SPECIFICATION

FIELD OF INVENTION

[001] The present invention relates to large scale industrial batteries for use in power supply shifting applications.

BACKGROUND OF THE INVENTION

[002] A primary concern in power generation using intermittent energy source such as wind and solar, is that the source is too variable to ensure continuity of supply to the load. The opposite problem exists when there is excess wind and/or low demand, such that the ability to offer energy at the high value opportunities during peak demand may be wasted. Various methods have been proposed for large scale energy storage in relation to an electricity grid or in industrial contexts using, for example, high temperature batteries, flow batteries, batteries composed of materials hazardous to the environment, or pumped water to store excess energy as potential energy above a hydro electric dam. [003] Canadian patent 1 ,055,566, for a "Load Levelling Battery Device", to Lindstrom,

May 29, 1979, discloses a Lead-Iron battery for load levelling in a power system, but this uses undesirable lead based electrolyte and electrode at the positive electrode.

[004] The Raccoon Mountain Pumped-Storage Plant in Tennessee, USA, uses pumped water storage between a lower reservoir and an upper reservoir measuring 528 acres, which is highly capital intensive and only suitable in very particular geographies. The system is not scalable.

[005] These existing methods do not focus on appropriate cost constraints on return of stored energy to the system. These systems also incur large potential or actual environmental costs. There is a need for a system using materials which are intrinsically low in cost, safe and pose comparatively less risk to the environment.

[006] In areas where wind power is viable, there is a need for an energy storage system capable of storage on the order of days to minimize the need for the use of redundant fuel based systems, and as such, a power shifting system must be scalable to a very large size.

[007] Traditional battery technology focuses on light weight, portability and high energy density, which are not the key considerations in a fixed system which is meant to store large amounts of power slowly for discharge over a period of days.

[008] Traditional measures of battery efficiency disregard the trade-off in capital cost. In backing up wind and solar power systems an efficient battery reduces the need for excess generating capacity. However in the case where the cost of the battery is high relative to the cost of the generating equipment the economics of a project could be better served using a low cost, less efficient battery and additional generating capacity to cover the electrical losses of the battery. [009] Further areas of cost saving may exist in using otherwise waste materials to replace more expensive electrode components.

[010] There is also a need for a battery system which is capable of being deployed in remote, low temperature environments.

SUMMARY OF THE INVENTION [01 1] The present invention is a secondary cell which combines in a novel way, the oxidizing/reducing reaction of CuS0 ₄ + MnS0 + 2H ₂ 0 <→ Cu + Mn0 ₂ + 2H ₂ S0 . Optionally, the presence of divalent and trivalent iron inhibits the accumulation of copper and manganese dioxide within the cell should it become disconnected from the electrode, through more favourable reactions involving Fe ⁺³ <--> Fe ⁺² , present in appropriate concentrations. [012] The rechargeable/secondary electrochemical cell uses inert electrodes in an aqueous electrolyte. The inert electrodes may be carbon. The electrolyte is an aqueous solution which includes the following: manganese II sulfate (MnS0 ₄ ), copper II sulfate (CuS0 ₄ ), sulfuric acid (H ₂ S0 ₄ ). To improve long term performance, iron II sulfate (FeS0 ₄ ), and/or iron III sulfate (Fe ₂ (S0 ) ₃ ) may also be added to the electrolyte.

[013] During charging, manganese IV oxide (Mn0 ₂ ) and/or manganese III oxide

(Mn ₂ 0 ₃ ) is precipitated onto the positive electrode and metallic copper is precipitated onto the negative electrode: according to the following reactions which occur at a charging voltage slightly greater than 1.17 Volts CuS0 ₄ + MnS0 ₄ + 2H ₂ 0 <→ Cu ^metal + Mn0 ₂ ^solid + 2H ₂ S0 ₄ Eq. (1)

[014] which can be separated into

Cu ⁺² + (S0 ₄ ) ^"2 + H ₂ 0 + 2e <→ Cu ^metal + H ₂ S0 ₄ + O ^"2 Eq. (2)

Mn ⁺² + (S04) ^"2 +H ₂ 0 + O ^"2 <→ Mn0 ₂ ^solid + H ₂ S0 ₄ + 2e ^" Eq. (3)

[015] Provided that the copper and manganese dioxide remain connected to the electrodes, the cell has a discharge voltage slightly less than 1.17 Volts. However, the cell chemistry should also be designed to address certain of side reactions, as well as the spontaneous separation of the precipitated solids from the electrodes.

