It’s the S-Curve, stupid: New model predicts half of world’s energy will come from solar by 2035

In the hazy first weeks of 2025 – with Los Angeles burning, Trump headed back to the White House, and Australia approaching an election that could be disastrous for climate and renewables – solar PV remains an unbroken ray of hope.

This remarkable technology, which owes a good deal of its modern success to Australian researchers and universities, dominates the new energy landscape all around the globe, growing at a rate that continues to defy expectations, all the while becoming cheaper, more efficient and faster to deploy.

According to estimates from the Global Solar Council and SolarPower Europe, the world reached the stunning cumulative total of 2 terawatts (TW) of installed solar capacity in November last year – a milestone that came just two years after the first terawatt mark, which took 68 years to notch up.

In Australia, rooftop solar alone regularly supplies the majority of daytime power in South Australia’s grid and in other state networks is gearing up to do the same.

In New South Wales, utility-scale solar generated more than 40 per cent of the state’s power for the first time in the first week of January – a remarkable milestone for one of Australia’s biggest remaining coal power holdouts.

But can solar keep up the pace? Or rather, can solar growth ramp up to the levels needed to triple renewables and meet increasingly urgent climate targets?

According to a newly launched climate modeling tool, the answer to these questions is a resounding ‘yes’ – or, more accurately, ‘you ain’t seen nothin’ yet.’

The S-Curve model, developed by Australian solar industry pioneer Andrew Birch, predicts that by 2035, half of the world’s energy needs will be supplied by solar in a classic S-curve technology shift.

Image source: Andrew Birch

The S-Curve projects forward solar’s historical trends, predicting that it will continue to fall in cost by 10% a year and grow at 25% a year. This will see solar energy eclipse nuclear power this year and eclipse oil by 2031.

“On current growth trends, solar is on track to displace 50 per cent of traditional energy supply within a decade,” says Birch, a UNSW PV engineering graduate and founding member of some of the leading global solar companies over the last 20 years, including OpenSolar.

“This should scare you if you’re still financing coal, oil or gas,” he adds.

Birch’s theory is that “three huge mistakes” – including a flawed equation at the heart of solar projections – have resulted in decades of inaccurate energy market forecasting on solar.

The first mistake, he says in a video on his newly launched website here, is the belief that solar cost reductions are “suddenly going to stop from nowhere.” The second mistaken assumption is that the market’s consistent growth of well over 25 per cent a year will also suddenly end.

“I’ve seen the analysts call the end to this high growth every single year, and they’ve been proven wrong again and again and again,” Birch says.

The final mistake Birch describes as more of an accounting problem. “We’re told by traditional energy brains that we need a certain amount of energy to run our economy, but over half of that fossil fuel energy is wasted when we burn it in our homes, cars and power plants,” he says.

The S-Curve seeks to correct this by using delivered energy as the metric underpinning projections, rather than primary energy. In this way, the projections show a solar electric economy will require 60% less energy than previously assumed.

“Solar’s learning curve has never ended,” says Birch. “In fact, its growth rate has increased. When you combine this growth trend with the lower energy needed with electrification you get a solar-dominated system within just 10 years.”

“Birchy,” as he calls himself, has a long and distinguished solar pedigree, having abandoned his first career choice, investment banking, to pursue a Master’s Degree in Photovoltaic Engineering at the University of New South Wales.

He then joined BP Solar, where he developed world-first PV financing solutions and designed the “feed-in tariff” model that kick-started the Australian solar market.

Following the advent of Google Earth, Birch co-founded Sungevity alongside Danny Kennedy, Alec Guettel and Adam Pryor, which pioneered the first software to provide instant online rooftop solar quotes, with sizing and measuring done remotely.

A decade or so later, Birch and Pryor started OpenSolar, the world’s first free solar software retailing and installation platform that has amassed more than 25,000 users in more than 150 countries.  

Currently, Birch is based in the UK where he has been collaborating with Professor Andrew Crossland at the Durham University Energy Institute on the best ways to support the growth of solar around the world, and to use solar electrification to benefit consumers. The pair has co-authored a white paper for Ed Miliband, the UK’s Secretary of State for Energy Security and Net Zero.

According to Birch, to solve the climate crisis, installed solar capacity needs to grow at a rate of 25% per annum. He says the Solar S-Curve can solve most of the climate challenge in a decade, as long as it is backed by the right policies.

“We’ve been told a clean transition will cripple the economy, when in fact, it will save us $9 trillion dollars a year by 2035,” he says.

“All we need is a level playing field. Just watch how quickly dirty fuels die in a fair fight when we stop the subsidies and remove clean tech tariffs.”

The “right policies,” according to Birch, including letting solar, storage and EVs compete on price. “Don’t add tariffs on cleantech, the jobs are all local, not in manufacturing,” the website says. “Remove all energy subsidies, nobody needs it.”

The second policy priority on the wish list is a little less contentious: the digitisation and automation of permitting and interconnection, to ensure speedy connection to the grid.

Finally, Birch is calling for an “Electric Protocol,” a standard set of rules for the world-wide-grid with uniform market-price treatment for all energy sources, of any size, connecting to the grid. 

“These allow all consumers and prosumers to access the time-of-day value of energy and the value of other services they provide to the grid (e.g. batteries can peak shave, regulate frequency, avoid infrastructure spend on the grid – battery owners should be compensated, so consumers get lowest cost grid),” the website says.

The key message Birch hopes to convey through his modelling is that the solar-driven shift to renewables is inevitable, not because the world is on a mission to halt dangerous climate change – although, wouldn’t it be nice – but because of the economics.

The S-Curve, he says, “challenges a pretty widely held consensus that fossil fuels will continue to dominate and it will cost us trillions of dollars to decarbonise our economy.

“The energy transition won’t cost us money, like we’re always told,” he says, in what could be a message directed straight to the nuclear obsessed leader of Australia’s federal opposition.

“The S curve is all powered by the fact that solar is now the best and the lowest cost solution for you the end customer.”