WO1997026697A1 - A portable electrical energy supply unit and associated method - Google Patents

Abstract

The integrated power distribution system includes a docking device (200) for containing and transporting a rechargeable battery (202) and a dwelling power system that draws power from the battery (202) for use in a dwelling. The battery (202), which is selected for power station compatibility and efficiency, is enclosed within a housing (204) that has an outlet receptacle (206) and a power switch (208). The outlet receptacle (206) is mated to a power plug of the dwelling power system as well as the recharging terminal of a recharging station. In this regard, non-standard plugs and receptables are employed to facilitate regulation of power station usage. In one embodiment, the docking device (200) includes a discharge controller that prevents the battery (202) from further discharging after a predetermined quantity of energy has been supplied by the battery (202) since the last recharge of the battery (202).

Description

A PORTABLE ELECTRICAL ENERGY SUPPLY UNIT AND ASSOCIATED METHOD

FIELD OF THE INVENTION

The present invention relates to the generation of photovoltaic electrical power and distribution of that power to residences and businesses in a community. More specifically, the present invention involves facilitating access to a solar powered battery charging station and regulating use of the station, as well as facilitating distribution and efficient use of such power by regulating electrical power output from the electrical energy supply unit.

BACKGROUND OF THE INVENTION People in some communities in the world do not have available utility-provided electrical power from an electrical grid or, if such power is available, it is not reliable. Several attempts have been made to provide alternative sources of electrical power to satisfy the needs of people in such communities. One technology that has been considered to provide power to such communities is to generate electrical power in the locality of the community using solar energy in a photovoltaic power generation facility.

One proposed method for supplying photovoltaic power to people is to outfit individual residences or businesses in a community each with a photovoltaic power generation facility. Such photovoltaic power generation facilities are, at present, however, very expensive and beyond the financial reach of many people. Also, such individual photovoltaic power generation facilities tend to be inefficient in the delivery and use of available photovoltaic power generation capacity. Another proposed alternative is to provide a central photovoltaic power generation facility which is wired by the use of electrical transmission lines to individual residences and businesses. Such a system may significantly reduce the cost of the photovoltaic power generating facility per connected consumer and may result in higher efficiency in delivery and use of the available photovoltaic power. One major problem with such a system, however, is that the cost of power transmission lines, including accompanying equipment and maintenance, is often prohibitively expensive. This is especially true in rural communities where residences and businesses tend to be widely dispersed, yet such communities have a great need for electrical power.

SUMMARY OF THE INVENTION In order to address the power needs of such communities, a solar powered battery recharging station has been developed. The present inventors have recognized that the potential benefits of such recharging stations can be enhanced by simplifying access to the recharging station and subsequent use of the power, by reducing the use of inefficient batteries in the system thereby increasing overall customer service and by regulating use of the recharging station for security and compatibility purposes. In this manner, the recharging station system can be profitably and efficiently run for the benefit of a greater number of people. According to one aspect of the present invention, a battery docking device, also referred to herein as a portable electrical energy supply unit, is provided for facilitating access to a solar powered battery recharging station and regulating use of the station. The recharging station may include a photovoltaic source, a battery charging terminal including a recharging outlet, such as a plug of a selected type, and a controller that receives power from the photovoltaic source and provides a selected charging signal to the recharging outlet. The controller and recharging outlet can be adapted to service a specific type of battery system for enhanced efficiency. The novel docking device includes a power station compatible rechargeable energy source or battery, a housing or portable container for use in containing and transporting the battery, and an electrical outlet, such as a receptacle, provided on the housing for mating with the recharging outlet of the station so as to recharge the battery.

The mating outlets of the recharging station and docking device are preferably of a type which is not standard in the power service area of the recharging station, thereby facilitating regulation of a recharging station access by inhibiting use of foreign units. In this regard, the housing can also be sealed to thwart attempts to substitute a foreign battery which may be inefficient or not compliant with recharging station specifications. The housing is preferably constructed from electrically insulating material which is resistant to degradation due to battery acid exposure. In addition, a vent can be provided in the housing to vent gases produced by the battery.

According to another aspect of the present invention, the novel docking device is employed in conjunction with a specially adapted dwelling power system for convenient and efficient dwelling use. The docking device includes a recharging outlet, as discussed above, and a power outlet for interfacing with the dwelling power system. The recharging outlet and power outlet can be the same or provided separately on the docking device housing. The power outlet is mated to a first dwelling outlet of the dwelling power system. The docking device further includes a discharge controller, also referred to as an electrical energy output regulator, for monitoring a discharge state of the battery, i.e., such as battery voltage, and controlling discharge from the battery in response to the monitored state. In particular, the discharge controller prevents the battery from discharging to a voltage that is so low that permanent and undesirable injury to the battery would result.

One problem encountered with supplying electrical power from the recharging station, however, is that different batteries exhibit different discharge capacities after recharging. Even the same battery will exhibit different performances at different stages during the battery's life. For example, it is common for a lead-acid battery to reach a maximum discharge capacity during the early part of the battery's life. Over time, however, the discharge capacity declines as the battery is no longer capable of accepting the same amount of charge during a recharging operation. This situation is problematic for at least two reasons. First, different consumers experience different battery performance per discharge depending on the state of the battery. This makes it difficult for the consumer to accurately predict the amount of energy available per recharge of the battery, and, therefore, to accurately predict and budget for obtaining the next recharge. Second, because different batteries have different discharge lives, it is hard for the operator of the recharging station to accurately predict and schedule battery rechargings for efficient operation of the recharging station.

In one aspect, the present invention addresses the problem of different batteries exhibiting different discharge capabilities by including in the docking device a discharge controller that prevents the battery from being further discharged after the battery has already supplied a predetermined quantity of electrical energy since the last recharge of the battery. In this way, similarly situated consumers receive the same amount of energy per recharge, regardless of the state of the battery's life, and each consumer experiences the same battery performance after each recharge cycle. Electrical power consumers and recharging station operators are, therefore, able to more accurately plan for and schedule battery recharges based on anticipated electrical power consumption per recharge.

Any device for monitoring electrical power consumption may be used to trigger disconnection of the battery when the predetermined quantity of electrical energy has been supplied. A preferred device is a current integrator that keeps track of the number of ampere-hours supplied by the battery since its last recharge and triggers a switch to disconnect the battery after a predetermined number of ampere-hours has been supplied by the battery. When the battery is then recharged, the current integrator may be reset to zero for use during the next discharge cycle.

