Nuclear and solar gaming Spain's technical constraints market

Jorge’s chart

A post by Jorge Antonio González Sánchez on LinkedIn shows a screenshot from ESIOS where Nuclear P48 sits at ~5,100 MWh while Nuclear PBF is at ~1,276 MWh, suggesting that nuclear power “doesn’t clear in OMIE” and enters through the back door via technical constraints (PDVP). We reproduce that exact chart using python-esios.

The chart replicates what Jorge shows. Over the weekend of March 1–2, Nuclear PBF averaged 2,753 MWh while P48 reached 5,709 MWh — 52% of nuclear generation bypassed OMIE’s competitive clearing. On weekdays the gap drops to 0%.

Isolating PDVP: PBF → PVP → P48

P48 includes intraday sessions on top of technical constraints. To isolate the pure PDVP effect, we add the PVP (the schedule after constraints resolution, before intraday sessions). The PBF→PVP gap is PDVP. The PVP→P48 gap is intraday.

On weekends, 77% of the gap comes from PDVP (technical constraints) and 23% from intraday sessions. PDVP is the main mechanism.

Solar, the mirror image

Solar does the opposite: it clears more than needed in OMIE knowing it will be curtailed in PDVP. We compare Solar PV PBF vs PVP.

On weekends, solar cleared 6,706 MWh on average in OMIE and was curtailed to 5,510 MWh by PDVP — an 18% curtailment. PBF always above PVP: solar bids more than what the system accepts after resolving constraints.

The ranking: who goes up and who goes down through PDVP

If only nuclear did this, it would be anecdotal. We expand to all technologies: the gap (PVP−PBF)/PBF measures who enters via PDVP (positive) and who gets curtailed (negative).

Technologies to the right of zero enter via PDVP (they produce more than they cleared in OMIE). Those to the left get curtailed. Nuclear rises by 12.8% on average. Solar is curtailed by 9.9% and wind by 11.7%. Pumped-storage hydro (UGH) moves -12.0% — it acts in both directions depending on system needs.

Heatmap: technology × month

The ranking shows the average effect, but how does it vary by month? The technology × month matrix reveals seasonal patterns — red means the technology is boosted by PDVP, blue means curtailed.

Nuclear (deep red) is consistently boosted by PDVP throughout the year, with peaks in winter. Solar and wind (blue) are curtailed, especially during months with high renewable output. Hydro oscillates between both colors, confirming its flexibility role.

Temporal evolution

Is this a constant phenomenon or has it worsened? We calculate the monthly PDVP gap for nuclear and solar.

The pattern intensifies over time. Summer months show a smaller effect (solar produces more, demand is more stable), while winter triggers heavier operator intervention. February 2026 marks the peak, coinciding with REE’s deepening of reinforced mode amid high winter renewable penetration.

Weekday vs weekend

The weekend average (16.8%) exceeds the weekday average (11.2%). The 75th percentile confirms it: 14.3% on weekends vs 0.2% on weekdays. Weekends, with lower industrial demand and a higher renewable share, force the operator into more PDVP intervention — and nuclear is the main beneficiary.

Conclusion

Jorge was right in his intuition: nuclear systematically operates outside the OMIE market and enters through technical constraints. Solar makes the inverse move. What the data adds is context:

1. It’s not just nuclear — pumped-storage hydro (UGH) and combined-cycle gas also rise through PDVP
2. It has intensified — the phenomenon grows throughout 2025 and spikes in February 2026
3. Weekends amplify it — less demand + more renewables = more PDVP

The crucial nuance: this isn’t fraud. It’s rational behaviour within the market rules. If the system operator is going to redispatch you anyway under reinforced mode, why compete in OMIE at a low price? The question isn’t whether companies optimise, but whether the PDVP design creates the right incentives.

All data is public and reproducible with python-esios:

pip install python-esios
esios indicators history 4 -s 2025-01-01 -e 2026-03-11   # PBF Nuclear
esios indicators history 39 -s 2025-01-01 -e 2026-03-11  # PVP Nuclear
esios indicators history 74 -s 2025-01-01 -e 2026-03-11  # P48 Nuclear