Patent Application
20100081014
The present invention relates to power systems based on microbial fuel cells which can generate electrical power from voltage gradients at sediment-water interfaces.
The Navy and other marine-based activities such as fisheries, marine researchers, and operators of merchant vessels utilize a wide variety of marine-deployed devices. These devices include acoustic Doppler velocity profilers, acoustic sensors, seismometers, conductivity and temperature probes, surveillance instrumentation and various chemical sensors and transponders. Such devices currently provide valuable information about marine environments and/or enable Navy activities within marine environments. Ongoing developments in low-power microelectronics, sensors, and data telemetry continually expand their scope and impact.
Typically, these in-water marine/oceanographic devices are powered by batteries. The key limitation of battery-based power supplies is battery depletion (i.e., exhaustion of energy content) which limits the period of time over which a sensor or instrument can operate. Although many marine/oceanographic devices deployed in water can operate for short periods of time that are easily sustained by batteries, many others (present or envisioned) are designed to operate unattended for longer periods of time. However, such long-term operation is only possible by having the device be retrieved and redeployed with fresh batteries or having additional devices deployed sequentially. Both scenarios are cost and resource intensive, compromise covertness, and interrupt continuity of operation.
As a consequence, the long-term uninterrupted (i.e., persistent) operation of such devices, widely recognized as a desired capability, is not possible. It is widely recognized that many of these sensors and instruments would provide greater benefit if they could operate persistently.
Alternatively, sometimes finite deployment durations for an instrument are set by other constraints, e.g. logistical considerations, limited required time for mission support, etc. In these cases it is typical for the sampling rate of the instrument to be directly determined by the expected battery depletion rate. Although higher sampling rates may be desired and be of benefit, lower sampling rates must be used to ensure battery life persists throughout the deployment duration. If additional power were available, a higher sampling rate for the instrument would in many cases produce a higher quality data product.
Solar-based power is a proven source of persistent low power for devices deployed on or just below the water surface. Solar-based power is, however, prone to fouling when utilized in marine environments limiting deployments of solar-powered devices up to 1-year in cold environments and substantially shorter in warm environments unless periodic cleaning of the device can be done. As light is attenuated rapidly with depth in water, devices deployed on the ocean bottom cannot benefit at all from solar power except in the cases of extremely shallow deployments or when attached by cables with surface buoys. The latter situation increases the risk of damage or destruction by fishing or shipping traffic.
Alternatively, marine/oceanographic devices deployed in water can be powered by direct connection to land-based power sources. The key limitation of land-based power supplies for marine/oceanographic devices deployed in water is their reliance on electrical cables which are very expensive to construct and deploy, which limit geographic scope and range of deployment, and which are susceptible to hazards including weather and trawling that can cause periodic shutdowns of their operation.
One solution to this problem that has been developed is the benthic microbial fuel cell (BMFC). See Reimers et al., “Harvesting Energy from the Marine Sediment-Water Interface,” Environmental Science and Technology, Vol. 35 No. 1, pp. 192-195 (2001); Tender et al., “Harnessing Microbially Generated Power on the Seafloor,” Nature Biotechnology 20, pp. 821-825 (2002); Bond et al., “Electrode-Reducing Microorganisms That Harvest Energy from Marine Sediments,” Science, Vol. 295, pp. 483-485 (18 Jan. 2002); and U.S. Pat. No. 6,913,854 to Alberte et al., all of which have an author or inventor in common with the present invention and are incorporated by reference into the present disclosure in their entirety.
The BMFC consists of an electrode embedded in anoxic marine sediment or in contact with anoxic porewater of anoxic marine sediment connected by an external electrical circuit to an electrode positioned in overlying water. In many fresh- and salt-water marine environments substantial organic matter resides in sediment which sustains microbial activity that is limited by flux of oxidants (such as oxygen and sulfate) into sediment from overlying water. Within the topmost millimeters to centimeters of such sediments, microorganisms preferentially deplete oxygen, causing microorganisms deeper in sediment to utilize less potent oxidants (such as sulfate) and generate as byproducts potent reductants (such as sulfide). As a consequence, a natural redox gradient exists across the sediment/water interface in which porewater within such marine sediment millimeters to centimeters beneath the sediment surface is enriched in reductants compared to overlying water. Because of this redox gradient, an electrode imbedded in such marine sediment or in contact with anoxic porewater of such anoxic marine sediment will equilibrate to an electrical potential that is often more than 0.7 volts negative compared to the electrical potential of a comparable electrode positioned in overlying water at open circuit (i.e., when the electrodes are not electrically connected).
