Europe's swift transition to a sustainable, low-carbon future will not happen without the engagement and involvement of citizens producing and consuming energy locally, experts say - and across the continent, there are signs it is happening.
A summer of wildfires, drought and record heatwaves fuelled by climate breakdown has combined with soaring gas and electricity prices, following Russia's invasion of Ukraine, to inject a new urgency into the switch to alternative, renewable sources.
From solar panels in the Netherlands to biomass burners in Spain, communities across Europe are increasingly making, consuming and selling their own energy, a trend the EU sees as vital if the bloc is to meet its climate targets.
According to the latest data, 2 million Europeans are now involved in 7,000 local energy communities across the continent, with numbers growing rapidly since EU directives promoting clean energy and energy communities were introduced in 2018 and 2019.
They will be key to Europe's green transition because, as heat pumps replace gas boilers and electric vehicles supplant internal combustion engines, highly centralised electricity production and distribution systems - power stations and grids - will simply not be able to adequately handle the huge increase in demand.
"At least, not on their own," said Gonçalo Mendes, a senior researcher and energy systems modeller from LUT University in Finland and part of a European Commission-funded initiative, GRETA, working to define and enable what it has dubbed "energy citizenship".
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The only way forward, Mendes said, is "to decentralise more and more, produce and consume more energy locally with sources like solar and wind - and boost storage and smart solutions for efficient energy management". All of which means involving ordinary citizens.
Some communities have operated successfully for years. The Bera Bera neighbourhood of San Sebastián in Spain has had a cooperative providing hot water and community heating to its more than 500 members since 1985.
One of the projects being studied by GRETA, the collective, known as Ur Beroa, has since moved with the times, abandoning heating oil for natural gas and adding a cogeneration system - to produce both heat and electricity, which it sells to the grid - 10 years ago, followed by a biomass boiler and solar panels.
"The first target for solar is self-consumption for 100 families," said board member Juan Luis Llorens. "The next step, next year, will be green hydrogen, to replace part of our current gas consumption. The goal now is obviously complete decarbonisation."
Llorens said Ur Beroa had been able to freeze its members' heating and hot water bills this year thanks to revenues from electricity sales, and was offering "the cheapest prices in town. My son lives outside Bera Bera, and his bills have exploded".
But if price is a big motivator for members, other aspects play a major part. "We make our own decisions," he said. "For those who care about the environment, we're making progress collectively, in a way that would be difficult individually. There's a sense of having control of something that's important in your life."
As things stand, Europe is "nowhere near" meeting its target of cutting greenhouse gas emissions by 55% in the next eight years, said Mendes, unless "we work urgently on the role everyday citizens will have to play. And to get there, we need to explicitly recognise the social side of the energy transition."
Lurian Klein, an academic expert on energy communities now working with Cleanwatts, said all the research on peer-to-peer energy sharing models showed they were "far more accessible, democratised, collaborative and socially just" than traditional top-down energy markets.
"Fundamentally, they thrive on social interconnectedness among end-users, rather than being based on competing economic self-interests," he said. "They reinforce positive social values, really strengthen empowerment and social engagement."
Fortunately, technology is now making it possible. "A lot is coming together," said Michael Pinto of CleanWatts, which has arranged financing, designed and installed systems to produce, store and trade electricity, as well as control and optimise consumption, for 100 communities in Portugal - with 2,000 more inquiries waiting.
"You have electricity needs that are going to double and grids that won't cope. But you now also have sustainables - solar panels - that are competitive now, and smart technology to measure, manage and balance production, storage and consumption efficiently."
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That means the options are basically either "blackouts and massive volatility, and completely rebuilding national grids", Pinto said, or "changing the way electricity is produced, delivered and consumed. More agile, more resourceful. That's local energy communities."
EU directives on energy communities are being incorporated into national law around the bloc at different speeds and with different incentives, but an ideal starting scenario for a new project, Pinto said, was "say, a big warehouse: large, big roof, low energy use".
In Portugal, that warehouse - projects also involve barracks, football clubs and village schools - can expect 20% to 30% off its electricity bills; in Austria it would get cashback. And the 80% excess it produces but does not use can be sold to locals, and beyond.
"There are tens of thousands of municipalities in the EU," said Pinto. "There are 8,000 in Italy alone - about 5,000 of them with fewer than 5,000 inhabitants. The potential here is just enormous. But it has to be - the challenge is enormous, too."
In the Netherlands, Steven Volkers of Grunneger Power in Groningen, which has 2,500 members, said the decade-old cooperative was born of people's "passion and frustration" at the slow pace of the green transition.
The cooperative owns two solar parks totalling 10,000-plus panels, as well as smaller sites on homes and buildings across the city, generating green electricity that it also sells to a sustainable energy provider with profits invested back into the collective.
It also offers help with insulation and installations. Dutch government targets - 50% community-owned and 30% sustainably generated electricity - underline a belief that "we won't reach sustainability targets without citizen participation", Volkers said.
Elsewhere, the potential is still being explored. In Bologna, Italy, a green energy community project (GECO) involving the university, municipality, residents' associations, the regional energy agency and other bodies has been under way since 2019 in the north-eastern district of Pilastro-Roveri.
"What's interesting is this is actually two districts in one," said Martina Massari of Bologna University's architecture department, which is leading the university's involvement in the GRETA project. "Pilastro is a 1960s residential area - 6,800 people, lots of social housing, mixed populations.
"Roveri, across the rail tracks, is industrial, lots of factories, warehouses - and the EU's largest solar power plant on industrial rooftops. They're slowly making the housing blocks more energy-efficient, which is essential, and interest among residents is growing rapidly as energy prices rise."
Carlo Alberto Nucci, a professor of electrical power systems at the university and technical lead for the project, said it was a pilot, "like a living lab", and recent government incentives for local energy communities in Italy would make a significant difference.
"What's fundamental is that we start to produce energy where it's consumed, and we can do that now because of renewables," he said, adding that ultimately, about 20% of energy produced in cities should come from energy communities.
Smart meters, connected appliances and end-user apps will be critical to the system's success, Nucci said. "A smart app can automatically switch on your home devices, choosing the best moment for you - and for the efficiency of the whole community - to use your washing machine, for example.
"Much of this is really about the concept that energy is of value, that information about it is really important, and that virtuous energy behaviours absolutely can make a difference - to both individuals and the community. This is all quite new."
Bologna's deputy mayor, Anna Lisa Boni, said the project was "clearly a fantastic idea" but was being held up, in part, by a delayed legislative process at national level and by bureaucracy. "The legal framework is very complex, the devil's in the detail - what happens with the various partner's VAT systems, for example," she said.
Ultimately, Mendes said, more than 80% of EU households could play an active part in the energy transition: "Energy citizenship, we call it. Obviously, awareness and engagement levels will differ. But it's all about agency."