WO2016187082A1

WO2016187082A1 - Sensor for measuring reflected light for optimizing deposited performance enhancement coatings on substrates

Info

Publication number: WO2016187082A1
Application number: PCT/US2016/032614
Authority: WO
Inventors: John Arthur DE V0S
Original assignee: De V0S John Arthur
Priority date: 2015-05-15
Filing date: 2016-05-15
Publication date: 2016-11-24
Also published as: ES2902683T3; US20180145628A1; EP3295120B1; EP3295120A1; US10574180B2; EP3295120A4

Abstract

An innovative portable reflected light sensor for non-destructively measuring characteristics of performance enhancement coatings applied to substrates such as solar photovoltaic panels is described. The innovative sensor provides a light source and a photodetector for measuring light incident on a substrate surface from the light source, and reflected to the photodetector. The spot size of the illuminated region of the substrate is at least 1 cm² in area, thus averaging over a relatively wide portion of the substrate surface relative to existing fiber optic devices. A single measurement may then be representative of the coating. The innovative portable reflected light sensor is adapted to measure substrates in the field, and is especially adapted for assessing coating quality during the coating process. The innovative sensor also comprises a signal processing circuit that performs analysis of the measurements and feeds back status of the coating to the operator for coating process control.

Description

SENSOR FOR M EASU RI NG REFLECTED LIGHT FOR OPTIM IZI NG DEPOSITED PERFORMANCE EN HANCEM ENT COATI NGS ON SU BSTRATES

CROSS REFERENCE TO PRIORITY APPLICATIONS

[0001] This international application claims the benefit of U.S. Provisional Application No.

62/162,617, filed on May 15, 2015.

FIELD OF THE INNOVATION

[0002] This invention relates to portable light reflectance sensors that measure surface or thin film characteristics for large substrates, such as solar photovoltaic panels.

BACKGROUND

[0003] Currently available light reflection sensors are not capable of measuring the light reflection from a relatively large spot size on the top surface of solar panels installed in the field and comparing the results before and after application of a performance enhancement coating. The very small spot size analyzed by a typical sensor using a fiber optic probe is insufficient to accurately measure in one reading an area large enough to determine the average performance across the whole solar panel of solution deposited performance enhancing coatings. This is due in part because variations in the top surface structure of solar panel cover glass and variations in solution deposited coating may not be adequately represented within the very small spot size read by the fiber optic probe. Multiple readings by such a probe would have to be done to develop a statistically significant number of samples to estimate average coating performance. Furthermore, typical fiber optic probe sensors require the use of a separate computing device, such as a laptop computer, to run the calculations required to produce human readable data. The process of taking numerous measurements and transporting and setting up a typical fiber optic sensor with a separate computing device for each solar panel to be measured is relatively cumbersome and time consuming compared with a device with integrated computing and human readable display that can determine the average performance difference in light reflection properties by taking just one measurement before and just one measurement after application of a performance enhancement coating.

SUMMARY

[0004] The instant innovation relates to application of liquid performance enhancing coating precursor solution to large substrates such as photovoltaic panels. The instant innovation is a portable light reflectance sensor for non-destructively determining characteristics of thin film performance enhancing coatings applied to a substrate, such as, but not limited to, a photovoltaic panel. It is particularly advantageous for outdoor installations, where photovoltaic panels installed in arrays or individually may be retrofitted with performance enhancement coatings, such as, but not limited to, anti-reflection coatings. The innovative portable light reflectance sensor provides a light source and a photodetector for measuring light incident on a substrate surface from the light source, and reflected to the photodetector. The spot size of the illuminated region of the substrate is at least 1 centimeter square in area_A thus averaging over a relatively wide portion of the substrate surface vs. the much smaller spot size of a fiber optic measuring device. A single measurement may then be representative of the coating. The innovative light reflectance sensor is adapted to measure substrates in the field, and is especially adapted for assessing coating quality during the coating process. The innovative portable sensor also comprises a signal processing circuit that performs analysis of the measurements and feeds back status of the coating to the operator for coating process control.

[0005] The coating of such panels may be facilitated by a mobile coating apparatus, such as detailed in co-pending U.S. Patent Application No. 14/668,956, incorporated herein in its entirety. The innovative detector comprises a light source adapted to illuminate a region of a substrate with a spot cross-sectional area of at least 1 cm², at the substrate surface, and a photodetector adapted to collect at least a portion of the light reflected from the substrate surface. In one embodiment, the innovative photodetector further comprises signal processing circuitry adapted to digitize the raw analog data collected by the photodetector. The

photodetector may comprise a spectrometer that resolves the intensity of reflected light as a function of wavelength. In other embodiments, the photodetector comprises a photodiode or phototransistor. Both types may integrate the total light intensity over the entire capture spectrum of the reflected light. A variation includes the use of a bandpass filter or cutoff filters to examine a portion of the visible or invisible spectrum, the latter referring to the infrared (IR) and the ultraviolet (UV) extensions of the visible spectrum. In other embodiments, sources having a more narrow range of wavelengths, such as lasers, light emitting diodes (LEDs), cold cathode and heated cathode gas discharge lamps, such as mercury lamps and inert gas plasmas, may be employed as light sources.

[0006] The relatively large spot size of the incident beam provides the advantage of spatially integrating surface features over the area covered by the illuminated region covered by the spot. In this way, the innovative reflectance sensor is further adapted to spatially and temporally integrate the spectral characteristics of the light reflected and collected from the illuminated region of the substrate, where the photodetector is in electronic communication with the signal processing circuit. The signal processing circuit may be adapted to perform read operations to capture the signals from the photodetector on receiving a command signal, and may be further adapted to extract and store digitized photometric data from the captured sensor signal. In addition, the signal processing circuit may be adapted to perform

computations on the photometric data, and then correlate the data to the one or more of the characteristics of the thin film coating on the substrate of interest. It is an aspect of one embodiment of the instant innovation that the correlated characteristics of the coating be transformed into control information to be fed back to either a human operator or to a controlling device for assessing the quality of the coating as it is applied from a liquid coating precursor solution, and if necessary adjusting the coating deposition method, or coating makeup characteristics. In this way, the deposition process may be steered to produce a finished coating having optimal performance.

[0007] A coating apparatus adapted to apply a film of liquid precursor solution that cures into a finished performance enhancement coating, such as, but not limited to, an anti-reflection coating, may be used in conjunction with the innovative portable reflectance sensor to provide a feedback component in the control loop of the coating process. The coating apparatus may be controlled manually by a human operator, or automatically or semi-automatically by an automated control system. In the automatic or semi-automatic cases, the innovative portable sensor may be used as a feedback component in a closed control loop.

[0008] It is an aspect of the innovation that the light source produce a light beam having a spot cross-sectional area of at least 1 cm² at the substrate surface. Commercially available light sensors based on total reflection and/or spectral reflection measurements used for measuring thin film or substrate surface characteristics use small spot sizes (typically 1-2 mm in diameter). Many of these devices are designed for use in measuring surface characteristics of small substrates, such as silicon wafers. For both large and small substrates, multiple readings taken at several locations on the substrate are generally necessary to obtain a representative sample of coating or surface characteristics. The larger spot size of the instant invention allows integration of superficial properties over an area 50 -100 times or larger than that provided by conventional fiber optic devices, providing a representative sampling of the local region of the surface from which the light is reflected.

[0009] It is another aspect of the invention to provide a means to correlate photometric data obtained from the light reflected off of a substrate surface and collected by the photodetector. For example, the surface may have a previously-cured performance enhancement coating, such as an anti-reflection coating, or a freshly applied liquid coating precursor solution. Optionally, the surface may be uncoated, where a measurement may be made to obtain baseline data of initial reflectance for a before-and-after comparison when a coating is applied. The raw photometric data collected may provide a measure of the reflectance of the substrate surface, as, for example, to measure the attenuation of percent reflection after application of an antireflection coating.

