H2LINKEDHBrFLOWBATTERY. WORKS AS AN ELECTROLYSER (r 83%) AND FUELCELL (r 83%). WHEN FED WITH SMR H2 USED NATURAL GAS r 13 % HIGHER THEN A CCGT.

 An HBr flow battery (e.g. Elestor) is a cheap large scale battery and has a reasonably high round trip efficiency of 70%. HBr and Br2, in solution in water, are stored in the same tank. The hydrogen gas also has to be stored and is a large part of the cost. But if you connect the HBr-flowbattery to a hydrogen network, you don’t need those expensive hydrogen gas storage. And … the HBr battery will also function as a separate electrolyser during charging and a separate fuel cell during discharging. Each with the very high efficiency of 84% (0,84 x 0,84 = 0,70). As an electrolyser, the HBr battery can supply hydrogen on sunny summer afternoons (or in winter during windy nights). When discharging the HBr-flowbattery it’s a very efficient fuel cell. But because of delivering hydrogen to a hydrogen network during charging this HBr flow battery must be during discharging fed with hydrogen somewhere else from the same hydrogen network. In case of hydrogen imported by gas tankers this H2NetConnectedHBrBattery is because of its efficiency of 84 % by far the most efficient application. At this moment there is no import of hydrogen.  But ... even as long as the hydrogen has to be still produced by reforming of natural gas, despite the reforming loss of energy of 25%, the efficiency for the used natural gas is very high! With (0.75 x 0.84) x 100% = 63%, this is even 13% higher than the 50% efficiency (upper value) of a (also much more expensive) CCGT power plant.

 While by connecting an HBr flow battery to a hydrogen grid you instantly have a very cheap and very efficient electrolyser. So when making this H2NetConnected HBr-flowbattery possible we can produce electricity during the ‘dunkelflaute’ round trip no use of extra natural gas.

 Given the low construction costs and cheap raw materials and the reasonably high efficiency per kWh, the hydrogen bromide flow battery (HBr) is already cheap and especially now that Elestor is building an installation together with Vopak (known for its large oil or chemical -HBr is very corrosive- storage tanks) in which the expensive hydrogen storage is replaced by a connection to the (nowadays Steam Methane Reforming-) hydrogen network. When the battery is charged with surplus solar power during the day in the summer (or with wind power at night in the winter), the battery feeds hydrogen into the hydrogen grid, which at those times replaces hydrogen produced with natural gas for, for example, a fertilizer factory. During discharging in the evening, the HBr flow battery extracts the same amount of hydrogen from the hydrogen grid that the battery previously supplied to the grid during charging. This hydrogen has to be generated by fossil fuel (SMR) cause there is still not a storage with green hydrogen (there is even no green hydrogen). By withdrawing exactly the same amount of hydrogen (the Br2 formed during charging must be converted back to HBr during discharging) than was supplied to the hydrogen network during the electrolyser phase, not a gram of extra hydrogen, and therefore extra natural gas, is consumed. 

 But has the cheaper HBr flow battery with a connection to the hydrogen grid a lower or even a higher roundtrip efficiency than the 70% with its own hydrogen storage?

About Elestor · Elestor

 Seeking for a source of hydrogen for discharging (producing electricity) a H2-Net Connected HBr-battery.

  During charging the hydrogen produced from the reaction 2 HBr + e à Br2 + H2 will be delivered to the hydrogen net. This means that during discharging the same amount of hydrogen has to delivered back from the hydrogen net. But which hydrogen? One option is immediately eliminated.

The reaction equation in the flow battery during discharge is

                                 Br2 + H2 --> 2 HBr - 73 kJ / mol ((energy is released)).

The reaction equation of the H2 production in the case of an H2O electrolyser is:

                                 H2O à ½O2 + H2 + 285 kJ / mol ((energy is necessary))

This means that if hydrogen has to be produced by electrolysis from water during the discharge of the HBr battery, for each H2 molecule, no less than 3.9 times as many kJ or kWh are required for the electrolysis than the number of kWh that can be produced in the HBr flow battery. Not even taking the conversion losses into account. In other words. It is therefore not desirable to use electrolysis hydrogen during the discharge of the HBr battery, which is simultaneously produced in the same regional electricity grid and therefore does not come from a storage facility or, for example, is supplied with a still not excisting hydrogen pipeline from Norway (hydropower) or Scotland.

