Patent Publication Number: US-8535821-B2

Title: Optical leak detection sensor

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/790,749, filed on May 28, 2010, which claims the benefit of U.S. Provisional Application No. 61/182,077 filed on May 28, 2009. The contents of these applications are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments disclosed herein may be directed to a sensor for detecting a fluid leak, specifically an optical sensor which detects a leak based on transmittance properties of the fluid. In particular, embodiments disclosed herein may be directed to an optical leak detection sensor for detecting a leak in a flow cell battery system. 
     2. Description of the Relevant Art 
     Reduction-oxidation (redox) flow batteries store electrical energy in a chemical form, and subsequently dispense the stored energy in an electrical form via a spontaneous reverse redox reaction. A redox flow battery is an electrochemical storage device in which an electrolyte containing one or more dissolved electro-active species flows through a reactor cell where chemical energy is converted to electrical energy. Conversely, the discharged electrolyte can be flowed through a reactor cell such that electrical energy is converted to chemical energy. Electrolyte solution is stored externally, for example in tanks, and flowed through a set of cells where the electrochemical reaction takes place. The electrolyte tanks and cells may often be stored in a housing, which offers protection for the electrolyte tanks and cells. Externally stored electrolytes can be flowed through the battery system by pumping, gravity feed, or by any other method of moving fluid through the system. The reaction in a flow battery is reversible. The electrolyte, then, can be recharged without replacing the electroactive material. The energy capacity of a redox flow battery, therefore, is related to the total electrolyte volume, e.g., the size of the storage tank. However, the electrolytes in the system and stored in the tank may be corrosive to the housing and other components of the battery, and possibly even harmful to people and the environment, if leaked to the exterior of the housing. Accordingly, it is important to monitor the components of the flow battery system for electrolyte leakage. 
     Many leakage sensors used in batteries and other environments to detect a leak of a hazardous or corrosive fluid, will detect the presence of a fluid and then provide an indication that there is a leak. However, in many instances, the fluid being detected is not indicative of a leak. Rather, the fluid may be ambient or environmental fluid, such as rain water. When a leakage sensor indicates a leak due to a fluid such as rain water, it takes time for a person to investigate the so-called leak, and determine that there is not, in fact, a leak. Accordingly, it is important to not only monitor the components of a flow battery system for electrolyte leakage, but also to discern between electrolyte solution and other fluids. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a redox flow cell battery system includes a pair of electrodes disposed in separate half-cell compartments; a porous or ion-selective membrane separating the half-cell compartments; and an electrolyte that is flowed through the half-cell compartments, wherein the electrolyte is stored in one or more electrolyte storage containers. A leak detector is positioned external to one or more of the electrolyte storage containers. The leak detector includes a device housing, the device housing having bottom surfaces. The leak detector also includes at least one light source in the device housing, the at least one light source emitting light that at least partially reflects from the bottom surfaces of the device housing, and is at least partially refracted by the bottom surfaces and fluid in contact with at least a portion of the bottom surface that the light is incident upon; and at least one light detector in the device housing, the light detector receiving the partially reflected light. 
     In accordance with some embodiments, there is provided a leak detection sensor for detecting a leakage of an electrolyte solution in a flow battery system. The sensor includes a sensor housing, the sensor housing being coupled to control electronics and is at least partially surrounded by a fluid and including a shielding member and a refractor lens, and having mounted therein at least one light source. The device also includes at least one light detector, wherein light emitted from the at least one light source is incident on the refractor lens and is at least partially refracted by an amount which is dependent on a refractive index of the refractor lens and the refractive index of the surrounding fluid, such that the amount of refraction at the refractor lens and the surrounding fluid causes a loss in a power of light detected by the at least one light detector, the light detector determines the power of the detected light, the control electronics converts the determined power into a corresponding frequency, the control electronics determine the type of fluid surrounding the device housing based on the frequency; and determines a leak if the type of fluid is determined to be an electrolyte solution. 
     Control electronics are used to control operation of the flow cell battery system, and are coupled to the leak detector. The control electronics determine the composition of fluid in contact with at least a portion of the bottom surfaces of the leak detector based on the difference between the measured light intensity and the intensity of light produced by the light source. If the determined composition of the fluid indicates the presence of the electrolyte solution, the control electronics shuts down the redox flow cell battery system. 
