Rooftop solar panel installations soared by almost half in the first six months of 2018 as businesses eclipse residential take-up for the first time.

In the January-June half, rooftop photovoltaic (PV) panel installations reached 701.9 megawatts, up 48.1 per cent from the same time a year earlier, according to Green Energy Markets, a consultancy.

NSW led the way with 183.6 MW of new rooftop panels, up 70 per cent from a year ago, adding the largest additional capacity of any state.

Queensland's 176.2 MW was the second largest during the half-year, up 35 per cent, while Victoria's 56 per cent jump to 86.8 MW lifted it to third spot.

The ACT posted the fastest growth, with installations up 130 per cent.

Household systems now average about 5 kilowatts per system as families try to cut their exposure to higher electricity prices.

Falling unit prices, driven by a huge expansion of capacity in China, have been another factor in stoking demand even as states such as NSW lower the feed-in tariff paid for exporting surplus power to the grid.

Commercial boom

The long-predicted jump in commercial-sized systems – those of more than 15 kW – is finally happening. Such demand accounted for a quarter of June's PV demand, according to Ric Brazzale, chairman of Green Energy Markets.

"If we continue on at the same rate of installations we will end the year at between 1450 MW to 1500 MW – this will be more than 30 per cent higher than the 1100 MW installed last year," he said.

However, when emerging demand for power stations of 100 kW or larger capacity is included, the full size of the market is likely to be much larger by the end of this year.

So far 639 MW of such systems have been accredited this year and Green Energy Markets predicts another 1400 MW will be completed or accredited by December.

All up, total solar installations could approach 4000 MW or close to triple the previous record set in 2017.

"It's sort of unprecedented," Mr Brazzale said.

Rapid payback

Helena Li, president of the Asia Pacific sales division of Trina Solar – one of China's big three module producers – said commercial users can better match energy generation with their own demands than households.

"It's a three-to-four years' payback now for commercial [users]," Ms Li said. "It makes more sense, especially with electricity [prices] rising."

Solar panel prices are now about 50 cents per kilowatt of capacity, a figure that could shrink to "something below 40 cents",  Mr Brazzale said.

Restrictions imposed last month in China – easily the world's biggest market – will be one factor, as surplus supplies get exported to countries such as Australia.

As good as it gets?

However, Australia's surge may be shortlived. The Renewable Energy Target – which is driving the jump in solar farms – will likely be achieved as much as two years earlier than the 2020 deadline, Mr Brazzale said.

Add to shortlist

Falling wholesale power prices should start to result in lower retail costs, while the rollback of feed-in tariffs – including in NSW this month – will also dim some of the allure.

"This year may be as good as it gets," Mr Brazzale said.

Trina Solar, though, is more optimistic. Falling battery costs should give storage "a very competitive price" for many solar PV owners, including households, by 2019 or 2020, according to Yin Rongfang, the company's president of global sales.