 So far I know there are three useful options remaining.

1. During discharging, previously saved hydrogen is supplied via the hydrogen network, which is produced from natural gas (by reforming).

 Reform ('grey') hydrogen must be purified before used in the HBr flow battery because of the sensitive membranes. The need for purification of reformed hydrogen is also necessary for the production of fertilizer.

2. From a hydrogen network with a (high-pressure) green hydrogen storage elsewhere on the hydrogen network.

The efficiency is then lower due to the 10% loss due to the high-pressure storage. It was also proposed to store the hydrogen gas in empty salt caverns (in Northern Netherlands) as a very cheap storage. Unfortunately, the hydrogen in a salt cavern becomes too contaminated for the membranes of an HBr battery.

3.The hydrogen is supplied from a gas tanker with imported green hydrogen.

 From a gas tanker (with of course hydrogen already stored), the loss of storage of self-produced hydrogen is therefore eliminated and it is only required that the gas tanker be moored at the gas terminal a little longer time at sunny or windy times when the HBr battery produces hydrogen. 

 Not only liquified hydrogen but also transported as elementary Fe (which reacts with steam to H2) or as green ammonia which is then transformed back to, very clean, hydrogen.

The hydrogen bromide flow battery, a promising cheap green electricity storage.

 Since 2014, Elestor has been working on the hydrogen bromide flow battery at a former KEMA site in Arnhem. The HBr flow battery is a competitor for lithium-ion, if not the competitor for stationary lithium-ion batteries. The HBr flow battery does not require scarce metals such as lithium, nickel and cobalt. Also not for the membrane such as platinum and iridium like in many fuel cells and electrolysers. The HBr battery works with bromine, which is much more widely available than lithium and should not be produced in polluting mines. Bromine is even a by-product of table salt extraction and is therefore much cheaper. During charging of the battery, hydrogen bromide splits into the elemental bromide Br2 and hydrogen gas H2. During discharge the bromidereacts with the same amount of hydrogen back to hydrogen bromide. Therefore, the HBr flow battery cannot be used indefinitely separately as an electrolyser or as a fuel cell. 

The disadvantage of the HBr flow battery is the high volumes that are required. Hydrogen bromide is a very corrosive substance and the storage of the hydrogen (in a closed application) takes up the most space.

Compared to hydrogen as energy storage, the HBr flow battery scores much better than the electrolysis - gas plant route. The HBr flow battery has a round trip efficiency of 70%. The round trip efficiency of the electrolysis - fuel cell or gas power plant route is only 35%. After all, 30% loss during electrolysis and 50% loss in the fuel cell or gas power plant. Unlike a fuel cell and gas power plant, no condensation heat is lost in the HBr flow battery. After all, no water(vapor) is formed in the HBr-battery when Br2 reacts with H2 to HBr.

 Bromide and hydrogen bromide dissolves in water and can also be stored as temporary precipitates in a tank. Hydrogen gas can also be stored in a gas storage facility. Both the bromine solution and the hydrogen gas can therefore be stored in separate tanks for a short or longer period of time. To be guided along the membrane during charging and discharging. At those times, the flow battery works as an electrolyser or as a fuel cell, respectively. Because of the separate tanks and membranes, this system is fairly easy to scale up in terms of both energy content (the tanks) and power (the membranes).

 Example of a Vopak storage tank. In Vlissingen (NL), Elestor and Vopak are building an HBr flow battery with an HBr/Br2 storage tank where the more expensive own hydrogen gas storage has been replaced by a connection to the (hopefully) gray hydrogen pipeline network. A Vopak tank can contain 250 MWh of Br2 (when it reacts with hydrogen). So 16 Vopak tanks could replace a 1000 MW h natural gas power plant for four hours.

