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Article Solar Measurements Using Smart Devices: A Cost-Effective Technique for Estimation of Solar Irradiance for Sustainable Energy Systems

Hussein Al-Taani * ID and Sameer Arabasi ID School of Basic Sciences and Humanities, German Jordanian University, P.O. Box 35247, Amman 11180, Jordan; [email protected] * Correspondence: [email protected]; Tel.: +962-64-294-444

Received: 16 January 2018; Accepted: 7 February 2018; Published: 13 February 2018

Abstract: Solar irradiance measurement is a key component in estimating irradiation, which is necessary and essential to design sustainable energy systems such as photovoltaic (PV) systems. The measurement is typically done with sophisticated devices designed for this purpose. In this paper we propose a smartphone-aided setup to estimate the solar irradiance in a certain location. The setup is accessible, easy to use and cost-effective. The method we propose does not have the accuracy of an irradiance meter of high precision but has the advantage of being readily accessible on any smartphone. It could serve as a quick tool to estimate irradiance measurements in the preliminary stages of PV systems design. Furthermore, it could act as a cost-effective educational tool in sustainable energy courses where understanding solar radiation variations is an important .

Keywords: smartphone; solar irradiance; smart devices; photovoltaic; solar irradiation

1. Introduction Solar irradiation is the total amount of falling on a surface and it can be related to the solar irradiance by considering the area under solar irradiance versus time curve [1]. Measurements or estimation of the solar irradiation (solar energy in W·h/m2), in a specific location, is key to study the optimal design and to predict the performance and efficiency of photovoltaic (PV) systems; the measurements can be done based on the solar irradiance (solar in W/m2) in that location [2–4]. The performance of a PV system, module or array depends on many factors, one of which is the solar irradiance the solar panels receive during the day (peak -hours) [3–5]. There are devices specifically designed to measure solar irradiance, such as the and the irradiance meter [2,3,6–9]. These devices can measure irradiance with high accuracy and cover a wide spectral range. These devices can be expensive and sometimes need special installation prior to the measurement. Therefore, cost-effective tools are needed to estimate the solar irradiance especially in the preliminary design stages. Recently, smartphones (smart devices) have not only served in communications and media, but also have been used for multiple scientific purposes such as teaching [10,11], medical care [12,13], environment [14] and [15]. The broad range of applications for smart devices comes from the different sensors embedded in them, such as an accelerometer, a digital compass, a gyroscope, a global positioning system (GPS), a microphone and a camera. Smartphone sensors have been widely used in research and education for scientific and educational experiments. For example, a survey has been done by Reese Bomhold [16] on mobile phone applications for undergraduate university students. The accelerometer sensor has been used to study the simple pendulum phenomena and harmonic oscillations [17–20]. In addition, the smartphone acceleration sensors were used to quantitatively analyze a system of coupled oscillators [21]. Furthermore, the smartphone ambient sensor has been used to study a system of two coupled springs [22]. The rotation sensors have been used to

Sustainability 2018, 10, 508; doi:10.3390/su10020508 www.mdpi.com/journal/sustainability Sustainability 2018, 10, 508 2 of 11 study the conservation of angular momentum, non-conservation of rotational kinetic energy [23], rotational energy in a pendulum [24], and the relation between angular velocity and centripetal acceleration [25,26]. In addition, the Coriolis acceleration was measured using the gyroscope and accelerometer sensors in a smartphone [27]. The applications of these sensors are not limited to mechanics. They also have been used to study different phenomena in magnetic fields [28–33], ultraviolet solar radiation [34–38], and measurements of solar current [39]. Mei et al. used the smartphone to measure the ultra-violet radiation (UV) and results were compared with a digital UV meter to validate the usage of the sensor on a smartphone [34]. Wilkes et al. have discussed the possibility of using the smartphone sensor as a UV camera system [40,41]. Finally, Gutierrez-Martinez et al. discussed the possibility of using smartphone devices for light measurements in a case study. Their study showed that the measurements were acceptable if high-precision data is not required but it can be a good reference in comparison with high professional devices that are designed for this type of measurement [42]. The smartphone camera can be used as an irradiance measurement tool, provided that a certain application is downloaded on the device for this specific purpose. In this work, the smartphone’s camera, along with a mechanical setup, is used to validate the usability of smartphone for measuring solar irradiance. It can serve as a quick method to give an indication of how a PV system will perform in a certain area in the preliminary design stages. In addition, this work can be used as an educational tool to help students understand the solar irradiance variability during the day and its relation to other design parameters. The measurements are taken by a smartphone and compared with those acquired by a digital solar irradiance meter. The practicality of the presented work is demonstrated by studying the relation between the solar irradiance and the incident , hour of the day, and tilt angle.

