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- The rationale for price caps on day-ahead auctions
- What triggered the price floor change
- The regional nature of the 1 May event
- The day-ahead to intraday transmission mechanism
- The residential solar problem
- Implications for short-term trading
- What we can expect next
Labor Day has joined the short list of calendar dates that matter to power traders for its impact on the supply-demand balance. On 1 May 2026, five bidding zones across central Europe cleared within one euro of the SDAC price floor. Around 1.6 GW of supply was rationed off the auction. By the end of the day, the German intraday market had reached a record low of -855 EUR/MWh.
The event activated a second trigger under the HMMCP methodology, moving the SDAC price floor from -500 to -600 EUR/MWh as of 28 May. This article covers how the floor change works and what it means for day-ahead and intraday trading going forward.
The rationale for price caps on day-ahead auctions
A price floor exists in the day-ahead auction primarily to protect market participants from clearing prices driven by technical errors or missing bids – edge cases that have nothing to do with fundamental supply and demand.
The intraday market operates differently. A hard floor there would simply push all selling activity into the balancing mechanism, creating a problem for system operators rather than solving one. That asymmetry explains why the day-ahead floor is a design feature while intraday prices are allowed to find their own level.
The -500 EUR/MWh floor served its purpose for years. However, it’s becoming insufficient as solar capacity across Europe grows and low-net-load events produce genuine fundamental prices below that level.
What triggered the price floor change
The rule is: if the day-ahead price hits the 70% threshold of the floor on two separate days within a 30-day window, the floor drops by 100 EUR/MWh. This is the HMMCP (Harmonized Maximum and Minimum Clearing Price) methodology, and it’s recursive, meaning the same rule applies at every new level.
1 May was the second such trigger event following 26 April. Subsequently, after a 28-day transition period, the day-ahead price floor will move from -500 to -600 EUR/MWh. During the transition, no new trigger can activate; the previous floor still applies. The next watch window opens around 29 May.
The -600 floor applies across all fully coupled SDAC bidding zones: Germany, France, the Nordics, Iberia, Italy, and most of Central and Eastern Europe. GB, Switzerland, and parts of the Western Balkans remain outside the rule. For more information on the coupling mechanism, see this article on how SDAC works.
The regional nature of the 1 May event
The 1 May event was regional, with DE-LU, Belgium, the Netherlands, France, and Austria all clearing within one euro of the cap in the same quarter-hour.
Poland, pulled along by market coupling, cleared at -489.90. Norway, by contrast, settled at +93.62 EUR/MWh in the same hour, as the Nordics remained firmly positive while solar-rich central Europe ran long.
Further east, Romania, Bulgaria, and Greece saw prices no lower than zero on the same day, because limited interconnector capacity prevented the transfer of excess generation from Western Europe.
On this day, DE-LU saw a 733 EUR/MWh spread on day-ahead between the midday trough and the evening peak, and that’s with the -500 cap binding throughout.
The day-ahead to intraday transmission mechanism
The driver of the event above is familiar: peak solar generation coinciding with a low-demand day (a public holiday in several European countries) and insufficient cross-border flexibility to absorb the surplus. These conditions – solar ramp on bank holidays – recur regularly across central Europe in spring and summer. Non-curtailable capacity, including an estimated 5–10% of total wind capacity that remains online during oversupply events, adds to the structural imbalance.
When supply at the floor exceeds demand at the floor, the auction mechanism stops clearing at the market price and becomes an administrative rationing mechanism. Non-flexible supply is allocated a pro-rata share of cleared volume; the rest goes uncleared. Since those assets continue producing, the volume has to settle somewhere.
The intraday outcome on 1 May follows directly from that rationing. Rationed assets either sell uncleared volume into intraday continuous or create system imbalance. Either way, additional supply enters the intraday market below the day-ahead reference price. When that volume is around 1.6 GW, the effect on the intraday clearing price is significant.
The -855 EUR/MWh intraday record reflects where the market actually cleared once the day-ahead floor was no longer a binding constraint on price formation. With a -600 floor, more of that rationed volume clears in day-ahead, and the day-ahead to intraday gap on extreme days should narrow. But the same mechanism applies at the new level, and the methodology has no defined stopping point.
The residential solar problem
The oversupply on days like 1 May is partly a curtailment problem, and not all solar is equal in that respect.
Owners of utility-scale solar parks can curtail these relatively straightforwardly. Residential installations are a different matter. Behind-the-meter systems in markets like the Netherlands often benefit from net metering subsidies that make it financially rational for households to keep producing even when wholesale prices are deeply negative. The economics that apply at the wholesale level simply don’t reach them.
This creates a growing mismatch between the consumer and wholesale markets. Professional solar operators must hold curtailment capacity to avoid losses on extreme days, while residential generation continues to flow regardless of price signals. Solutions are emerging, such as dynamic contracts and third-party curtailment services for residential customers. Still, the gap between retail and wholesale incentives remains a contributor to floor-binding events.
Implications for short-term trading
The floor change touches several parts of a short-term trading operation.
The most immediate issue is operational. Anywhere -500 is hard-coded as a price bound – bid generation logic, optimization models, backtests, VaR limits – needs to be updated and parameterized. Planning for -700 and beyond is a realistic 12-month scenario.
Secondly, historical day-ahead data is now censored above the old floor. Any model trained on it will underestimate the depth of negative price events. For day-ahead price forecasting, this means recalibrating probabilistic tails and being explicit about where the floor previously masked true clearing prices.
Intraday tail risk is also shifting. -855 EUR/MWh is the current reference point for stress sizing, and that number will move as the floor steps. Low-net-load days, particularly high-solar weekends and public holidays in spring and summer, carry meaningful intraday tail risk regardless of where the day-ahead floor sits.
For flexibility assets, the economics are moving in a clear direction. The 733 EUR/MWh day-ahead spread on 1 May illustrates what a textbook battery arbitrage day looks like under the current market structure. Wider realized spreads strengthen the case for batteries, electrolyzers, and downward-flexible demand. Capturing the deep-negative tail is becoming a more meaningful part of the revenue picture.
Finally, the 1 May case is a reminder that SDAC coupling transmits floor-binding events across borders. When DE-LU binds, neighboring zones follow. Traders with positions in coupled zones are exposed to events that originate elsewhere in the network.
What we can expect next
The next trigger threshold under the -600 floor is -420 EUR/MWh (70% of -600). The 28-day lockout from the May 1 event expires on 29 May. After that, a new trigger is possible.
The conditions that produced 1 May will happen again, with sunny weekends in July and August as the natural candidates. Given the frequency with which these conditions have produced floor-binding events in recent years, planning for another trigger before the end of Q3 is reasonable.
As we’ve written before, the value of anticipating these moments rather than reacting to them is material. Knowing a day ahead that a low-net-load event is likely gives traders time to position in day-ahead, adjust intraday exposure, and make curtailment decisions before the market clears at the floor. If you’d like to see how Dexter models floor-binding events in your portfolio, get in touch.