     In an embodiment, a method of detecting a fluid leak in a redox flow cell battery system, the redox flow cell battery system comprising a pair of electrodes disposed in separate half-cell compartments; a porous or ion-selective membrane separating the half-cell compartments; and an electrolyte that is flowed through the half-cell compartments, wherein the electrolyte is stored in one or more electrolyte storage containers, and a leak detector is positioned external to one or more of the electrolyte storage containers. The leak detector includes a device housing, the device housing including bottom surfaces; at least one light source in the device housing; and at least one light detector in the device housing. During use, light is emitted from the light detector. The emitted light is at least partially reflected from the bottom surfaces of the device housing, and is at least partially refracted by the bottom surfaces and fluid in contact with at least a portion of the bottom surface that the light is incident upon. At least a portion of the at least partially reflected and partially refracted light is detected using at least one of the light detectors. The composition of fluid in contact with at least a portion of the bottom surfaces of the leak detector is determined based on the difference between the measured light intensity and the intensity of light produced by the light source. 
     In another embodiment, a leak detector includes a device housing, the device housing comprising bottom surfaces; at least one light source in the device housing, the at least one light source emitting light that at least partially reflects from the bottom surfaces of the device housing, and is at least partially refracted by the bottom surfaces and fluid in contact with at least a portion of the bottom surface that the light is incident upon; and at least one light detector in the device housing, the light detector receiving the partially reflected light; and control electronics coupled to the leak detector. The control electronics determine type of fluid in contact with at least a portion of the bottom surfaces of the leak detector based on the difference between the measured light intensity and the intensity of light produced by the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description of embodiments and upon reference to the accompanying drawings in which: 
         FIG. 1  depicts a flow battery system; 
         FIG. 2  is a diagram depicting a sensor for detecting fluid leakage; 
         FIG. 3  is a flowchart depicting a method of detecting fluid leakage; 
         FIG. 4  is a diagram depicting a sensor for detecting fluid leakage; 
         FIG. 5  is a diagram depicting the refraction of a light within a sensor; and 
         FIG. 6  is a diagram depicting a sensor for detecting fluid leakage used in a flow battery system. 
         FIGS. 7A ,  7 B, and  7 C illustrate top, cross-section, and bottom views of a shielding member illustrated in  FIG. 6 . 
     
    
    
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood the present invention is not limited to particular devices or methods, which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include singular and plural referents unless the content clearly dictates otherwise. 
     Reference will now be made in detail to embodiments disclosed in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates a flow battery system  100  according to some of the embodiments described herein. As shown, flow battery system  100  includes two half-cells  108  and  110  separated by a membrane  106 . An electrolyte  124  is flowed through half-cell  108  and an electrolyte  126  is flowed through half-cell  110 . Half-cells  108  and  110  include electrodes  102  and  104  respectively, in contact with electrolytes  124  and  126 , respectively, such that redox reactions occur at the surface of the electrodes  102  or  104 . In some embodiments, multiple flow battery systems  100  may be electrically coupled (e.g., stacked) either in series to achieve higher voltage or in parallel in order to achieve higher current. As shown in  FIG. 1 , electrodes  102  and  104  are coupled across load/source  120 , through which electrolytes  124  and  126  are either charged or discharged. The operation of a flow cell and the composition of a membrane is further described in U.S. patent application Ser. No. 12/217,059, entitled “Redox Flow Cell,” filed on Jul. 1, 2008, which is incorporated herein by reference. Construction of a flow cell stack is described in U.S. patent application Ser. No. 12/577,134, entitled “Common Module Stack Component Design” filed on Oct. 9, 2009, which is incorporated herein by reference. 
     When filled with electrolyte, one half-cell (e.g.,  108  or  110 ) of flow battery system  100  contains anolyte  126  and the other half-cell contains catholyte  124 , the anolyte and catholyte being collectively referred to as electrolytes. Reactant electrolytes may be stored in separate tanks and dispensed into the cells  108  and  110  via conduits coupled to cell inlet/outlet (I/O) ports  112 ,  114  and  116 ,  118  respectively, often using an external pumping system. Therefore, electrolyte  124  flows into half-cell  108  through inlet port  112  and out through outlet port  114  while electrolyte  126  flows into half-cell  110  through inlet port  116  and out of half-cell  110  through outlet port  118 . 