Rechargeable battery: The reagents that react and create or store an electric current are contained in a solid casing. The storage capacity is therefore not scalable.

Flow battery: The reagents are stored in separate tanks. The storage capacity is therefore scalable.

Electrolyser: Hydrogen is produced from water ((as an energy carrier)) using an electric current.

Fuel cell: By passing hydrogen and oxygen across a membrane, an electric current is created.

Base load: Electricity is produced continuously. Like a nuclear power plant. So there is still extra electricity when there is little wind and sun. But the base load also promotes low and even negative prices for weather-dependent power sources.

Peak supply: Electricity is only produced when there is a shortage of wind and solar energy (dunkelflaute). As a result, wind and solar energy no longer become negative in price. On the contrary, cheap wind and solar power can first be purchased for this peak supply. Such as the HBr-flowbattery.

 An HBr flow battery temporarily works as an electrolyser. After all, hydrogen is created. However, this must be stored. Because the HBr flow battery ultimately works as a fuel cell for generating electricity. However, this requires exactly the same amount of hydrogen as that produced during the electrolysis of hydrogen bromide. See the reaction equation. However, if the HBr flow battery can extract hydrogen again after being supplied to a hydrogen network while discharging elsewhere, the HBr flow battery works as a separate electrolyser and as a separate fuel cell and is in that case a power plant.

The round-trip efficiency for storing excess solar or wind power is approximately 70%. Elestor calculates a cost price of € 0.07 per kWh for its flow battery (with its own hydrogen storage and therefore without connection to a hydrogen pipeline) for 100 charging and discharging cycles per year.

 In addition, the number of profitable charging and discharging cycles (in addition to the round trip loss) is determined by the variable cost price per cycle. The cost price aIn addition, the number of profitable charging and discharging cycles (in addition to the round trip loss) is determined by the variable cost price per cycle. The cost price of the HBr flow battery mainly consists of the investment costs, while the lithium-ion battery experiences wear with every charge and discharge cycle. The number of (cost-effective) charging cycles is therefore higher with the HBr flow battery.

 No expensive own hydrogen storage, but connection to the (grey) hydrogen network

 The storage of the hydrogen gas is the most difficult and therefore the most expensive. And it is precisely this more expensive storage where Elestor will make an important difference in terms of cost price. An HBr flow battery is being built in Vlissingen in which the hydrogen tank is replaced by a much cheaper connection to an existing hydrogen pipeline. According to Elestor, the cost price per kWh then drops to € 0.05 per kWh. (The cost of storage in a lithium-ion battery is at least double).

Connection to a hydrogen pipeline fed with hydrogen that is simultaneously produced through electricity consumption (electrolysis) is of course not an option.

 After all, green hydrogen is mainly a hype. Because 'only produced with surplus electricity from sun and wind'. The fact is, however, that electrolysers (other than the HBr flow battery) are very expensive and that because of the necessary operating time, people will happily continue to produce the so-called 'green' hydrogen. While there is no surplus of green energy at all and the coal and gas power plants therefore have to run extra hard. Times when it is even much more efficient to produce so-called green hydrogen directly from natural gas using the trusted Steam Methane Reformings process. The process by which the chemical industry, for example, has been producing the hydrogen it needs directly from natural gas for almost a hundred years for the production of fertilizer. Not only because it is simpler, the energetic return is also twice as high. Steam Methane Reforming has an efficiency of 75%.

 Steam Methane Reforming: CH4 + 2 H2O (steam)   -- 750 C -- > CO2 + 4 H2 efficiency approx. 75%

 The so-called green way of hydrogen production through electrolysis with electricity from a gas power plant has an efficiency of only 35%. Due to the 50% efficiency (based on the upper value of natural gas combustion) of a modern CCGT gas power plant for the required electricity multiplied by the 70% efficiency of the subsequent conversion of electricity to hydrogen. This hydrogen production would then be converted back into electricity in the fuel cell phase of the HBr battery with another conversion loss (17%). There will then preferably be a loss of 100 - (0.5 x 0.7 x 0.83 x 100) = 71%. After all, it takes almost four times as many kJ to produce the required hydrogen molecules from water molecules as the reaction of Br2 with the same amount of H2 produces 2 HBr in kJ. A business case that will hopefully not survive even in the 'green' hydrogen subsidy land. This is the case if the HBr flow battery is connected to a 'green' hydrogen network where the hydrogen required for discharge would be produced through electrolysis. In short, not a useful application.

