Modular low cost trackerless spectral sensor

Abstract

A non-tracking solar sensor device and systems. The non-tracking solar sensor system includes a transparent hemispherical dome enclosure for receiving light. A diffuser is disposed with the enclosure for diffusing the light. A photodiode sensor array senses at least one discrete wavelength of the diffused light. A data acquisition module is configured to receive a sensor signal from the sensor array, the signal indicative of light quality at least one discrete wave band for processing via a processor module.

Claims

1. A non-tracking solar sensor system, comprising: a housing; a lens disposed at one end of the housing for collecting solar irradiance; a grating that disperses light into different spectral orders; a collimating lens disposed between the lens and the grating; a linear detector array disposed at an opposite end of the housing; and a focusing lens disposed between the grating and the linear detector array; wherein the linear detector array comprises: a first photodiode sensor disposed within the housing portion, a filter wheel positioned intermediate the first photodiode sensor, the first photodiode sensor arranged to receive filtered light; and a second photodiode sensor disposed on an exterior of the housing and arranged to sense an unfiltered light.

2. The system of claim 1, further comprising: a data acquisition module for receiving data from the linear detector array.

3. The system of claim 1, wherein the focusing lens focusses dispersed light onto the linear detector array.

4. The system of claim 1, further comprising: a computer system that receives digital data from the data acquisition module for processing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The application will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which:

(2) FIG. 1 is an exemplary solar spectral irradiance profile for a solar cell site.

(3) FIG. 2 shows an exemplary embodiment of a non-tracking spectral irradiance sensor including a filter wheel.

(4) FIG. 3 shows an exemplary embodiment of a non-tracking solar sensor using the sensor of FIG. 2.

(5) FIG. 4 shows an alternate exemplary embodiment of a non-tracking solar sensor with a custom collimating and focusing lens, using the sensors of FIG. 2.

(6) FIG. 5 shows a comparison graph of the extraterrestrial spectral irradiance a transmittance profile of the measured spectral irradiance.

(7) FIG. 6 shows the reconstructed spectrum from the Spectral Transmission Model provides a close correspondence with the full-band measured spectrum.

(8) FIG. 7 shows a comparison of short circuit current between the EKO spectrometer and the measured photodiode data with spectral reconstruction using the Spectral Transmission Model of the present disclosure.

(9) FIG. 8 shows an alternate embodiment of a non-tracking solar sensor system.

DETAILED DESCRIPTION OF THE INVENTION

(10) Before turning to the figures which illustrate the exemplary embodiments in detail, it should be understood that the application is not limited to the details or methodology set forth in the following description or illustrated in the figures. It should also be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting.

(11) Referring to FIG. 1, a typical solar spectral irradiance for Albuquerque, N. Mex. is shown. Responsivity of a silicon solar cell, and the possible discrete solar wavelengths that will be measured with the discrete spectral sensor are illustrated in FIG. 1. FIG. 1 shows an exemplary solar spectral irradiance 100, and the responsivity curve of a Silicon solar cell. The vertical lines represent the monitored discrete bands 102. The discrete spectral bands 102 are typically 10 nm wide, except for the band 102 at 500 nm which is 40 nm wide. A spectrometer measures the solar spectrum at a high resolution (1-2 nm). The spectrometer typically uses two different sensors. One sensor measures short wavelengths and another sensor measures longer wavelengths, or infrared radiation (IR). The disclosed system and methods apply a spectral sensor to measure sunlight at several discrete wavelengths, e.g., five or six discrete wavelengths. These discrete wavelengths are predetermined based on solar spectral analysis. Five discrete wavelengths are sufficient for full spectrum reconstruction. The solar spectral bands having the greatest relevance for the spectrometer are determined, e.g., based on aerosols, particulates, and precipitable water in the atmosphere. It should be noted that the disclosed embodiments may be modular and therefore are reconfigurable for selectively sensing solar irradiance in predetermined bands. By interchanging the modular photodiodes or filters the solar spectrometer can be tuned as desired to focus on wavelengths or bands of interest for the particular application.

(12) In an embodiment, five measurements of the solar spectrum are suitable to accurately reconstruct a profile of the solar spectrum. In an exemplary embodiment the discrete wavelengths within the silicon (Si) responsivity curve may be limited. The wavebands may be extended into the infrared radiation band for other PV technologies or sensor applications.

(13) The non-tracking spectral sensor eliminates the need for a two-axis tracker. A non-tracking sensor may be used in, e.g., PV plant facilities without access to two-axis trackers. With the modular versatility for a wide variety of spectral filters that can be utilized for analyzing discrete bands across the entire spectrum, as well as the utility of a fixed position sensor, a stationary spectral sensor may be implemented for a variety of locations and applications in many of atmospheric conditions.

(14) Referring to FIG. 2, an embodiment of a non-tracking spectral irradiance sensor 10 including a filter wheel is shown. Spectral irradiance sensor 10 may measure up to twelve bands using just one photodiode sensor module 10. A horizontally aligned filter wheel 12 is disposed within an opaque cylindrical enclosure or housing 11 open at an end 15 and having a transparent quartz window 13 covering the opening 15, for admitting solar irradiance. Filter wheel 12 is disposed above a photodiode sensor 14, e.g., a spectrum selective Si photodiode sensor. Sensor 14 collects data at predetermined intervals, e.g., every twenty seconds. In an embodiment a second sensor 16 may also be utilized, second sensor is not equipped with a filter wheel 12. Second sensor 16 monitors unfiltered, i.e., clear-sky irradiance measurements. If second sensor 16 does not detect clear-sky conditions, the sensor may transmit a signal to disable primary sensor 14, beneath filter wheel 12, to prevent it from operating, for ensuring the highest quality in data. Filter wheel 12 is linked mechanically to a motor 17 by a shaft 19, for rotating the position of wheel within enclosure 11.

(15) Referring next to FIG. 3 one embodiment for a non-tracking solar sensor is shown. A dome enclosure 20 is disposed above a diffuser 22 and a photodiode sensor array 24. The incident solar radiation indicated by arrows 26, 28, 30, is collected within dome enclosure 20. Inside dome enclosure 20 are diffusing elements 22 and baffles 32, which direct uniform solar radiation 26, 28, 30, to sensor array 24. Sensor array 24 includes multiple solar sensors 10 (FIG. 2) at the bottom of dome enclosure 20. Dome enclosure 20 is substantially transparent and collects and integrates the incident solar radiation. Sensors transmit analog signals to a data acquisition module 25. Data acquisition module 25 converts the analog signals to digital data and forwards, e.g., via data link 27, to a computer system, e.g., PC or server, for processing the digital data.

(16) Referring next to FIG. 4, an alternate embodiment for a non-tracking solar sensor is shown. Incident solar radiation 26, 28, 30 is collected with a custom lens 40. A small exit port 42 at the bottom of the lens directs a portion of solar radiation light 26-30 to a collimating lens 44. Light 26-30 is collected with lens 44 and then transmitted through a grating 46. Grating 46 disperses the light into different spectral orders. A focusing lens 48 is positioned below grating 46 to receive the dispersed light, and focuses the dispersed light on a linear detector array 50. Linear detector array 50 includes a plurality of sensors 10 (FIG. 2). Analog signals may transmitted and converted to digital data for processing, as described above with respect to FIG. 3.

(17) Software is used to process the sensor data that is received by sensors 10. Sensor data is transmitted first to a data acquisition module 25 for conversion to digital formatted data for processing. Optimization algorithms are coupled with atmospheric modeling code and accurately reconstruct the solar spectrum. A regression analysis with interacting coefficients is used to predict, e.g., the PV short-circuit, directly from the sensor measurements. In an embodiment at least four wavelength bands may be used for correlation to the PV short-circuit current. The measurements over these wavebands may be used to verify the form of a short-circuit current profile.

