9. Frequently asked questions
This section answers common questions about ESS behaviour in normal operation and during fault-finding.
Q1 Can ESS operate without solar?
Yes. Solar is optional. ESS works with grid-tie PV inverters, MPPT solar chargers, a mix of both, or no PV at all. A system without PV is typical of virtual power plants, where many small storage systems support the grid at times of peak demand.
Q2 Can standard AGM or GEL batteries be used in a system that cycles daily?
Standard AGM and GEL batteries are not recommended for systems that cycle the battery every day. For lead batteries, the high internal resistance of OPzS and OPzV types should also be considered in the design.
Q3 When is a grid meter needed?
A grid meter is needed only when AC loads or sources are present on the input (grid) side of the inverter/charger. When everything is connected to the output side, all power exchanged with the grid passes through the inverter/charger, which meters the exchange itself, so no grid meter is needed.
Q4 Can ESS be used in a vehicle or a boat?
No. After the shore cord is unplugged, the system needs a moment to detect the loss of mains and open the back-feed relay. During those seconds the shore-power plug is live, with 110/230 VAC on the terminals. The exact time depends on local grid-code requirements. The same applies to any installation where the wiring is not protected against accidental disconnection, such as a cable with a user-removable plug, or a portable power supply.
Q5 Does AC-coupled PV keep working during a power cut?
It depends where it is connected. AC-coupled PV on the AC-Out keeps running during a grid failure, because the inverter/charger forms a local micro-grid for it to synchronise to. AC-coupled PV on the AC-In stops, because it behaves as an ordinary grid-tied installation with no grid to synchronise to.
Q6 Does the grid-tie inverter's feed-in need configuring?
Feed-in for both AC-coupled and DC-coupled PV is set in the Grid feed-in menu on the GX device. See Feed-in for what each setting can do, and Zero and limited feed-in with PV inverters for which PV inverters can be limited.
Q7 Why does the grid setpoint default to 50 W rather than 0 W?
A small positive setpoint provides a buffer that prevents unintentional export when a large load switches off before the system can react. A system regulating to exactly 0 W tends to overshoot into export at that moment; a slight positive value keeps the flow drawing lightly from the grid instead.
Q8 Why does the battery not charge from the grid even with a positive grid setpoint?
Check the Grid metering setting. If it is set to External meter but no external meter is installed, the battery will not charge from the grid, even with a positive grid setpoint. Set Grid metering to Inverter/charger when no external meter is present.
Q9 What is the difference between the two Optimized modes?
Both modes store surplus PV in the battery for later use. They differ only in how the minimum SOC is handled: Optimized with BatteryLife dynamically manages it so the battery is regularly recharged to a healthy level, while Optimized without BatteryLife holds it fixed at the configured value. Optimized with BatteryLife is recommended for most systems.
Q10 Why is the Limit charge power setting missing from the menu?
It appears only when DVCC is disabled. When DVCC is enabled, the setting is hidden, and the system-wide maximum charge current is configured instead under Settings → System Setup → Charge Control → Limit charge current, which applies to all charging devices together.
Q11 Can feed-in briefly exceed the configured limit?
Yes. Limit system feed-in is a target. Under some conditions, such as a large load disconnecting or a sudden rise in solar production, the actual feed-in may briefly exceed the target until the system regulates the inverter output back within the limit. If the system is not feeding in at all, or is feeding in less than expected, see Q26 instead.
Q12 Can Opportunity Loads and Dynamic ESS run at the same time?
No. Both manage energy at the system level and need control over how energy is allocated, so only one can be active at a time. Dynamic ESS optimises energy flows against electricity prices and forecasts, while Opportunity Loads optimises the local use of surplus solar by controlling flexible loads.
Q13 An Optimized mode is selected, but grid power is not being used to charge the battery. Why?
In the Optimized modes, the battery is charged only from PV, except in two circumstances, both related to protecting battery health:
Sustain: the battery has been discharged deeply enough to trigger the sustain mechanism. See Sustain.
Slow charge: BatteryLife is active and raising the minimum SOC. See BatteryLife.
Q14 The battery discharges and is then recharged every night. Why?
The nightly recharge may be part of the Sustain protection. Consider raising the minimum SOC, for example by 5%, and observe the effect. Alternatively, the sustain voltages can be lowered in VEConfigure, but with caution, especially for lead batteries, as the sustain levels are designed to prevent early battery damage.
