Berlin  - Ambitious plans by electricity group Vattenfall to capture carbon dioxide from power stations and dump it deep underground came under fire Monday, a day before a pilot plant near Berlin goes into operation.

Vattenfall sees carbon capture and storage (CCS) as a key answer to global warming, which is largely blamed on CO2 released when fossil fuels burn. But environmentalists charge that the technology uses far more energy than existing power generation.

"Our project at Schwarze Pumpe puts us at the forefront of this technology in the world," said Tuomo Hatakka, the chief executive of Vattenfall Europe, referring to the plant site.

The Finnish-born executive heads the Swedish group's Berlin-based subsidiary.

Reporting his remarks on Monday, the newspaper Frankfurter Allgemeine Zeitung said Hatakka argued the process could pay its own way, because companies will have to buy EU allowances for every ton of carbon dioxide they release into the air.

"In tandem with EU-wide trading in emission rights, CCS will be economic. At 30 to 35 euros per emission certificate, the technology breaks even," said the executive.

The 30-megawatt pilot plant at Schwarze Pumpe is a very small one intended to test the technology. Carbon dioxide emitted when lignite coal burns will not be vented up a chimney but piped away, compressed to a liquid and pumped into deep, porous rock.

Vattenfall plans to build two "demonstration plants" 10 times that size in Germany and Denmark by 2015 at the latest. Hatakka said the company aimed to commission its first "large-scale CCS power station" in 2020.

A German nature-conservation group, BUND, denounced the project Monday as simply a cover allowing Vattenfall to expand its network of conventional coal-fired power stations in Germany.

A BUND staffer, Thorben Becker, said it was still uncertain if CCS worked on a large scale. CCS power stations would obtain 10 per cent less power from the coal than conventional plants did, and it was not clear if there were enough suitable sites to dump the CO2.

"Instead of concentrating on far cheaper renewable energy, Vattenfall is locking itself in for decades to converting climate-damaging brown coal into electricity," he said. (dpa)