(18) In an exemplary embodiment a spectrum reconstruction method uses a spectral transmission model based on a condensed version of developed Sandia Spectral Transmission Model based on a condensed version of Equation 1 below:

(19) $\begin{array}{cc}{I}_{\mathrm{sc},\mathrm{Meas}\mathrm{Temp}.\mathrm{Corrected}}=\frac{I_{\mathrm{sc},\mathrm{Meas}}}{1+{\alpha }_{\mathrm{Th}}\left(T_{\mathrm{cell}}-25\right)}& \mathrm{EQ}.1\end{array}$

(20) And the measured irradiance E is defined by Equation 2 below:
E=r.sup.2TE.sub.0,  EQ. 2
where E.sub.0 is the extraterrestrial irradiance at AM.sub.0 measured above the earth's atmosphere, T is the total atmospheric transmittance affected by attenuation through the atmosphere, and r is the ratio of the average to actual sun to earth distance. In turn the atmospheric transmittance T can be estimated from the measured irradiance on the ground by Equation 3:

(21) $\begin{array}{cc}T=\frac{E}{r^2{E}_0}& \mathrm{EQ}.3\end{array}$
since the extraterrestrial irradiance is fairly constant anywhere above the atmosphere.

(22) Atmospheric attenuation may be caused by aerosols, ozone, gases, water vapor, and Rayleigh scattering. Each constituent affects different parts of the spectrum. By using the calibrated values of the photodiodes as well as the respective values of E.sub.0, according to Equation 3 the respective transmission values are computed as indicated in as presented in FIG. 5 which shows a comparison graph (a) of the extraterrestrial spectral irradiance compared to the measured spectral irradiance at 11:40 am local time on Oct. 1, 2014 in Albuquerque, N. Mex., and the data from the calibrated spectral sensors, indicated by dots for the same day and time; and graph (b) shows a transmittance profile of the measured spectral irradiance shown in graph (a) and the corresponding calculated transmittance from the photodiode spectral sensors indicated by dots. Note that the r.sup.2 factor was not taken into account in the calculation.

(23) Using this calibrated data of FIG. 5, each of these transmission points may be used to optimize and compute the spectrum according to their respective time series values. This functionality of the Spectral Transmission Model computes the spectrum based on fundamental atmospheric physics. After the optimization algorithm is complete the spectrum may be calculated and compared to the spectral irradiance measured by the wide-band EKO spectrometers.

(24) Referring to FIG. 6, based on data taken at solar noon on Oct. 1, 2014, the reconstructed spectrum from the Spectral Transmission Model provides a close correspondence with the full-band measured spectrum. Calculated spectrum shown on line 60 is based on discrete photodiode measurements and computation within the Sandia Spectral Transmission Model is compared with a measured full-band spectrum 65 from an EKO spectrometer for Oct. 1, 2014. Next, using this data with Eq. 4 one is able to compare the calculated short circuit current. Referring next to FIG. 7, the results of a comparison of short circuit current between the EKO spectrometer, indicated at line 70, and the measured photodiode data with spectral reconstruction using the Spectral Transmission Model indicated at line 75, for Oct. 1, 2014 shows close agreement to within a low RMS error of 0.05.

(25) Referring next to FIG. 8, an alternate embodiment of a non-tracking solar sensor system 300 is shown. The non-tracking solar sensor system 300 includes a convex reflective mirror 302 for receiving incident white light 304, and reflecting the light 304 at an optical collimation lens 306. Collimating lens 306 directs collimated light rays at an array 314 of optical sensors 308 and filters 310. In the embodiment of FIG. 8, hemispherical reflective mirror 302 is shown placed at the bottom of system 300 to direct light 304 upwards into the detector array 314. Optical wavelength separation may be accomplished using dichroic mirrors 312. Dichroic mirrors 312 may be placed to selectively reflect predetermined portions of the solar spectrum while passing others. The ratios of signals between sensors may be used to describe the overall solar spectrum.

(26) While the exemplary embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments.

(27) The present application contemplates methods, systems and program products on any machine-readable media for accomplishing its operations. The embodiments of the present application may be implemented using an existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose or by a hardwired system.

(28) It is important to note that the construction and arrangement of the low-cost spectral sensor and analyzer, as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application.

(29) As noted above, embodiments within the scope of the present application include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media which can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

(30) It should be noted that although the figures herein may show a specific order of method steps, it is understood that the order of these steps may differ from what is depicted. Also, two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. It is understood that all such variations are within the scope of the application. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.