Spain — Electricity Grid Oscillation Patterns

Oscillation Waves — How to Read

Each line tracks a distinct electricity source, smoothed to reveal seasonal rhythm.

Smoothing: A centred rolling mean suppresses daily noise — use 7d for recent detail, 30d for seasonal patterns, 90d for multi-year trends.

Terracotta vertical bands mark meteorological summer (Jun 21 – Sep 22). This is when solar peaks and gas falls. The denser vertical lines you may see in Dec/Jan are simply the year-boundary axis ticks — not shading.

Purple dotted line + shaded envelope = 3-year seasonal baseline ± 1 standard deviation. Any reading outside the band is statistically unusual.

Baseline(d) = mean(demand_DOY=d | years 2023–25)

Generation Stack — How to Read

Stacked areas show the cumulative contribution of each source to total supply at any moment.

Read each band's vertical thickness = that source's output in GW. Bottom to top: Nuclear (stable baseload) → Hydro → Wind → Solar → Gas/CCGT.

The dotted demand line overlaid shows whether the stack covers demand. A gap above = imports or storage draw; a gap below = export surplus.

Key pattern: the Gas band (top) compresses each summer as solar displaces it — this is the merit order effect in action.

Residual load = Demand − (Wind + Solar + Hydro)
Stack total = Nuclear + Hydro + Wind + Solar + Gas

Renewable Share — How to Read

The % of total demand met by wind, solar, and hydro combined — Spain's primary decarbonisation metric.

RE% = (Wind + Solar + Hydro) ÷ Demand × 100

The dashed line at 60% is Spain's PNIEC 2030 interim renewable target. When the green area clears it, low-carbon sources are majority suppliers.

The oscillation range of 58–72% reflects the seasonal swing: high in summer (abundant solar) and lower in winter (less daylight, higher heating load).

The gas proxy line (terracotta, dotted) is RE-inverse scaled — as RE% rises, gas falls. A tightening correlation over time confirms structural displacement, not just weather-driven variation.

2026 vs Baseline ▶ — How to Use

Animates 2026 YTD actual demand drawing in against the 2023–25 historical seasonal norm.

Press play — the chart zooms to Oct 2025–Apr 2026 and draws the terracotta 2026 line against the purple baseline band. You can visually assess whether 2026 is tracking normally.

Z-score (statistical distance from norm):
z = (x₂₀₂₆ − μ_baseline) ÷ σ_baseline

|z| > 1.96 = significant at 95% · |z| > 2.58 = significant at 99%

Current: z = −1.94 (−6.2% below baseline) — just inside the 95% threshold, consistent with post-blackout demand suppression and growing behind-the-meter solar reducing grid draw.

Seasonal Radial — How to Use

A polar chart where each spoke = one calendar month and the radius = average GW output for that source.

Why polar? Energy generation is cyclical — the polar format closes the annual loop so the eye immediately reads seasonal dominance and offset between sources.

Reading it: A large filled area = high generation across those months. Solar (amber) peaks in summer spokes; Wind (sage) peaks in autumn/winter spokes. Where shapes overlap = months of balanced mixed generation.

What to look for: the degree of angular offset between Solar and Wind tells you how well Spain's resource mix self-balances. Ideal = near-mirror image, minimising storage need.

Use ↺ Reset Radial View after zooming or rotating.

✦ * 28 Apr 2025 — Iberian Grid Collapse

~60 GW shed in under 5 seconds. Largest blackout in EU recorded history. Full restoration ~18 hours.

Root cause — loss of grid inertia: With ~70% renewable penetration that morning, few synchronous generators were spinning. Inertia (H) determines how fast frequency falls when generation trips:

df/dt = −ΔP ÷ (2H · S_base)

Low H → rapid frequency collapse → cascading under-frequency protection trips across Iberia.

This is the definitive case study for why high-renewable grids require synthetic inertia — grid-forming inverters, flywheels, or fast-response storage — alongside generation capacity. The violet marker on every chart tab pinpoints the event.