EasySolar-II GX 48/5000/70-50 MPPT 250/100 GX for a domestic battery-first PV installation

Q&A and troubleshooting
,
1

I am evaluating a Victron EasySolar-II GX 48/5000/70-50 MPPT 250/100 GX for a domestic battery-first PV installation in NE Scotland (yes, we do actually get sunlight!)

The intended architecture is:

PV array → internal MPPT → 48V LiFePO4 battery

Grid supply → AC-in / charger (or alternative charger if necessary) → battery

Battery → inverter → dedicated consumer unit supplying selected house circuits

The inverter output would supply a dedicated consumer unit and would not be connected to circuits supplied directly from the grid.

The intended operating philosophy is:

  • PV is the primary energy source.
  • Battery is the primary energy buffer.
  • Loads are normally supplied by the inverter.
  • Grid power is only used as a backup battery charging source when battery SOC falls below a defined threshold and PV not available.
  • No export functionality is required.
  • No ESS, dynamic tariffs, grid balancing or energy trading functions are required.

I am trying to determine whether the EasySolar-II GX can be configured to operate as follows:

  1. PV charging always active.
  2. Mains AC-in normally ignored
  3. Mains AC-in enabled only below a configurable SOC or battery voltage threshold.
  4. mains AC-in used solely for battery charging.
  5. AC-out continuously supplied by the inverter.
  6. No normal Mains AC passthrough operation.

Specific questions:

  • Can AC-in be used purely as a backup charging source while AC-out remains permanently inverter supplied?
  • Does enabling AC-in necessarily involve AC passthrough or transfer-switch operation?
  • Is there any permanent electrical connection between AC-in neutral and AC-out neutral?
  • How does the internal neutral-earth relay behave in this operating mode?
  • Is there a documented configuration example similar to the above?

I am interested in the technical capabilities and wiring topology of the EasySolar-II GX rather than ESS or export-oriented installations.

I’ve looked at the manuals, however a few questions have remained.

2

Yes, but why. Which benefit do you hope to get from physically disconnecting from the grid versus using a standard ESS configuration? For example, you would limit your whole house consumption to the 5kVA your inverter can provide. Whenever your load would surpass that, your MP would first have to synchronize to mains, then switch to it in order to avoid an overload shutdown. With an ESS you simply remain connected to the grid, if the load is greater than the MP can deliver then the remainder gets fed by the mains. ESS does not mean that you need to feed back surplus PV energy to grid if thats the concern.

No

Yes

Permanent no, but when ACin is switched through then the Neutral (and the Phase) on ACout will be the same as ACin.

For all the above, charger and inverter are physically the same thing, the same IGBTs are used just in different power flow directions. See the block diagram

Just like in any other. When ACin is switched through then the N-PE relay is off, if ACin is not switched through then the N-PE relay is on.

This is possibly the closest thing to an official documentation regarding deliberately ignoring ACin

3

Thanks - that’s helpful.

Perhaps I should explain the intended operating philosophy more clearly.

My objective is not export or energy trading. It is primarily resilience and reduction of imported energy.

The intended operation would be:

  • PV charges the battery whenever solar energy is available.
  • House loads are supplied from the inverter output.
  • High-current loads such as ovens, showers and kettles remain on the grid supply and are not connected to the inverter-backed consumer unit.
  • Typical inverter-backed loads would be lighting, sockets, IT equipment, TV, router, heating controls and water supply pump.

The behaviour I am trying to achieve is:

  • PV and battery supply the inverter-backed loads whenever possible.
  • If battery SOC falls below (for example) 20%, the system accepts AC input and charges the battery.
  • During this period the inverter-backed loads continue to operate normally.
  • Once battery SOC reaches (for example) 50%, AC input is no longer used and the system returns to PV/battery operation.

In other words, I am trying to minimise grid usage while maintaining battery reserve and resilience during periods of poor solar generation.

