We have not found any official forecast for 2 August 2027, either of a power cut or of the opposite, and we are not going to make one up. What can be calculated is how much Sun a solar panel loses: in Madrid the eclipse will last 137 minutes and cover 41.7% of the solar disc on average, with a maximum of 86.1% at around 10:51 Spanish time (CEST, UTC+2). And we know what the grid operators said about earlier eclipses. For the partial eclipse of March 2025, Red Eléctrica, which runs Spain’s electricity grid, calculated that photovoltaic output on the mainland could fall by more than 3.5 GW, and it guaranteed supply. For last summer’s eclipse it forecast about 5 GW less and wrote that this was not expected to affect its ability to meet demand.
What a panel loses, city by city
A panel produces according to the light it receives, and during the eclipse the Moon covers a part of the Sun’s disc that changes minute by minute. Our engine calculates that part for each city. This is the geometry of the disc, not measured output: what each installation produces will also depend on the clouds, as Red Eléctrica points out, and on the installation itself.
| City | Minutes of eclipse | Disc covered, on average | Maximum | Minutes with more than half covered |
|---|---|---|---|---|
| Madrid | 137 | 41.7% | 86.1% | 56 |
| Seville | 138 | 44.8% | 98.4% | 59 |
| Málaga | 140 | 45.2% | 100% (total) | 61 |
| Valencia | 141 | 42.9% | 90.4% | 60 |
| Barcelona | 141 | 40.0% | 81.6% | 55 |
| Bilbao | 133 | 37.6% | 74.4% | 50 |
| A Coruña | 129 | 37.1% | 73.4% | 47 |
| Las Palmas de Gran Canaria | 129 | 38.6% | 77.2% | 49 |
The average is calculated over the minutes the eclipse lasts in each city. The maximum is the one on each town page; the minutes and the average come from the minute-by-minute curve calculated at its centre, which can differ by a tenth. In Madrid, at twenty-minute intervals, the covered part goes like this: 21.3% at 10:06, 54.1% at 10:26, 83.9% at 10:46, 72.2% at 11:06, 40.5% at 11:26 and 13.0% at 11:46. The exact time for your town is in when is the eclipse.
What Red Eléctrica said
In March 2025, two days before that Saturday’s partial eclipse, Red Eléctrica explained that it had developed forecasting algorithms to model the obscuration and estimate how much photovoltaic output would fall, so as to size the reserves that make up for the drop. Its estimate: mainland photovoltaic output could fall by more than 3.5 GW at around half past eleven, depending on the weather. Across Europe, the ENTSO-E operators estimated a drop of up to 21 GW between 8:50 and 12:43 UTC, mainly in Germany, the Netherlands and Spain. Red Eléctrica presented that work as a rehearsal for the total eclipses still to come: last summer’s and the one in 2027.
For last summer’s eclipse, its model calculated obscuration curves by area and a maximum drop of about 5 GW, around 13% of peak demand on a typical August working day. Red Eléctrica described it as a limited and temporary impact: the eclipse came when photovoltaic output is already starting to fall naturally, it would only bring that fall forward and deepen it a little, and it did not coincide with the August demand peak. It expected no significant effect in the Balearic or Canary Islands. Even so, it announced measures: coordination with official bodies, with the other European operators and with the generation and distribution control centres, more reserves and safety margins, and constant monitoring. We have not read an official review of what happened that day.
What ENTSO-E said in 2015
The first eclipse to put the European grid to the test was on 20 March 2015. ENTSO-E, the association of European transmission system operators, wrote beforehand that for the first time an eclipse would have a significant effect on the secure operation of the system. With about 90 GW of photovoltaic capacity installed in continental Europe and clear skies, it calculated that output could fall by 34 GW at 9:41 UTC, and that power could change by more than 400 MW per minute on the way down and 700 MW per minute as the Sun returned. It put Spain’s installed capacity at 6,739 MW, with a drop of 1,392 MW at that moment, 4% of the European total. Afterwards, ENTSO-E summed it up like this: it was the first of its kind, a real stress test, and it was passed successfully.
What changes in 2027
Last summer’s eclipse came when photovoltaic output was already falling because of the time of day. The one on 2 August 2027 comes in mid-morning, with the Sun climbing: on the mainland and the Balearic Islands, the partial eclipse begins at 09:40 (Ayamonte) and ends at 12:15 (Es Castell, on Menorca). Red Eléctrica already listed it in March 2025 among the total eclipses to come, but we have not found a forecast in megawatts for that day, either from Red Eléctrica or from ENTSO-E. If they publish one, theirs is the figure that counts. We calculate how much of the Sun is covered in each municipality and when, and you will find it in Will I see it?. What the eclipse does to the temperature is covered in how much does the temperature drop during an eclipse.
Sources: Red Eléctrica garantiza la seguridad de suministro durante el eclipse solar parcial de este sábado — Red Eléctrica (in Spanish: forecasting algorithms, the 3.5 GW on the mainland, the 21 GW in Europe and the rehearsal for the total eclipses); “Eclipse solar: medidas preventivas para un impacto limitado en la generación solar”, a Red Eléctrica press release, in its press room (in Spanish: the 5 GW of last summer, the 13% of demand, the Balearic and Canary Islands and the preventive measures); Solar Eclipse 2015 - Impact Analysis — ENTSO-E (installed capacity, expected drop, rates of change and figures for Spain); ENTSO-E and SolarPower Europe release a joint report — ENTSO-E (the review of the 2015 eclipse); eclipseando data (fraction of the disc covered minute by minute, from the skyfield + DE440s engine).
If you would like something to keep from the eclipse, the shop prints T-shirts, mugs and posters with the name of your town, the time of its maximum and its seconds of totality. See the merchandise →
Remember: never look at the Sun without proper eye protection (filters made to EN ISO 12312-2). The official reference for safe viewing in Spain is the IGN (in Spanish): eclipses.ign.es.