* Renewables, idled coal plants help Germany meet demand

* France sees price spikes as nuclear insufficient

* French nuclear future big debate point in elections

PARIS, Feb 14 (Reuters) - Germany came to the rescue of France during last week’s cold snap by massively exporting electricity to its neighbour, silencing critics who slammed Berlin last year for abruptly shutting down 8 nuclear reactors after the Fukushima disaster.

Critics said such a decision would put Europe’s electricity supply balance at risk and waved the possibility of widespread blackouts as a result.

“The cold snap was a situation most experts feared and we managed without bigger problems,” said Stephan Schnorr, German power trader at utility Dong Energy.

Instead, it was France which suffered from supply tightness last week, pushing prices to two-year highs and prompting the grid to issue warnings urging the public to refrain from using electrical equipment, such as washing machines or coffee makers.

France, Europe’s biggest electricity exporter, reverts to imports during peak demand periods.

France heavily relies on electric heating developed by successive governments to meet supplies generated by the country’s 58 nuclear power reactors. Germany, however, uses a variety of heating methods including gas and fuel oil heaters.

This means that during cold snaps, French electricity demand goes through the roof, forcing the country to import at full capacity from its neighbours during peak demand.

When French demand reached a new all-time high last Wednesday, the country imported from Germany at full capacity in nearly all hourly blocks, grid operator data showed.

French electricity demand rises by 2,300 MW, or the equivalent of two nuclear power reactors, per one degree Celsius drop in temperatures, double the demand surge seen 20 years ago.

PRICE SPIKES IN FRANCE

While France was struggling with high demand, Germany, which houses 37 percent of the world’s solar plants, relied on its growing renewable energy output and resurrected idled coal-fired plants to cover a rise in electricity demand.

A spokesman for Amprion, Germany’s largest high-voltage network, said the situation on the network was very tense.

“Our colleagues are intervening on the network much more than usually, but everything is under control,” he said.

By contrast, France, the world’s most nuclear dependent nation which faces presidential elections in April, last week experienced supply tightness which led to dreaded price spikes predicted by experts.

French day-ahead power for peakload delivery, the 0800-2000 CET period when demand is highest in the day, rose as high as 628 euros per megawatt-hour (MWh) on the EPEX Spot electricity exchange on Feb. 9, more than four times higher than the previous day.

France’s electricity demand has been reaching new record highs nearly every winter as 30 percent of homes use electric heaters and as many as 65 percent of new homes are heated using electricity.

“One million mobile electric heaters are sold in France every year, give or take, especially in large spaces,” said Jean Bergougnoux, a former chief executive of French energy giant EDF .

“Many of them are used during cold periods, in poorly heated locations and/or poorly insulated ones,” he added.

The government has defended high use of power for heating by arguing its nuclear power plants provide steady supply, but record prices have put this in doubt.

Socialist presidential candidate Francois Hollande has vowed to cut France’s dependence on nuclear power and to shut down its oldest nuclear plant on the German border if elected, making nuclear power one of the main issues of the election campaign.

In contrast, President Nicolas Sarkozy’s centre-right government is trying to convince voters that nuclear power plants should run as long as possible nearly a year after the Fukushima disaster in Japan shook the world.

The government on Monday published a report saying electricity bills would rise less in the years to come if the country prolongs the lifespan of its ageing nuclear reactors. (Editing by Muriel Boselli and James Jukwey)