Innovation gives solar a battery boost

In 1979, in the depths of an energy crisis sparked by the Iranian revolution, US President Jimmy Carter had solar panels installed on the roof of the White House. It was a symbolic move to showcase Carter’s goal of making renewable power a key part of the US energy system by the year 2000.

Unfortunately, the nascent technology was strikingly inefficient. In the 1980s, photovoltaic panels converted less than 10 per cent of the sunlight they received into electricity. The White House panels were removed after just seven years by Ronald Reagan, who also gutted the US R&D budget for solar power.

It may have taken decades to recover from that false start, but today’s panels are considerably more efficient. “Primary terrestrial PV technology continues to make pretty impressive progress,” says Nancy Haegel, director of the National Center for Photovoltaics at the US National Renewable Energy Laboratory. It is now commonplace for solar panels to have a conversion efficiency of around 22 per cent. The current record, set earlier this year by Chinese company Longi, is 27.8 per cent.

“Progress marches on,” says Haegel. “People sometimes refer to it as ‘incremental’, but it’s really not. It’s really technologically driven — and incremental over time adds up to pretty significant.”

The problem is that conventional silicon solar PV panels are now approaching their maximum theoretical efficiency of around 30 per cent. 

To achieve further advances, researchers are experimenting with “tandem” panels. These overlay a conventional silicon panel with a panel made of perovskites (a family of materials that have specific crystal structures) to increase the spectrum of light that can be absorbed. Longi also holds the world record for a silicon-perovskite tandem cell, hitting a conversion efficiency of 34.9 per cent in April.

Constant solar?

Dave Jones, chief analyst at energy think-tank Ember, highlights another breakthrough that could help accelerate the solar boom. “For me, the major innovation is not the solar panel, but the battery that sits alongside it,” he says. Chinese companies have made significant progress in commercialising containerised batteries over the past year, he says — a departure from the traditional model of installing batteries in racks and buildings.

A containerised battery resembles a “plug and play” device, says Jones. “That makes batteries far quicker, cheaper and easier to install than they’ve ever been before.” Consultancy BloombergNEF estimates that battery storage costs fell by a third last year and projects that costs will halve again by 2035.

Installing batteries alongside solar reduces the need for investment in transmission lines. It also opens the door for solar to play a much greater role in a country’s energy mix, since battery storage means solar power can be relied upon to provide greater volumes of power whenever it is needed.

In some locations, it is no longer a “pipe dream” to believe an energy system could run entirely on solar and batteries, says Jones. Indeed, Ember’s research suggests it is already economically feasible to get more than 90 per cent of the way to constant solar generation in some of the world’s sunniest cities, including Las Vegas, Muscat and Johannesburg.