     At least one electrode  102  and  104  in each half-cell  108  and  110  provides a surface on which the redox reaction takes place and from which charge is transferred. Suitable materials for preparing electrodes  102  and  104  generally include those known to persons of ordinary skill in the art. Examples of electrodes  102  and  104  are also described in U.S. patent application Ser. No. 12/576,235, entitled “Magnetic Current Collector” filed on Oct. 8, 2009, which is incorporated herein by reference. Flow battery system  100  operates by changing the oxidation state of its constituents during charging or discharging. The two half-cells  108  and  110  are connected in series by the conductive electrolytes, one for anodic reaction and the other for cathodic reaction. In operation (i.e., charge or discharge), electrolytes  126  and  124  (i.e., anolyte or catholyte) are flowed through half-cells  108  and  110  through I/O ports  112 ,  114  and  116 ,  118  respectively as the redox reaction takes place. Power is provided to a load  120  or received from power source  120 , depending on if the flow cell battery is in discharging or charging mode, respectively. 
       FIG. 2  depicts a sensor  100  for detecting fluid leakage. As shown in  FIG. 2 , sensor  100  includes a sensor housing  102  which is at least partially surrounded by a fluid  104 . In an embodiment, sensor housing  102  may be made of any suitable material which is resistant to corrosion (e.g., polyethylene glass or an acrylic material). In an embodiment, sensor  100  may be positioned in a flow battery system having flow battery cells and electrolyte tanks (such as the flow battery system depicted in  FIG. 1 ). When positioned in a flow battery system, sensor  100  may be positioned at a location in a cavity of the flow battery system that is external to the electrolyte tanks In particular, sensor  100  may be placed in the flow battery system in a cavity which is at a position which is below the electrolyte tanks so as to detect any leakage of the electrolyte solution, as shown in  FIG. 6 . In some embodiments, multiple sensors  100  may be placed at different locations within the flow battery system, internal and/or external to the electrolyte tanks 
     Sensor  100  further includes a light source  106  which emits light  108 . Light source  106  may be, for example, a light emitting diode (LED) or a laser. Light  108  is incident on bottom surfaces  110  of sensor housing  102 , wherein the light  108  is at least partially reflected  112 , and partially transmitted  114  into fluid  104 . In an embodiment, bottom surfaces  102  of sensor housing  102  may be surfaces of a refractor lens. As shown in  FIG. 2 , partially transmitted light  114  is refracted by a predetermined angle as it enters fluid  104 , as will be discussed in detail below. Sensor  100  further includes light detector  116 , which may detect partially reflected and refracted light  112 . Light detector  116 , for example, may be a photodiode. As further discussed in detail below, partially reflected and refracted light  112  has a power or intensity which depends on the refraction of emitted light  108  by fluid  104 , which is indicative of the type of fluid  104  surrounding sensor housing  102 . Light detector  116  measures this power, from which the type of fluid  104  surrounding sensor housing  104  may be determined. In an embodiment, light detector  116  converts the power or intensity of refracted light  112 , and converts the power or intensity into a frequency, the frequency being used to determine the type of fluid  104  surrounding housing  102 . 
     As further shown in  FIG. 2 , light detector  116  is partially shielded from light source  106  by shielding member  118 . Shielding member  118  may prevent stray photons from emitted light  108  from being detected by light detector  116 . Shielding member  118 , in one embodiment, includes apertures  119 , positioned in optical alignment with light source  106  and light detector  116 . Top, cross-section and bottom views of shielding member  118  are depicted in  FIGS. 7A ,  7 B and  7 C, respectively. 
