The total solar eclipse on 12 August is expected to reduce European photovoltaic output by as much as 9.7 GW under clear-sky conditions, with the principal generation movement occurring between approximately 19:15 and 21:30 Central European Summer Time.
The eclipse will be total across parts of Spain and Portugal and partial across much of Europe. Its direct physical effect in the Balkans will be smaller than in Iberia, France or Italy. Its market effect will be wider because it arrives during the continental evening ramp, when solar output is already declining and demand remains elevated by cooling loads.
Grid operators can forecast the event with considerably greater accuracy than a weather-driven renewable shortfall. Thermal plants, hydro reserves, batteries, demand response and cross-border schedules can therefore be prepared in advance. The difficulty is the condition of those balancing resources.
Romanian hydropower is weak, one of the two 680 MW Cernavodă reactors is unavailable, and the remaining unit faces a renewed shutdown risk as Danube levels continue to fall. Hungary’s Paks nuclear plant has only begun restoring capacity after severe cooling-water constraints, while Slovenia’s Krško reactor has been operating below normal output because of high Sava temperatures.
Western Europe is also contributing less surplus power. French nuclear output could be constrained by as much as 7.3 GW at Wednesday’s midday peak, equivalent to approximately 12 per cent of the French reactor fleet. German wind generation is forecast to fall by 8.1 GW to about 4.7 GW, roughly 60 per cent below the seasonal norm.
French day-ahead power rose 21.8 per cent to €142.50/MWh on 11 August, while the equivalent German contract increased 22.8 per cent to €138.50/MWh. These are not Southeast European settlement prices, but they reduce the amount of inexpensive western electricity available to flow eastward through Austria, Slovenia and Hungary.
The eclipse itself is unlikely to cause a general supply failure. Its trading importance lies in the speed of the change. Reserve providers must absorb the downward movement in solar output and the subsequent recovery, while the evening market is already leaning on gas, coal, batteries and scarce hydro.
Intraday volatility may consequently exceed the change in daily baseload. Traders carrying short positions into the evening face the risk that forecast errors in cloud cover, cooling demand or reactor availability compound the predictable solar ramp. Batteries with energy remaining after the ordinary sunset discharge will have unusually valuable flexibility.
