The fall in power consumption was mainly due to lower industrial production last year, Eles said in a statement.
In December alone power consumption was 14.2% lower year-on-year at 997 million kWh.
Slovenia's power plants produced a total of 14.314 billion last year, up 9.7% year-on-year and 3.6% above target.
The country imported 6.142 billion kWh in 2008, slightly changed from a year earlier. Exports of electricity rose by around 35% to 7.736 billion kWh.