[016] One important side reaction during changing is the formation of manganese III sulfate as follows: CuS0 ₄ + 2MnS0 ₄ <→ Cu ^metal + Mn ₂ (S0 ₄ ) ₃ Eq. (4)

[017] The copper so formed is deposited on the electrode, and the manganese III sulfate remains available in the solution to contribute to the discharge energy of the cell. However, it may also convert to manganese II oxide (Mn0 ₂ ) through the following disproportionation reaction: Mn ₂ (S0 ₄ ) ₃ + 2H ₂ 0→· MnS0 ₄ + Mn0 ₂ ^solid + 2H ₂ S0 ₄ Eq. (5)

[018] The disproportionation reaction of Eq.(5) is favoured over the side reaction of Eq.

(4) by decreasingly acidic electrolyte.

[019] Another side reaction which is detrimental to the chemistry of the cell is the formation of oxygen gas at the negative electrode under the following reaction.

2CuS0 ₄ + 2H ₂ 0→· 2Cu + 2H ₂ S0 ₄ + 0 ₂ Eq. (6)

[020] The reaction of Eq. (6) can occur at a voltage similar to that of the reaction in Eq.

(1), but is hindered by higher concentrations of manganese in the electrolyte and by lower current density on the positive electrode during charging. [021] The long term operation of the cell through repeated charge/discharge cycles can result in the loss of precipitated Mn0 ₂ and Cu from the electrode, and the reaction in Eq. (5) may also result in precipitated Mn0 ₂ accumulating on the bottom or sides of the cell. Since neither Mn0 ₂ nor Cu will redissolve into the electrolyte without a charge transfer, a small concentration of iron II sulfate (FeS0 ₄ ), and/or iron III sulfate (Fe ₂ (S0 ₄ ) ₃ ) can be added to the electrolyte solution. When the cell is being charged or discharged, both divalent and trivalent iron will be present in the electrolyte if either is present in the electrolyte. With some loss in cell efficiency, divalent iron will scavenge Mn0 ₂ , and trivalent iron will scavenge Cu, according to the following reactions:

2FeS0 ₄ + Mn02 + 2 H ₂ S0 ₄ →· Fe ₂ (S0 ₄ ) ₃ + MnS0 ₄ + 2H ₂ 0 Eq. (7) Fe ₂ (S0 ₄ ) ₃ + Cu FeS0 ₄ + CuS0 ₄ Eq. (8)

[022] The trade off for being able to scavenge the fallen copper and manganese II oxide, is that the Fe ⁺² > Fe ⁺³ side reaction shunts some current uselessly across the cell, reducing efficiency but increasing cell longevity. With Fe comprising less than 0.2% of the electrolyte, a cell efficiency (measured as kWh out/ KWh in) of over 50% is achievable. [023] The cell uses rough or porous electrodes which favour deposit of the copper metal and manganese dioxide on the electrodes. A suitable electrode can be made from rough or porous carbon, or carbon felt. Other methods for producing porous electrodes are known in the art (including dissolved polystyrene nanoporous electrode), and may also be suitable for this application provided that the electrode material is non-reactive with the electrolyte, and the production cost is low. The electrodes should have large surface areas, with or without a thinly deposited coating of metal or oxidizer (as applicable) prior to use, to reduce the likelihood of metal or oxidizer falling off the electrodes.

[024] An electrode using calcined petroleum coke (CPC) chips compressed about a centrally disposed carbon tube connector can be a more cost effective solution. CPC chips have rough and porous surface, and form good electrical conductivity when compressed. CPC is readily available as a waste product from crude oil refining (and oil sands refining in particular). While CPC can be used as a fuel, its use as fuel may be subject to emissions regulation. Alternative uses which sequester the carbon (such as in this proposed use in the electrodes of secondary cells) are preferred. A piece of carbon rod is provided with a sealed electrical connection to a sheathed wire of appropriate materials for immersion in the electrolyte. The carbon rod connector is disposed centrally within an appropriately shaped mesh tube, and CPC chips compressed within it. Compression may be caused by the mesh itself or additional windings of string or cord. [025] At an industrial size, the cell does not require a separator to prevent bridging of the space between electrodes by metal or oxidizer, because the precipitated layers remain thin relative to the electrode spacing. Also, the porous nature of the electrodes retains the precipitated materials. Avoiding separators reduces the costs to manufacture and maintain the cell. [026] The arrangement of electrodes within the cell according to an appropriate lattice can help ensure more uniformity of electrode spacing over the full extent of the area of the positive electrodes and negative electrodes.