Preferably, the discharge controller both prevents the battery from supplying electrical power in excess of the predetermined quantity and prevents the battery from discharging to a voltage below a predetermined voltage. In normal operation, however, disconnection of the battery will occur based on the quantity of power delivered. A voltage-based disconnect is, however, available as a back¬ up to prevent damage to the battery. The discharge controller — in conjunction with various features of the recharging station compatible battery, sealed housing, and the recharging station itself — provides for efficient use of the photovoltaic source to benefit more users.

In one aspect, the docking device is used to power a dwelling, such as a home or business, via a specially adapted dwelling power system. The dwelling power system includes at least the first dwelling outlet, referenced above, for mating with the power outlet of the docking device and potentially a second outlet for providing power to a light and/or other appliance in the dwelling. The first and second dwelling outlets are of different types. For example, the second outlet can be a standard outlet for the geographic or power service area for compatibility with readily available appliances, whereas the first outlet is compatible with the power outlet of the docking device which is preferably different from the local standard so as to facilitate regulation of recharging station use.

In one embodiment, the present invention includes an integrated battery docking device/dwelling power system. The docking device includes a 12 volt, deep cycle battery sealed within a high strength polyethylene housing. A three-prong electrical receptacle is provided on the housing. The receptacle is a dual-use receptacle for both mating with a recharging terminal of a recharging station and mating with a power plug of a dwelling power system. A 12 volt switch may also be provided on the housing to selectively connect and disconnect the battery and housing outlet. The docking device further may include a control board for preventing further discharge of the battery when the battery voltage reaches either a predetermined voltage limit or the battery has discharged a predetermined quantity of energy.

The dwelling power plug is connected, via a fuse/terminal box to two or more switch boxes installed within the dwelling. Each of the switch boxes preferably includes two outlets, one of which is operated by a switch. A nine watt, 12 volt fluorescent light with included inverter/ballast is provided for compatible and efficient use in the power system. As discussed above, the outlets of the switch boxes are different in type from the outlet/plug at the docking device/dwelling power system interface. In this regard, the different types of outlets may be standard outlets for different geographic or utility areas. The docking device and dwelling power system, together with hooks, brackets and/or other installation hardware are conveniently provided as a pre-packaged unit. These items are preferably matched to a local photovoltaic recharging station and may be distributed by the station operator to ensure system compatibility.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram schematic of a photovoltaic electrical power distribution facility of the present invention. Fig. 2 is a block diagram schematic of the controller of an electrical power conversion system shown in Fig. 1. Fig. 2A is a graph of a typical control signal generated by the controller of Fig. 2 and provided to the plurality of dc-to-dc converters.

Fig. 3 is a block diagram schematic of one of the dc- to-dc converter of a power conversion system shown in Fig. 1.

Fig. 4 is a flowchart indicating an algorithm implemented by the controller for determining a maximum current signal. Fig. 5 is a flowchart indicating an algorithm implemented by the controller for determining a float voltage signal.

Fig. 6 is a perspective view of an electrical power delivery system of the present invention for providing an electrical connection between the controller and the plurality of the dc-to-dc converters.

Fig. 7 is an illustration of an individual transporting a rechargeable electrical battery to a photovoltaic electrical power distribution facility in accordance with the present invention.

Fig. 8 is a block diagram schematic of another embodiment of the photovoltaic electrical power distribution facility of the present invention.

Fig. 9 is a perspective view of a docking device for use in connection with a photovoltaic electrical power distribution facility such as shown in Fig. 1.

Fig. 10 is a diagram of a dwelling power system for use with the docking device of Fig. 9. Fig. 11 is an exploded view of another embodiment of a docking device for use in connection with a photovoltaic electric power distribution facility such as shown in Fig. 1. Fig. 12 is a perspective view of the embodiment of the docking device as shown in Fig. 11.

DETAILED DESCRIPTION The present invention relates to an integrated docking device and dwelling power system for use in powering a dwelling using power from a remote photovoltaic source. The photovoltaic source provides power to a photovoltaic power distribution facility. The facility delivers output power to one or more recharging terminals, whereby a rechargeable electrical power source, such as a battery, may be temporarily connected to the facility for battery charging purposes and disconnected from the facility after charging. The charged battery can then be transported to a dwelling and connected to a dwelling power system.

In the following, a docking device (also referred to herein as a portable electrical energy supply unit) for transporting a battery and interfacing the battery with the photovoltaic power distribution facility and with the dwelling power system is described first. The dwelling power system is then described. Finally, details of a photovoltaic power distribution facility are set forth.

Referring to Fig. 9, the docking device of the present invention is identified by the reference numeral 200. Generally, the docking device 200 includes a battery case 202 enclosed within a housing 204, a charge/output receptacle 206, a switch 208 and a discharge control board 210, which functions as an energy output regulator. The battery case 202 encloses the voltaic cells that make up a battery. The battery case 202 and control board 210 are schematically illustrated as phantom boxes in Fig. 9. In the embodiment shown in Fig. 9, the housing 204 is a portable container and, preferably, the docking device 200 has a total weight of less than about 25 kilograms and occupies a volume of less than about 20,000 cubic centimeters to enhance the device's portability, so that a consumer may easily carry the docking device 200 between a dwelling where power is consumed and a distant recharging station where the battery is recharged following use.

Preferably, the board 210 is kept compartmentaIly separated by the battery case 202 from the active components of the battery to prevent damage to the board 210. The battery case 202 is typically sealed to prevent communication of the active components of the battery with the compartmental volume within the housing 204 where the board 210 is located

The housing 204 is used to contain and transport the battery, board 210 and related components. Accordingly, the housing 204 is constructed from lightweight and strong material. Additionally it is desired that the housing 204 provide protection for the internal components against the elements and be constructed from an electrically insulating material that is resistant to degradation upon exposure to battery acid or other chemicals. It is also desirable to seal the housing 204 in a manner that discourages substitution of a foreign battery into the housing 204, as such a battery may be incompatible with other system components, interfere with proper operation of the discharge control board 210, etc. In the illustrated embodiment, the housing 204 is formed from high strength, molded polyethylene. The housing 204 is formed in two halves sealed together by a steel band 212, although any locking mechanism could be used. Appropriate internal brackets, molding, foam or the like (not shown) can be provided to immobilize the battery case and board 210. In a preferred embodiment, illustrated in Figs. 11 and 12, the top and bottom of the docking device 200 should contain complimentary mating surfaces 512 and 520 so that the docking device 200 is easily stackable with other similar devices, especially during recharging.