2. Experimental Setup and Measurements Procedure As the objective of this experiment is to demonstrate the use of smartphones in measuring the solar irradiance for the purpose of education and scientific experiments, we have used two types of instruments for measuring the solar irradiance. The first one is a solar irradiance meter of model Solar Survey 200R from SEWARD that has been calibrated by the manufacturer, which is one of the high technology instruments that are used in the solar radiation measurements. These measurements are used to determine the usability of a certain area for photovoltaic systems and thermal installation. This model has a photovoltaic reference cell of response between ~0.3 and 1.2 µm [43], a solar irradiance measurement range of 100–1250 W/m2, and a resolution of 1 W/m2. Also, there is a built-in compass of 0–360◦ range and 1◦ resolution [6]. The cost of this irradiance meter is in the range of a couple of thousand dollars. The data taken with this model was used to validate the measurements taken by a smartphone. An application called “Pyranometer App 2.0” by Hukseflux Thermal Sensors [44], has to be downloaded to the smartphone before proceeding to the measurement section. The application is free and can be downloaded from the App store [45] or an equivalent one can be found in Google Play [46]. A diffuser also has to be placed on top of the camera, as seen in Figure1. The diffuser allows for a full-sky field of view while the camera alone has a 30-degree field of view. The application can store all the measurements such as the irradiance in W/m2, date and local time of measurement, and . A mechanical setup, shown in Figure2, is proposed to help with the required measurements. It consists of a freely-rotating platform where the smartphone will be attached. The whole platform and the cross bar can be rotated horizontally. There is also a compass attached at the top for reference. This setup has been made in the workshop and has already been used in our previous work [31], which contains more details about the setup. When the platform rotates vertically, it changes the tilt angle and the incident angle. The objective of this experiment is to validate our use for smartphones as a tool for solar irradiance measurement. Sustainability 2018, 10, 508 3 of 11 Sustainability 2018, 10, x 3 of 11 Sustainability 2018, 10, x 3 of 11

Figure 1. Smartphone device with the application interface and the required filter covering the FigureFigure 1. Smartphone 1. Smartphone device device with with the applicationthe application interface interface and and the requiredthe required filter filter covering covering the the camera. camera. camera.

Figure 2. The experimental mechanical setup. FigureFigure 2. 2.The The experimental experimental mechanical mechanical setup. setup. The procedure of this experiment is as follows: The procedure of this experiment is as follows: The• procedureA smartphone of thissolar experiment irradiance sensor is as follows: is downloaded on an iPhone 7 from Hukseflux for free • A smartphone solar irradiance sensor is downloaded on an iPhone 7 from Hukseflux for free and then the filter is used to cover the camera, as shown in Figure 1. • A smartphoneand then the solar filter irradiance is used to cover sensor the is camera, downloaded as shown on in an Figure iPhone 1. 7 from Hukseflux for free and then the filter is used to cover the camera, as shown in Figure1. • The smartphone is placed horizontally of the semicircular Teflon piece where the tilt angle is 0◦ and simultaneously a solar irradiance meter is used, as shown in Figure3. SustainabilitySustainability2018 ,201810, 508, 10, x 4 of 114 of 11

• The smartphone is placed horizontally of the semicircular Teflon piece where the tilt angle is 0° • A calibrationand simultaneously is done beforea solar irradiance doing any meter measurements. is used, as shown The in calibration Figure 3. is done by entering a benchmark• A calibration value is of done irradiance before doing corresponding any measurements. to the current The calibration irradiance. is done The appby entering suggests a this valuebenchmark to be found value from of weatherirradiance stations corresponding in the currentto the current location irradiance. for that timeThe app of thesuggests year. Wethis used the valuevalue measuredto be found by from the irradianceweather stations meter in for the the current calibration location of for the that app. time The of data the isyear. taken We every used the value measured by the irradiance meter for the calibration of the app. The data is taken half hour from 9:00 to 15:00 continuously and simultaneously with the solar irradiance meter. every half hour from 9:00 to 15:00 continuously and simultaneously with the solar • Anotherirradiance set of meter. measurements is taken to demonstrate the relation between the tilt angle and the solar• Another irradiance set of using measurements the smartphone is taken only.to demonstrate The mechanical the relation setup between is used the in tilt this angle part and to the help in ◦ rotatingsolar the irradiance smartphone using atthe the smartphone required angle.only. The The mechanical measurement setup is is takenused in for this tilt part to help from in 0 to 60◦ atrotating a fixed the day smartphone hour, where at the the required rotation angle. of the Th surfacee measurement is facing is south.taken for tilt angles from 0° to 60° at a fixed day hour, where the rotation of the surface is facing south.