[027] Very large cells of this type may suffer from stratification of the electrolyte. Optionally, a mixer (such as a small pump, bubbler or agitator) may circulate, mix or agitate the electrolyte from bottom to top to break up any stratification which might occur in the electrolyte during charge/discharge cycles as the electrolyte density changes. This mild stirring reduces concentration gradients within the cell which might otherwise cause uneven deposition of solids on the electrodes. Mild circulation of the electrolyte permits large scale single cells using the foregoing chemistry.

[028] Cells of this type disclosed, may be interconnected with a remote sporadic power source to help stabilize energy supply.

[029] The electrolyte may be doped with spectator ions or organic compounds to depress the freezing point of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[030] Figure 1 is a diagram showing the cell chemistry during the charge cycle.

[031] Figure 2 is a diagram showing the cell chemistry during the discharge cycle.

[032] Figure 3 is a side view of an electrode for use in the cell, and Figure 3A is a cross section view along section lines A-A, and Figure 3B is an enlarged view at the region B. [033] Figure 4 is the diagram of an industrial sized example of the electrochemical secondary cell with a recirculating pump. [034] Figure 5 is a front view of one example cell within a 205 litre drum. Figure 5A shows a cross section of an embodiment of the cell using carbon tube electrodes. Figure 5B shows a cross section of an embodiment of the cell using CPC chip based electrodes.

[035] Figure 6 is a diagram of a system of the present invention incorporated into a power grid with intermittent sources.

DETAILED DESCRIPTION OF THE INVENTION

[036] Certain embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings.

[037] Figure 1 describes the charge cycle, wherein copper solid is deposited on electrode (10) according to the reaction (13) while manganese dioxide is deposited on electrode (11) according to reaction (14), provided that a charging voltage in excess of 1.17 Volts (an approximate threshold of 1.25 Volts may be used) is applied by voltage source (15) across the circuitry (12) connecting electrode (10) and electrode (11).

[038] Figure 2 describes the discharge cycle for the cell of Figure 1 , wherein copper previously solid deposited on electrode (10) and manganese dioxide previously deposited on electrode (11) power circuit (16) having load (23) according to reaction (21) at the copper electrode and reaction (22) at the manganese dioxide electrode, at approximately 1 Volt.

Electrolyte Example 1

[039] In one example, the electrolyte solution comprises manganese (II) sulfate, copper (II) sulfate, sulfuric acid and water. The cell functions satisfactorily over a wide range of concentrations of each of the 4 ingredients, subject to the following constraints which are addressed in accordance with the art. Copper (II) sulfate is moderately soluble in water, approximately 17% by weight of the anhydrous product forming a saturated solution in water at room temperature. Manganese (II) sulfate is also moderately soluble in water, approximately 32% by weight of the anhydrous product forming a saturated solution in water at room temperature. The solubility of both is limited by the total concentration of sulfate ion and diminishes with decreasing temperature. Therefore, the above amounts cannot be attained simultaneously in the same electrolyte and the solubility of CuS0 ₄ and MnS0 ₄ are further decreased with the addition of sulfuric acid. The desire to maximize the concentrations of Cu and Mn ions in the appropriate ratio, is offset by the desire to improve conductivity of the cell and to depress the freezing point of the cell, through the addition of acid.

[040] The following solution has been found to perform satisfactorily in a rechargeable cell, without the precipitation of the dissolved salts at room temperature, at the concentrations indicated: a. 14.0% by weight anhydrous MnS0 ₄ ; b. 7.7% by weight anhydrous CuS0 ; c. 9.3% by weight anhydrous H ₂ S0 ₄ ; and d. Water. Electrolyte Example 2

[041] In a second example, the following solution has been found to perform satisfactorily in a rechargeable cell, without the precipitation of the dissolved salts at temperature down to -25 °C, at the concentrations indicated: a. 7.8% by weight anhydrous MnS0 ; b. 1.7% by weight anhydrous CuS0 ; c. 18.6% by weight anhydrous H ₂ S0 ₄ ; and d. Water. Electrolyte Example 3

[042] In a third example, various concentrations between those of example 1 and example 2 have been found to function satisfactorily in a rechargeable electrochemical cell, subject to limitations of mutual solubility. Cells with higher Cu to Mn ratios tend to be less stable with respect to the evolution of oxygen gas from the positive electrode. Cells with lower H ₂ S0 ₄ concentrations tend to have higher internal resistance and freezing point. Production of Mn ₂ (S0 ₄ ) ₃ during charging is promoted by higher Mn concentration and acidity.