The battery contained within the housing 204 is preferably a rechargeable 12 volt, deep cycle battery which retains excellent efficiency over a large number of recharging cycles. In this regard, various commercially available rechargeable lead-acid batteries may be employed. Preferably, the battery is of a type having a non-flowable electrolyte so that if the battery case 202 becomes physically damaged, the electrolyte will not spill, as would be the case with liquid electrolytes. A preferred electrolyte is in the form of a gel. Switch 208 is a conventional 12 VDC switch and is employed to connect and disconnect the electrical outlet 206 from the battery. Outlet 206, as previously discussed, is preferably of a type different from the standard in the geographic or utilities area. In this regard, a standard outlet for a different area or a custom outlet can be employed. The specific outlet employed may vary depending on the area where the photovoltaic power facility operates. A primary function of the discharge control board 210 is to monitor the discharge state of the battery and prevent further discharge once the battery has reached a predetermined discharge limit. For example, in the illustrated embodiment, the control board 210 may be provided with an automatic cut-off limit of 12 volts. That is, the battery will not be allowed to discharge below 12 volts, thereby preserving battery efficiency and extending battery life. The discharge state can be monitored by providing a current meter in conjunction with a resistor of a known value (or adjustable to various known values) and applying the battery potential across the resistor. The battery voltage can then be determined based on knowledge of the resistance and current and a cut-off switching circuit can be arranged to respond as desired. Furthermore, the discharge control board 210 is capable of preventing further electrical energy from being supplied by the battery when a predetermined amount of energy has been discharged from the battery since the last recharge of the battery. For example, the control board 210 may automatically cutoff power when about 30 to 50 ampere-hours has been supplied from the battery. The quantity of ampere-hours discharged from the battery may be measured by integrating over time the current supplied. Thus, controlling the discharge of electrical power in this manner ensures that each docking device delivers an equivalent amount of electrical energy to each customer following each recharge.

An important aspect of the present invention is the repeatable delivery of an equal amount of electrical energy to each similarly situated customer. Although the receptacle 206, switch 208 and battery are illustrated as being interconnected via the control board 210, it will be appreciated that any suitable arrangement may be employed. Fig. 9 also shows a vent tube 214 extending from a vent port 216 through the battery case 202 to a vent port 218 of the housing 204. The tube 214 is employed to vent gases, such as hydrogen gas, that may be generated by a lead-acid battery so as to alleviate hazards relating to gas build up within the housing 204. The tube 214 is preferably sealed at each port 216 and 218 to substantially prevent leakage of gas, moisture or the like into the housing 204.

Referring to Fig. 10, a dwelling power system for interfacing with the docking device 200 is generally identified by the reference numeral 220. The power system 220 interfaces with the docking device 200 via a three- prong power plug 222 mated to the receptacle 206 of docking device 200. It will thus be appreciated that the plug 222 matches the plug of the power station charging terminal(s) . Plug 222 is connected to a fuse/terminal box 224 by power line 226. Box 224 includes safety fuse terminals for limiting current in the dwelling power system 220 and also houses terminals for connecting power line 226 to first 228 and second 230 room power lines for providing power to separate rooms or areas of the dwelling.

Each of the room power lines 228, 230 supplies power to a switch box 232, 234 which may be installed within a room of the dwelling. In the illustrated embodiment, each switch box 232, 234 has two receptacles 236a,b and 238a,b, one of which is operated by a switch 240, 242. Conveniently, at least one of the outlets 236a, 236b, 238a, 238b is a standard outlet of the geographic or utility service area of the dwelling, so as to readily receive a television pigtail or other appliance plug, and is therefore different than the receptacle 206 of docking device 200. The power system 220 further includes light fixtures 240, 242 powered by switch boxes 232, 234 via power lines 244, 246 and mated plugs 248, 250. Each fixture 240, 242 includes a vertically disposed fluorescent light source 252, 254 housed within a reflector cone 256, 257. For enhanced efficiency, each light source 252, 254 in the illustrated embodiment includes a 9 watt fluorescent bulb and a 12 VDC inverter/ballast. All of the components of Figs. 9-10 may be provided as a pre-packed unit supplied by the power station operator to ensure maximum power station compatibility/efficiency. The pre-packaged unit may further include appropriate installation hardware.

Figs. 11 and 12 show another embodiment of the docking device 200 in which the housing 204 is made up of a cap 504 and the battery case 202, which together contain the battery, including the active components of the battery enclosed in the battery case 202 and the battery terminals 510 that extend through the battery case 202. The board 210 is compartmentaIly separated from active components of the battery by the battery case 202, with the board 210 being in one compartment defined by the top of the battery case 202 and the cap 504, and the active components of the battery being in a separate compartment defined by the battery case 202. The terminals 510 of the battery extend out of the battery case 202 and into the compartment within the cap 504 to facilitate electrical connection of the battery to the discharge control board 210.

With continued reference to Figs. 11 and 12, the docking device 200 may contain complimentary interlocking surfaces 512 and 520 on the top and bottom surfaces of the docking device 200. The cap 504 also contains the electrical outlet 206 for electrically connecting the docking device 200 to a dwelling power system or a battery recharging station, as the case may be. Preferably, a locking device, such as a steel belt, may be fixed along the interface of the cap 504 and the battery case 202 to prevent access to the interior of the docking device 200. Referring now to Fig. 1, an electrical schematic of a photovoltaic electrical distribution facility 10 is shown, with the facility 10 having a solar array 12, a plurality of batteries 14, and an electrical power conversion system 11 which controls and regulates distribution of electrical power from the solar array 12 to the batteries 14. The electrical power conversion system 11 includes a controller 16, a power bus 18, a control bus 20, a common bus 21, and a plurality of dc-to-dc converters 22. Each dc-to-dc converter charges a separate one of the plurality of batteries.

The power conversion system 11 allows for the independent charging of multiple removable batteries 14 that can have different discharge levels. In typical operation, any number of discharged batteries can be added to the system and charged batteries can be removed from the system at any time. The controller 16 does not gather any information regarding the charge status of the individual batteries. Instead, the controller monitors the output power of the solar array 12 and controls the combined current draw of the dc-to-dc converters 22 from the solar array by providing an appropriate control signal to the dc- to-dc converters via the control bus 20. The solar array preferably includes one or more collections of 40 solar modules, or panels, with each module typically producing an output power of 24 watts that peaks at an optimum current of .75 amps at maximum insolation. The system controls the dc-to-dc converters to adjust their draw of output current from the array in response to insolation changes.

