Night will fall on Europe’s power system a little early on Wednesday evening, as an eclipse is set to block solar generation across parts of the continent.While the rare celestial event is expected to draw thousands of tourists eager to witness the eclipse from northern Spain, it will make for a more complicated afternoon than usual for technicians operating the region’s increasingly solar-reliant power grids.Fortunately, there’s been plenty of time to prepare. A solar eclipse, though rare, can be predicted centuries in advance. And this time, the impact on solar generation will be fairly muted. The sun will be nearing the horizon when the moon obscures it, meaning alternative sources of generation will already be ramping up to meet evening demand.Still, the eclipse could knock out a meaningful amount of solar generation, leaving the shortfall to be covered by other sources such as natural gas, hydropower and nuclear plants. As a precautionary measure, the UK’s grid operator issued a warning on tight margins for Wednesday evening, asking market participants to offer spare generation to help meet demand while the sun is blocked.Solar farm operators in Spain say they are well prepared for the eclipse. Pablo Blazquez Dominguez / Getty ImagesShow caption: Solar farm operators in Spain say they are well prepared for…Britain’s National Energy System Operator forecasts a margin shortfall of nearly 1.8 gigawatts for Wednesday evening starting at 5 pm local time. While such warnings are typically a winter phenomenon, they’ve become increasingly common this summer as extreme heat across Europe curbs output from traditional sources including nuclear and hydropower.“The notice has been issued as a precautionary measure to the market due to the solar eclipse and there is no risk to customer electricity supplies,” a spokesperson for NESO said in an emailed statement.Britain’s biggest household energy supplier, Octopus Energy, has asked customers to not use electricity during the eclipse to avoid being forced to make up for the shortfall in solar energy power by turning on gas-fire power plants, which cause carbon emissions. To incentivise customers, Octopus Energy has offered one hour of free energy on Sunday to those that alter their habits on Wednesday night.The eclipse will be total in Spain. Getty ImagesShow caption: The eclipse will be total in Spain. Getty Images“The effects are quite far-reaching geographically, all the way across Europe,” Ryan Carson from the energy forecasting team at the UK’s National Energy System Operator said in a presentation last week. “We have been analysing this since about one year ago.”Varying impactFor the UK, the eclipse will hit around 8 pm and likely reduce generation by a bit over 1 gigawatt, with 95 per cent of the sun obscured, Mr Carson said. Across Europe, the impacts will vary, depending on the time of the eclipse, its extent and the size of the country’s solar fleet. Overall in Europe, if the conditions are clear, solar output could decrease by about 9.7 gigawatts starting at about 7:15 pm, according to a forecast from the Entso-e group of European power grid operators.In Spain, where the eclipse will be total, solar farm operators say they’re well prepared and coordinating closely with Red Electrica, the nation’s power-system operator.Acciona, which has some solar assets directly in the path of the eclipse, does not expect a major impact because the event coincides with sunset, when solar output is already declining. The company has nonetheless incorporated the eclipse into its generation forecasts.Play01:10Out of this world: three celestial events happen on Wednesday“Everything is included in our models,” said Manuel Calleja, Head of Centres at Acciona Energía. “We include the eclipse in the forecast that we share with the TSO, so they know in advance how photovoltaic production is going to reduce.”He said flexible resources such as hydroelectric plants and combined-cycle gas turbines would be available to make up for any temporary loss of solar output, though those facilities would typically be running or preparing to meet Spain’s evening peak in electricity demand.While this eclipse will have a relatively minor impact, another is headed for Europe next summer — and that one will strike in the late morning, when solar can be the biggest source of electricity across much of the continent.Agencies contributed to this report