[0010] Another measurement derived from the raw photometric data may be the thickness and quality of coverage of a fresh layer of coating precursor solution. The photometric data may be in the form of spectral intensity data. In this case, the photodetector may incorporate a spectrometer that can scan over a range of wavelengths. In other embodiments, the photodetector may be a simple photodiode or phototransistor that is adapted to measure across a broad spectrum of light, and may be used to measure intensity integrated over the entire visible, near IR and UV spectrum to which is it sensitive, or a portion thereof, if, as an example, a bandpass filter is used. It is another aspect of the instant innovation that this information may be used for feedback control in a coating process control loop for the coating apparatus. The coating apparatus may be controlled by a human operator in one set of embodiments, thus the control loop is an open loop, or may be machine-controlled in another set of embodiments, necessitating a closed feedback control loop.

[0011] The signals may be used to indicate the thickness of a coating. As an example, a relatively high average reflectance intensity reading and a shift toward the reddish part of the spectrum in the reflected light may indicate that a performance enhancement coating is too thick as applied. The operator or automatic control system may need to adjust the speed of the applicator, or decrease coating precursor solution viscosity. As the spot size is large, variations normally encountered in both coating non-uniformities and variations in the underlying substrate surface, such as photovoltaic panel cover glass or photovoltaic cell surface, are integrated over the spot area and collected by the photodetector. Thus, the photodetector receives a reflection spectrum that is averaged over the relatively large spot size. The spectral intensity data may be averaged over a range of wavelengths to determine a predominant component or spectral region. By subtracting the reading from one area measured prior to coating from the reading of the same area after coating, variations other than those of the coating itself may be canceled out. [0012] Multiple readings may be made, for example, over very large areas where several locations on the substrate surface or multiple substrate surfaces may be sampled. In this way, the uniformity of surface characteristics may be assessed. As an example, for an anti-reflection coating, the uniformity of the coating thickness and quality may be quantified. This is particularly advantageous for applying new coatings to a substrate such as a photovoltaic panel or to multiple substrates such as a solar panel array. An operator of a coating apparatus may use the innovative portable reflectance sensor to monitor the quality of the coating process by measuring the spectral characteristics of the reflected light. As an example of a method of use, an operator of the coating apparatus may first take baseline measurements on an uncoated photovoltaic panel, then apply a thin film of liquid precursor solution that will cure to form a finished coating, such as an antireflection coating.

[0013] The innovative portable reflectance sensor may include signal processing circuitry comprising an on-board microprocessor and memory, on which may be stored one or more algorithms and/or look-up tables for correlation of measurements to known film

characteristics. As an example, the portable sensor may include a spectrometer that is programmed to scan a range of wavelengths and record spectral intensities. The data may be digitized and stored as binary data in the on-board memory, where the microprocessor may compare the intensity data reflected from the freshly applied liquid coating to the baseline data taken from the bare (uncoated) surface of the photovoltaic panel. In another embodiment, the data may also be offloaded to an off-board data storage and retrieval system, accessed by the portable sensor using wired or wireless means. [0014] As an example of process control by use of the innovative portable sensor, the comparison algorithm may reveal that the reflection spectral intensities are higher than expected for an antireflection coating, and moreover the intensities are stronger in the red end of the spectrum measured, having been red-shifted in comparison to the expected spectrum reflected (for example in comparison with a ¼ wave-thick index matching film). These spectral characteristics would indicate that the coating is too thick. In this example, it may be thicker than the ¼ wavelength thickness necessary to cancel reflections at more centralized

wavelengths, thus being detuned and allowing longer wavelengths to be reflected than would be the case for a film with the proper ¼ wavelength thickness.

[0015] A further aspect of the innovation may be the inclusion of an algorithm to present recommendations to the operator as to steps required to adjust the coating process to optimize the coating. Here, the coating thickness may be a function of applicator speed and viscosity of the liquid coating precursor solution. The coating process may be adjusted, for example, by changing applicator speed, or by changing solution viscosity. In addition, the coating thickness may be corrected, if found to be out of specification by measurements taken with the innovative portable sensor, by applying a make-up coating.

