HELSINKI, January 17, 2011 (AFP) - Extreme weather and disruptions to power generation caused electricity bills to spike on average by nearly a fifth during 2010, Finland's Energy Market Authority said Monday.

"All in all the electricity bills for homes rose by 18 percent in one year," the Authority said in a statement, adding that the figure was 20 percent for households who used electricity for heating.

The increase was more pronounced for homes with short one- or two-year contracts with power companies, who saw their bills spike by 30-40 percent in the beginning of January.

The agency blamed the rises on diminished supply caused by dry conditions which handicapped hydropower, back-to-back unusually cold winters and production stoppages in Sweden's nuclear power grid.

Rises in the cost of fuel also fed price increases, as did a rise in the cost of electricity transmission prices and an increased energy tax.