The taboo on temporary use of fossil fuels harms the energy transition. So please connect the HBr flow battery to a gray H2 network.

However, the taboo of also using gray hydrogen, and therefore natural gas for the time being, for a green process must be abandoned. During the first 20 years, natural gas will still be needed for an efficient power supply during shortages of wind and solar energy. And that will only get longer if technical progress such as the HBr flow battery linked to the gray hydrogen grid is held back. For example, linking to a gray hydrogen pipeline, and thus saving on expensive hydrogen storage, will make investment in an HBr flow battery much cheaper and therefore allow the storage of surplus wind and solar power much faster.

Calculation of the efficiency of an HBr flow battery linked to the gray hydrogen grid (not 70 but no less than 83% efficiency).

ll only get longer if technical progress such as the HBr flow battery linked to the gray hydrogen grid is held back. For example, linking to a gray hydrogen pipeline, and thus saving on expensive hydrogen storage, will make investment in an HBr flow battery much cheaper and therefore allow the storage of surplus wind and solar power much faster.

Calculation of the efficiency of an HBr flow battery linked to the gray hydrogen grid (not 70 but no less than 83% efficiency).

 The round trip efficiency of the HBr battery is 70%. If the loss during charging and discharging is the same (assumption), then the efficiency is r for both the electrolyser phase and the fuel cell phase:

                              r.r. 100% = 70%

                               r² . 100% = 70%

                               r² = 70/100

                                efficiency r = V- 0.7 = 0.837 so 83.7%. (V- stands for the radical sign 😀) 

 

 During charging, the HBr flow battery works as an electrolyser on green energy. Green hydrogen is then produced with an efficiency of 83.7% and is supplied to the hydrogen grid. This efficiency is very high for the already relatively cheap HBr flow battery compared to other electrolysers. The limiting factor is only the HBr stock. When the stock rans out of HBr, the reaction 2 HBr --> Br2 + H2 can off course no longer take place. However, this should be not a problem because a surplus of solar and/or wind energy is also temporary.

After this yield as a green electrolyser, the HBr flow battery will work as a fuel cell during discharging. However, the HBr flow battery must use (post-purified) gray hydrogen for this. Gray hydrogen is made by reforming natural gas. The efficiency of reforming natural gas is 75%. This SMR hydrogen is then converted into electricity in the HBr flow battery during the discharge phase with an efficiency of 83.7%. The total efficiency of the natural gas that is first reformed and then converted into electricity as hydrogen gas in the HBr flow battery is (0.75 x 0.837) x 100% = 62.7%. Calculated with the upper value, this is 13% higher than when the same natural gas is consumed in a CCGT natural gas power plant.

 Where in this calculation and reasoning has gone the loss as a result of reforming natural gas into hydrogen gas? The answer is quite simple. When charging the HBr flow battery, the reforming of natural gas into hydrogen gas is avoided. Therefore, the (25%) reforming loss during discharging of the HBr flow battery can be offset with the saving of the same amount of gray reforming hydrogen during charging. 

 Of every 100 kWh that goes into the HBr flow battery during charging, 70 kWh still comes out (after all, the efficiency of the HBr flow battery itself remains 70%). But per required amount of natural gas for the required return of the (then) gray hydrogen instead of running a CCGT gas power plant, the number of kWh produced is higher (70 instead of 56).