[0016] In further embodiments of the innovation, measurements of air temperature and surface temperatures of the substrate may be incorporated into the portable sensor system design and algorithms. Thermal measurements may be used for further optimization of the coating process, as evaporation rates and curing rates may be taken into consideration by the optimization algorithm, preferably stored in on-board memory and executed by an on-board microprocessor, thereby adjusting the recommendations to the operator as to the optimal coating speed and solution viscosity, for example. In further embodiments, humidity sensors may also be a part of the sensor array to further refine the coating process, if, as an example, relative humidity affects the evaporation rate of the solvent used in the precursor solution, or if humidity affects (or is necessary to initiate) the curing chemistry of the coating.

[0017] In other embodiments of the instant innovation, an automated control system may replace the operator of the coating apparatus as being the recipient of the feedback from the innovative portable sensor signal processing circuitry. The automated control system may be adapted to directly respond to the feedback issuing from the innovative portable sensor signal processing circuitry. In one example, the innovative portable sensor may be mounted on a coating apparatus, and configured to continuously or intermittently measure the surface characteristics by refection spectrometry. In this example, the portable sensor is aimed at the substrate surface behind the apparatus, so that the freshly coated surface may be measured. The characteristics of the freshly applied coating may be assessed, and the speed of the coating apparatus may be controlled by a closed feedback loop. In other embodiments, one portable sensor may be situated in such a way as to measure the substrate reflection before coating and another portable sensor may be situated to measure the substrate reflection after coating, with the difference in reflection measurements being used to inform the coating process.

BRIEF DESCRIPTION THE DRAWINGS

[0018] Fig. la. Schematic representation of the componentry of the innovative portable sensor, showing an embodiment comprising a photodetector.

[0019] Fig. lb.. Schematic representation of the componentry of the innovative portable sensor, showing an embodiment comprising a spectrometer. [0020] Fig. 2a. Operational schematic of the innovative portable sensor.

[0021] Fig. 2b. Zoom view of an illuminated portion of a substrate surface (coated or uncoated), showing surface irregularities and non-uniformities

[0022] Fig. 3. Mobile coating apparatus example deployed on a photovoltaic panel, where the innovative portable sensor is mounted on the chassis of the apparatus.

[0023] Fig. 4. A side-sectional view of an embodiment of the innovative portable sensor mounted on a coating apparatus.

[0024] Fig. 5. Schematic diagram of an electronic control system embodiment for controlling a mobile coating apparatus.

DETAILED DESCRIPTION

[0025] Fig. la details a schematic of the instant innovation as described. Portable sensor system 100 is shown in active deployment as a portable device, where it is disposed on a substrate surface, where substrate 101 is undergoing measurement. Incident light source 102 shines light, which may be substantially broadband light ('white' light) or narrow banded colored light, emanating from a variety of light sources. For instance, incandescent light sources may be used having coatings yielding different IR and visible spectra, or black body temperatures, as is commercially available with incandescent bulbs. Other sources may be used as well, such as mercury lamps, inert gas glow discharge (cold and heated cathode) sources, LED or laser sources. In addition, 'white' light sources using bandpass or cutoff filters may be employed. The choice may be dictated by the desired spectral range of the incident light. Light rays are shown incident on substrate 101, and reflected specularly to photodetector 103.

[0026] Additional embodiments of this innovation may include multiple light sources of the same or different types and multiple photodetectors of the same or different types. The different types may be used to detect more accurately particular wavelengths of interest. For example, a light source and/or photodetector tuned to more accurately identify blue wavelengths in conjunction with a light source and/or photodetectors tuned to more accurately identify green and or red wavelengths may provide accurate information about the

characteristics of the coating without having to integrate over the whole spectrum. Such specially tuned light sources and/or photodetectors may operate in parallel or sequentially to each other in the measurement process.

[0027] This is shown in Fig. la, where secondary photodetector 104 is positioned to gather peripheral light emanating from source 102. Signals from photodetectors 103 and 104 are routed to signal processing board 105 via cables 106. Board 105 is also in electronic or electrical communication with light source 102 via a cable (106). In addition, board 105 is in electronic communication with display 107. An additional output port 113 is shown on board 105, where output port may be a USB port, RS232 port or a parallel port for data exchange with an external computing device. In other embodiments, a wireless communication IC, such as a Bluetooth, cellular or wifi IC may also be included for wireless communication with an external computing device or the internet.