     Light source  106  and light detector  116  may also be coupled to external control electronics and controls in a control box  120 , which may provide a control signal for emitting light  108  at a predetermined power and wavelength, and may further receive a signal from light detector  116  indicative of the power, or frequency of partially reflected and refracted light  112 , and perform calculations to determine the type of fluid  104  surrounding sensor housing  102 . The intensity or wavelength of detected light may be manifested as a current, voltage, or frequency that is produced by the detector. Control electronics may be embodied in a processor that includes processor-accessible storage medium configured to store instructions to be executed by a processor. Generally speaking, a processor-accessible storage medium may include any storage media accessible by a processor during use to provide instructions and/or data to the processor. For example, a processor accessible storage medium may include storage media such as magnetic or optical media, e.g., disk (fixed or removable), tape, CD-ROM, or DVD-ROM, CD-R, CD-RW, DVD-R, DVD-RW, or Blu-Ray. Storage media may further include volatile or non-volatile memory media such as RAM (e.g. synchronous dynamic RAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.) SDRAM, low-power DDR (LPDDR2, etc.) SDRAM, Rambus DRAM (RDRAM), static RAM (SRAM), etc.), ROM, Flash memory, non-volatile memory (e.g. Flash memory) accessible via a peripheral interface such as the Universal Serial Bus (USB) interface, etc. Storage media may include storage media accessible via a communication medium such as a network and/or a wireless link. 
       FIG. 3  is a flowchart illustrating a method  200  of detecting fluid leakage and will be discussed in conjunction with  FIG. 2  to illustrate the operation of sensor  100  shown in  FIG. 2 . Sensor  100  is first placed in a desired location ( 202 ). In an embodiment, sensor  100  may be used in a flow battery system, and thus may be placed in a flow battery system enclosure. Light source  106  emits light  108  ( 204 ), which is at least partially reflected by bottom surfaces  110 , and at least partially refracted by any fluid  104  disposed in the illuminated portion of the enclosure. Light detector  116  detects partially reflected light  112  ( 206 ), and measures a power of partially reflected light  112  ( 208 ). The measured power may then be converted into a corresponding frequency ( 210 ). From the frequency, the type of fluid  104  surrounding sensor housing  102  ( 212 ) may be determined. In embodiments where sensor  100  is used in a flow battery system, light detector  116  or external electronics may determine if fluid  104  is an electrolyte solution ( 214 ), thereby indicating a leak of the electrolyte solution. If fluid  104  is determined to be an electrolyte solution, light detector  116  or external electronics may trigger an alarm ( 216 ), so that a user or operator may be informed of the leak and take measures to contain or fix the leak. If fluid  104  is determined to not be an electrolyte solution, sensor  102  will emit light  108  to continue to monitor for leaks. In alternate embodiments, an indication of a leak condition may also be displayed to indicate that a leak is present, regardless of whether the leak is an electrolyte or other fluid. In some embodiments, light  108  may be emitted periodically or continuously. In addition, light  108  may be emitted on command from a user or operator. 
       FIG. 4  is a diagram illustrating a sensor  300  for detecting fluid leakage according to some embodiments. Sensor  300  is nearly identical to sensor  100  shown in  FIG. 2 , and operates in a nearly similar manner, and therefore the structure and operation of sensor  300  that is identical to sensor  100  is not be repeated herein. As shown in  FIG. 4 , sensor  300  includes a beam splitter  302  which is interposed between light source  106  and bottom surfaces  110 . Beam splitter  302  diverts a portion of light  108  to a second light detector  304 , which may be optically coupled to first light detector  306  or to external electronics. Consistent with at least this embodiment, second light detector  304  receives light  108  in its unattenuated state, having its initial intensity and wavelength. Light  108  detected by second light detector  304  may be used to provide an accurate reading of the initial power, wavelength, frequency, etc. of light  108 , which may then be provided to external electronics in control box  120  to establish a baseline for use in comparing with partially reflected and refracted light  112  received at first light detector  306 . In some embodiments, second light detector  304  may be coupled with first light detector  306  to provide a differential measurement of the power of partially reflected and refracted light  112  for determining the type of fluid  104  surrounding sensor housing  102 . 
     As discussed above, fluid  104 , may be any type of fluid, and embodiments disclosed herein may distinguish between the types of fluids. For example, fluid  104  may be air, which may be indicative that areas of the flow battery system external to the electrolyte tanks are dry and that no leak is present. Fluid  104  may also be an electrolyte solution, indicating that there is a leak. However, fluid  104  may be a different type of fluid, in particular, water. The presence of water in a flow battery system may be attributed to condensation, rain, or groundwater seepage, but does not indicate that the electrolyte tanks are leaking Accordingly, embodiments disclosed herein not only detect the presence of a fluid, but also may distinguish between different fluids such that a leak is detected only when the electrolyte solution has begun collecting in the areas of the flow battery system external to the electrolyte tanks Embodiments disclosed herein distinguish between different types of fluids using the known refractive index n of fluids. 