Q15 What is auto-recharge?
The system automatically recharges the battery from the grid when the SOC drops 5% or more below the Minimum SOC set in the ESS menu. Recharging stops once the battery reaches the Minimum SOC level.
Q16 Why must a single-phase system on a three-phase grid connection be installed on phase L1?
The system regulates against the phase the inverter/charger is installed on and expects that phase to be L1. On L1, with Multiphase regulation set to Total of all phases, the single-phase system balances the combined power of all three phases correctly, and the system visualisation on the GX device reflects the true state of each phase. If the inverter/charger is installed on L2 or L3 instead, the phase visualisation is shown against the wrong phase and the regulation is impaired, so the system does not compensate the phases as intended. Installing on L1 is therefore required, not merely recommended.
Q17 Why does VRM data for split-phase and three-phase systems not match the utility bill?
This does not apply to systems that use a VM-3P75CT, EM24, EM530 or EM540 energy meter.
In an installation with no dedicated energy meter, or one that uses an ET340 meter, energy imports and exports are accumulated per phase, and the total imported and exported energy is the sum across all phases. The utility meters in many countries use a different method, billing on the total net energy imported across all phases. Because of the difference between the two methods, the data shown on VRM and on the utility meter may vary.
With Multiphase regulation set to Total of all phases, the default, the variation is more pronounced. That setting specifically makes full use of the billing arrangement in which energy exchange between phases is not billed, but it appears as simultaneous import and export in systems that count total import and export rather than total net energy. This causes the "to grid" and "from grid" counters on VRM to increase while multiphase regulation is operating. It can also occur where PV inverters are used, even with regulation set to Individual phase. Systems using a VM-3P75CT, EM24, EM530 or EM540 energy meter, which accumulate total net energy, are not affected. The energy meter selection guide identifies which meters accumulate energy in this way. See also Multiphase regulation.
Q18 What happens to loads on the AC-In during a grid outage?
They are not powered. For anti-islanding safety, loads on the AC-In side are always disconnected during a grid outage. Only loads on the AC-Out are backed up, from the battery and from PV when available.
Q19 Even when the battery is full, the system stays connected to AC-In. Why?
This is normal in the Optimized modes. The question is often raised by those familiar with the earlier Hub-1 or Hub-2 configurations in a series installation, where the system switched to inverter mode once the battery was full enough. That approach had disadvantages, because an inverter provides a weaker voltage supply than the grid, which could lead to flickering lights, or to inverter shutdown on overload when a large load was switched on. In the Optimized modes the system always remains connected to the grid, even when the battery is full. The power drawn while connected is not substantial, so the configuration offers the stability of the grid without significant additional grid consumption.
Q20 Why is the VE.Bus state showing pass-through?
With ESS, the VE.Bus system is in pass-through (VE.Bus state: passthru) under the following conditions:
The GX device is no longer receiving data from the grid meter. This applies only to systems configured to use an external grid meter, and relates to the Grid meter required setting.
In a system with a CAN-bus-connected lithium battery, the GX device is no longer receiving information from the battery over the CAN-bus.
Charging the battery is not allowed (BMS maximum charge current is 0 A, or maximum charge power is 0 W) and there is excess PV power.
Discharge is not allowed and the loads on AC-Out would force the inverter/charger to exceed the AC input current limit. Discharge may be blocked because the BMS blocks it (DCL = 0), or because the battery SOC is below the minimum SOC setting; discharge is allowed again once the SOC is at least 3% above the set level.
A grid code is in use that requires battery discharging to be enabled through the aux inputs. Check the grid code in VEConfigure against the electrical signals provided to the inverter/charger's aux inputs.
Loss of Mains (LOM) detection is causing problems, often in combination with a high-impedance connection to the utility. For details, see VEConfigure: grid codes and loss of mains detection.
Q21 How can low-battery warnings be suppressed?
In an off-grid or backup system, a warning when the battery is almost empty is useful. In a system where the battery is used to optimise self-consumption and is normally depleted every day, the notification is not needed.
The low-battery warning pop-up on the GX device is disabled from the inverter/charger menu: select Setup, then Alarms, and set the Low DC voltage alarm to Alarm only.
The red blinking LED on the inverter/charger, which warns of a low battery, cannot be disabled.