Figure 3. Setup orientation, smartphone pointing north and rotating toward south. Figure 3. Setup orientation, smartphone pointing north and rotating toward south. Figure 4 shows a schematic diagram that illustrates the incident ray of the solar radiation on the Figuresurface4 with shows surface a schematic diagramangle (γ) thatequal illustrates to zero. In the this incident figure, N ray = North, of the S solar = South, radiation and E on= the surfaceEast, with β issurface the tilt angle; azimuth θi is anglethe angle (γ) equalof incidence to zero. between In this the figure, sun ray N =and North, the normal S = South, to the andsurface. E = East, The solar incidence angle can be calculated according to reference [1]. The incident angle, for a β is the tilt angle; θi is the angle of incidence between the sun ray and the normal to the surface. Thesurface solar tilted incidence in such way angle facing can south, be calculated is given by: according to reference [1]. The incident angle, for a surface tilted in such way facing south,= is ( given − )by: + ( − ) (1) where is the solar angle, is the geographic latitude, and is the . All = ( − ) + ( − ) measured in degrees. cosθi sinδsin ϕ β cosδcos ϕ β cosω (1) where δ is the solar declination angle, ϕ is the geographic latitude, and ω is the hour angle. All measured in degrees. Sustainability 2018, 10, 508 5 of 11 Sustainability 2018, 10, x 5 of 11

FigureFigure 4. Schematic 4. Schematic vector vector diagram diagram showing showing the the main main axesaxes andand vectors. The The surface surface azimuth azimuth angle angle (γ) was taken(γ) was to taken be zero to be since zero thesince surface the surface is heading is headin northg north and and tilted tilted in in such such wayway facingfacing south. south.

3. Results and Discussion 3. Results and Discussion In this work, the measurements were taken on 17 November 2017 at a location in the northern partIn this of work,Amman-Jordan the measurements with local werelatitude taken and on longitude, 17 November φ and 2017 Le, atgiven a location by 32° in N the and northern 36° E, part ◦ ◦ of Amman-Jordanrespectively. Table with 1 localsummarizes latitude the and measured longitude, anϕd calculatedand Le, given solar by radiation 32 N andparameters 36 E, respectively. using Tablesmartphone1 summarizes and theirradiance measured meter and at calculated zero tilt angle solar ( radiationβ = 0). The parameters percentage using differences smartphone of the and irradiancemeasured meter solar at zeroirradiances tilt angle are (alsoβ = 0).shown The in percentage the table. differencesThe mean absolute of the measurederror of the solar measured are alsoirradiance shown values, in the between table. The the meansmartphone absolute and errorirradiance of the meter, measured is 40.23 irradiance W/m2. values, between the smartphone and irradiance meter, is 40.23 W/m2. Table 1. The incident angle in degrees and solar irradiance in W/m2 measured by smartphone and irradiance meter at different day hours. Table 1. The incident angle in degrees and solar irradiance in W/m2 measured by smartphone and irradiance meter at Solar different Irradiance day hours.in W/m2 Day Hour Smartphone Irradiance Meter Incident Angle (Degree) Percentage Difference (%) 9:00 Solar520 Irradiance in 500 W/m 2 68.66 4.00 9:30 617 590 64.16 4.57 Day Hour Smartphone Irradiance Meter Incident Angle (Degree) Percentage Difference (%) 10:00 667 658 60.17 1.36 10:309:00 702 520 500708 68.6656.81 0.85 4.00 11:009:30 797 617 590780 64.16 54.2 2.18 4.57 10:00 667 658 60.17 1.36 11:30 766 782 52.45 2.05 10:30 702 708 56.81 0.85 12:00 735 735 51.65 0 11:00 797 780 54.2 2.18 12:3011:30 575 766 782630 52.4551.84 8.73 2.05 13:0012:00 667 735 735662 51.6553.02 0.76 0 13:3012:30 622 575 630620 51.8455.11 0.32 8.73 14:0013:00 419 667 662510 53.0258.02 17.84 0.76 14:3013:30 418 622 620421 55.1161.63 0.71 0.32 15:0014:00 315 419 510317 58.0265.83 17.840.63 14:30 418 421 61.63 0.71 15:00 315 317 65.83 0.63 Figure 5 shows the solar irradiance versus the hour of the day measured by smartphone and irradiance meter. The measurements were performed at flat surface where the tilt angle is equal to Figure5 shows the solar irradiance versus the hour of the day measured by smartphone and irradiance meter. The measurements were performed at flat surface where the tilt angle is equal to zero (β = 0). In reference to the expected deviation of 30% as reported in the application manual [44], the results measured by the smartphone are in good agreement with those measured by irradiance Sustainability 2018, 10, x 6 of 11 SustainabilitySustainability 2018,, 10,, x 508 6 of 116 of 11 zero (β = 0). In reference to the expected deviation of 30% as reported in the application manual [44], zerothe (β results = 0). In measured reference toby the the expected smartphone deviation are in ofgood 30% agreement as reported with in the those application measured manual by irradiance [44], meterthemeter results and and themeasured the maximum maximum by the deviation smartphonedeviation of of the arethe current incurrent good measurements measagreementurements with was those within within measured 20%. 20%. Itby It is isirradiance clearly clearly seen, seen, themeterthe radiation andradiation theis maximum getting is getting higher deviation higher as the as of daythe the day goescurrent goes by, wheremeas by, whereurements the sun the getswassun closerwithingets closer to 20%. the to normalIt theis clearly normal to the seen, to surface the and,thesurface radiation hence and, the is incident hencegetting the higher angle incident (θasi) theangle decreases. day (θ i)goes decreases. by, where the sun gets closer to the normal to the surface and, hence the incident angle (θi) decreases.