When the power conversion system 11 is operating at the optimum current, adding a dc-to-dc converter to the system to charge a discharged battery would increase the current draw from the solar array, which would decrease the array's output power. The controller senses such a decrease in the array's output power and returns the system to the optimum current level by incrementing the control signal until it encounters a peak in the array's output power. The dc-to-dc converters are then again drawing the maximum available power from the solar array.

The batteries 14 are charged at a constant current until their voltage approaches a float voltage, whereupon the batteries float at a trickle charge current until removed from the power conversion system 11. A battery's float voltage depends on the battery's type and temperature. For example, a lead-acid battery typically has a float voltage that varies from about 14.7 volts at 15 degrees Fahrenheit to about 12.7 volts at 120 degrees Fahrenheit. Accordingly, the controller also monitors the ambient temperature and provides information to the dc-to- dc converters 22 regarding the appropriate float voltage based on the temperature. Preferably, the float voltage information is included in the control signal provided to the dc-to-dc converters via the control bus 20.

The operation of the controller 16 is most conveniently described with reference to FIGS. 2, 2A and 4. The controller includes a microprocessor 24 and accompanying circuitry that monitor the output current and output voltage of the solar array 12 and provide a control signal to the dc-to-dc converters 22 via the control bus 20. More particularly, a voltage sensor 26 measures the solar array's output voltage, and a current sensor 28 measures the solar array's output current. The current sensor 28 can include a brass ribbon (not shown) of low resistance, e.g., 20 milliohms, connected in series with the common bus 21, which serves as the return for the power bus 18, and can further include a shunt voltage sensor (not shown) for measuring the voltage drop across the brass ribbon. The voltage measurement from the voltage sensor 26 and the current measurement from the current sensor 28 are transmitted on lines 30 and 32, respectively, to the microprocessor 24. The microprocessor implements an algorithm (shown in Fig. 4 and discussed below) to produce the control signal that is provided to the dc-to-dc converters 22, for setting the battery charging current and the battery float voltage.

Preferably, the control bus 20 is a single conductor, and the control signal (Fig. 2A) is a multiplexed bi-phase pulse signal that includes alternating positive float voltage pulses and negative maximum current pulses. The controller 16 produces this control signal using circuitry that includes a digital-to-analog (D/A) converter 34, an inverter 36, a multiplexer 38, and a line buffer 40. More specifically, the microprocessor 24 has ten output lines 42 used to generate the control signal. Eight of the output lines are connected to the D/A converter. The microprocessor places a digital word or number associated with the desired level of the control signal on the eight output lines. The other two output lines are connected to the multiplexer and are used to multiplex the desired signal polarity onto the single wire of the control bus 20. More particularly, the control signal (Fig. 2A) includes a maximum current pulse 44 having a negative voltage amplitude and a float voltage pulse 46 having a positive voltage amplitude. The negative voltage amplitude of the maximum current pulse represents a current draw and the positive voltage amplitude of the float voltage pulse represents a float voltage level to the dc-to-dc converters 22. For reasons to be discussed later, a maximum current pulse having an amplitude of zero voltage sets the dc-to-dc converters to draw maximum current while a maximum current pulse having an amplitude of -5.0 volt sets the dc-to-dc converters to draw a minimum or zero current. Similarly, a float voltage pulse having an amplitude of +5.0 volts sets the float voltage to a maximum value while a float voltage pulse having an amplitude of 0 volts signal sets the float voltage to a minimum value.

The microprocessor 24 sets the positive and negative amplitudes of the control signal by generating an eight bit word on the eight output lines mentioned before. Each of these eight output lines is connected to one of the input resistors of a resistor array 47 of the digital-to-analog converter 34. The input resistors are each connected to a summing node 48 of an operational amplifier 50 having a feedback resistor 52. The resistors in the resistor array and the feedback resistor are sized to implement the desired conversion system. For example, to implement binary conversion of the digital word, the first input resistor of the resistor array and the feedback resistor have a standard resistance value R, the second input resistor has a value of 2R, the third input resistor has a value of 4R and so on until the eighth input resistor that has a value of 128R. Thus, the resistors have a binary relationship that define 256 steps allowing .4% increments in the analog signal of the digital-to-analog converter. The inverter 36 inverts the analog signal to provide a negative analog signal.

The multiplexer 38 has two input lines 54, an output line 56, an enable input line 58, and a select input line 60. One input line of the multiplexer is directly connected to the output of the D/A converter 34, and the other input line is connected to the output of the inverter 36. Accordingly, the multiplexer receives the positive amplitude pulses of the analog signal at one input line and the negative amplitude pulses of the analog signal at the other input line. In operation, the microprocessor 24 places a binary number representing the desired amplitude of float voltage pulse 46 on the eight output lines and sets the select input line 60 so that the multiplexer 38 will select the -22- positive analog signal for the output on the multiplexer output line 56. The microprocessor then toggles the enable input line 58 to place the positive analog pulse or signal on the multiplexer output line. The microprocessor then places a binary number representing the desired amplitude of the maximum current pulse 44 on the eight output lines and sets the select input line so that the multiplexer will select the negative voltage signal for output on the multiplexer output line. The microprocessor then toggles the multiplexer's enable input line to place the negative voltage pulse or signal on the multiplexer output line. After the microprocessor places the binary number on the eight lines and sets the select input line, the microprocessor provides a short delay before toggling the enable input line of the multiplexer to allow the digital- to-analog converter 34 to settle thus avoiding voltage spikes on the control bus 20. This process of setting the maximum current pulse and the float voltage pulse is repeated every 50 milliseconds. The buffer amplifier 40 merely receives the control signal on the multiplexer output line and drives the control bus with the control signal.