[0028] In other embodiment of this innovation, one or more secondary photodetectors may be used in conjunction with the primary photodetector to measure and monitor the light output from the one or more light sources themselves, and feed data back to the microprocessor in order to correct for light source fluctuations or light source drift that can change the reflection measurements This is shown in Fig. lb, where photodetector 103 is replaced by lens 108. Lens 108 gathers reflected light and focuses it to the entrance of an optical fiber coupler 109. Light is then guided via optical fiber 110 to spectrometer or spectrophotometer 111, which is shown to be tied to board 105 via cable 106. Board 105 may comprise a microprocessor that reads spectral data from spectrometer 111 on command. Other embodiments of the instant innovation may comprise a combination of spectrometer 111 and photodetector 103. An example of a suitable miniature spectrometer to fulfill this role is an Avantes AvaSpec Micro, the STS Microspectrometer from Ocean Optics, to name a few of a number of suitable devices.

[0029] In Fig. 2a, the basic schema of the innovative portable sensor is again shown, with substrate 201 illuminated by light source 202, and reflecting light to photodetector 203, which feeds its signal to signal processing board 204. According to the innovation, the spot size cross- sectional area is at least 1 cm² in area. In Fig. 2b, a zoom view of the region illuminated by the incident light is shown. The illuminated region has a plurality of non-uniformities in a portion of coated substrate, where a plurality of small asperities and thin areas are present, resulting in micro-variations of coating thickness. In this embodiment, photodetector 203 is not adapted to spatially resolve the light impinging upon it. Individual light rays reflected from the totality of these micro-variations may be integrated when collected at the photodetector 203 such that the intensity variations in the individual light rays are spatially averaged as to a single signal level. Photodetector 203 may comprise a spectrometer, adapted to resolve light intensity as a function of wavelength. Alternatively, photodetector may comprise a photodiode or phototransistor adapted to yield a voltage level corresponding to the averaged light intensity of the reflected light. Filters, such as bandpass or cutoff filters, may furthermore be used to block portions of the light spectrum in conjunction with a photodiode or phototransistor detectors to approximate a spectrometer. [0030] Referring again to Fig. 2a, the signal generated by photodetector 203 is fed to signal processing circuit 204, which is in electronic communication with photodetector 203. In Fig. 3, a coating apparatus 300 of the type described in co-pending U.S. Patent Application 14/668,956, incorporated herein in its entirety, is shown moving along substrate 301. The speed and trajectory of coating apparatus 300 may be fully manually controlled by a human operator, or may be at least partially controlled automatically, with some degree of guidance or handling by a human operator. Coating apparatus 300 comprises coating heads 302 and a mounted embodiment of the instant innovation 303. An arrow shows the direction of travel by apparatus 300. The instant innovation (portable sensor) 303 is shown mounted on the chassis 304 of coating apparatus 300, where it extends over aft or rear portion.

[0031] In Fig. 4, a detailed side sectional view of the innovative portable sensor 400 based on the mounted embodiment 203 of Fig. 2. Portable sensor 300 as described in the instant disclosure is shown mounted on the rear side of chassis 401 of the mobile coating apparatus. Also shown affixed to chassis 401 is coating head 402 and motor 403 that is coupled to wheel 304. Portable sensor 400 is shown as a side sectional view, revealing internal components. These components comprise light source 405 and photodetector 406, where source 305 shines a wide beam of light making a spot size with a cross-sectional area of at least 1 cm², on the surface of substrate 409. Light is reflected from substrate 409 to photodetector 406.

[0032] As specified above, photodetector 406 may be a spectrometer adapted to scan over a range of wavelengths, or a photodiode or phototransistor that integrates light intensities over a large range of wavelengths. As described above, the raw signal from photodetector 406 is fed to signal processing board 407, comprising a microprocessor and an on-board memory. The microprocessor may execute algorithms stored in on-board memory that digitize the analog signal to binary data, then analyze the data as photometric measurements such as spectral data, or overall reflectance data to show changes in surface reflectance before and after application of a coating solution by the coating apparatus. The analysis routines may require baseline data for comparison, thus requiring a measurement of the uncoated substrate or of a previously coated substrate. Before-and-after data may be compared, and changes in the spectral characteristics or reflectance values may be correlated to coating characteristics, such as film thickness.