Figure 5. Solar irradiance in W/m2 versus day hour at zero tilt angle for smartphone and irradiance Figure 5. Solar irradiance in W/m2 versus day hour at zero tilt angle for smartphone and irradiance Figuremeter 5. measurements.Solar irradiance in W/m2 versus day hour at zero tilt angle for smartphone and irradiance meter measurements. meter measurements. The effect of the incident angle and day hour on the solar radiation is shown in Figures 6 and 7 forTheThe both effect smartphone of the the incident incident and angle anglesolar and andirradiance day day hour hour mete on on ther, the solarrespectively. solar radiation radiation The is shown isfigures shown in Figuresshow in Figures three 6 and6 andaxes7 7 forfor (irradiance, bothboth smartphone smartphone time, and and and incident solar solar irradiance angle).irradiance Starting meter, mete respectively.inr, the respectively. morning The the figuresThe sun figuresray show is far threeshow from axes threethe (irradiance,normal axes to time,(irradiance,the and surface incident time, axis, and angle). and incident it Starting gets angle). closer in Starting the reaching morning in the a themorningmaximum sun ray the at issun farnoon ray from isthen far the fromdecreases normal the normal toafterwards. the surface to axis,theTherefore, surface and it getsaxis, the closer solarand irradiance reachingit gets closer areaches maximum reaching its maximu at a noon maximumm thenwhen decreases theat incidentnoon afterwards.then angle decreases is minimum Therefore, afterwards. at noon. the solar irradianceTherefore, reachesthe solar its irradiance maximum reaches when its the maximu incidentm when angle the is minimumincident angle at noon. is minimum at noon.

Figure 6. The relation between Incident angle, irradiance, and Day hour using the smartphone. Figure 6. 6. TheThe relation relation between between Incident Incident angle, angle, irra irradiance,diance, and and Day Day hour hour using using the smartphone. the smartphone. SustainabilitySustainability 2018,, 1010,, x 508 7 of 117 of 11

Figure 7. 7. TheThe relation relation between between Incident Incident angle, irradi angle,ance, irradiance, and Day hour and using Day the hour solar using irradiance the solar irradiancemeter. meter.

To further verify the the validity validity of of smartphone smartphone us usee for for this this application, application, the themeasurement measurement of solar of solar irradianceirradiance is is done done at at a a certain certain day day hour hour during during the the day day but but for fordifferent different tilt tiltangles. angles. The Theday dayhour hour is is fixedfixed at 13:00 while while the the title title angle, angle, β,β is, ischanged changed between between 0° and 0◦ and 60° 60as◦ summarizedas summarized in Table in Table 2 and2 and shown in Figure 8. shown in Figure8.

