From physicist to solar pioneer

For decades, Professor Wilfried van Sark has been researching the technologies and systems shaping the energy transition. From the early days of solar cell research to today’s challenges around smart grids, storage, and electric vehicles, his career has closely mirrored the rise of photovoltaics. As he retires, ahead of his Valedictory Lecture, Van Sark reflects on a career driven by curiosity, interdisciplinarity, and a belief in the power of students as “change agents”.

“The Club of Rome report changed everything”

Van Sark’s interest in sustainability began long before solar panels became a common sight on Dutch rooftops. “The starting point was really the Club of Rome report in 1973,” he says, referring to the influential report The Limits to Growth, which warned about the environmental and societal consequences of unchecked economic and population growth on a finite planet. “At that time, I was in my early teens and attended what was officially a Catholic high school, but in practice was very left-wing and environmentally minded. Many teachers and students were strongly influenced by the report, and that shaped my thinking.”

He went on to study physics at Utrecht University, later combining it with an environmental science minor that brought together students and researchers from biology, sociology, and other disciplines. “It was interdisciplinary before we even called it that,” he laughs.

The starting point was really the Club of Rome report in 1973

His route into solar energy research came almost by accident. After a proposed thesis on subsurface water flows was rejected for not being “physics enough”, he saw an opportunity for a thesis measuring the efficiency of solar cells at the FOM-institute AMOLF in Amsterdam. From there, Van Sark built a career that took him through Radboud University Nijmegen, Utrecht University’s Debye Institute for Nanomaterials Science, and eventually to the interdisciplinary natural-social science Copernicus Institute of Sustainable Development, based at the Faculty of Geosciences.

Integrating solar into society

Over the years, Van Sark’s work evolved from improving solar cell efficiencies in the lab to thinking about how solar energy systems function within society more broadly. He was appointed professor of Integration of Photovoltaics in 2018. “My current work goes in two directions. One is the physical integration of photovoltaics into the environment; in buildings, façades, on (agricultural) land, or even on water. The other is how solar energy, which is not produced continuously throughout the day, can be integrated into the wider energy system.”

“Not too much solar, just too much at the wrong moments”

Back when Van Sark started in solar research, photovoltaics was still niche. Today, the Netherlands has around 30 gigawatts of installed solar capacity. “What surprises me most is how incredibly fast photovoltaics have grown,” he says. “But I’m also surprised — and worried — by how slowly we are phasing out fossil fuels.”

What surprises me most is how incredibly fast photovoltaics have grown. But I’m also surprised — and worried — by how slowly we are phasing out fossil fuels.

The rapid growth of solar energy is also creating new technical challenges. “On a sunny day in May, the Netherlands produces far more solar electricity than we immediately need,” he explains. “That doesn’t mean we have too much solar power. We simply have too much at the wrong moments.” That shift, he says, means storage, smart charging, accurate forecasting, and energy system modelling are becoming just as important as solar panels themselves.

Scepticism for nuclear energy

Van Sark’s views on the energy transition are — characteristically for him — outspoken, and this includes his scepticism about nuclear energy. “As a physicist, I actually find nuclear technology fascinating,” he says. “However, the societal and environmental consequences have always made me opposed to it”. Instead, he believes Europe can build a reliable low-carbon energy system through combinations of solar, wind, storage, and smart energy management.

As a physicist, I actually find nuclear technology fascinating. However, the societal and environmental consequences have always made me opposed to it.

That systems perspective has shaped much of his later research. Van Sark points to his research exploring vehicle-to-grid systems, where electric cars can both charge from and discharge electricity back into the grid. “In Utrecht’s Lombok we collaborate with WeDriveSolar and now have over 100 bidirectional electrical vehicles and charging points,” he says. “Cars like these could help solve congestion problems in the electricity network if more widely rolled out.” 

From physicist to transdisciplinary researcher

Long before transdisciplinarity became a key term within sustainability science, Van Sark was already combining physics with biology and systems thinking, working closely with societal partners to co-develop questions and carry out research. It was not an obvious path for someone trained as a physicist. When asked what he is most proud of, he takes a minute to answer. “Probably this evolution from monodisciplinary physicist into a transdisciplinary researcher working closely with society,” he reflects. 

Most of our alumni continue working in sustainability-related fields, in ministries, consultancies, research organisations, and companies. They are our ‘change agents’. That gives me hope.

One contribution that unexpectedly gained national significance was his work estimating solar electricity production in the Netherlands. “Around ten years ago, with several national stakeholders, we developed a standard estimate that one kilowatt of installed solar capacity would generate roughly 875 kilowatt-hours per year,” he says. “CBS has used that figure for years in national reporting to the EU. It’s ‘my number’, in a sense, at least that’s how people generally refer to it.”

Students as “change agents”

Teaching and supervising students has remained one of the most rewarding aspects of his career. “For PhD students, I really enjoy guiding them through solving research problems,” he says. “The best moments are when they begin surprising me, taking initiative, developing new ideas, even writing their own research proposals.” He also admits he enjoys small-scale seminars more than large lecture halls. “In a room of 100 students, maybe only ten are really listening,” he says with a smile. “So I focus on those ten.”

Asked whether he feels hopeful about the future of sustainability, he points again to students. “Most of our alumni continue working in sustainability-related fields, in ministries, consultancies, research organisations, and companies,” he says. “They are our ‘change agents’. That gives me hope.”

Looking ahead

Retirement will not mean disappearing entirely from the university. Van Sark will continue as a scientific advisor in several consortia and expects to remain a familiar face around the office. “It will be difficult to completely get rid of me, though I definitely won’t miss management meetings,” he says with a laugh. Alongside occasional guest lectures, he is also looking forward to having more time for the things he enjoys. “Music and my bands, travelling, and having less stress and more control over my own workload!”

In a room of 100 students, maybe only ten are really listening. So I focus on those ten.

Looking out from his office, Van Sark points towards the Van Unnik Building, the former home of the Copernicus Institute of Sustainable Development, which is currently under renovation. During initial redevelopment conversations some ten years ago he calculated that rooftop solar alone would never be enough to power the tower. “You would need façade integration as well,” he says. Now that the redevelopment is finally moving forward, he is curious to see what happens next. “Maybe they’ll finally do it.”

Before leaving, he offers one final piece of advice for the next generation. “Don’t rely too much on AI,” he says. “People still need to develop knowledge, critical thinking, and experience independently. Otherwise, we risk becoming too lazy intellectually. Rewatching the movie WALL-E can be quite insightful in that regard.”