LITTLETON, Colorado, June 20 (Reuters) - Natural gas-fired power generation in the United States has climbed nearly 6% through June 17 from the same period a year ago, as above-normal temperatures lifted use of power-hungry air conditioners.

U.S. power generation from natural gas from Jan. 1 through June 17 was just over 30 million megawatt hours (MWh), according to data compiled by LSEG.

That total compares to 28.4 million MWh during the same period in 2023, and is the highest gas output reading since at least 2021, LSEG data shows.

Power generation from clean sources including nuclear plants, hydro dams, solar parks and wind farms climbed 7.6% from 2023 to a record 33.5 million MWh, and clean output is set to rise further during peak solar production periods.

But natural gas looks set to remain the largest single fuel source in the U.S. power system, and will likely be deployed in even greater quantities over the coming months as demand for cooling systems rises during the hottest time of year.

In turn, U.S. power sector emissions from gas use will likely also climb to new highs in 2024, potentially accelerating the climate warming trends that are fuelling increased higher gas demand in the first place.

GAS UP, COAL DOWN

Natural gas accounted for a 39.7% share of total U.S. power generation from Jan. 1 through June 17, LSEG data shows.

That share is up from 39% during the same period last year, and marks gas' highest power share since at least 2021 for that period.

Reduced use of coal in the U.S. power system accounts for some of the higher gas use. Coal's share of this year's power mix was 15.4% through June 17, down from 16% a year ago and a 23% share during the same period in 2021.

Power firms are expected to make further cuts to coal use in generation going forward as part of ongoing emissions reduction efforts and a longer-term target to decarbonize the U.S. power system.

However, higher overall power demand means that suppliers have been forced to keep increasing the overall volume of fossil fuels used in generation, even as supplies from clean power sources continue to climb.

Total power generation this year is up 3.8% from the same period a year ago, as higher power use by air conditioners, data centers, vehicle chargers and businesses push up overall demand.

To meet the higher load requirement, power firms have lifted the combined volume of power generated by natural gas and coal by the same degree, to 41.7 million MWh.

CLEAN RECORDS

While natural gas remains the primary U.S. power fuel, output of several clean energy sources has hit records so far this year.

From Jan. 1 through June 17, wind power generation was an all-time high 9.6 million MWh, up 9% from the same period in 2023, while solar generation was up 38% to a record 3.607 million MWh.

Output from nuclear reactors was up 3.4% to 14.98 million MWh - the highest in more than three years - while hydro generation climbed 1.4% to the highest since 2022.

The overall share of clean power in the U.S. generation mix also climbed to a new record this year of 44.3% through June 17, compared to 42.7% a year ago.

Even so, output from fossil fuels - which includes a diminishing volume of crude oil-fired generation as well as natural gas and coal - remains the backbone of the U.S. grid system.

KEY SYSTEMS

While gas-fired output has climbed by nearly 6% nationally, there are several key U.S. power systems where gas-fired output has jumped by larger margins.

The Electric Reliability Council of Texas (ERCOT) system has boosted gas output by 10% from the Jan. 1 to June 17 period of 2023, LSEG data shows.

Gas generation in the Southwest Power Pool (SPP), which produces power for all or parts of 14 states across the Midwest and West, has climbed by nearly 14%.

Power producers in Florida have lifted gas generation by 10% through June 17, but are likely to increase gas-fired output higher still during July and August, which are the hottest months of the year in the state.

The PJM Interconnection system, which provides power for consumers across Pennsylvania, New Jersey and Maryland, has upped natural gas output by 6% and coal-fired output by 5% so far this year.

In power systems throughout the U.S. - including California which has the highest proportion of clean power among major states - gas-fired output is likely to climb over the coming months as temperatures peak and boost air conditioner use.

Higher gas use in generation will in turn yield higher power sector emissions, which in peaked last summer peaked at around 98 million metric tons of carbon dioxide in July and August, according to energy think tank Ember.

In 2024, gas emissions are already tracking ahead of last year's record pace, and loads could top 100 million tons a month for the first time if gas use continues to climb.

(Reporting by Gavin Maguire; Editing by Jamie Freed)