LITTLETON, Colorado, July 10 (Reuters) - Australia's electricity producers lifted generation from fossil fuels by more than from clean power sources during the first half of 2024, undermining the momentum of the country's energy transition from polluting fuels.

Utilities generated 76.55 terawatt hours (TWh) of electricity from fossil fuels during the first six months of this year, which was 4.2% more than during the opening half of 2023, data from energy think tank Ember shows.

That jump in fossil fuel-fired generation was the largest for that time frame in at least nine years, and highlights the enduring challenge facing Australian power producers as they try to wean generation systems away from fossil fuels.

In contrast, utilities increased electricity from clean power sources by only 1.3% during the first half of 2024 from the same period last year, which was the smallest rise in clean generation during the first half of the year since 2017.

The sluggish growth pace of clean power output saw clean power's share of Australia's generation mix shrink for the first time in seven years, to 35.6% of total utility-supplied electricity generation.

HYDRO HIT

A key drag on clean generation was a nearly 14% fall in hydro power output during January to June from the year before.

Low rainfall in key southern areas during the southern hemisphere summer clipped hydro power output to 6.45 TWh, down from 7.5 TWh during the same period a year ago and the lowest for that period since 2017.

Output from wind farms also shrank during the first half of the year, by 5.3% from the first half of 2023, which left solar farms as the main contributor to Australia's clean power generation expansion so far this year.

SOLAR SHINES

Utility-supplied solar electricity generation during the first half of this year was a record 21.5 TWh, up 12% from the first half of 2023.

That strong growth pace exceeded all other forms of generation in Australia's power system so far this year, and helped cement solar as Australia's main clean electricity generation source.

Even so, the intermittent nature of solar generation - which stops completely at night and can dip sharply during cloudy periods - has meant that Australian utilities have been forced to crank up generation from fossil fuels this year to ensure overall electricity supplies expanded to meet demand.

KING COAL

Coal remains the largest single power generation fuel in Australia, accounting for 67 TWh of electricity during the first half of the year.

That total is up 4.4% from the same period in 2023, to the highest since 2021.

Coal's share of total generation was 56.3%, compared to 55.7% during the first half last year.

Generation from natural gas was 9.6 TWh, up 3% from the first half of 2023.

Emissions from fossil fuel use in power generation were 70.22 million metric tons during January through June, up 2.85 million tons from the first half of last year and the highest in two years.

That emissions count is liable to rise further above last year's total as the southern hemisphere winter sets in and output from solar plants declines just as demand for heating rises.

A steep recovery in both wind and hydro generation over the coming months during the traditional peak output periods of both power sources could help lift total clean electricity output, and may possibly limit the overall volume of fossil fuel use in Australian power generation.

But with fossil fuel generation already running 4% ahead of last year's pace through the opening six months, 2024 looks set to be another year of growth in fossil fuel-fired output in Australia despite ongoing efforts to decarbonise electricity production.

(Reporting by Gavin Maguire; Editing by Emelia Sithole-Matarise)