In demand: The growth in the use of solar power has been beyond most expectations. Photo: Justin McManus
Back in its 2003 annual report, Energex, the main power distributor serving south-eastern Queensland, noted a "growing awareness" among customers of the need to minimise their environmental impact and to reduce greenhouse gas emissions.
As proof of this, solar photovoltaic systems in the region duly doubled that financial year, by 70 units to 138.
It's a tide, a big wave, that's going to be difficult to turn back
Fast forward to 2011-12 and annual installations had soared 1000-fold, or 72,500, with a further 74,000 rooftop systems added last year.
Michael Fraser, AGL chief executive. Photo: Agus Mordant
"I don't think anybody predicted we'd have this kind of volume," Energex chief executive Terry Effeney said.
Hefty feed-in tariffs prompted much of the residential rush into solar PV, so much so that Queensland overtook more populous NSW early last year to be Australia's largest sun-powered state.
Even with the Campbell Newman government's slashing of the Queensland tariff a year ago, households continue to take up solar PV, with Energex alone registering almost 10,000 units in the past four months.
"It's a tide, a big wave, that's going to be difficult to turn back," said Paul Meredith, a researcher at University of Queensland's Global Change Institute.
That tide, though, is bringing challenges that are not yet well understood or anticipated. And as solar spreads around the country, south-east Queensland offers pointers to what other regions can expect.
One issue is the uneven distribution of these generate-it-yourself power kits.
Areas north of Brisbane, such as Godwin Beach, Ningi and Sandstone Point, have solar panels blanketing almost one in three rooftops, while inner city suburbs have only a fraction of that.
"It does provide a challenge in areas where you have high penetration levels of PV," Mr Effeney said.
A rule of thumb is that beyond about 30 per cent penetration "you then start to potentially have voltage issues on the network", he said.
Mr Effeney, who is also chairman of the national industry group Energy Networks Association, stresses that so far "it's not a safety issue, per se" but one of compliance with regulations. Voltage fluctuations, for instance, can affect the life of appliances, such as some lighting.
Energex is testing the use of batteries and devices such as static compensators, to allow greater solar penetration without costly investment into transformers.
"We have to watch very carefully because we have to assume, correctly, that solar PVs are going to continue, [that] the level of penetration is going to increase," he said. "We are tending to be a little bit on the cutting edge of this."
Another place also at that edge has been Carnarvon in Western Australia, which in 2011 limited the amount of solar PV capacity to 1.15 megawatts on the local network.
The Australian Renewable Energy Agency (ARENA) is also investigating how grid limits may restrict the take-up of clean energy - including how to predict problems and overcome them.
"The networks are justifiably concerned about the network reliability issues," Professor Meredith said. "There are genuine concerns that [high solar PV penetration] could affect the stability and the reliability of that network."
The University of Queensland is planning a PV research facility to address these issues and also go further. "How do you make a positive impact on the power system?" he said.
Solar power, when used with battery storage, may be able to smooth, shift or control loads, he said, adding that demand management would also have a role to play.
Michael Fraser, chief executive of power giant AGL, said utility-scale PV plants, which feed directly into transmission rather than distribution networks, may eclipse rooftop PV in the future.
Mr Fraser this week unveiled AGL's plans to proceed with two solar power plants costing $450 million for Broken Hill and Nyngan in western NSW. The 155-megawatt capacity will meet the power needs of about 50,000 homes, and be about 15 times bigger than Australia's largest plant.
"In my view, the most cost-effective way to develop solar is with large-scale projects," Mr Fraser said. "You get the economies of scale.
"You can overcome a lot of those issues that are potentially there if you get too big a concentration of rooftop solar in an area without the network infrastructure to support it."
Jack Curtis, a vice-president of First Solar, which will supply the 2 million panels for the AGL plants, predicts solar PV plants will be competitive with wind in three to four years. By 2016, in fact, such plants "will not require subsidies any more", he said.
The AGL plants needed about $272 million in federal and state aid, so that gap is still a wide one, whether solar is on the roof or in vast arrays.
And on Friday, the $10 billion Clean Energy Finance Corp (CEFC) announced it had reached agreement to lend $60 million to Moree Solar Farm to build a 56-megawatt solar photovoltaic power plant in NSW. The plant will provide power for about 15,000 homes and avoid more than 95,000 tonnes of annual carbon-dioxide emissions, CEFC said.
NSW Energy Minister Chris Hartcher, just back from a tour of Germany with its many hectares of solar panels, said the state's residents continued to embrace solar PV for their roofs even after a generous subsidy was stripped two years ago.
Some 70,000 households had bought PV since, "without any encouragement, without any subsidy", the minister said.
Back in Queensland, Energex's Mr Effeney said with solar PV prices falling and technology improving, that trend is likely to continue.
"They are part of the new world, and they won't need feed-in tariffs to incentivise them," he said.