Electrolyte Example 4

[043] In a fourth example, small amounts of iron can be dissolved into the electrolyte in addition to the four base components of the electrolyte. For instance, iron can be introduced in either trivalent or divalent form through the addition of Fe ₂ (S0 ₄ ) ₃ or FeS0 ₄ . Using divalent iron is somewhat preferred as the trivalent iron can interfere with the precipitation of copper on the negative electrode. Concentrations as high as 1 % by weight of FeS0 ₄ are tolerated within the copper/manganese cell, but 0.25% or less by weight of FeS0 ₄ should be sufficient in preventing build up of manganese dioxide or copper solids in places of the cell not in electrical connection with the electrodes.

Electrolyte Example 5

[044] In a fifth example of an electrolyte of the copper/manganese cell, the electrolyte can have the following concentrations: a. 9.39% MnS0 ₄ , b. 2.55% CuS0 ₄ , c. 0.2% FeS0 ₄ , d. 13.95% H ₂ S0 ₄ , and e. 73.91 % H ₂ 0 resulting in a theoretical maximum of 4.28 A-hr/kg of electrolyte. This electrolyte remains liquid above -15 °C. Below this temperature, the water component of the electrolyte starts to freeze, and forms a slush. Mechanical Configuration of Electrodes

[045] Both positive and negative electrodes may be made from carbon. Carbon is resistant to chemical attack by the electrolyte ingredients during charge, discharge and standby. While copper can be used for the negative electrode, it would deform in shape as the copper is repeatedly dissolved and deposited during discharge and charge cycles. Carbon can be used in the form of chips, rods, plates, bars , mechanically confined chip, or in felt or other fibrous or fabric forms. If the surface of the carbon electrodes is overly smooth, the deposited manganese dioxide or copper metal may be less likely to adhere to the electrodes, and would fall into solution resulting in a loss in cell efficiency.

[046] In a first example of the mechanical configuration of the electrodes within the cell, the electrodes are fabricated carbon tubes. A second example is carbon felt. A third example is carbon chip. These types of electrode configurations are advantageous when the deposited layers of metal and oxidizer are thin and when the current density at the electrode surface is low. These conditions characterize the cells having the electrolytes noted in the examples above. Mechanically confined carbon chip or carbon felt has a rough, porous surface, providing good adhesion to precipitated manganese dioxide and copper.

[047] The third example of mechanically confined carbon chip may, in some instances, be preferred as a lower cost solution. Calcined petroleum coke (CPC) chip may even be available at a negative cost in some North American markets, and in chip form, provides increased surface area for the reactions, at decreased cost compared to fabricated rods. [048] Figure 3 shows one example of a carbon electrode which may be used in the copper/manganese secondary cell discussed above. A support shaft (34) aids in fabrication of the electrode and provides structural support. Figure 3A shows the cross section on horizontal plane A-A, in which CPC chips (31) are compressed about the support shaft (34) within a mesh tube (33). Figure 3B shows an expanded vertical cross section in the region B. In Figure 3B, electrical wire (36) is anchored in a nonporous (impermeable to the electrolyte) carbon plug connector (32), in electrical connection with and surrounded by mechanically confined/compressed CPC chips (31). To improve electrical connectivity, the CPC chips must be compressed, so windings (35) further compress the packed CPC chips (31) about the support shaft (34) and the connector (32). In the example tested, a 2" diameter fibreglass mesh screen tube (33), forms an outer boundary to the electrode, with a 7/8" CPVC tube forms an inner core (34). The annular space between is packed with CPC chips (1/4" nominal size) (31). Polypropylene cord or twine (35) is wound tightly around the exterior of the mesh tube (33), in a spiral pattern to keep the CPC chips (31) under compression and preserve electrical connectivity. The carbon plug connector (32) shields the metal wire (36) from exposure to the electrolyte, and shows good conductivity up to about 50 cm from either end of the electrode. If the electrode shown is 1 meter in length, the connector (32) should be centrally disposed. Longer electrodes could use multiple connectors (32) or thicker electrodes may be shown to have even greater conductivity, and/or permit larger spans between connectors (32). Mechanical Configuration of Cell 1

[049] Figure 4 shows a copper/manganese dioxide cell in housing (41), with an electrolyte level (42) submerging electrodes (43) which are connected by design as either positive electrodes (44) or negative electrodes (45). The cell is sealed by removable cover (46), and recirculating pump (47) redistributes electrolyte from the bottom of the cell to the top, in a turn-over up to once per charge discharge cycle. A slight density difference in the electrolyte formed on discharge causes some layering within the electrolyte which is easily mixed at low input energy to maintain cell performance.

