It is important to appreciate that (like all products) there are applications for which the Redflow product is a great fit - and play very well to its considerable strengths and advantages.
Likewise there are (of course) some applications for which the Redflow product suit is not such a good technical fit.
A helpful overview of the applications that are best suited to these products is provided at the Redflow web site, here:
If your application sits well in the table noted above, lets now look at some of the other reasons why a Redflow product may be a good fit for your application:
Self-Monitoring and Automatic Battery Self-Protection
A plethora of things that damage conventional batteries:
- Complete discharge
- Leaving unplugged for extended periods to run completely flat
- Exposing to very high or very low temperatures while operating
- Charging or discharging at an excessive rate for an extended period of time
... and these are all mitigated against with ZCell using its on-board controller. T
Long periods spent unplugged, or totally empty, are irrlevant for this type of battery. When ready, just apply power and the battery comes back to life.
Attempts to operate the battery beyond safe operating limits (temperature or current) result in the battery disconnecting itself (and raising an alarm via the ZCell BMS).
Issues that are potentially recoverable automatically result in the battery reconnecting later.
Issues that indicate permanent problems result in the battery staying offline until manual intervention is undertaken. Remote access and analysis capability in the Redflow BMS allows such issues to be detected remotely.
No reserved capacity requirement and no expected loss of discharge capacity with age
Our flow battery technology allows for some unusual positive characteristics in these respects.
There is no reserved capacity in the battery, meaning that 100% of the battery discharge capability is available in every discharge cycle.
Compare and contrast with the impact on operating life of (truly) deep-cycling other battery types.
In addition, the expectation is that the capacity to output the full 10 kWh on a discharge cycle will be retained over the expected operating life of the battery.
This allows systems to be designed for the actual output requirement per cycle, without alowance for either reserved capacity at the start of life, or for the further loss of output capacity of the battery with age.
Compare and contrast this to the capacity reservation and expected loss of output capacity with age in most lithium based battery systems.
Relatively linear charge profile, no special charge/discharge curves
The ZBM battery has a relatively linear charge profile, all the way from 'empty' to 'full'. The charge rate does vary a little in response to temperature and state of charge changes, but not to the extent that applies for a conventional battery.
Unlike (say) a lead-acid battery (which has to be run up and down through specific charge/discharge profiles to maximise its operating life), a ZCell is charged by applying 57 Volts at a charge current of up to 50 Amps. The battery charges from empty (0%, zero volts) to full (100%), and then automatically stops further charging via its onboard control system when it reaches the 100%.
Other battery types require a multi-phase charging profile to be applied, and can also be very 'non-linear' in their charge time (taking much longer to charge the 'top half' of the battery compared to the time needed to charge the 'bottom half'.
Not prone to over-current conditions during charging
The internal resistance of the ZBM2 inside ZCell is typically about 0.1 Ohms. Providing the charge voltage is set correctly (both maximum and preferred being 57 Volts), the interaction between this internal resistance and the typical open-circuit-voltage of the ZBM2 (52V nominal) is such that the maximum current accepted by each battery will normalise at or below the 50A level that the battery is designed to accept.
In other words, providing the charge voltage is set to circa 57V, each battery will accept only a maximum of the (intended) 50A of charge current, as an automatic consequence of the interaction between the charge voltage maximum and the internal resistance of the battery.
If you have 'x' batteries in a parallel ZCell string, you can configure a max charge current of 50A times the number of batteries (e.g. 3 batteries means 150A, etc etc) - and you won't have an over-current scenario develop, even if some of the batteries are not online or not accepting charge at any given time.
As an indication, the underlying current equation here nets out roughly as follows:
(57V - 52V) / 0.1 = 50A
Where 57A is the charge voltage, 52V is the typical Open-Circuit-Voltage during the charge cycle and 0.1 Ohms is the typical internal resistance of the ZBM cell.
The battery is intended to be essentially a no-maintenance device during normal operation.
It is recommended that the battery is inspected physically on a roughly annual basis to check for things like dust buildup on the ventilation paths and to ensure that wildlife hasn't moved in, but otherwise the battery is intended to operate as a sealed system in practice.
Battery operation can be suspended with zero self discharge
A ZBM can be 'hibernated' (shut down in a controlled manner), at any state of charge (anywhere from full to empty), and turned off.
In this state, the battery is 'on standby', and can be re-started at short notice with the application of a relatively trivial amount of energy (think in terms of less than 100 watts for less than 60 seconds).
In hibernation, there is zero 'self discharge' occurring in the battery - it is truly 'off' at that point (but with any charge energy in the battery available for access once it is switched 'on' again)
This allows a number of interesting applications including:
- Having some (or all) batteries in a cluster charged up and placed into hibernation for later use - much like a generator set, but without the downsides of leaving a generator on standby for long periods.
- Increasing the efficiency of applications requiring a long period of relatively low energy output rate, by operating only a subset of a larger set of batteries at a given time, and sequencing the batterise on and off line in a cyclic manner. The point (in part) being to leverage the lack of self-discharge when a battery is in hibernation.
Batteries in a parallel string can be at different states of charge
The ZBM chemistry and system supports having batteries at different states of charge in the same parallel string of batteries.
In designs that routinely include up to six batteries per cluster and have been demonstrated at up to 45 batteries in parallel to date, it is possible to have some batteries running normally, some running in 'discharge-only' mode, and some completely offline (whether performing self-maintenance cycles or because of a wish to focus energy charge/discharge in other batteries in the cluster at that time).
This leads to a number of benefits, including a capacity to add or remote batteries without having to re-balance the other batteries in the cluster, and allows the implementaition of interesting strategies around batteries cycling between these states in coordinated ways.
On board data logging allows for long term trend analysis and remote diagnostics
The combination of performance and environmental logging inherent in the onboard control system combined with the ZCell BMS allows performance monitoring and data logging including the recording and observation of long term operating trends in the battery energy system.
The BMS supports a routine and standard 'cloud attached' operating mode where this data is uploaded to a Redflow cloud and may be accessed both by the integrator, the end customer, and also by Redflow, to allow for remote diagnostics in the case of system faults or warranty claims, and so that the system performance can be easily monitored remotely in general.