Renewable share falls as more of Europe bakes

Renewable share of EU generation, grouped by how many countries were in a heatwave on the same day. Each point is the mean; the band behind it spans the min–max across that bucket’s days, with both ends printed, and each is labelled with the number of days behind it.

How the EU generation mix shifts with temperature

The whole EU mix as a share of generation, read against how hot Europe is. Each country’s temperature is weighted by its own average electricity demand, so the index follows the load rather than the map — a plain average of thirty countries would mix Finland with Greece and describe nowhere. The axis starts at 23 °C: below that the bins hold three to eight days of cool May weather and say nothing about heat response. What is left is 85 of the 108 warm-season days, every column carrying nine or more. Bands are ordered so the two largest movers sit against the flat edges, where a changing width is easiest to judge: gas on the baseline, wind against the ceiling.

Across 23 °C to 33 °C, solar rises from 18.0% to 21.4% and overtakes hydro and then nuclear to become the single largest source. But gas gains twice as much — 8.4% to 16.1%, nearly doubling — because wind nearly halves, 18.5% to 9.9%: the same stagnant anticyclone that brings the heat also stops the wind, and solar’s gain is largely spent replacing it rather than meeting new demand. Nuclear holds its share almost exactly; coal drifts up two points.

What solar does to the price

Day-ahead price and solar share, hour by hour, averaged across each country’s own heatwave days. A daily average hides this completely: solar displaces the marginal generator for about six hours and then stops, so the effect only exists at the hourly level. The two panels share one time axis and are deliberately not overlaid on a second y-scale, which would let the eye read a correlation out of an arbitrary choice of scaling.

The price curve is the mirror image of the solar curve. Germany bottoms at −€13 at 13:00, when solar is 68% of its generation, then reaches €225 by 20:00 once solar is gone — a €238 swing inside eight hours. Spain runs the same shape. Italy does not: at 51% solar its midday price only falls to about €104.

The lesson is that share alone does not set the price — what matters is whether solar displaces the most expensive unit. Italy’s residual demand is met almost entirely by gas, so the price stays pegged to gas even at half solar; Germany’s residual includes wind, coal and imports, so its price collapses. Checked against the same calendar days for all three countries, the three price within 20% of each other at 03:00 and 21:00 and differ threefold to fivefold at 13:00, so this is the solar hours and not a difference in dates or gas costs.

Which countries’ demand rises most in a heatwave

Both pools drawn in full: the grey band spans the min–max of daily demand across normal days with a dot at the mean, the red band the same across heatwave days. Weekdays are compared with weekdays and weekends with weekends. Values are indexed so each country’s normal-day mean sits at 100 — Cyprus runs 0.9 GW and France 45, so raw megawatts on one axis would flatten every small country to a sliver. The figure at the right is the gap between the two means; hover any row for the raw megawatts.

Heat burden this year

Heatwave days per country so far this year, shaded by count, with the peak temperature reached.

How much of the extra demand was met by gas and by trade

Extra gas generation and the trade response on heatwave days, each as a share of the extra demand, stacked so the combined contribution is visible. The trade bar is named from each country’s actual position: for an importer it is extra imports; for an exporter like France it is an export cut — power kept at home, not power bought in. Both are measured directly — gas is a single ENTSO-E production type, trade is metered cross-border flows — so nothing is reconstructed.

How to read it: above 100% means gas and imports together delivered more than the demand rise — the surplus replaced generation that fell at the same time (wind, hydro, nuclear derating). Negative means the country met its extra demand domestically with other fuels while its gas or its imports actually fell. A bar pointing left is not missing data; it is a country that leaned the other way. The figure after each bar is the size of the demand change itself, since a large share of a small change carries little weight; countries whose demand rose less than 2% are left out because a share of roughly nothing is noise.

Does interconnection displace gas?

Change in net trade position against change in domestic gas generation, one dot per country. Moving right means the country kept more power at home during heatwaves — by importing more or by exporting less: France sits far right not because it imported (it exported on every single heatwave day) but because its exports fell. Bottom-right means trade did the work and gas burn fell; top-left means gas did the work while power still flowed out. This is a correlation, not a causal claim — and it is directional, not a single EU answer.

What fell most in each country during its heatwaves

The two components that dropped furthest in each country, across all 2026 heatwave days against all non-heatwave days of the same season and day type. The country is tinted by its largest faller and the badge names both, with a ▼ in that component’s colour.

Figures are power, in gigawatts or megawatts, not percentages: the trade component crosses zero, so a percentage on it is meaningless — Bulgaria’s net imports fall by 4.9 GWh/day on a negative base, which arithmetic reports as +36%. Ranking is within each country, so it reads as “what moved most here” rather than “who moved most in Europe”: Germany’s wind loss of 4.1 GW and Slovenia’s hydro loss of 95 MW are each their own country’s biggest.

What rose most to replace it

The same construction for the two components that rose furthest, with a ▲ in each component’s colour. Net trade is included alongside the fuels because for several countries it is the largest single move — but read it as a change in position, not a purchase: France’s +2.8 GW is an export cut, electricity kept at home rather than bought in.

Average hourly demand and generation by source

One panel per country, averaged over that country’s heatwave days inside 28 July–12 August 2026: Greece and Italy 16 days of 16, Hungary 14, Romania 13, France 8. Generation stacks above the zero line, net exports fall below it, and demand rides on top as the dark line. The x-axis is the hour of the day in local time, so Romania and Greece (EEST) are not shifted against the others (CEST) — midday means midday in every panel. Each panel has its own y-scale in GWh, because Italy peaks near 45 GWh and Romania near 7; the peak is printed beside each country name.

Storage is discharge only. ENTSO-E publishes pumping as a separate consumption series we do not ingest, so unlike the Ember version this band never dips below zero, and Hungary and Romania report no pumped storage at all.

Generation and demand do not close exactly, and the reason differs by panel. Where supply runs above demand — France around midday — it is pumped storage charging: the pumps draw power that never appears as consumption in this data, so generation looks larger than the load it serves. Where supply runs below demand — Italy in the evening — it is generation below ENTSO-E’s unit-size reporting threshold, plus borders outside the EU network: Greece exchanges with Albania, North Macedonia and Turkey, and Italy with Malta and Montenegro, none of which appear in ENTSO-E’s transparency flows. Greece has only two neighbours in the data (Bulgaria and Italy), which is why its midday surplus is the largest of the five.

Cooling response curve

Average demand indexed to each country’s mild-weather baseline (100 = demand at 16–19 °C), against daily maximum temperature. The selected country is highlighted; the rest are context.

How the gap was covered, fuel by fuel

Everything that changed on heatwave days for the selected country, in GWh/day. To the right, what rose and covered the gap; to the left, generation that fell and had to be replaced as well. The black marker is the demand increase that had to be met.

Anatomy of the largest event

The selected country’s longest heatwave this year, with a week either side. Three panels share one time axis — they are deliberately not overlaid on a second y-scale, which would invent a correlation from an arbitrary alignment.