APRIL 20248IN MY OPINIONSTORAGE TECHNOLOGIES FOR OFFSHORERENEWABLE ENERGYBy Olivier Lodeho, Technology Director, Subsea 7Wind offshore Fields are the preferred Renewable energy in many countries to meet their carbon reduction ambitions either to feed their domestic energy demand in electricity while limiting greenhouse gas emissions or to decarbonise their O&G facilities. However, like all renewable energy, offshore wind, despite more favourable winds offshore than onshore, are still intermittent and not pilotable. This means their output varies in intensity along the time without any control and therefore induces several challenges on grid networks and their management. We can identify 3 types of intermittences: · Type I. Intermittences from weeks to months, which could be illustrated by seasonal variations.· Type II. Intermittences from Hours to days, which could be represented by the day/night period· Type III. Intermittences from second to hours: which could represent a wind fluctuation or a cloud in front of the sunThose variations are different in time scale and in intensity and can be overcome/mitigated by different technical solutions like VSD and Batteries for Type I, Batteries, HPES for Type II, Hydrogen for Type III are some examples.Here we will look at 2 technical solutions based on subsea pumped Hydro technology, called: · ROPES: Repurposing Offshore Pipelines for Energy Storage· Power Bundle: subsea dedicated pipeline system for energy storageSubsea pumped Hydro Energy storage principle: The principle is to charge seawater into a subsea pressured res-ervoir with a pump powered by the excess of energy produced by a set of offshore wind turbine and to release this water through a turbine generating power when wind does not blow or not enough. We can therefore identify 2x sub-assemblies: · ECU system: Energy Conversion Unit composed by the pump and the turbine· PCS Pressure containment system: which is under pressure and receive the sea water.The ECU can be installed on topside or subsea while the PCS will be subsea for the following reasons: · No space constraints· Minimise energy loss by being subsea with a stable cold sea-water temperature and therefore limiting heat losses and maximise system efficiency· Take advantage of the water depth for improving pressure dif-ference and therefore energy storage capacity of the system.This PCS can be done in several ways and using pipelines, allow to take advantage of existing supply chain from Oil & Gas industry and therefore reach interesting cost levels.If pipelines already exist in the vicinity of the Offshore Wind Olivier Lodeho
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