Can the EasySolar-II GX be configured to operate in this manner, even if AC-In is only used occasionally when battery SOC falls below a defined threshold?

4

Yes.

But what you describe is literally just an ESS but worse.

You want to stay disconnected from grid, run on battery power, when that power runs out you want to recharge from grid, then disconnect again to run on battery power again. Why. Thats just wasting energy. You are loosing about 12% when charging from grid, and then another 12% when running on batteries again. In the end you need to buy 25% more energy from the grid than you would have needed in an ordinary ESS by just running in parallel with the grid.

In an ESS this would be

  • PV and battery supply the inverter-backed loads whenever possible.
  • If battery SOC falls below (for example) 20%, the system stops inverting and supplies the loads from the grid.
  • During this period the inverter-backed loads continue to operate normally.
  • Once PV recharges battery SOC for example to 50%, inverting will start again, supplying the loads from PV/battery
  • Should the battery be full but PV is still generating, you could even cover the rest, or parts, of your other loads that are on the ACin side of the inverter, further reducing the energy bill

Again, just because you would run an ESS does in no way mean you need to export energy or take part in trading.

Yet you achieve none of that.

Yes, follow the link in my first answer. Or if you want to look into something a bit more flexible than the generator assistant, all of this can be programmed in NodeRed, but requires programming. Either by yourself (NodeRed isnt that hard to get into, at the beginning of the year i virtually had no idea about it and so far automated quite a few things with it) or you find someone to do it for you.

Feel free to build your system the way you want it, it will work

5

Thanks — that makes sense, I appreciate your response.

The manuals are there, but it’s not always clear.

My aim is to use PV as the primary energy source, not simply to run the system as a conventional grid-supported ESS if I can avoid it, more of an off-grid setup but with grid back up - hence starting with the high use, lower power items and keeping the difficult stuff on grid.

Ultimately for power outages, I have solid fuel for kettles and cooking - or can do without if it’s only a few hours but the other stuff I’d want powered - the resilience side of my argument.

For the solid fuel system I have, circulating pumps are needed as a heat sink so I would want them running.

Initially I had circulating pumps via inverter, of a car battery, with car charger plugged into mains.

It’s this concept I’m looking at, but using PV for the house circuits running off the battery.

The EasySolar seems to do this, but maybe not?

Equally I may change my philosophy to something it does do, if close enough to the concept.

Cost is also a benefit - although the extent of that depends on the use of the remaining mains consumers.

The way I understand the system:

  • PV charges the battery to 100% or whatever it can.
  • The battery/inverter supplies the inverter-backed loads.
  • If the battery depletes, AC-in/pass-through can operate and battery charging can commence.

That is acceptable up to a point.

My concern is winter operation in North-East Scotland. In winter I may only have useful PV generation for a fairly short part of the day, and during much of that period I am likely to be out, so house demand is low. I want that daytime PV to go into the battery so it is available later when I am home and using lighting, sockets, IT/TV equipment, heating controls and the water pump.

What I do not want is for the battery to be fully charged from the grid overnight, leaving little or no headroom for PV the following day.

What I am trying to achieve is more like:

  • PV charges the battery whenever available.
  • Battery supplies the backed-up loads when possible.
  • If SOC falls too low overnight or during poor solar conditions, AC-in is accepted.
  • Grid charging only recovers the battery to a configurable partial SOC, for example 40–50%, but PV remains at up to 100%.
  • AC-in is then ignored/disconnected again so PV has headroom to charge the battery during the following day.
  • I accept that some conversion losses are unavoidable when using AC-in to support or recharge the system, but ideally grid energy use and any associated detrimental conversion should be kept to a minimum.

I am starting with a modular system, so I can later move more circuits across, add PV, or add battery capacity once I have real-life performance data, especially over winter.

Is that behaviour achievable with EasySolar-II GX using standard ESS settings, the Generator Assistant, scheduled charging, or Node-RED? In particular, can grid charging be limited to a partial SOC rather than charging the battery fully from mains?