There is sometimes a benefit in being able to inject AC energy to a hybrid inverter (e.g. Sol-Ark, Deye, SunSynk etc) via the DC solar input connections. In effect, this can simulate solar energy using an AC grid energy source.
Two examples of use cases for this approach are:
1. Building a site requiring three phase AC output, but where the available incoming AC grid supply feed has only a single phase (e.g. Australian rural sites supplied from a Single-Wire-Earth-Return, or SWER, power feed)
2. Simulating solar energy in a lab or site prototyping scenario, where it is useful to create 'virtual' solar at a time, and for a duration, that can be directly controlled.
Note that for case 1, another approach that exists in principle (not tested by Redflow), via the use of a single phase to three phase AC converter unit, such as this one:
(randomly googled, not a product recommendation)
A Suitable Power Supply
This article notes a specific power supply that has been tested and verified as capable of being 'accepted' as if it was a DC solar panel string, by a hybrid inverter.
These inverters have multiple DC solar string inputs, so that one input could be used by the power supply noted here, and the other could still be used to connect 'real' solar panels.
If this results in insufficient DC energy input capacity to support the site load (if both DC strings were really needed for solar panels, for instance), this shortfall could in turn be addressed by installing a cluster of hybrid inverters instead of a single unit. Most hybrid inverters of the sort noted here are able to be connected in clusters of up to 'several' units (consult the data sheets for the brand under consideration for the specific cluster-size limit for that brand). The more units in the cluster, the more DC 'solar' inputs are available to add in more solar panel strings and/or more of the power supplies described here.
What is required for this purpose (using AC grid energy as a 'simulated DC solar string' energy input) is a power supply that has the following characteristics:
- Supplies DC power at a voltage suitable for connection to the DC solar input terminals of a hybrid inverter; and
- Has a current-limiting function so that it can supply a known, maximum, amount of current to the inverter and no more (so that the hybrid inverter does not 'over draw' from the power supply and cause it to shut down); and
- Has a dry-contact on/off control input, allowing (if desired) automated on/off control via the Redflow BMS (or via some other mechanism) so the AC grid energy can be activated only when required (e.g. when the battery cluster state of charge is getting low).
An example of a power supply that has all of these characteristics, and that has been tested and found to be suitable for use with Sol-Ark and Deye "Low Voltage" hybrid products, is the Meanwell CSP-3000-250:
This product is (at the time of writing) available from 'the usual suspects', e.g.: RS, Element14, Mouser, DigiKey etc.
This product delivers 250 volts DC at up to 3000W, with current limiting and optional remote on/off control.
The unit can be configured (with a rotary adjustment knob) in to set the maximum output power that it will deliver, if the AC input source has less than 3000W available.
This energy source, due to the built in current limiting function, is safely accepted as a 'DC Solar' energy source into the unit.
This power supply can substitute for an AC grid energy input for this purpose for hybrid models that will not achieve 'Battery Activation' from AC grid sources alone.
The power supply can be automatically activated under BMS control in appropriate circumstances (e.g. all batteries depleted and/or low battery SoC more generally).
This control can be achieved via the BMS "Digital I/O" engine, to turn on and off automatically in the presence/absence of the BMS' internal "Support Power Needed" (SPN) flag and/or when the battery cluster SoC is below a chosen threshold.
Here are some screen shots of the BMS configuration to achieve this outcome - this is set up in the "Digital IO" menu area of the BMS . First, add the BMS 'Device' to the setup in the Device tab to allow access to the BMS relay, and then create a "Periodic" rule to use it. Then 'Apply Changes'.
Note that (as per the CSP-3000-250 manual, attached to this article) - that the 'dry contact' control of this power supply requires specific wiring to be attached to the #1 connector (designated 'CN1' in the manual).
In particular, per page 6 of the attached manual, we recommend using the remote control arrangement designated '2.2(b)' . This wiring arrangement requires only a cable, and doesn't need an external resistor.
Note that this arrangement is such that closing the dry contact pair turns the supply off, and when this control path is open circuit, the supply will be turned on.
Hence the BMS relay should be wired into that control cable via the BMS relay "Normally closed" output, such that until support power is needed, the Power supply output is suppressed. Once support power is needed, then the BMS activates the relay, the dry-contact pair opens, and the supply can fire up.
Here are some snippets from the manual to show the suggested wiring arrangement and the pinout of connector 'CN1':
- The unit must run in 'constant current continuous' mode - meaning the jumper installed across pins 5&6 of the unit when delivered must be removed. That's easy, as this jumper must be replaced with the new control connector running to the BMS anyway.
- Use the control potentiometer on the unit to tune the peak current output to an appropriate level for your requirements - something around 1500W is suggested as a good starting point for initially testing this setup, but it can of course be raised all the way to 3000W if required (make sure the AC input to the power supply has an appropriately rated cabling and circuit breaker)
See photos below, showing the attachment and use of this unit on a Deye hybrid inverter, for testing purposes: