However, the sector's net profit dropped by 5.7% to EUR 220.8 million over 2017, with TEŠ, the Šoštanj-based coal-fired power station, affecting the figure the most.
TEŠ's loss last year totalled EUR 58.53 million, up from EUR 32.59 million the previous year.
The industry generated EUR 725 million in net operating profit, a drop of 1.3% over 2017's record figure.
The GZS attributed it to growing labour costs and costs of goods, materials and services as well as to a lower net profit.
The number of employees in Slovenia's energy industry rose by 2.4% to 11,511, the second consecutive annual rise after the figure had been falling for several years.
The average monthly gross pay per employee in the sector stood at almost EUR 2,500, up 1.8% annually, the GZS says.