Connection of the electrodes by an external circuit of appropriate resistance results in sustainable electron flow (electrical current) from the sediment imbedded electrode (termed “anode” because of its negative voltage) to the electrode in overlying water (termed “cathode” because of its positive voltage). Current is sustained at the anode by continual oxidation of reductants in sediment porewater and at the cathode by continual reduction of oxidants in water. The acquired electrons flow from the anode through the external circuit where they can do work (such as power a marine deployed sensor or instrument) and continue with diminished potential to the cathode. Continual supply of the electrode reactants and continual removal of the electrode products by natural processes ensure long-term (persistent) low-power generation (typically 0.01-1 W depending on size) at low voltage (typically about 0.4 V). However, the BMFC cannot be used directly to effectively power in-water marine/oceanographic devices without an effective control/monitoring interface.
This summary is intended to introduce, in simplified form, a selection of concepts that are further described in the Detailed Description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Instead, it is merely presented as a brief overview of the subject matter described and claimed herein.
The present invention provides a marine power system based on a microbial fuel cell such as a benthic microbial fuel cell (BMFC). In accordance with the present invention, one or more BMFCs can be connected to one or more batteries such as a nickel metal hybrid (NiMH) or sealed lead acid (SLA) battery and can be used to charge the batteries for long-term persistent underwater use. At any time some of the connected batteries are being charged by the BMFC, while others are being used to power a connected device. By using electrically isolated fuel cell converters, the batteries can be charged while in circuit. With non-isolated converters, pairs of batteries can be switched between offline charging and online discharging. The battery system can be controlled by a system that includes a microcontroller that periodically measures system voltages and currents, swaps the batteries being charged, and records the system results for post-mission analysis. The batteries can be connected to an underwater monitoring system such as the Acoustic Doppler Current Profiler (ADCP) or Shallow-Water Environmental Profiler in Trawl-Safe Real-Time Configuration (SEPTR) systems used by the U.S. Navy and can provide long-term persistent power supplies to such systems.
The aspects and features of the present invention summarized above can be embodied in various forms. The following description shows, by way of illustration, combinations and configurations in which the aspects and features can be put into practice. It is understood that the described aspects, features, and/or embodiments are merely examples, and that one skilled in the art may utilize other aspects, features, and/or embodiments or make structural and functional modifications without departing from the scope of the present disclosure.
For example, the present invention is often described in the context of two exemplary configurations in which a benthic microbial fuel cell (BMFC) is used to power batteries for an Acoustic Doppler Current Profiler (ADCP) system and a Shallow-Water Environmental Profiler in Trawl-Safe Real-Time Configuration (SEPTR) systems. However, one skilled in the art would appreciate that the battery system of the present invention can be used with any microbe-energy based underwater fuel cell or to power any suitable device and that many other configurations and applications of a BMFC-powered battery system can be made. In addition, although the present invention is described in the context of particular components, such particular components are merely exemplary and other similar or otherwise compatible components may also be used within the scope and spirit of the present disclosure.
A schematic of an exemplary BMFC microbial fuel cell is shown in
The University of Rhode Island Ocean Engineering Department has been working with the U.S. Naval Research Laboratory to develop BMFCs for low-power consuming seafloor applications of extended duration. This activity required the development of control and monitoring systems to regulate discharge of the BMFCs and to monitor their performance without consuming a significant portion of the low power they generate. As noted above, using the naturally occurring potential gradient difference created from microbial decay in marine sediment, BMFCs generate power on the order of about 0.4V. In order to make use of BMFC generated power for oceanographic devices that tend to use power periodically, the 0.4 V BMFC power output must be boosted in voltage to a useful level and stored for use.
