«Green» Power Plants at Sea

Gemini/Svein Toenseth

Imagine the Norwegian oil field Statfjord, in a few years: On an abandoned oil platform you could find a gas power plant that supplies electricity to Norways main oil fields - without generating CO₂ emissions!

This concept appears to be technically feasible. It would reduce Norways CO₂emissions by more than 4 %, and it will give investors an internal rate of return comparable to new power plant projects onshore.

These are the conclusions of a preliminary study carried out by IKU Petroleum Research, an institute in the SINTEF Group. The report is based on the following offshore scenario:

A combined cycle power plant, producing 300 MW of electricity net, and a CO₂ sequestering plant are located on the Condeep platform at Statfjord A. This is one of the first large platforms to go out of production on the Norwegian continental shelf.

The power from this plant supplies the three main Norwegian oil fields Statfjord, Gullfaks and Snorre by AC cable. The capacity of the plant will be sufficient to replace the present power production from gas turbines on these fields.

The sequestered CO₂ is compressed and dried, and then injected into an underground formation.

«Substituting the present gas turbines on the neighbouring platforms, such a power plant at Statfjord can reduce Norways CO₂ emissions by almost 4,5 %. This concept appears not only to be technically feasible. Our economic estimates show that this project may give an internal rate of return of about 17 %, which is comparable to new power projects onshore, says senior researcher Erik Lindeberg.

Robust Economy

He has conducted the preliminary study together with project manager Torleif Holt. The study has been carried out for Bellona, a Norwegian environmental organization.

«Our economic figures are first estimates and have large uncertainties. However, the sensitivity analysis shows that the economy is robust with respect to variation in all important cost factors. In our opinion, the results justify further studies and more detailed analyses», says Holt.

In the IKU report, only Statfjord A is considered. But according to the report, the technical and economical considerations will be very similar for other locations, provided that both a CO₂ deposit site, gas supply and local power market are close to the platforms.

Incomes from the sale of electricity

The incomes of the project will be generated by the sale of electricity to offshore installations. The price estimates for this energy are based on estimations of the cost of the present power production at these installations. Due to the CO₂ taxes that have to be paid from such installations today, an offshore power plant could get more than 0,40 NOK/kWh for its electricity, according to Holt and Lindebergs calculations.

A "lighter green" version

A similar concept at Statfjord without the removal of CO₂ from the power plant, would cost less and give more power, as no machinery and energy is needed for the sequestering of CO₂. Such a project will, according to the report, give an internal rate of return of about 32 %, provided that all the power (360 MW) can be sold offshore.

Even without the separation and disposal of CO₂, this would be a «green» project. Due to the high thermal efficency of a combined cycle power plant, compared to the gas turbines it would substitute, also this solution would reduce Norways CO₂ emissions substantially. According to the IKU report, the reduction would be 0,7 million ton per year in this case. This corresponds to 2 % of the present Norwegian emissions.

«By extending the lifetime of the large Condeep platforms, the removal costs are postponed. This represents an important contribution to the economy of our offshore gaspower concept», emphasize Holt and Lindeberg.