[050] The long dimension of the carbon portion of the electrode is one limiting factor in the conductivity of that electrode. Various configurations can be proposed to limit the distance between carbon portions of the electrode and the conductive metal contact of that electrode. As more advanced carbon electrodes become available, use of them in the cells of this invention to obtain new dimensions should be considered within the scope of the present invention.

Mechanical Configuration of Cell 2

[051] Figure 5 shows a cell configured in a standard 205 litre drum (50) with positive terminal (51) and negative terminal (52). Two different cells have been tested in the drum configuration using different elections. Figure 5A shows a second example of the cell using 90 fabricated carbon tube electrodes which are either positive electrodes (55) or negative electrodes (56). Plastic tube sheet (53) lines the drum (50) and vertical structural tubes (54) may also be provided. A recirculating pump or other mixing device (not shown) should also be used as was the case in cell 1.

Mechanical Configuration of Cell 3

[052] The third example of the cell is a version of the drum shown in Figure 5B, in which 57 CPC chip based electrodes are positioned in the drum (50) as either positive electrodes (57) or negative electrodes (58). The same liner (53) and vertical supports (54) from the cell 2 may be used, and a recirculating pump or other mixing device (not shown) should also be used as was the case in cell 1.

Industrial application

[053] Batteries may be formed using the individual cells of the present invention.

Connecting the cells within the battery in parallel maintains low voltage across individual batteries, with increased current. Configured in this way, whole batteries, rather than individual cells, can be monitored for faults by establishing relatively tight thresholds for permitted voltage across each battery during charge or discharge. Alternatively, individual cells within a parallel battery may be monitored and turned on and off based on fault characteristics without a need to deactivate the entire group of cells.

[054] The system has a low output voltage over a single cell and low power density.

This is not seen as a particular drawback where cost of materials and not size of materials is the primary concern. An ultra large power storage system permits use of very large inexpensive batteries constructed with the above noted materials which provide significant cumulative power delivery and energy storage at a low total cost basis.

[055] High internal resistance of carbon based components for the electrodes are overcome using large surface areas of electrode in contact with the electrolyte. Again, the large size of the system is designed to reduce inefficiencies.

[056] Individual cells of this system experience significant self discharge rates (approximately 1 % per day) which would not be suitable for long term (i.e. multiple weeks or months) power storage. However, the proposed application of power supply shifting does not require long term storage, as during periods of storage there is an oversupply of electricity to maintain the charge within the cells. Similarly, the energy storage density required by the proposed application is much lower than for batteries required in electric vehicle batteries or for batteries used in high-demand portable appliances. The power density (megawatts efficiently deliverable divided by weight/volume of the installation) is related to the energy density by the drawdown time. Using 25 hours as a benchmark, the required power density in megawatts per tonne becomes 4 percent of the energy density in megawatt-hours per tonne. This drawdown- time is longer than for many smaller-scale high-performance battery applications, which further justifies the use of the atypical battery materials [057] In remote installations, where the size of the installation is not limited by land value, these low cost, large volume cells may provide an economic advantage. The use of CPC chip, a waste product from petroleum refining, provides the added advantage of sequestering carbon which might otherwise be burned as fuel. [058] This cell may include using a common electrolyte (i.e. no separator between positive and negative areas of the cell), so as to simplify the system and keep maintenance and operations costs low.

[059] One objective of the immediate invention is to provide an inexpensive means for electrical energy storage on the scale of hundreds of megawatt-days. This energy storage capability can be used to exploit hour to hour and day to day differentials in electricity prices, or to store wind or solar energy in a supply smoothing application. Two key design criteria are used to quantify successful operation of the system of the present invention: 1) The capital cost of the energy storage unit (dollars capital investment per stored megawatt-hour) must be less than competing technologies and low enough to make the system commercially attractive. 2) Subject to constraints as dictated by objective no. 1 , the efficiency of the energy storage unit (megawatt-hours returned to the grid divided by megawatt-hours initially drawn) must be maximized and operating and maintenance costs must be kept at a minimum.