Thus, in accordance with the present invention, the BMFC voltage can be boosted to a useful level, for example by means of DC/DC converters, to a voltage capable of charging a battery such as a 12V sealed lead acid (SLA) or nickel metal hybrid (NiMH) battery. This conversion needs to be done very near the electrodes to minimize line IR losses, which accumulate quickly over short distances for these low voltage/high current generators. Sets of such BMFC-charged 12V batteries can then be combined to provide higher voltages, either by removing batteries from the active circuit for charging, or by charging multiple batteries in series by means of isolated converters. Converters that can be used to boost BMFC voltage include the current mode converters developed for this project by Northwest Metasystems to charge 12V batteries with an efficiency of 60-70%.
As described in more detail below, the present invention provides a microbial fuel cell power system wherein batteries such as 12V SLA and NiMH batteries can be charged from microbial fuel cells such as BMFCs. In accordance with the present invention, one or more BMFCs can be connected to one or more batteries and, using a voltage booster such as a DC/DC converter, can be used to charge the batteries for long-term persistent underwater use. At any time some of the connected batteries are being charged by the BMFC, while others are powering a connected device. By using electrically isolated fuel cell converters, the batteries can be charged while in circuit. With non-isolated converters, pairs of batteries can be switched between offline charging and online discharging. A microbial fuel cell power system in accordance with the present invention can include a control and monitoring system that periodically measures system voltages and currents, swaps the batteries being charged, and records the system results for post-mission analysis. To save power, the controller can be in an inactive state until being awoken, for example by a remote signal or a real time clock connected to the microcontroller. Once awake, the controller can record information regarding the BMFC and the connected batteries such as system and battery voltages and charge/discharge currents and can switch the batteries being charged by the BMFC, for example by means of latching relays. The batteries can be connected to an underwater monitoring system such as the Acoustic Doppler Current Profiler (ADCP) or Shallow-Water Environmental Profiler in Trawl-Safe Real-Time Configuration (SEPTR) systems used by the U.S. Navy and can provide long-term persistent power supplies to such systems.
These and other aspects of the present invention will be described in more detail below.
As noted above, in accordance with the present invention, a set of BMFCs can be connected to a corresponding set of batteries to be charged from the microbial generated BMFC voltage. As illustrated in the exemplary embodiments shown in
In accordance with the present invention, a BMFC-based battery system can also be connected to a controller/monitor 205 to switch the batteries connected to the BMFC from an offline/charging state to an online/active state. The controller is woken up periodically, e.g., by a real time clock or by a remote signal, to monitor the status of the battery system and record performance data. The controller receives date and time information, either from the real time clock or the remote signal, and at predetermined intervals, e.g., once a day, once a week, etc., alternates the batteries being charged and those being discharged.
In order to ensure that the controller/monitor does not excessively drain the BMFC power it is important that the controller consume only a very small amount of power when on and preferably no power when it is off. Thus, in one exemplary embodiment, a microcontroller used in accordance with the present invention can comprise one or more object-oriented programmable integrated circuits programmed in Basic such as the OOPIC microcontroller produced by Microchip Technology, Inc. as the core low power computer. The OOPIC is a very small microcontroller which consumes 16-20 mA at 5 volts (80-100 mW) when on and OA when off. It operates and is programmed via 9600 baud RS232 3 wire serial communication and has a 4 channel/10bit A/D converter expanded by multiplexer chips to 12 channels for monitoring voltages and currents via current sensing ICs. Its programs are stored on EEPROM, and immediately start from the beginning each time the OOPIC is powered up. In addition, notes from the previous time awake can be stored in the EEPROM below the program and can be used determine previous actions taken by the controller and provide information for use by the OOPIC in performing one or more of its functions during the current wake cycle. At the end of the program the processor turns off power to keep power consumption to a minimum. As described in more detail below, no system power is used by the controller until woken up.
As noted above, because the BMFC generates such a small voltage, the controller also needs to be kept asleep most of the time to avoid consuming a large fraction of the available power. For example, if allowed to run continuously, a 100 mW OOPIC would consume nearly all of the power generated by a 100 mW BMFC. To prevent such a drain on the available BMFC power, the controller can be turned on, either by a real time clock in some embodiments or by a remote signal in others. Little or no system power is used by the OOPIC until it is woken up. Once awake, the OOPIC can check the date, monitor/control the system status and even operate a low power pump via PWM output for enhancing BMFC electrode performance.