     Isotropic media such as water, air, and electrolyte solution, have different refractive indices, which are determined by the decrease or increase in velocity of light as it enters the medium. This refractive index, n, is determined by n=c/V where c is the speed of light in a vacuum, and V is the phase velocity of the light wave in the medium. The refractive indices n of many common materials are known. For example, the refractive index n of air is 1, the refractive index n of water is 1.333, the refractive index n of glass is 1.5, and the refractive index n of an electrolyte solution such as used in a flow battery system is about 1.35-1.55, depending on the concentration of the electrolyte in the solution. When light is incident at a boundary between two different dielectric media, the light is at least partially reflected and partially refracted. The Law of Reflection states that the angle of incidence at this boundary is equal to the angle of reflection from the boundary. The refraction of the light is dependent on the increase or decrease of velocity of the light in that medium. The refraction may produce a change in an angle of the light such that n i  sin θ i =n t  sin θ t , n i  being the refractive index of the first medium, θ i  being the angle of incidence, n t , being the refractive index of the second medium, and θ t , being the angle of the light transmitted in the second medium. This is known as Snell&#39;s Law. 
       FIG. 5  is a diagram illustrating the refraction of a light within a sensor. As shown in  FIG. 5 , light  108  is incident on bottom surface  110  at a first area A 1 , at an angle of incidence θ i1 , reflected from bottom surface  110  at an angle of reflectance θ r1  which is equal to the angle of incidence, and transmitted into the material of bottom surface  110  at an angle of transmission θ t1 . In embodiments such as those shown in  FIG. 5 , bottom surface  110  has a non-negligible thickness such that refraction occurs as light  108  is incident on bottom surface  110 . However, in some embodiments, bottom surface  110  has a negligible thickness, which does not cause substantial diffraction, such that diffraction only occurs as if light  108  were incident on fluid  104 . In some embodiments, light  108  may be directed into bottom surface  110  by a waveguide or fiber optics made of the same material as bottom surface, such that no refraction occurs when light  108  is incident on bottom surface  110 . 
     Returning to  FIG. 5 , the light transmitted into bottom surface  110  is incident on fluid at a second area A 2 , at an angle of incidence θ i2 , which is equal to θ t1 , reflected off bottom surface  110  at an angle of reflectance θ r2  which is also equal to the angle of incidence, and transmitted into fluid  104  at an angle of transmission θ t2 . The light reflected off fluid  104  is again incident on bottom surface  110  at a third area A 3 , at an angle of incidence θ i3 , which is equal to θ t1 , reflected off bottom surface  110  at an angle of reflectance θ r3  which is also equal to the angle of incidence, and transmitted into sensor housing  102  at an angle of transmission θ t3 . The light transmitted into the interior of sensor housing  102  is then incident at a fourth area A 4  on bottom surface  110 , at an angle of incidence θ i4 , reflected off bottom surface  110  at an angle of reflectance θ r4  which is also equal to the angle of incidence, and transmitted into bottom surface  110  at an angle of transmission θ t4 . As shown in  FIG. 5 , the reflected light  112  having an angle of reflectance of θ r4  is transmitted to light detector  116 . Using Snell&#39;s Law and the Law of Reflection, above, and knowing the initial angle of incidence, and the refractive indices n 1 , n 2 , and n 3 , respectively, for sensor housing  102 , bottom surface  110 , and fluid  104 , all of the angles of incidence, transmittance, and reflectance can be determined. Similarly, knowing each of the angles of incidence, transmittance, and reflectance, as well as the refractive indices n 1  and n 2 , respectively, for sensor housing  102  and bottom surface  110 , the refractive index n 3  for fluid  104  can be determined. 
