DESS not charging when sell price is 0

Ran into something similar last summer with my narrowboat setup running Victron kit and Octopus Agile. When export prices tanked negative for a whole day, the system basically threw its hands up — solar was being curtailed and the batteries sat there doing nothing useful.

Ended up finishing the day with less charge than I started with, which felt completely backwards when there was decent sun available.

The way I understand it, DESS gets confused when there's no financial incentive to store — it's optimising for value rather than just... keeping the batteries topped up. Makes sense on paper but in practice it's a bit daft if you're actually relying on that stored energy to get through the evening.

For the static caravan I just use a simple float/absorption profile and don't touch DESS, which sidesteps the whole issue. But on the boat where I'm running smarter scheduling it's genuinely a problem.

A few things I've been wondering:

• Is there a way to set a minimum SOC floor that DESS has to respect regardless of pricing signals?
• Does anyone use a manual override on these zero/negative price days, or is there a smarter workaround in the Victron settings?
• Could you run a scheduled charge window via VRM that effectively ignores DESS for that period?

Feels like the algorithm needs a "just fill the batteries if the sun's out" fallback for edge cases like this. Would be curious whether anyone's cracked it — especially those running Agile long term. Negative prices are becoming more common, not less, so this is only going to matter more.

@HelenThompson — that truncated "sol" is killing me, finish the story! 😄

But yes, I know exactly what you mean. Had the same behaviour on my static caravan setup last spring. When Agile went negative all afternoon, my DESS target SOC basically froze — wouldn't charge or discharge sensibly, just sat there confused.

The culprit in my case was the minimum sell price threshold in the ESS assistant config. Victron's logic essentially treats £0.00 or negative as "undefined" rather than "definitely don't export."

Fix that sorted it:

• Set a negative floor value (say -£0.05) explicitly
• Re-ran the ESS assistant in VictronConnect
• Scheduled a forced charge window via Node-RED for those negative-price slots instead

Been solid since. Fogstar cells on the battery side, nothing clever there — purely a config issue on the Cerbo.

What firmware are you running? That matters quite a bit here.

@HelenThompson the "sol" cliff-hanger is genuinely painful 😄

What you're describing is a known edge case in DESS (Dynamic ESS) — when Agile export rates go negative or zero, the optimiser essentially loses its incentive to discharge, but depending on your firmware version it can also refuse to charge because it's calculating a zero or negative arbitrage margin and decides doing nothing is optimal.

Fix that worked on my narrowboat setup: set a minimum sell price floor in the DESS config (I use 1p/kWh) so the algorithm always has some reference value to work with rather than dividing-by-zero-style logic failures.

Also worth checking your Victron Cerbo GX firmware — versions around v3.3x had a specific patch for negative-price handling. Update via VRM if you haven't recently.

Fogstar Drift cells here, no BMS complaints once DESS stopped fighting itself.

@HelenThompson finish your sentence, for crying out loud.

@DevonDweller you were doing the same thing two seconds later, so.

Anyway — DESS treating a £0 or negative sell price as "don't bother" is well documented if you dig through the Victron community forums. It's not a bug exactly, it's just the algorithm being thick. It optimises around profit, so zero profit = zero effort.

Workaround I've used on my shepherd's hut setup: set a minimum SOC floor so it's forced to charge regardless of what DESS thinks the economics are. Not elegant but it stops the battery sitting at 40% because the algorithm had an existential crisis over a -2p export rate.

Check your minimum SOC and self-consumption settings in VRM. Victron's own documentation on this is genuinely rubbish, fair warning.

@BatteryTim the irony of three people all trailing off mid-sentence in the same thread about a system that stops mid-process is not lost on me 😄

Anyway — I hit something similar with my static caravan setup last winter. Fogstar batteries, Victron Multiplus, also on Agile. When export dropped to zero or went negative, the DESS logic seemed to decide there was simply no point in the whole exercise and just... sat there doing nothing.

What actually sorted it for me was setting a minimum sell price floor in the Victron configuration — essentially telling it "if you can't sell for at least X, just hold the charge rather than export." Stopped the confused inaction immediately.

Worth checking whether your DESS has a similar floor setting before assuming it's a bug. Mine wasn't broken, just being oddly literal about the economics.

@RetiredNurse58 I can't breathe 😂 This whole thread is performance art at this point.

Right, I'll actually try to be useful before I also mysteriously trail o—

On the actual problem: when Agile export prices hit zero or go negative, DESS can interpret "no revenue from selling" as "no point in charging either," which is daft logic but there it is. The workaround I've seen work reliably is setting a minimum State of Charge floor that DESS can't override, so it'll still top up regardless of what the export price is doing. On Victron kit you can do this through VRM or directly in the ESS settings on the GX device. Keeps the battery from sitting flat just because the grid's having a weird day.

Has @HelenThompson actually managed to finish that original sentence yet, or are we all still waiting?