In embodiments using a real time clock, the OOPIC can be awoken by an electronic alarm, for example, from an I2C real time alarm clock chip (DS1337) with its own multi-year lithium battery which can maintain crystal-controlled date and time without using any system power. The Real Time Clock (RTC) can be programmed to wake up the system at a specific date and time or at any of several intervals. Alternatively, a controller at a remote site can be programmed to send a wake-up signal to the controller at the desired intervals. For example, the RTC can be programmed to wake up the OOPIC once a day to switch the batteries being charged and once an hour to record system information such as voltage and current use. The wake-up time for switching the batteries can coincide with one of the hourly wake-up cycles so that the battery switching is performed in addition to the hourly monitoring functions or can be programmed to be a separate wake-up that is staggered from one of the hourly wake-up cycles so that the battery switching is performed independently from the monitoring functions.
In other embodiments, the OOPIC can be woken up remotely by applying a few volts of power to one of the RS232 handshake lines which is connected to a parallel wakeup circuit which switches on both the controller and RS232 power. In this embodiment, the remote signal also can be used to effect reprogramming and system configuration changes if such changes are desired.
As noted above, the microcontroller can be operatively connected to a memory device such as a micro SD card connected to an independent micro SD card logger (for example, the DOSONCHIP card logger made by Wearable, Inc. or the μALFAT chipset made by GHI Electronics, LLC). Using the logger, the memory device can be used to store long term measurements over many months, for example, by means of serial FAT16 ASCII files. The logger uses very little power, for example, only 3-5 mA at 3.3 volts when not writing, and a momentary 40-70 mA to write.
The OOPIC communicates with the logger in low power TTL serial ASCII.
Communication with the surface (as well as programming) is done via RS232 serial using an RS232 chip (MAX242) that manufactures +/−10V RS232 signals from +5V when enabled with only a few milliamps of additional power consumption. This chip is connected to TTL serial lines on the OOPIC controller and SD card logger from which it produces RS232 signals capable of driving over 100 m of cable at 9600 baud. The OOPIC can have RS232 signals available directly, but these signals are too weak to drive long cables. Power to the SD card logger and the RS232 chip is controlled by the OOPIC. The OOPIC controls their power to minimize consumption, and when the OOPIC is asleep the controller subsystems don't consume any power. In an exemplary embodiment, the controller can be woken up, report data, accept commands, or be reprogrammed, all through an 8-wire 3×RS232 serial cable (1-OOPIC, 2-SD logger, 3-ADCP or AUX device). The main power latching relay can be triggered with a few volts on one of the RS2332 handshake lines. The OOPIC does not normally use the handshake lines, requiring only transmit, receive and ground signals for programming (and communication on the same lines).
After the completion of a mission using a power system in accordance with the present invention, for example, after completion of a SEPTR mission, the SEPTR device can be recovered and the SD card removed so that the power system performance data can be retrieved. In other embodiments, the performance data can be accessed by means of a cable such as an 8-pin serial program connector and cable connected to the controller/monitor. In still other embodiments, the controller can include a transmitter such that the recorded performance information can be periodically transmitted to a receiver at a remote site, for example, as part of a wake-up cycle triggered by a remote signal described above.
The microcontroller can be programmed to awake periodically for very short periods of time to monitor a multi-month system deployment and record the results on a memory medium such as an SD card. For example, the microcontroller can be programmed to awake once an hour for 20 seconds (0.55% on time), keeping the average controller power consumption of the control system very low, e.g., to less than 2 mW averaged over an hour or more for the SEPTR controller with high power Panasonic 4PDT latching relays (133 mA to switch). The ADCP controller uses even smaller Omron DPDT relays which consume almost 1/10 the relay power, reducing average power consumption to less than 1 mW.
As described above, an underwater power system in accordance with the present invention can monitor and control the charging of batteries such as 12V NIMH or SLA batteries from the BMFC converter/charger so that such batteries can be used to persistently power their connected devices. Charging is a continuous process which is monitored periodically, e.g., once per hour, with time, voltage and current measurement values being saved as ASCII files on a memory such as an SD card and the batteries charged being switched periodically, i.e., once per day, by means of latching relays.
