DESS sells to the grid at a negative price

Anyone else noticed their DESS doing something spectacularly daft with negative export prices? Mine decided that paying the grid to take my electricity was apparently a great business strategy — Victron's algorithms clearly missed the module on not losing money.

Switched over to Green mode after reading about similar chaos on the Victron community forums, and honestly it's been far more sensible since. The issue seems to be that in certain modes, DESS will cheerfully charge your batteries and then flog that energy back at a loss when Octopus Agile goes negative — essentially your Fogstar cells are doing the hokey cokey with cash you don't have.

The logic should be: negative price = hold tight, don't export, maybe run the kettle seventeen times. Instead it's seemingly: negative price = opportunity.

For anyone running a hybrid off-grid setup with grid-tie capability, worth double-checking your DESS settings around:

• Minimum sell price threshold (if your firmware even exposes this)
• Green mode vs Optimised mode behaviour differences
• Whether your feed-in tariff agreement actually penalises you for negative periods

Curious whether this is purely a DESS firmware quirk or if certain Cerbo GX firmware versions make it worse — I've seen wildly different behaviour reported across versions.

Anyone on the Victron community thread linked above found a proper fix, or are we all just poking settings in the dark hoping for the best? My MultiPlus deserves better decision-making than I apparently get from the software meant to optimise it.

@MultiPlusFan yes, seen exactly this with my garden office setup — Victron MultiPlus II paired with Fogstar Drift cells. DESS seemed completely blind to the negative pricing window on Agile and just merrily pushed export anyway.

Worth checking whether your minimum SOC settings are overriding the price logic — mine was set to discharge regardless once it hit a certain time slot, completely ignoring the actual rate.

A few things I'd try:

• Force a manual schedule override during known negative periods
• Check if DESS is pulling live Octopus pricing or just using a cached/delayed feed
• Raise a ticket with Victron — they pushed a DESS firmware update recently that supposedly improved price signal handling

Has anyone confirmed whether the latest DESS build actually fixes this, or is it still gambling with our exports?

@MultiPlusFan DESS's Dynamic ESS algorithm will happily sell into negative prices if you haven't set a proper minimum sell price floor in the Node-RED configuration — it's optimising for grid interaction, not your wallet, because by default it treats negative prices as just another data point rather than a hard stop.

Set minGridFeedInPrice to 0.0 (or frankly a small positive figure if you're on Agile) and it'll stop this financial self-harm immediately.

Worth also checking your ESS schedule overrides aren't fighting the DESS logic — I've seen Victron setups where conflicting rules cause the algorithm to behave like it's had one too many.

Fogstar Drift cells are excellent @MelKing83, but they won't thank you for cycling unnecessarily at a loss either — lithium deserves better accountancy than that.

@MultiPlusFan oh blimey, this is giving me flashbacks — had something similar with my static caravan setup last winter. Can I ask, are you on Octopus Flux or one of the other bidirectional tariffs? I'm wondering whether DESS is failing to pull the negative price data in time before it commits to the export schedule, or whether it's just completely ignoring the floor setting altogether.

What firmware version are you running on the Cerbo? I've seen chatter on the Victron community forum suggesting some builds had dodgy API sync with the tariff providers. Also — have you manually set a minimum sell price in the DESS settings? Pretty sure there's a field for it but I'll be honest I've never been 100% certain it actually does what it says on the tin 🤔

So DESS looked at a negative export price and thought "yes, brilliant, let's pay someone to take our free electricity" 😂

Reminds me of when my motorhome setup decided the optimal strategy was draining my Fogstar cells to 10% at 2am "just because."

@OldSailor mentions the minimum SOC setting