BRUSSELS - Electric cars must be backed by smart power networks if they are to help the world's climate problems, environmentalists warned on Monday as European ministers prepared to debate a strategy for the sector.

Industry ministers will meet on Tuesday in San Sebastian, Spain to discuss how to realign power infrastructure, equipment standards and the marketplace so that European carmakers can race ahead of rivals in Japan, China and the United States.

The European Union has succeeded in cutting the link between economic growth and rising carbon emissions, but has failed to control the transport sector where output of carbon dioxide has soared by 38 percent over the last 20 years, EU data has shown.

European Commission President Jose Manuel Barroso has pledged to reverse that situationby trying to decarbonise transport, and new rules for cars, vans, lorries and motorcycles are being considered.

The sources of power for electric vehicles will top the agenda in San Sebastian, documents show, amid warnings some can can do more harm than good.

The provision of electricity may need to be adapted to drivers' charging patterns, causing new electricity demand peaks, says a discussion paper for the talks, seen by Reuters.

SMART NETWORKS

For example, drivers' natural tendency to plug in their cars when they get home and charge them overnight will increase demand for steady baseload power generation, which in countries such as Poland comes mostly from coal.

Charging them on electricity produced with coal results in equal or higher emissions than for comparable conventional vehicles, warned a report on Monday by Dutch consultants CE Delft, written for four environmental groups.

About 400 grams of carbon dioxide are emitted on average for every kilowatt-hour of electricity in the EU, but this can more than double if coal is used, says the report.

The answer is to integrate electric cars with a smart electricity network, which would charge vehicles only when there was an abundance of green power from sources such as windfarms, said Franziska Achterberg of Greenpeace, one of the groups that commissioned the report.

In cities, electric cars are estimated to spend 95 percent of their time sitting in garages, giving ample opportunity for flexible battery-charging and absorbing any problematic spikes in renewable power production such as when the wind blows hard.

Cars' batteries might even put electricity back into the network when household demand is high, serving as a back-up power source. But smart power networks are a largely untested concept and need both research and funding to take off.

Ministers in San Sebastian will also discuss how to boost research into better and greener batteries, how to build national networks of standardised charging stations and how to target any financial support.

Green politician Claude Turmes, from Luxembourg, said his group opposed any fresh state subsidies for energy and automotive companies without strong environmental criteria.

If not, this will just be a green wash, he added.

(Editing by Keiron Henderson)

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