 The numbers stated are the calculated energy equivalents with the incoming wind and solar power during charging set to 100. The efficiency of the flow battery itself remains 70%, so the outgoing electricity remains 70. The efficiency in the electrolyser and fuel cell phase is, as an assumption , just as high, namely 83.7%. The production of SMR reforming hydrogen requires 112 equivalents of natural gas (84 / 0.75 = 112). If the same amount of natural gas were used in a CCGT gas power plant (r=50%), the electricity yield is only 56 equivalent (112 x 0.5 = 56). However, thanks to the HBr battery, the 112 equivalent of natural gas does not yield 50 but 70 equivalent. Thanks to the HBr battery, the efficiency of the natural gas is therefore not 50%, but (70/112) x 100% is 62.5%. That is 13% higher efficiency of the HBr flow battery connected to a pipe with green hydrogen from a high-pressure storage.

  The efficiency of the HBr flow battery with its own hydrogen storage is 70%. If your own hydrogen storage is replaced by a connection to a hydrogen network with high-pressure storage (for example at offshore wind farms to save on part of the electric transport network), the efficiency decreases in direct proportion to the storage loss. This loss can amount to 10%. This is offset by a lower cost price for the construction of the HBr flow battery.

 Connecting the HBr flow battery to the H2 grid with import H2 from a gas tanker. The HBr battery can then work with a high efficiency (84%) as an electrolyser and as a fuel cell.

 According to reports, green hydrogen shall be in the future delivered to The Netherlands by gas tankers. The first point has to be where this green hydrogen can be used most efficiently. At the top of the so-called hydrogen ladder is the replacement of the current gray hydrogen in our chemical industry, such as fertilizer production. However, nothing needs to change here, because the HBr battery shall  produce the same amount of hydrogen that an HBr battery will use. (Because of the reversabel reaction 2HBr <--> Br2 + H2). What must change is that with the arrival of the HBr flow batteries, the HBr batteries will produce hydrogen during surpluses of wind and solar energy, and the unloading of hydrogen from the gas tanker(s) will be temporarily throttled. So this same amount of hydrogen can be used in the HBr- flow battery during discharging.

 With its own hydrogen storage, the HBr flow battery with its high efficiency cannot operate continuously as an electrolyser (efficiency 84%) or as a fuel cell (efficiency 84%). Because without (re)generation, the HBr or Br2 will eventually run out. By connecting to a hydrogen pipeline linked to a tanker with imported hydrogen, the HBr flow battery can function as a separate high-efficiency electrolyser and high-efficiency fuel cell. The limiting factor is then only the amount of solar and wind energy. And that is exactly what a battery is intended for. 

 So thanks to the coupling of an HBr flow battery to a pipe with hydrogen imported by gas tankers

1. When there is a power surplus, the HBr flow battery works as an electrolyser with an efficiency of 84%.

 2. while it can also work during a power shortage as a very cheap fuel cell with an efficiency of 84%.

 In addition to the fact that the HBr flow battery, as a high-efficiency fuel cell, must necessarily work as a high-efficiency electrolyser during power surpluses (otherwise the Br2 will run out) and therefore necessarily have to pump the same amount of hydrogen back into the hydrogen grid, the HBr flow battery also appears to be more efficient for supplying electricity. than if the import H2 were to directly replace gray hydrogen:

 100 MWh H2 with 84% ​​efficiency produces 84 MWh of electricity.

 For the 100 MWh of H2 that is not currently used to replace gray H2, 100 / 75% reforming efficiency = 133 MWh of natural gas is now consumed.

 If the 133 MWh of natural gas were used to produce electricity, only 133 times 50% efficiency would produce 67 MWh of electricity.

 With a connection to a hydrogen grid, the HBr flow battery will not only become a lot cheaper, but will also function as a separate electrolyser and a separate fuel cell with a very high efficiency of 84% for both. Naturally, exactly the same amount of hydrogen must be returned in the fuel cell phase. The fact that fossil natural gas must be used for reforming for the hydrogen for the time being should not be a fundamental objection. After all, in addition to a cheap electrolyser, you also obtain a conversion of natural gas to electricity that is no less than 13% higher than the current most efficient CCGT power plant, despite the 25% reform loss. Moreover, with an efficiency of 84%, it will also be the most efficient application of hydrogen, which will be imported with gas tankers in the future.

Leon Nelen.