c h ( e r r o r ) {/ / R e po r t problem wi th p a r s i n g t h e JSONc o n s o l e . l o g ( ” P a r s i n g e r r o r : ” + e r r o r ) ;

}} e l s e {

/ / Re po r t problem wi th t h e r e s p o n s ec o n s o l e . l o g ( ” Response e r r o r : ” +

h t t p . STATUS CODES[ r e s p o n s e . s t a t u s C o d e ] ) ;}

} )/ / To be c o n t i n u e d i n F ig . 9 . .

Fig. 8. First-part of the Node.js application that controls the WeMo using the Edison. This code is continued in figure 9.


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/ / C o n t i n u i n g J a v a S c r i p t Code l i s t i n g from Fig . 8v a r wemo = new Wemo ( ) ;

wemo . d i s c o v e r ( f u n c t i o n ( d e v i c e I n f o ) {i f ( d e v i c e I n f o . f r i e n d l y N a m e == ’Wemo Mini 4 ’ ){

c o n s o l e . l o g ( ’Wemo Device Found : %j ’ , d e v i c e I n f o . f r i e n d l y N a m e ) ;/ / Get t h e c l i e n t f o r t h e found d e v i c ev a r c l i e n t = wemo . c l i e n t ( d e v i c e I n f o ) ;/ / We want t o l i s t e n t o e r r o r e v e n t s ( e . g . d e v i c e o f f l i n e ) ,/ / Node w i l l th row them as an e x c e p t i o n i f l e f t unhand ledc l i e n t . on ( ’ e r r o r ’ , f u n c t i o n ( e r r ) {

c o n s o l e . l o g ( ’ E r r o r : %s ’ , e r r . code ) ;} ) ;/ / Handle B i n a r y S t a t e e v e n t sc l i e n t . on ( ’ b i n a r y S t a t e ’ , f u n c t i o n ( v a l u e ) {

i f ( d e v i c e I n f o . f r i e n d l y N a m e == ’Wemo Mini 4 ’ )s w i t c h S t a t e = ( v a l u e === ’ 1 ’ ) ;

c o n s o l e . l o g ( ’ Device %j t u r n e d %s ’ , d e v i c e I n f o . f r i end lyName ,v a l u e === ’1 ’ ? ’ on ’ : ’ o f f ’ )

} ) ;i f ( d e v i c e I n f o . f r i e n d l y N a m e == ’Wemo Mini 4 ’ ){

c o n s o l e . l o g ( ’ P r i c e i s n e g a t i v e ? ’ , p r i c e I s N e g a t i v e ) ;c o n s o l e . l o g ( ’ Swi tch S t a t e ? ’ , s w i t c h S t a t e ) ;i f ( ( p r i c e I s N e g a t i v e ) && ( ! s w i t c h S t a t e ) ){

c l i e n t . s e t B i n a r y S t a t e ( 1 ) ;s w i t c h S t a t e = t r u e ;

}i f ( ( ! p r i c e I s N e g a t i v e ) && ( s w i t c h S t a t e ) ){

c l i e n t . s e t B i n a r y S t a t e ( 0 ) ;s w i t c h S t a t e = f a l s e ;

}}

}} ) ;

} ) ;

/ / Wait f o r 5 mins and c a l l t h i s f u n c t i o n a g a i ns e t T i m e o u t ( p e r i o d i c A c t i v i t y , 3 0 0 0 0 0 ) ;v a r timeNow = new Date ;c o n s o l e . l o g ( ’ p o l l i n g f o r p r i c e s a t %j ’ , timeNow ) ;

}

Fig. 9. Second-part of the Node.js application that controls the WeMo using the Edison. This code is a continuation of figure 8.


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