Acoustic Doppler Current Profiler (ADCP) instrument in accordance with the present invention. Such an exemplary power system can include two 12V batteries 201a and 201b wired in series that can be charged by means of a single isolated BMFC converter/charger 202. In accordance with the present invention, controller 205 can wake up each hour to monitor voltage and currents, and can periodically switch which one of batteries 201a and 201b is being charged. The ADCP can be programmed to consume anywhere from 0.1 to 1.2 watts of power within its normal operational specifications for reasonable current measurement accuracies. Thus, the combined system described here can either extend the deployment duration of an ADCP maintaining a normal sampling frequency or allow for a higher sampling frequency (i.e. higher power consumption) over a pre-determined deployment duration, with benefit to the measurement quantity or quality.
For a more power-hungry SEPTR environmental profiler system, a 24V power system in accordance with the present invention can be used. In an exemplary embodiment of such a SEPTR system shown in
The ADCP and SEPTR systems described above are designed to stand alone and log data to a microSD card within the monitor/controller. However, in other embodiments, the BMFC control system can be cabled ashore so that operations can be monitored in real time.
With microbial fuel cell systems expected to provide 10-1000 mW of power, it can be a challenge for the control and monitoring system to consume a small fraction of the available power and to be able to run for years. The present invention addresses this problem by having the controller disconnect itself from all power at the end of each wakeup cycle, then using a separate real time clock alarm with independent multi-year lithium battery to reconnect the controller at programmed intervals.
Thus, by combining a low power BMFC microcontroller, real time clock, SD card logger and latching relay components, the present invention can provide a seafloor microbial fuel cell battery system that consumes very little power and can run for years. In addition, connecting this system to a communications system such as an internet-based microcontroller using FTP and TCP/IP Telnet functionality when the system can be cabled or wirelessly connected ashore can allow real-time monitoring and control. Because no power is consumed by the controller when it is asleep, realistic long-term deployment simulation of these systems can be achieved by automatically advancing the time being kept by the real time clock wakeup system to just before the next wakeup time, then putting the system to sleep as usual. By reducing the on time duty cycle from 0.5% to 50% a year long deployment can be simulated in under 4 days.
It should be appreciated that one or more aspects of a microbial fuel cell power system as described herein can be accomplished by one or more processors executing one or more sequences of one or more computer-readable instructions read into a memory of one or more computers from non-volatile or volatile computer-readable media capable of storing and/or transferring computer programs or computer-readable instructions for execution by one or more computers. Non-volatile computer readable media that can be used can include a compact disk, hard disk, floppy disk, tape, magneto-optical disk, PROM (EPROM, EEPROM, flash EPROM), SRAM, SDRAM, or any other magnetic medium; punch card, paper tape, or any other physical medium such as a chemical or biological medium. Volatile media can include a memory such as a dynamic memory in a computer.
Although particular embodiments, aspects, and features have been described and illustrated, it should be noted that the invention described herein is not limited to only those embodiments, aspects, and features. It should be readily appreciated that modifications may be made by persons skilled in the art, and the present application contemplates any and all modifications within the spirit and scope of the underlying invention described and claimed herein.
For example, envisioned applications of the present invention can include numerous marine sensors presently powered by batteries and thus limited in duration by battery depletion, which could provide scientific and/or operational and/or cost savings benefit if their duration could be greatly extended. Undersampling of the high frequency content of ocean signals is a widely recognized problem in oceanography and the present invention could provide a great benefit to a wide variety of ocean sensor uses by facilitating higher frequency sampling over set deployment durations. Benthic microbial fuel cells and control systems therefore in accordance with the present invention can be deployed in a wide range of environments such as the continental margins, fresh water lakes, rivers, estuaries, and harbors and can power a wide range of sensors and other instruments. It is envisioned that the invention disclosed here could also significantly impact next generation Department of Defense Distributed Netted Sensors Warfighting Capabilities and the Autonomous Operations Future Naval Capability as they pertain to in-water operations by increasing duration of battery-powered system components and reducing the frequency of cost and resources needed for intensive maintenance of battery-powered system components due to depletion of their batteries.
All such embodiments, configurations, and applications are also contemplated to be within the scope and spirit of the present disclosure.
This application claims the benefit of priority based on U.S. Provisional Patent Application No. 61/096,347 filed on Sep. 12, 2008, the entirety of which is hereby incorporated by reference into the present application.
| Number | Date | Country | |
|---|---|---|---|
| 61096347 | Sep 2008 | US |