[0033] For this conclusion, a look-up table may be employed by the microprocessor, or calculation formulas may be employed as part of the algorithm. As an example, a red shift in the reflectance spectrum may indicate that the film is too thick. The algorithms may then generate feedback control data that may be output as human-readable values, or as command signals to motor drive electronics, forming a closed control loop with the motor drive. Referring to Fig. 4, signal processing board 407 is shown in electronic communication with drive electronics of motor 403 via signal cable 408. The command signals may command the motor to slow down, since the film thickness decreases at slower speeds of the mobile coating apparatus.

[0034] An embodiment of the above description is shown more explicitly in the diagram of Fig. 5, showing a control system 500 for a mobile coating apparatus, for example, as described in co-pending U.S. Patent Application 14/668,956, the contents of which are incorporated herein in their entirety. The exemplary mobile coating apparatus control system 500 may be governed partially or fully by microprocessor 501, which may be physically incorporated on signal processing board 502.

[0035] Microprocessor 501 is shown to be in electronic communication with both

photodetector/spectrometer 503 and motor controller electronics board 504. Analog voltage or current signals issuing from photodetector/spectrometer 503 may be digitized to binary code by an analog to digital converter (ADC) unit residing on photodetector 503 itself, or by an ADC integrated on the microprocessor chip, or by a separate ADC unit residing on signal processing board 502. Raw analog signals generated by photodetector/spectrometer 503 may constitute photometric data, wherein the photometric data may comprise spectral information, or at least integrated light intensity information. The photometric data in turn relate characteristics of the coating, in the uncured or cured state, such as total reflectance, spectral reflectance, and indirect measurements such as film thickness and roughness. Conversion of photodetector signals into binary format may constitute photometric data, read by microprocessor 501.

[0036] Consequently, microprocessor 501 may issue motor control commands generated by one or more algorithms embodied in software stored in a RAM or ROM accessible by microprocessor 501, where the algorithms process the output of photometric data from photodetector/ spectrometer 503. Commands issued by microprocessor 501 may be received by motor control electronics board 504 in the form of continuous analog voltage levels or voltage pulses to drive a stepper motor or a dc motor, either type shown schematically by motor 505. Both motor direction and speed may be controlled by motor control electronics board 504. The control circuitry constitutes a closed-loop embodiment of the mobile coating apparatus control system, which is automatic control based on decisions made by algorithms embodied in the software executed by microprocessor 501.

[0037] In another embodiment, the mobile coating apparatus control system may be an open- loop control system. Microprocessor 501 is also shown to be in electronic communication with human-readable display 506, whereas motor control electronics board 502 is shown also to be in electronic communication with manual motor control console 507. In the open-loop control scheme, a human operator may read output displayed on human-readable display 506, which may be a serial or parallel input LCD display. In the example shown in Fig. 5, a selection switch 508 is provided to select between manual control or microprocessor control of the motor controller electronics. To facilitate manual coating process control, the analysis algorithms embodied by software stored on a RAM or ROM accessible to microprocessor 501 may be adapted to communicate process optimization recommendations that are electronically displayed to the human operator, using human-readable display 506 disposed on a hand-held or apparatus -mounted innovative portable sensor, as an example. Microprocessor 501 may also be in electronic communication with a wireless network interface (not shown) adapted to transmit data over the internet wirelessly in some embodiments for display on a computing device.

[0038] Characters output from microprocessor 501 to human-readable display 506 may be in a format understandable to the human operator, and indicate, for example, recommendations of motor speed and/or direction may be controllable by the human operator, in order to maintain optimized coating quality. The decision as to what speed the apparatus should be travelling along the substrate, for example, may be based on photometric data generated by photodetector/spectrometer 503. By way of example, the photometric data may indicate coating thickness, which may be dependent on the speed of the apparatus. These

recommendations may also include exhortations to decrease the viscosity of the coating solution, and or change the make-up coating to optimize coating performance. In the open-loop control embodiment, control data are output to the human operator by means of human- readable display 506. The human operator may read and interpret the control data, and control the speed and direction of motor 505 by means of manual motor control console 507. Rotary manual speed control 509 may comprise a potentiometer or a rotary encoder. Other forms of manual control may be used, such as a linear slider potentiometer. Double throw switch 510 may be manipulated to control motor direction, causing the mobile coating apparatus to advance in the forward direction or reverse.

