On a suburban street in Perth, amid the pre-war homes and the peppermint trees, evidence of Australia’s transforming energy system is all around.

Almost every second property has solar panels bolted to the roof, pumping out electricity as the bright West Australian sun rides high in the midday sky.

Among them is the house owned by Alan Benn, a retired electronics engineer.

Mr Benn bought his first rooftop solar panels 20 years ago, when the systems were small – and expensive.

“The actual total cost of the solar power system at that time was about $19,000,” Mr Benn said.

“The $8,000 [subsidy] brought it down so my expense was $11,000.

“And that was just for a 1.5 kilowatt system, which is about a third of the size of what people buy nowadays … and they pay $5,000 for it.”

Officially, according to the Clean Energy Regulator, there were 507,862 solar installations on WA homes and businesses as of June 30.

Less officially, the regulator believes about one in every three WA households has a system.

Nationally, almost four million households and businesses have solar panels.

The continued rise of rooftop solar across the country has been a remarkable success story, with Australia the clear global leader in the adoption of the technology.

But in WA – home to the world’s biggest isolated or “island” grid in the south western corner of the state – the uptake of solar also poses some thorny questions.

What happens when you have so much solar power that it threatens to overload the grid at certain times?

And how much more difficult is it to manage that problem when your electricity system is all alone and doesn’t have anyone to bail it out?

An isolated grid

Kate Ryan runs the WA arm of the Australian Energy Market Operator (AEMO), which is responsible for keeping the lights on in the country’s main electricity systems.

She said WA’s isolation meant it was having to find answers to those questions much sooner than almost anywhere else in the world.

“We don’t have the ability to borrow from our neighbours, or indeed, to give them the benefit of our excess supply at times when we have it,” Ms Ryan said.

Tony Wood, the energy program director at the Grattan Institute, said South Australia was often held up as the poster child of the renewable energy transition.

Mr Wood said about 75 per cent of South Australia’s power came from green sources such as wind and solar, which sometimes accounted for all its needs – and more.

It’s a similar story around the world from Asia to Europe and North America, where grids are meshed together to allow electricity trading and provide greater resilience.

But Mr Wood said WA was, in many ways, a more fascinating example of the transition because of its isolation.

“South Australia is getting to the point where on average it’s 100 per cent renewable,” he said.

“But that means sometimes it’s 200 per cent and sometimes it’s almost nothing.

“Now, that’s an example of the benefit of being connected to a larger grid, which of course Western Australia doesn’t have.”

Ms Ryan said solar power was a “tremendous” opportunity for the energy system because it was so cheap and Australia was so sunny.

But she acknowledged in WA “it comes with challenges, like when the cloud cover comes over, and might very quickly reduce the amount of rooftop solar being generated”.

“That means, as the grid operator, we need to find other sources of supply to meet that,” she said.

“And we’ve got to find that locally within our grid.”

Storage the silver bullet

For Ms Ryan, a big part of the answer was simple enough – storage.

“I think storage of electricity is really the silver bullet, I guess, the way that we harness that opportunity,” she said.

“And that’s storage at all levels.”

To that end, WA was making big bets on large-scale storage.

State-owned utility Synergy already has a 100MW “big battery” with 200MW/h of capacity and a second, much bigger battery with 800MW/h of capacity is under construction next door.

Meanwhile, private companies led by French renewable energy player Neoen are building a raft of massive batteries.

These include a 560 megawatt installation with a whopping 2240 mw per hour of capacity near Collie, a town south of Perth that is the traditional home of WA’s coal power industry.

But there are calls for smaller batteries to help soak up the excess solar power in the middle of the day.

There are “community” batteries that tended to be medium-sized, built by the network poles-and-wires companies and could act like banks, storing solar excess power for times it was needed.