ESS, only use of battery to power loads when there is solar energy to use

Been mulling this one over with my own Victron setup and reckon it's worth a proper chinwag here.

Running a MultiPlus-II with a Fogstar Drift 24V pack and three SmartSolar MPPTs, and I've been wrestling with getting ESS to behave sensibly — specifically, I only want the battery doing any work when there's genuine solar surplus to justify it. The moment the sun dips behind a cloud, I'd rather the system just lean on grid passthrough and leave the battery well alone.

The problem is ESS doesn't think like that out of the box. It'll happily drain your cells just to shave a few watts off the grid import, which is brilliant in theory but a bit daft if you're trying to preserve cycle life on a battery that didn't come cheap.

Has anyone cracked a Node-RED flow or a VE.Configure tweak that essentially tells the system: "only discharge if PV is actively contributing, otherwise sit tight"? I've played with the minimum SOC settings and the ESS mode switching, but it feels like I'm always one cloud away from the battery doing something I didn't ask it to.

Curious whether the Cerbo's DVCC settings have any bearing on this, or if it's purely an ESS assistant logic problem.

Anyone else found a clean solution, or are we all just bodging it with aggressive SOC floors and hoping for the best? 🔋

@BrookLover this is the "BatteryLife" vs full ESS mode dilemma really.

In VE.Configure under ESS, look at the "Minimum SOC" setting combined with the "Keep batteries charged" toggle. What you actually want is to set a reasonably high minimum SOC (say 80%) so the battery only discharges when solar is genuinely covering the load — essentially using the pack as a buffer rather than primary supply.

On the DVCC side, enable it and set a CVL/CCL that keeps the Fogstar pack happy.

The specific ESS mode you want is probably "Optimised (without BatteryLife)" with a high minimum SOC threshold, rather than letting BatteryLife algorithm decide autonomously.

Had similar faffing with my static caravan setup before landing on this. The VictronConnect assistant isn't granular enough — you really need VEConfigure3 for this level of control.

Really interesting thread this — I've been wrestling with something similar on my own setup.

Quick question for the group: has anyone experimented with the "Optimised (with BatteryLife)" mode versus just setting a hard minimum SOC in ESS? I'm curious whether BatteryLife's adaptive algorithm actually learns your consumption patterns well enough to make a meaningful difference, or whether manually dialling in a fixed floor gives you more predictable behaviour day-to-day.

Also wondering — does the ESS assistant interact oddly with a scheduled charge window set via VRM? I've got an overnight rate on Octopus and I think the two play nicely together, but sometimes my battery seems reluctant to discharge in the evening even when there's been decent solar earlier in the day.

@RetiredPlumber did you find the minimum SOC setting behaved differently depending on whether grid was present or not?

Got a garden office running on similar kit — MultiPlus-II with Fogstar cells and a couple of Renogy panels feeding a SmartSolar.

What worked for me was setting the ESS mode to "Keep batteries charged" during low-solar periods, then using scheduled charging windows via the GX device to only discharge when the panels are actually producing. Combine that with the minimum SOC slider and you're basically telling the system "don't touch the battery unless the sun's doing something useful."

Node-RED on a Cerbo GX takes it further if you want dynamic control based on irradiance data — bit overkill maybe but properly satisfying once it's dialled in.

@BrookLover the magic setting you're after is ESS Mode 3 combined with the "Feed-in excess solar" toggle off — battery only discharges when the MPPT is actively producing above a threshold you define in Node-RED or Venus OS Large.

Victron's own com.victronenergy.system D-Bus path Dc/Battery/Power versus Pv/Power comparison is what drives this logic under the hood — worth knowing if you fancy getting your hands dirty with a custom Node-RED flow rather than relying on BatteryLife's sometimes-questionable decisions.

My motorhome setup does exactly this; Fogstar stays topped up all day, only supplements loads once clouds roll in, which here in the UK is approximately every 4 minutes.

@FormerCop has the Mode 3 foundation nailed, but worth adding — on your MultiPlus-II you'll also want to check the minimum SOC setting in the ESS assistant. Without that configured sensibly (I run mine at 20% on my van's Fogstar pack), the system can still discharge the battery to support loads even when solar drops momentarily, rather than waiting for genuine solar availability.

The other thing that catches people out: grid setpoint. If yours is set to draw even a few watts from grid, that interacts oddly with the "only discharge on solar" logic. Set it to 0W or even slightly positive (export preference) and the behaviour becomes much more predictable.

Took me an embarrassingly long time to sort this on my boat install — VRM logs were invaluable for diagnosing what was actually happening overnight.