Example of Method of Use

[0039] An example of how the instant innovation is employed will now be described. A substrate such as a photovoltaic panel may be deployed in an array or individually in an outdoor setting. It is desired to retrofit the panel with an anti-reflective coating, for which a coating apparatus of the type disclosed in co-pending U.S. Non-provisional Patent Application No. 14/668,956 is provided. This coating device may comprise wheels and coating heads such that it may be deployed to roll over a photovoltaic panel and deposit a liquid coating pre-cursor solution that is to be cured after application.

[0040] An operator equipped with a portable version of the innovative portable light reflectance sensor may deploy it on the panel surface before the coating is applied, to obtain a baseline measurement of percent reflection of incident light as the photometric data. After the baseline measurement, the coating is applied by the coating apparatus. A second percent reflection measurement is then taken. Data from both measurements are digitized by the signal processing circuit and stored in an on-board memory.

[0041] The data are then processed by the signal processing circuitry on-board the instant portable sensor, as described above, where the two measurements are compared. A change in percent reflection obtained, with data from the second measurement correlated to the state of the newly applied coating solution. The signal processing circuit then displays the information to the operator. If the coating is too thick or thin, instructions or recommendations are displayed to the operator as a method of feeding back to the operator in control to adjust the speed of the coating apparatus, or to alter the viscosity of the coating solution. The information may also be conveyed by connection to a laptop computer, or wirelessly to a smart phone in possession of the operator at the site, or to personnel at a remote site.

[0042] The embodiments of the innovation disclosed and described above are exemplary, and by no means are meant to be construed as limiting the innovation. It is recognized by persons skilled in the art that other variations are possible without departing from the scope and spirit of the innovation, as claimed in the claims below.

Claims

1. A portable sensor for determining characteristics of thin film coatings applied to a substrate, comprising:

(i) a light source adapted to illuminate a region of a substrate with a spot cross-sectional area of at least 1 cm², at the substrate surface;

(ii) a photodetector adapted to collect at least a portion of the light emanating from said light source that is reflected from said substrate surface, said photodetector adapted to output an electronic signal proportional to one or more characteristics of the reflected light; and

(iii) a signal processing circuit in electronic communication with the photodetector, wherein said processing circuit is adapted to read and process the electronic signal output by the photodetector.

2. The portable sensor of claim 1, wherein the signal processing circuit is further adapted to extract photometric data from said electronic signal output by the photodetector.

3. The portable sensor of claim 2, wherein the photometric data are measurement data of reflection intensity from a substrate surface.

4. The portable sensor of claim 2, wherein the photometric data are an array of measurement data of spectral intensity over a wavelength range from a substrate surface.

5. The portable sensor of claim 2, wherein the photometric data are measurement data of percent reflection from a substrate surface.

6. The portable sensor of claim 2, wherein the photometric data are measurement data of averaged spectral intensity over a wavelength range from a substrate surface.

7. The portable sensor of claim 2, wherein the signal processing circuit is further adapted to compare photometric data captured from the photodetector on successive read operations.

8. The portable sensor of claim 2, wherein the signal processing circuit is further adapted to correlate the data extracted from the photodetector signal to one or more characteristics of a thin film coating at the time of processing the signal output by the photodetector.

9. The portable sensor of claim 8, wherein the signal processing circuit is further adapted to output at least one of the one or more correlated characteristics of a thin film coating in a human-readable format.

10. The portable sensor of claim 9, wherein the signal processing circuit outputs the at least one of the one or more correlated characteristics of the thin film coating in a human-readable format to a human-readable display.

11. The portable sensor of claim 8, wherein the signal processing circuit outputs the at least one of the one or more correlated characteristics of the thin film coating to an external computing device.

12. The portable sensor of claim 11, wherein the external computing device is accessed wirelessly.

13. The portable sensor of claim 8, wherein the signal processing circuit outputs the at least one of the one or more correlated characteristics of the thin film coating to an external storage device.