When a battery 14 is fully charged, the charge current is reduced to a trickle charge until the battery is removed from the system. Accordingly, the dc-to-dc converter 22 must have an indication of the battery's float voltage, to prevent damage to the battery and to extend the battery's useful life. This float voltage is known to vary with ambient temperature. An electronic thermometer 62, such as a thermistor, is provided to measure the ambient temperature (T) and to provide a temperature signal to the controller 16. Using the temperature signal, the controller adjusts the amplitude of the float voltage pulse 46 of indicate the appropriate float voltage to the plurality of dc-to-dc converters 22. In this connection, it is assumed that all of the batteries have a temperature at or near the measured ambient temperature T. To set the maximum current pulse, the controller 16 implements an algorithm shown in Fig. 4. In an initial step 100, the controller reads the output voltage (V) and output current (I) of the solar array 12. The controller then, in step 102, calculates the solar array's output power and, in step 104, either steps the maximum current pulse I up or down one level (approximately .4%) . The controller again reads the solar array's output voltage and output current at step 106 and calculates the new output power at step 108. The controller then proceeds to step 110, where it determines whether the newly calculated power is greater than or less than the previously computed power. If it is greater, the controller returns to step 104 of stepping the level of the maximum current pulse in the same direction. If, on the other hand, it is determined at step 110 that the newly computed output power remains the same or has decreased, the controller proceeds to step 112, where it changes the direction of the current step command, and then returns to step 104 of stepping the level of the maximum current pulse, this time stepping it in the opposite direction.

By way of example, if the combined current draw by the dc-to-dc converters 22 is less than the optimal current for consuming the peak available power from the solar array 12, a step down in the combined current draw will cause a decrease in the solar array's output power whereupon the controller 16 will reverse the direction of the current step. An increase in the combined current draw will increase the solar array's output power and the controller will continue to increase the amplitude maximum current pulse 44 by incremental steps until the output power decreases whereupon the controller will reverse the direction of the current step. If the combined current draw of the dc-to-dc converters is more than the optimal current, then an increase in the combined current draw will cause the solar array's output power to decrease whereupon the controller will reverse the direction of the current step. A decrease in the current draw will cause the solar array's power output to increase. Accordingly, the controller will continue to decrease the current draw until the solar array's output power again starts to decrease.

It should be noted that the amplitude of the maximum current pulse 44 on the control bus 20 never remains constant even though the peak available power from the solar array 12 remains constant. If the power system 11 is operating at the optimum point of maximum available power, the controller 16 will increment the amplitude of the current pulse by one step from that point causing a slight reduction in the solar array's output power. In response, the controller will reverse the direction of the increment step of the amplitude of the current pulse and return the system to the point of maximum output power. Since the solar array's output power will increase, the controller will continue to increment the amplitude of the current pulse in the same direction whereupon the solar array's output power will again decrease. Again, in response to the decrease, the controller will reverse the increment direction and so on. Thus, the power conversion system 11 will operate within .4% of the optimum current and will not increment more than two steps in any one direction unless the available output power of the solar array, and hence the optimum output current, changes. The slight .4% fluctuation in the charge current is relatively slow and is not significant in efficiently consuming the maximum available output power.

The algorithm for setting the amplitude of the float voltage pulse 46 is shown in Fig. 5. To implement the algorithm, the controller 16 merely reads the temperature of the thermometer 62, at step 114, and sets the amplitude of the float voltage pulse accordingly, at step 116.

The operation of the dc-to-dc converters 22 is most conveniently understood with reference to Fig. 3. Each dc- to-dc converter draws a current I_c from the power bus 18 at the solar panel's output voltage and supplies a charging current Ic to the battery 14. Each dc-to-dc converter includes a switch-mode power converter 64, positive and negative pulse amplitude discriminators 66 and 68, a control circuit 69, and light-emitting diode (LED) status indicators 70. The switch-mode power converter, using pulse-width modulation, controls the dc-to-dc converter's current draw I_c from the power bus.

The positive pulse amplitude discriminator 66 detects the amplitude of the positive amplitude pulses of the control signal received on the control bus 20 and produces a corresponding float voltage signal for output on line 72. Similarly, the negative pulse amplitude discriminator 68 detects the amplitude of the negative amplitude pulses of the control signal received on the control bus 20 and produces a corresponding maximum current signal for output on line 74. The control circuit 69 receives the first input signal on line 72, for setting the float voltage for the battery 12, and the second input signal on line 74, for setting the maximum current draw from the power bus 18. The control circuit 69 also is connected, via lines 76 and 78, to the battery 12, so that it can measure its voltage level and thereby determine its state of charge. Based on the received float voltage signal and maximum current draw signal, and further based on the battery voltage measurement, the control circuit produces an error signal that is coupled via line 80 to the switch-mode power converter 64. This controls the power converter such that an appropriate current draw from the power bus 18 is maintained. The maximum current pulse 44 affects only those dc-to- dc converters 22 that are drawing a current I_c above the threshold current set by the amplitude of the maximum current pulse. In other words, lowering the maximum current signal has an effect first on the dc-to-dc converters that are drawing the most current from the power bus 18.

The dc-to-dc converters 22 preferably each have LED status indicators 70 to indicate the battery's charge status. More particularly, the status indicators include three LED's that indicate a charging battery, a full or ready battery, and an open breaker. The open breaker LED indicates if a fuse (not shown) on the power bus 18 has blown.