Table 2. Solar irradiance in W/m2 measured by smartphone and calculated incident angles at Table 2. Solar irradiance in W/m2 measured by smartphone and calculated incident angles at different different tilt angles in degrees. tilt angles in degrees. Smartphone Irradiance Tilt Angle (Degree) Incident Angle (Degree) MeasurementsSmartphone (W/m Irradiance2) Tilt Angle (Degree) Incident Angle (Degree) 0 Measurements667 (W/m2) 53.0 5 0795 667 48.2 53.0 10 5933 795 43.4 48.2 15 101055 933 38.7 43.4 20 151205 1055 34.0 38.7 25 201214 1205 29.4 34.0 30 251333 1214 24.9 29.4 35 301453 1333 20.7 24.9 40 351542 1453 16.9 20.7 45 401598 1542 13.9 16.9 50 451642 1598 12.1 13.9 55 501612 1642 12.3 12.1 60 551570 1612 14.3 12.3 60 1570 14.3 Figure 8 shows the effect of tilt angle on the solar irradiance measurement. The graph shows that, Figureas β increases,8 shows so the does effect the of irradiance. tilt angle onAs theβ increases, solar irradiance θi decreases measurement. as it gets closer The graphto the normal shows that, to the surface vector, resulting in a larger irradiance being incident on the surface. Weather as β increases, so does the irradiance. As β increases, θi decreases as it gets closer to the normal to the surfacefluctuations vector, have resulting a direct in effect a larger on the irradiance irradiance being and incident hence some on the measurements surface. Weather might fluctuations be different have athan direct expected effect onas evidenced the irradiance by the and constant hence someirradiance measurements between 20° might and 25° be differenttilt angles. than The expected global as Gsc (1361 W/m2) [47] has been added in◦ the figure◦ and the 30% deviation error bars, as evidenced by the constant irradiance between 20 and 25 tilt angles. The global solar constant Gsc mentioned in the application manual, have been shown in the figure as well. (1361 W/m2)[47] has been added in the figure and the 30% deviation error bars, as mentioned in the application manual, have been shown in the figure as well. SustainabilitySustainability2018 2018, 10, 10, 508, x 88 of of 11 11

2 FigureFigure 8. 8.Irradiance Irradiance in in W/m W/m2versus versustilt tiltangle angleat ata a fixed fixed day day hour. hour.

DespiteDespite itsits lacklack ofof highhigh accuracy,accuracy, ourour methodmethodcan canact actas asan an indicator indicatorwhere wherean anaccurate accurate measurementmeasurement isis notnot required but but rather rather how how the the me measurementasurement changes changes with with certain certain parameters. parameters. This Thisexperiment experiment can canalso also be beused used as asan an effective effective educational educational tool tool to to help studentsstudents developdevelop aa betterbetter understandingunderstanding of of concepts concepts related related to to solar solar irradiance, irradiance, such such as as the the relation relation between between solar solar irradiance irradiance andand solar solar incident incident angle angle as as well well as as the the inclination inclination angle angle of of the the surface surface (tilt (tilt angle). angle).

4.4. Conclusions Conclusions InIn this this paper, paper, we we presented presented a methoda method for for solar sola irradiancer irradiance measurement, measurement, which which takes takes advantage advantage of smartphones’of smartphones’ widespread widespread use and use availability. and availability. We proposed We proposed two experiments two experiments to validate to ourvalidate method. our Themethod. first one The is first to quantify one is to how quantify the solar how irradiance the solar irradiance changes and changes how theand angle how ofthe incidence angle of incidence changes duringchanges the during day. The the measurements day. The measurements were also taken were by also an taken irradiance by an meter irradiance for comparison. meter for comparison. The second experimentThe second uses experiment a mechanical uses a setup,mechanical which setup, allows whic theh smartphone allows the smartphone to rotate vertically to rotate to vertically show the to solarshow irradiance the solar dependenceirradiance dependence on the tilt angle. on the The tilt mechanical angle. The setupmechanical is also setup accessible is also and accessible can be built and incan the be workshop built in the with workshop low-cost materials.with low-cost The mate proposedrials. methodThe proposed has a lowermethod accuracy has a lower than a accuracy typical irradiancethan a typical meter. irradiance However, meter. it is very However, reliable it to is indicate very reliable change to in indicate irradiance change and itsin irradiance variability and when its wevariability change different when we parameters. change different Also it isparameters. cost-effective Also and it easilyis cost-effective accessible and to anyone easily whoaccessible owns ato smartphone.anyone who It owns could a alsosmartphone. serve as aIt great could educational also serve toolas a togreat understand educational solar tool irradiance to understand variability solar andirradiance the interaction variability between and the different interaction parameters between in different PV solar parameters panels design. in PV solar panels design.

Author Contributions: Author Contributions:Hussein Hussein Al-Taani Al-Taani wrote wrote the the paper, paper, performed performed the the measurements, measurements, and and contributed contributed to to the the analysis. Sameer Arabasi designed the experiment and contributed to the writing and analysis. analysis. Sameer Arabasi designed the experiment and contributed to the writing and analysis. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest.

References

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