Underwater Storage Technologies for Offshore Wind Energy ByPrince

Underwater Storage Technologies for Offshore Wind Energy By-Prince Preet Saini

OUTLINE ØObjectives ØOffshore wind –current status ØKey challenges ØEnergy storage methods §Underwater Pumped Hydro Storage §Underwater Compressed Air Energy Storage Ø Discussion

Objectives q. To inform about the underwater storage technologies which can be used to reduce the intermittent nature of offshore wind farms. q. How energy storage can help offshore wind energy.

Offshore Wind Energy – Current Status Source- US-DOE, NREL, GLOBAL WIND ENERGY COUNCIL(GWEC)

Key Challenges • Cost and Technological risks associated with Offshore wind energy • Intermittent nature of offshore wind energy causes supply-demand imbalance • Offshore wind electricity delivery and grid integration • Increasing understanding of the benefits and cost of offshore wind

ENERGY STORAGE METHODS • Underwater Pumped Hydro Storage • Underwater Compressed Air Energy storage

UNDERWATER PUMPED HYDRO STORAGE

Underwater Pumped Hydro Concrete Sphere

HOW THIS WORKS

Design concept CENTRALIZED CAPACITY • Several storage units are connected and the power is generated from single turbine & generator. • Additional pipes are needed to connect the units to turbine which leads to more pressure loss in the system. • Lower investment cost for power generating components but additional cost for extra pipelines DECENTRALIZED CAPACITY • Each unit containing a separate turbine and generator • Higher investment cost for mechanical components • Pipe network containing several tanks not needed.

Figure- Construction of a scale model Source- HOCHTIEF Solutions AG

Technical Feasibility Study • • • Operational depth is 300 m – 700 m which is suitable for present pumping technologies. Design of the storage vessel is spherical due to optimal pressure distribution. Turbine capacity (5 MW) which is comparable to offshore wind turbine. All mechanical components are inside the sphere which can be easily retrieved with a remotely operated vehicle. Reduced corrosion because of low oxygen concentration and low temperature at higher depths. Big scale spherical construction technologies already exist. Source- Sten. Sea Project Report

Comparison of Underwater PHS with Land based PHS • In underwater pumped hydro storage technology, there is no alteration of existing landscape • The target cost per KW of installed power(without considering the cable cost ) as given by St. En. Sea is 1238 €/KW as compared to 1300 €/KW for land based pumped hydro storage • UW-PHS can be integrated easily with offshore wind energy farms since it can be installed relatively closer to it as compared to land based pumped hydro storage. • Flora-Fauna-habitat compatibility and aquatic species protection may be an issue in underwater storage.

UNDERWATER CAES

METHODS OF INTEGRATION A land based UWCAES system A UWCAES system located on an offshore platform

ENERGY BAGS

Comparison of Underwater CAES and conventional CAES • The cost/meter cube of air storage is still high for underwater CAES as compared to conventional CAES. • Geological suitability for underwater CAES is more than 30% as compared to conventional CAES which is less than 5%. • In conventional CAES a portion of volume is unused since the pressure varies as air is supplied to turbine but in underwater CAES , the pressure remains constant due to variable volume energy bags. • Efficiency of mechanical components is higher in underwater CAES. • Underwater CAES requires minimal land footprint as compared to oversized cavern in conventional CAES and is ideal for island nations & coastal regions.

DISCUSSION • The demand for energy is going to increase significantly. • Energy production from offshore wind parks is going to increase significantly as we have seen from the offshore wind energy data of European and Asian countries. • The concept of underwater CAES and underwater pumped hydro storage is scalable and efficient and can be integrated with offshore wind to reduce its intermittent nature. • The technology needed to harness and store energy is present. • According to 2010, United Nation Environment Program , close to 80% of the world population lives closer than 100 km to a sea or an ocean, That means : Energy storage close to the sea or an ocean along with offshore wind energy farm can be beneficial.

Thank You