Each dc-to-dc converter 22 is designed so that an amplitude of the maximum current pulse 44 of zero volts corresponds to maximum current draw from the power bus 18 whereas an amplitude of -5.0 volts corresponds to minimum current draw from the power bus. Accordingly, the failure or removal of the controller 16 from the system 10 likely will cause the control signal to drift to zero volts and thus cause the dc-to-dc converters to draw as much current as each individually can. Likewise, the dc-to-dc converter is configured so that if the amplitude of the float voltage pulse 46 is zero volts, the dc-to-dc converter sets the battery float voltage to a minimum voltage of 12.7 volts. It is recognized that at these voltage and current levels, the dc-to-dc converters will not completely charge their respective batteries 12 and, in combination, most likely will not operate to consume the solar array's maximum available power. However, the system 10 will still function to significantly charge the batteries, even though the controller fails to provide any control signal. A more detailed drawing of the connection of the control 16 and the dc-to-dc converters 22 to the power bus 18, the control bus 20, and the common bus 21 is provided in Fig. 6. These three buses are shown as solid, spaced- apart rods, preferably of nickel-coated aluminum and having a diameter of 1/4 inch. Each dc-to-dc converter is mounted on a separate printed circuit board 82 having three clips 84 arranged in a triangular manner. The clips are aligned with the parallel bus rods such that each clip connects to a different rod. When the printed circuit board is clipped onto the three rods, the triangular spacing of the clips allows the dc-to-dc converter to be held in a stable fashion. Accordingly, other dc-to-dc converters or other power loads can be added to or removed from the power bus and the control bus in a simple fashion. In addition, the controller 16 will compensate for these new power loads and drive the system such that it draws the peak available power from the solar array. Also, the controller can be mounted on a printed circuit board that also has clips like the printed circuit boards of the dc-to-dc converters to allow simple removal and/or replacement of the controller. Preferably, the clips 84 are each three snap fuse connectors that can handle a nominal current of 30 amps. It should be recognized that ac motors such as water pump motors can be powered by replacing the dc-to-dc converters 22 discussed above with dc-to-ac converters. The dc-to-ac converter's current draw from the power bus 18 can be varied by changing the converter's ac frequency. In addition, the solar array 12 can be replaced by most any type of power source having an optimum current for producing the maximum output power that is less that the power source's maximum output current. The photovoltaic electrical power distribution facility 10 is particularly advantageous for providing electrical energy to a population in a remote locality not serviced by the power grid of a conventional electrical power utility. As shown in Fig. 7, the photovoltaic electrical power distribution facility 10 includes the solar array 12, the rechargeable electric batteries 14 and the electrical power conversion system 11, which the controller 16, the power, control and common buses 18, 20 and 21, respectively, and the dc-to-dc converters 22 (Fig. 1) . The rechargeable electric batteries 14 are distributed to individuals living near the facility 10 who use the batteries at their residences and/or work sites. After use, the individuals bring the batteries back to the facility 10 for additional charging. Thus the mobility of the batteries 14, in combination with the capability of the photovoltaic electrical power distribution facility to temporarily receive the batteries 14 for charging, provide for a novel electrical distribution system and method which avoids the need for grid connected utility power and the need for electrical transmission wires and related equipment for delivering power to individuals. As discussed above, the power conversion system, as described with reference to FIGS. 1-6, adjusts the charging rate of the batteries based on the condition of the batteries and the performance of the solar array to optimize the use of electrical energy available from the solar array. It should be recognized, however, that other power conversion system configurations could be used and that even less efficient power conversion systems could be used with the present invention without detracting from the spirit of the novel photovoltaic power distribution method of the present invention.

With reference to Fig. 8, an electrical schematic is shown for another embodiment of a photovoltaic electrical power distribution facility 10 of the present invention including additional features which may be incorporated, individually or in any combination, into the facility 10 to enhance the power distribution capabilities of the facility 10 and to make it easier for individuals to use the facility 10 for obtaining electrical power. These additional features permit metering the power provided by the facility 10 to a battery, electronically paying and collecting a battery charging fee of a customer to the facility 10, testing the initial discharge level of a battery prior to charging, testing the condition of a battery to be charged and storing and releasing of electrical energy generated by a photovoltaic array in excess of that required to charge batteries which may be connected for charging at any given time. To facilitate these additional features, the facility, as shown in Fig. 8 includes, for each station at the facility 10 at which a battery 14 may be temporarily connected for charging, a charging station controller 120, a power flow switch 124, a current sensor 128, and a battery tester 132 associated with each DC-DC converter 22 and battery 14. It should be recognized that a single charging station controller 128 and a single battery tester 132 could be used for all batteries by providing a microprocessor to control their operation and to switch their connection from one battery to another as needed. Also included, as shown in Fig. 8, is a storage controller 136 and an energy storage bank 140 which are connected to the power bus 18.

The charging station controller 120 meters the energy provided to the associated battery 114 being recharged and collects a battery charging fee from individuals. The charging station controller 120 receives a current signal from the current sensor 128 indicating the amount of current provided to the battery. The charging station controller 120 multiplies the current by the time the current was applied by the DC-DC converter 22 in order to calculate the instantaneous power and thereby the time averaged energy provided to the battery. This amp-hour measurement is summed to produce a measure of the total energy input to the battery. A monetary rate per unit of energy, such as an amp-hour, delivered to the battery is then used to calculate the battery charging fee.

The charging station controller 120 electronically collects the calculated battery charging fee through a debit card system. As used herein, a debit card includes a card which permits electronic payment of the battery charging fee such as by making an electronic withdraw from an account at a financial institution such as a bank or by making an electronic transfer of prepaid credits from the card itself. For example, an individual may purchase a prepaid monetary credit on a debit card and may use the debit card to pay for battery charging services. The individual inserts the debit card into a magnetic card input/output (I/O) device 144 within the charging station controller 120 and communicates with the station controller 120 via a keypad 148 and a display 152. The charging station controller 120 reads a magnetic strip on the debit card with the card I/O device 144 in order to determine the present credit balance. When the present credit is sufficient to begin battery charging, the charging station controller 120 toggles on the power flow switch 124 to enable the transfer of energy to the battery 14. While the battery is recharging, the charging station controller 120 meters the energy provided to the battery, computes the battery charging fee, and compares the battery charging fee against the present credit on the debit card. When the battery 14 is fully charged and/or the battery charging fee equals or exceeds the original credit available on the debit card, the charging station controller 120 toggles off the power flow switch 124 to halt the transfer of energy to the battery 14. The station controller 120 then computes a new credit balance by subtracting the battery charging fee from the original credit and records the new credit balance on the magnetic strip on debit card via the card I/O device 144. The individual is notified via the display 152 that the battery is fully charged or that battery charging has been prematurely halted due to an insufficient credit balance. When the charging has been prematurely halted, the user could purchase additional credit in order to complete battery charging. At the end of the transaction, the debit card is returned to the individual for later use in purchasing additional battery charging credit. The charging station controller 120 further enables a user, though use of the keypad 148, to adjust the amount of total charge delivered to the battery 14 or the rate of charge of the battery 14 by specifying a time period for recharging or by specifying a total amount of energy to be delivered to the battery. Also, the user could specify recharging on a priority basis. The station controller generally charges a fee rate that increases with an increase in energy delivered to the battery. In response to an individual specifying a time period, or a total energy input, for recharging, the charging station controller 120 adjusts the maximum current limit for the associated DC-DC converter 22 so as to adjust the rate of energy flow to the associated battery and thereby the time required to recharge the battery. In response to an individual specifying a total energy input into the battery, the charging station controller will cause the charge to be discontinued when the specified energy has been delivered to the battery, assuming the battery has not already been fully charged. In response to an individual specifying recharging on a priority basis, the charging station controller 120 recharges the battery 120, along with other batteries 114 previously specified as priority, at an accelerated rate relative to lower priority batteries and/or allows an individual to temporarily disconnect a lower priority battery from the facility 10 and to replace it with a higher priority battery. Specifying a special charging feature, such as those just described generally will cause a higher fee to be calculated for the charge than if no special feature had been selected. Other special charging features could also be provided for.