     In some embodiments, sensor  100  determines refractive index n 3  of fluid  104 , and thereby determines the type of fluid  104 , by measuring a power of the at least partially reflected and partially refracted light  112  received by light detector  116 . The power of a light incident at an area A, such as areas A 1 -A 4 , is given by the equation:
 
 I   i   A  cos θ i   =I   r   A  cos θ r   I   t   A  cos θ t ,
 
where A is the surface area of incidence, I is the radiant flux density of the incident, reflected, and transmitted light, and θ is the angle of incidence, reflectance, and transmittance. From this equation, the power at each of the four areas of incidence A 1 -A 4  can be determined. As can be determined using the above equation in conjunction with  FIG. 5 , the total power of partially refracted light  112  received by light detector  116  is less than a power of initial light  104  due to refraction. The power or intensity of the partially refracted light  112  detected by light detector  116  may then be converted into a corresponding frequency. As shown in  FIG. 3 , the frequency may then be compared with predetermined frequencies to determine the type of fluid  104 . As shown in  FIG. 3 , if fluid  104  is determined to be an electrolyte solution, a leak is detected, and an alarm may be triggered. However, if fluid is determined to be, for example, water or air, a leak is not present, and sensor  100  continues to monitor for leakage. Alternatively, the composition of fluid in contact with at least a portion of the bottom surfaces of the leak detector may be determined based on a current output and/or voltage output of the detector in response to the incident light.
 
     In some embodiments, the refractive index n 3  may be measured in order to determine the type of fluid  104 . Using Snell&#39;s Law and the Law of Reflectance above, as well as trigonometric identities, an equation for the power of the light reflected off bottom surface  110  at angle of reflectance θ r4  can be determined which is in terms of the initial power of light  108 , and refractive indices n 1 , n 2 , and n 3 . By knowing the initial power of light  108 , and the value of the refractive indices n 1  and n 2  of sensor housing  102  and bottom surface  110 , a value for the refractive index n 3  of fluid  104  may be determined. The determined refractive index n 3  of fluid is then compared with known refractive indices to determine the type of fluid  104 . As shown in  FIG. 3 , if fluid  104  is determined to be an electrolyte solution, a leak is detected, and an alarm may be triggered. However, if fluid is determined to be, for example, water or air, a leak is not present, and sensor  100  continues to monitor for leakage. 
     In some embodiments, sensor  100  is operated when fluid  104  is air and the frequency of the signal output from light detector  116  is noted. In this fashion, sensor  100  may be calibrated against air. The frequency of light will decrease as the index of fluid  104  increases and may become close to zero when the index of fluid  104  matches the index of bottom surface  110 . The concentration of electrolyte in fluid  104  can be determined by the decrease of the frequency of the signal from light detector  116  in comparison with the frequency of the signal from light detector  116  when fluid  104  is air. Sensor  100  may be calibrated against other fluids such as water or some other fluid that may potentially be present. 
       FIG. 6  is a diagram illustrating a sensor for detecting leakage  102  used in a flow battery system  500 , according to some embodiments. As shown in  FIG. 6 , flow battery system  500  includes a flow battery cabinet  502 , which houses a flow battery cell  504  that is coupled to electrolyte storage tanks  506 . Although  FIG. 6  illustrates two electrolyte storage tanks  506 , consistent with some embodiments, flow battery cabinet may house more than two electrolyte storage tanks  506 . As shown in  FIG. 6 , sensor housing  102  is positioned at a bottom portion of flow battery cabinet  502  so as to detect any fluid  104  which may be collecting in the bottom portion of flow battery cabinet  502 . In some embodiments, sensor housing  102  corresponds to sensor  100 . In some embodiments, sensor housing  102  corresponds to sensor  300 . Sensor housing  102  is electrically coupled to external electronics and controls  118 , which transmits and receives signals to and from sensor housing  102  for detecting the presence of fluid  104 , and determining the type of fluid  104 . As shown in  FIG. 3 , if fluid  104  is determined to be an electrolyte solution, a leak from electrolyte storage tanks  506  or flow battery cell  504  is detected, and external electronics/controls  118  may trigger an alarm. If fluid is determined to be, for example, water or air, a leak is not present, and the sensor continues to monitor for leakage of electrolyte. 
     Accordingly, some embodiments as disclosed herein may provide a leakage sensor which is not only able to detect the presence of a fluid, determine the type of fluid, and determine whether the fluid is a leaking fluid that poses a potential problem. 
     In this patent, certain U.S. patents, U.S. patent applications, and other materials (e.g., articles) have been incorporated by reference. The text of such U.S. patents, U.S. patent applications, and other materials is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is specifically not incorporated by reference in this patent. 
     Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.