ESS continuous export with AC-THOR after heater turns off. Do I need ET112?

Been thinking about this one as it's relevant to my tiny house setup too.

Running an EasySolar 48/3000 here (similar to the situation that prompted this) and I've been looking at adding an AC THOR for immersion heating. The question of whether you need an ET112 for proper ESS behaviour is one I keep going back and forth on.

My understanding is that without a grid meter the EasySolar has no reference point for what's actually being exported — so when the AC THOR finishes its heating cycle and drops its load, the system can briefly push excess into the grid before the MPPT backs off. Whether that matters depends on your DNO agreement and how sensitive your export limiting setup needs to be.

A few things I'm genuinely unsure about:

• Does the built-in MPPT 150/70 respond fast enough to prevent any meaningful export burst, even without an ET112?
• Is the ET112 mandatory for ESS zero-export, or just best practice?
• Anyone running this combo in the UK with a G98/G99 compliant setup — what did your DNO say?

The ET112 is only around £60 from the usual Victron suppliers so it's not a massive cost if it sorts the problem cleanly. But if the system behaves correctly without it I'd rather keep things simple — fewer components, fewer failure points, which matters when you're living off-grid full time.

Would be interested to hear from anyone who's actually tested export behaviour with a clamp meter before and after fitting the ET112. Real-world data beats the manual every time in my experience.

Hey @Thommo, good question! The ET112 (or ET340 if you've got three phase) is pretty much essential for proper grid-point metering in this scenario. Without it, your ESS doesn't have accurate visibility of what's actually happening at the import/export point, so when the AC THOR cuts out, the system can't react quickly enough and you'll get that burst of continuous export.

The ET112 sits at your grid connection and gives Victron real-time feedback to throttle the inverter output accordingly. Without it you're essentially flying blind on the control loop.

Worth checking your VE.Configure settings too - make sure your ESS assistant is actually configured to use the meter readings rather than relying on internal calculations alone. What firmware are you running on the EasySolar? Some older versions had sluggish meter response times that made this worse even with the ET112 fitted.

From my narrowboat setup I've learned that without a proper grid-point meter, the Multiplus (or EasySolar in your case) is essentially flying blind — it can't see what's happening downstream of its AC-out.

The AC THOR will happily absorb surplus, but the moment it steps down or switches off, you get that burst of export because the ESS algorithm hasn't reacted fast enough. The ET112 closes that loop properly by giving real-time grid measurements to the CCGX/Cerbo, letting ESS compensate almost instantly.

Worth noting — on a narrowboat I run mine without grid connection obviously, so this particular headache doesn't apply to me, but I've watched it bite several marina liveaboards who are grid-tied. Every single one solved it by fitting the ET112 at the grid connection point rather than anywhere else.

Don't scrimp on the meter placement — it has to be grid-side.

Been through exactly this on my boat. The bit people miss is the lag between the THOR dropping load and the ESS algorithm responding — without the ET112 sitting at the grid point, you're essentially flying blind for those few seconds, and that's when you get the unwanted export spike.

Even with everything configured correctly in VEConfigure, the ESS can't suppress what it can't measure fast enough. The ET112 gives it eyes on the actual import/export figure in near real-time.

Worth noting — on a boat you're often dealing with a marina's supply agreement that explicitly prohibits export, so for me it wasn't even a choice. The ET112 was non-negotiable from day one.

Victron's own ESS design guide is pretty unambiguous about this. It's not expensive relative to the rest of the kit — just buy it and sleep better.

What @ExChippie72 said about lag is the crux of it, and I've seen this first-hand on my own boat. The EasySolar doesn't know the THOR has finished its cycle — it just sees a sudden drop in local consumption and briefly reads that as excess to push to the grid.

Without the ET112 sitting at the grid point giving the ESS real-time import/export figures, the algorithm is essentially flying blind for those few seconds. On mine, that gap caused enough continuous export to trigger my DNO's G98 protection twice before I worked it out.

The ET112 is around £80 from online suppliers — genuinely non-negotiable if you're running any dynamic AC load alongside ESS. Victron's own documentation on ESS assistant confirms the grid meter as mandatory for proper zero-export behaviour, not optional.