Email notifications are suppressed in the VRM Portal by setting Automatic alarm monitoring to Only alarms.
Q22 In an Optimized mode with no feed-in, the AC input current fluctuates widely and sometimes goes negative. Why?
This is normal. The current shown is the RMS current, which does not represent real power or real energy fed into the grid. Around 0 W of real power the RMS current is high, caused by the X-capacitors in the inverter/charger. The input power readings are a more reliable indication of power and energy, and fluctuate much less.
Q23 Why does the system switch off in overload?
Switching off in overload while connected to the grid is caused by the Loss of Mains (LOM) detection linked to the grid code configured in VEConfigure. It occurs when the AC supplied at the AC-In is weak, meaning the connection to the utility has a higher impedance than usual, for example a generator, or an old or remote property connected by a cable that is too long or too thin. For the solution and configuration options, see VEConfigure: grid codes and loss of mains detection.
Q24 Why are the loads powered by the grid instead of the battery or solar?
Work through the following checks when loads are supplied from the grid but are expected to be supplied from the battery:
Check that the system is not preventing discharge because the battery SOC is below a limit. See Controlling depth of discharge .
For a managed lithium battery with a CAN-bus connection, check that the battery has not disabled discharging. In the Device List, open the battery entry, then the Parameters submenu, and check the Discharge Current Limit (DCL). A value of zero means the battery is instructing the system not to discharge further. This also shows as reason code #4.
The ESS relay test may still be pending. The inverter/charger must perform a relay test before it can use battery power, which requires it to run briefly in inverter mode with enough spare battery capacity. If the battery voltage is too low when connecting to the grid, the system starts in pass-through or charging mode and will not feed in, supply the loads from the battery, or export DC-coupled solar power until the battery is recharged sufficiently. The relay test is performed once the battery voltage rises above 14V, 28V or 56V, or the SOC rises above 20%. The ESS relay test entry in the Advanced submenu of the inverter/charger shows either Pending or Completed, and is visible only on systems with the ESS Assistant installed.
Feed-in may be disabled by a grid code (such as the German or Australian grid code) that uses the aux1 input to disable feed-in, where aux1 is also used by something else such as an AC sensor or a BMS. Clear the relevant option in the grid-code settings to prevent this. See also Q26.
Check that the rocker switch on the inverter/charger is set to On rather than Charger-Only. When set to Charger-Only, the unit will not discharge the battery. This must be checked physically, as the switch state is not shown on VRM or the GX device. On a MultiPlus-II the rocker switch is at the bottom of the unit and must be in the I position, not the II position.
If none of the above resolves the problem, temporarily disable LOM to rule it out as the cause. See VEConfigure: grid codes and loss of mains detection.
Q25 Why does the system refuse to discharge the battery?
The system withholds battery discharge for a small number of defined reasons, all of them protective or configured:
The battery SOC is at or below the minimum SOC. Discharge resumes once the SOC rises at least 3% above the limit.
An intelligent battery connected via CAN-bus has set its Discharge Current Limit to zero, instructing the system not to discharge. This shows as reason code #4.
The inverter/charger's rocker switch is set to Charger-Only rather than On.
The ESS relay test is still pending, because the battery has not yet been charged enough to perform it.
BatteryLife or Sustain has disabled discharge to protect the battery from a prolonged low state of charge.
See also the checklist under Q24, and Controlling depth of discharge for how the depth-of-discharge limits work.
Q26 Why is the system not feeding in to the grid, or feeding in less than expected?
Feed-in can be limited or prevented by the grid code and by the condition of the grid itself, independently of the ESS settings. Check the following:
The aux1 input is in use. Some grid codes use the aux1 input to disable feed-in. If aux1 is also used for something else, such as a separate assistant, a jumper or a temperature sensor, feed-in can be blocked unintentionally. Check the grid code settings in VEConfigure against what is actually connected to aux1, and clear the relevant grid code option if it is not wanted.
The system has only just connected to the grid. Some grid codes, for example in Spain, prevent feed-in for several minutes after the system connects. This is normal behaviour; wait for the delay to pass before investigating further.
The grid is unstable. Frequency variation or voltage instability can disable feed-in and some other ESS features. This is more common where the local electrical infrastructure is weak.
The grid voltage is too high. Feed-in is limited or stopped when the grid voltage rises above the limit set by the grid code. Feed-in resumes once the voltage falls back within the permitted range.