[060] In general, the present disclosure relates to an electrochemical cell, but also includes: the specific cells engineered from the generalized electrochemical cell chemistry; freezing point depressed cells, cells with a common electrolyte (i.e. no separator between positive and negative areas of the cell); power systems which use battery fields of these cells to store energy during periods of excess supply and to load level during periods of insufficient supply; electrodes used in such cells; and the particular cells designed and claimed in the embodiments. [061] A complete charge is defined as occurring when copper is maximized at the negative electrode or manganese dioxide is maximized at the positive electrode (i.e. virtually all of one of the corresponding ions has been depleted from the electrolyte and the solid deposited on its respective electrode). Full discharge occurs when either all copper or all manganese dioxide has been dissolved off its respective electrode. In practice, tolerance limits may be placed on the voltage of the system such that the discharge cycle may be notionally determined by depleting a certain percentage of the active solids, such that a base remains for the following cycle.

[062] Figure 6 describes a plant using batteries (61) of the present invention to store electrical power from solar power sources (63), wind power sources (62) or the power grid (66) during periods of excess production or low electrical power cost and to return such power to the grid (66) during peak demand or wind or sun drop off. The plant further comprises a power switching station (64) and monitoring/control systems (65) to monitor the battery (61) for charge state and any voltage problems which may indicate a need for refurbishment or individual cells. The power switching station (64) is capable of opening circuits at individual batteries to shut off voltage supply or generation from failed batteries. The monitoring/control systems (65) are capable of signalling a technician to refurbish individual cells.

[063] In a preferred example, a first lattice of a large number of interconnected compressed CPC chip tubes are immersed in the electrolytic fluid as the negative electrode with spacing between them for a second lattice of a large number of interconnected compressed CPC chip tubes partially submersed in the electrolytic fluid as the positive electrode. Using the preferred electrolyte noted above in electrolyte example 5 and the CPC chip electrodes of Figure 3, the battery has been demonstrated to be capable of storing and then discharging approximately 1 amp per electrode pair, and approximately 3.6 kWh per 1000 litres of electrolyte. A cell with 1000 litres of electrolyte can be charged and discharged at a rate of approximately 300 Watts over a 12 hour period. The circulating pump, if this is the form of mixing used, need only be used briefly (2% duty cycle) between the discharge cycle and the charge cycle and requires less than 1 % of the power available during a charge cycle to maintain sufficient uniformity in the electrolyte. The power requirements for mixing become de minimus as the size of the cell is scaled up. A maintenance voltage of 1.25 Volts and 1.5 Amps per 1000 litres can keep the battery in a fully charged state and overcome self discharge. The battery is able to return about 50% of stored energy to the grid based on observed electrical losses during charge, discharge and standby.

[064] A plant of the present invention would be composed of arbitrarily large individual cells up to 1 mWh per cell or larger, connected in series or parallel as required.

[065] In order to connect the DC battery system of the present invention to the AC power grid or wind power source, rectifiers, inverters and transformers (64), are used in known ways to connect the battery and the power control system (65) determines when and whether a given battery in the plant will either charge from the power source, discharge to the grid or be on standby.

Testing

[066] Three test cells using the electrolyte of Example 5 above were tested.

[067] Cell 1 (Figure 4) was housed in a 20 litre rectangular plastic enclosure. It had 20 electrodes using at total of 5.4 kg of CPC chips and 16 litres of electrolyte. Cell 1 was able to produce 60 W-hrs over 12 hours (nominally 5 amps at 1 volt), with an overall efficiency (W-hr out/W-hr in) of 53.8%.

[068] Cell 2 (Figure 5A) was housed in a 205 litre plastic drum. It had 90 electrodes made from fabricated carbon tubes, using a total of 52.3 kg of carbon and 146 litres of electrolyte. Cell 2 was able to produce 200 W-hrs over 12 hours (nominally 16.67 amps at 1 volt), with an overall efficiency (W-hr out/W-hr in) of 52.8%.

[069] Cell 3 (Figure 5B) was housed in a 205 litre plastic drum. It had 57 electrodes made CPC chips, using a total of 49.7 kg of carbon and 152 litres of electrolyte. Cell 3 was able to produce 345 W-hrs over 12 hours (nominally 28.75 amps at 1 volt), with an overall efficiency (W-hr out/W-hr in) of 54%. The increased surface area of the CPC chip significantly improved performance over the fabricated carbon tube electrode, and with a significant cost reduction for input materials.

[070] The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.