The charging station controller 120 operates with the battery tester 132 to permit checking the discharge level of a battery and checking the condition of a battery 14 to determine if the battery should be replaced. To test the discharge level of a battery 14, the station controller 120 toggles off the power flow switch 124 to halt the flow of power to the battery 14 while the battery tester 132 connects a resistive load having a known resistivity across the terminals of the battery 14. The station controller 120 measures the current signal from the current sensor 128. Using the known resistivity of the load and the sensed current, the station controller 120 computes the discharge level of the battery. The recharging efficiency of a battery is tested by the battery tester 132 measuring the temperature of the battery and providing a temperature signal to the station controller 120. Preferably, the battery tester 132 includes a temperature sensor (not shown) , such as a thermistor, which is in thermal communication with the battery so as to sense the battery's core temperature. The charging station controller 120 monitors the increase in battery temperature as a function of the recharging energy delivered to the battery in order to determine the amount of energy that is lost as heat due to the battery's recharging inefficiency. The individual is notified of the battery's recharging efficiency via the display 152 and is advised to repair or replace the battery when the battery's inefficiency reaches a predetermined threshold.

The energy storage bank 140 and the storage controller 136 function to collect energy from the power bus 18 when the solar array 12 generates more energy than can be efficiently utilized by the recharging batteries 14 and functions to return the collected energy back to the power bus 18 when the recharging batteries 14 can efficiently use more energy than the solar array 12 can generate. In this manner, the energy storage bank 140 increases the efficiency of the conversion system 10 while the energy generated and used within the system 10 varies due to factors such as varying insolation on the solar array 12 and the varying number and energy needs of the recharging batteries 14. The storage bank 140 may comprise any energy storage device or devices capable of storing, for a period of from several minutes to several hours, the excess energy generated by the solar array. Furthermore, the storage bank 140 should have sufficient energy storage capacity to permit storing of sufficient energy to provide electrical energy as needed to charge a discharged battery for a duration of at least 5 minutes and, preferably, for a duration of greater than about 30 minutes. Such energy storage devices include electrical energy storage devices such as capacitors and batteries as well as mechanical energy storage devices such as a liquid head or a flywheel.

In a further aspect of the present invention, a method is provided for supplying electrical power in specific unit quantities from the docking devices of the present invention to residences and businesses that are distant from and not electrically interconnected with the location where the electrical power is generated. The method includes the steps of charging a portable electrical energy supply unit, such as a docking device, at a first location, such as the photovoltaic power distribution facility; transporting the portable electrical energy supply unit to a second location, such as a residence or a business, where electrical energy is consumed; and consuming electrical energy from the portable electrical energy supply unit, with energy output being regulated to prevent further discharge after a predetermined quantity of energy has been supplied from the portable electrical energy supply unit.

The portable electrical energy supply unit includes a rechargeable electrical power source, such as a rechargeable battery, electrically connected with an energy output regulator. The output regulator prevents the rechargeable electrical power source from supplying electrical energy after a predetermined quantity of energy has been supplied from the rechargeable electrical power source since the last recharge. Typically, the quantity of energy supplied by the rechargeable electrical power source is tracked by integrating over time the amount of current delivered from the rechargeable electrical power source. Therefore, the output regulator is capable of preventing power from being discharged from the rechargeable electrical power source when a predetermined amount of ampere-hours have been supplied. Additionally, the output regulator preferably also prevents the rechargeable electrical power source from supplying power after the voltage across the rechargeable electrical power source has dropped to a predetermined level, in the event that the voltage drops to an undesirably low level prior to the portable electrical energy supply unit having supplied the predetermined quantity of electrical energy. Although the foregoing discloses the preferred embodiments of the present invention, it is understood that those skilled in the art may make various changes to the preferred embodiments without departing from the scope of the invention. The invention is defined only by the following claims.

Claims

What is claimed is: l. A portable electrical energy supply apparatus for use in connection with distributing electrical power generated by a photovoltaic power station, the photovoltaic power station including a photovoltaic source, a battery charging terminal having a charging outlet of a first selected type and a charge controller, operatively interposed between the source and terminal, for receiving power from the source and providing a selected charging signal to the battery charging terminal, said apparatus comprising: a rechargeable electrical battery that is capable of receiving said selected charging signal so as to store energy from said photovoltaic source; housing means for use in containing and transporting said battery; housing outlet means, supported by said housing means, including a housing outlet of a second selected type for mating with said charging outlet of said first selected type so as to electrically interface said housing outlet means to said photovoltaic power station; and interconnection means, operatively interposed between said battery and said housing outlet means, for electrically interconnecting said battery to said outlet means whereby said battery receives energy from said photovoltaic source; wherein said apparatus provides for photovoltaic power station charging compatibility and for convenient power station docking.

2. The apparatus of Claim 1, wherein each of said charging outlet of said first selected type and said housing outlet of said second selected type is incompatible with standard outlets of a power distribution area of the power station, thereby facilitating regulation of photovoltaic power station usage.

3. The apparatus of Claim 1, further comprising first dwelling outlet means, adapted for installation within a dwelling, for use in providing power to said dwelling, said dwelling outlet means including a dwelling outlet of said first selected type for mating with said housing outlet of said housing outlet means.

4. The apparatus of Claim 3, further comprising second dwelling outlet means, electrically interconnected to said first dwelling outlet means, for use in providing power to said dwelling, said second dwelling outlet means including a second dwelling outlet of a third selected type different from said first and second types.

5. The apparatus of Claim 1, further comprising: recharging terminal means, supported by said housing means and electrically interconnected to said battery, for use in recharging said battery with energy from said remote photovoltaic power source; discharge control means, operatively interposed between said battery and said housing outlet means, for controlling delivery of power from said battery to a first electrical line outlet of a dwelling; wherein said first electrical line outlet of said dwelling mates with said housing outlet of said second selected type.

6. The apparatus of Claim 5, wherein said discharge control means comprises means for monitoring a discharge state of said battery and controlling discharge from said battery responsive to said monitored state.

7. The apparatus of Claim 5, wherein said discharge control means comprises a switch associated with said outlet means for selectively interconnecting said battery and said outlet means.

8. The apparatus of Claim 5, further comprising a second electrical line outlet, adapted for installation within said dwelling, for use in powering an electrical appliance, wherein said second outlet is of a third type different from said outlet of said first selected type and said first electrical line outlet.

9. The apparatus of Claim 1, wherein: said housing outlet means provides for dual use, said housing outlet means being electrically interconnectable with said photovoltaic power station when said battery is being charged and said housing outlet means being electrically interconnectable with a dwelling when power to said battery is supplying electrical power.

10. The apparatus of Claim 9, further comprising switch means, operatively associated with said housing outlet means, for selectively interconnecting said battery with said photovoltaic power station and said dwelling.

11. The apparatus of either one of Claim 1 or 9, further comprising discharge control means, operatively interposed between said battery and said housing outlet means, for monitoring a discharge state of said battery and controlling discharge from said battery responsive to said monitored state.

12. The apparatus of any one of Claims 1, 5 and 9 wherein said housing means substantially encases said battery so as to inhibit access to said battery other than via said outlet means.

13. The apparatus of any one of Claims 1, 5 and 9, wherein said housing is constructed from an electrically insulating material that is resistant to battery acid degradation.

14. The apparatus of any one of Claims 1, 5 and 9, wherein said interconnection means comprises switch means for selectively interconnecting said housing outlet means to said battery.

15. The apparatus of any one of Claims 1, 5 and 9, further comprising vent means, extending between said battery and said housing means, for venting gases produced by said battery.

16. The apparatus of Claim 1, further comprising: a discharge controller operatively electrically interconnected with said battery, said discharge controller preventing said battery from supplying electrical energy when a predetermined quantity of energy has been supplied from said battery since a last recharge of said battery; wherein said housing means encloses and contains both of said battery and said discharge controller, to provide for portability of the apparatus between a first location where said rechargeable energy power source is recharged and a second location where electrical energy stored in said battery is consumed.

17. The apparatus of any one of Claims 1, 5, 9 and 16, wherein the apparatus weighs less than about 25 kilograms.

18. The apparatus of any one of Claims 1, 5, 9 and 16, wherein the apparatus occupies a volume of less than about 1000 cubic centimeters.

19. The apparatus of any one of Claims 1, 5, 9 and 16, wherein the apparatus comprises a top and a bottom, said top and bottom having complimentary interconnecting surfaces so that each apparatus is stably stackable.

20. The apparatus of any one of Claims l, 5, 9 and 16, wherein said housing means includes a locking mechanism to prevent access into the interior of said housing means.

21. The apparatus of any one of Claims 1, 5, 9 and 16, wherein said battery comprises a voltaic cell having an electrolyte that is substantially not flowably mobile, to prevent inadvertent spills of electrolyte from the apparatus.

22. The apparatus of Claim 16 wherein said housing outlet comprises a first receptacle capable of accepting a first electrical plug for supplying electrical power from the battery when said apparatus is connected to an external electrical load, said first receptacle also capable of accepting a second electrical plug for receiving electrical power when said battery is being charged at said photovoltaic power station.

23. The apparatus of Claim 16, wherein said housing means comprises a first compartment and a second compartment that is substantially physically separated from said first compartment, said first compartment housing said battery and said second compartment housing said discharge controller.

24. The apparatus of Claim 23, wherein said first compartment substantially encases active components of said battery, with terminals of said battery extending to outside of said first compartment, said second compartment includes the interior of a cap attached to the outside of said first compartment, said cap housing said discharge controller and portions of said terminals that extend to outside of said first compartment.

25. The apparatus of Claim 16, wherein said predetermined quantity of electrical power output is from about 30 ampere-hours to about 50 ampere-hours.

26. The apparatus of Claim 16, wherein said discharge controller is capable of preventing said battery from supplying electrical energy when voltage across said battery is less than a predetermined voltage prior to the predetermined quantity of energy having been supplied from said battery since a last recharge of said battery

27. The apparatus of Claim 16, wherein the predetermined quantity of energy is measured from said battery by integrating over time electrical current supplied from said battery.

28. A method for supplying electrical power in specific unit quantities to remote locations, the method comprising the steps of: transporting a portable electrical energy supply unit from a first location to a second location; said electrical energy supply unit comprising a portable container enclosing a battery and an energy output regulator with which said battery is operatively electrically interconnected; said first location being a location where said electrical energy supply unit is electrically charged for storage of electrical energy; said second location being a location distant from said first location where electrical energy from said portable electrical energy unit is consumed; wherein said output regulator prevents said battery from supplying electrical energy, at said second location, when a predetermined quantity of energy has been supplied from said electrical energy supply unit since a last charging of said battery.

29. The method of Claim 28, wherein the unit is adapted for being temporarily received in and electrically interconnected with a recharging station, said recharging station being capable of temporarily receiving, electrically interconnecting with and charging a plurality of said electrical energy supply units with electricity supplied by a photovoltaic electrical power generator.

30. The method of Claim 28, wherein said energy output regulator is capable of preventing said battery from supplying electrical energy, at said second location, when voltage across said battery is less than a predetermined voltage, when said voltage across said battery drops below said predetermined voltage prior to having supplied said predetermined quality of energy since a last charging of said battery

31. The method of Claim 28, wherein said predetermined quantity of energy is measured in ampere- hours and said energy output regulator integrates over time electrical current supplied from said electrical energy supply unit since a last charging to determine when the quantity of energy supplied by said electrical energy supply unit exceeds said predetermined quantity.

32. A portable electrical energy supply unit useful for distributing electrical power in specific metered quantities to remote locations, the unit comprising: a rechargeable electrical power source capable of supplying electrical energy when connected with an electrical load external to the unit; an energy output regulator operatively electrically interconnected with said rechargeable electrical energy power source, said energy output regulator preventing said rechargeable electrical power source from supplying electrical energy when a predetermined quantity of energy has been supplied from said rechargeable electrical energy power source since a last recharge of said rechargeable electrical energy power source; and a portable container enclosing said rechargeable electrical power source and said energy output regulator, to provide for portability of the unit between a first location where said rechargeable energy power source is recharged and a second location where electrical energy stored in said rechargeable electrical power source is consumed.