14. The portable sensor of claim 13, wherein the external storage device is accessed wirelessly.

15. The portable sensor of claim 1, wherein the substrate is a photovoltaic panel coated with an energy enhancement film.

16. The portable sensor of claim 15, wherein the energy enhancement film is an antireflection coating.

17. The portable sensor of claim 1, wherein the substrate is a photovoltaic panel which is part of an outdoor photovoltaic panel array.

18. A substrate coating system, comprising:

(i) a substrate coating apparatus having a means for applying a liquid precursor of an coating to said substrate;

(ii) a means for controlling said substrate coating apparatus;

(iii) a portable sensor, comprising: (a) a light source adapted to illuminate a region of a substrate with a spot size of at least 1 cm² at the substrate surface;

(b) a photodetector adapted to collect at least a portion of the light emanating from said light source that is reflected from said substrate surface; and

(c) a signal processing circuit in communication with the photodetector, wherein said processing circuit is adapted to perform read operations to capture the signal read from the photodetector; and

(iv) a means for controlling said substrate coating apparatus based on analysis of photometric data.

19. The substrate coating system of claim 18, wherein the signal processing circuit is further adapted to extract photometric data from said captured portable sensor signal.

20. The substrate coating system of claim 18, wherein the substrate is the surface of a photovoltaic panel.

21. The substrate coating system of claim 18, wherein the photovoltaic panel is part of an outdoor photovoltaic panel array.

22. A method for using a portable sensor for determining characteristics of thin film coatings applied to a substrate, comprising the steps of:

(i) providing a substrate adapted to receive an energy enhancement coating;

(ii) providing a substrate coating system, comprising:

(a) a substrate coating apparatus having a means for applying a liquid precursor of a coating to said substrate;

(b) a means for controlling said substrate coating apparatus;

(c) a portable sensor, comprising:

(i) a light source adapted to illuminate a region of a substrate with a spot cross-sectional area of at least 1 cm² at the substrate surface;

(ii) a photodetector adapted to collect at least a portion of the light emanating from said light source that is reflected from said substrate surface; and

(iii) a signal processing circuit in communication with the photodetector, wherein said processing circuit is adapted to perform read operations to capture the signal read from the photodetector; and

(d) a means for controlling said substrate coating apparatus based on analysis of

photometric data.

(iii) obtaining a first set of photometric data from the substrate, wherein light from the light source of said portable sensor is reflected off of the substrate surface to the photodetector of said portable sensor from at least one position on said substrate, said first set of photometric data processed by said signal processor circuit;

(iv) applying an energy enhancement coating to the substrate;

(v) obtaining a second set of photometric data from the substrate, wherein light from the light source of said portable sensor is reflected off of the coated substrate surface to the

photodetector of said portable sensor from at least one position on said substrate;

(vi) comparing the first and second sets of photometric data, and correlating this comparison of the data to one or more of the characteristics of the coating; and vii) adjusting the means for controlling said substrate coating apparatus based on at least one of the one or more correlated characteristics of a thin film coating.

23. The method of claim 22, wherein the step of adjusting the means for controlling said substrate coating apparatus comprises reading, by a human operator, data displayed on a display device to said human operator, wherein the human operator manually adjusts control parameters of the means for controlling said substrate coating apparatus according to the data displayed.

24. The method of claim 22, wherein the step of adjusting the means for controlling said substrate coating apparatus comprises a closed loop control system comprising a

microprocessor that determines the adjustments based on analysis of photometric data.

25. The method of claim 22, wherein the step of adjusting the means for controlling said substrate coating device comprises making adjustments to the rate of deposition of coating solution from the substrate coating apparatus for optimizing the performance-enhancement properties of the coating.

26. The method of claim 22, wherein said photometric data are spectrally resolved intensity measurement data over a range of wavelengths.

27. The method of claim 22, wherein said photometric data are percent reflectance measurement data.

28. The method of claim 22, wherein said substrate is a surface of a photovoltaic panel.

29. The method of claim 28, wherein the photovoltaic panel is part of an outdoor photovoltaic panel array.