SESSION TITLE Dr. H. Pirouz Kavehpour Professor & Vice Chair, Mech. & Aerospace Eng. University of California, Los Angeles USA

Energy Storage System for Solar Energy Systems from Utility Scale to Small Scale Over-rated and Under-rated Parameters and Alternatives to Batteries

Applications of energy storage Why Storage is Needed Applications of energy storage Lack of availability High cost of energy at different time (Energy business) Renewables

Agenda Energy Storage technologies Key Concepts Conclusions Applications from utilities based to behind the meter Review of available technologies Key Concepts Power vs. Energy Discharge time Challenges Conclusions

Superconducting Magnetic Energy Storage Methods Energy Storage Mechanical Chemical Electromagnetic Thermal Pumped Hydro Flywheel Batteries Hydrogen Sensible Heat Latent Heat Superconducting Magnetic Flow Batteries Solid State Capacitors Thermochemical Compressed Air (CAES) Brahim Dincer, Marc Rosen, (2011) “Thermal Energy Storage, Systems and Applications” Second Editions

Energy Storage Technologies Mechanical Systems Pump-Hydro Compressed air energy storage (CAES) Flywheels Non-Mechanical Systems Batteries Super Capacitors Superconducting Magnetic Energy Storage

Pump-Hydro Works based on hydro-power plant concept

Compressed Air Energy Storage Based on combination of gas turbine technology and Brayton Cycle

Flywheel Based on Newton’s first law

Batteries Several types of batteries are available for different storage applications High power High energy density

Other Technologies Super Capacitors Super-conducting Magnetic Energy Storage (SMES) High power Very short discharge time

Energy Storage Space

We store Energy not Power Power vs. Energy Energy Energy is a property of objects which can be transferred to other objects or converted into different forms, but cannot be created or destroyed. Unit: kWh, Jouls Energy per unit time is Power. Power The ability to work Unit: kW, MW Large power is needed for for large applications. Utility scale storage provides high power, while residential scale requires lower power. We store Energy not Power

Discharge time Time of dispatching the energy at a given power. Different applications requires different discharge time. Residential ratchet charge requires short discharge times. Frequency regulating requires very rapid discharge times. For most of renewable energy, longer discharge times are desired. Batteries are not capable of longer discharge time yet. Pump-hydro and CAES can provide longer times.

Key Challenges

“Important” Parameters Efficiency $/kW.hr $/kW LCOE

Efficiency of Energy Storage System “Round trip” Efficiency Different than “thermodynamic efficiency” How important is efficiency? Depends on whom you asked!

Cost of Energy Stored $/kW.hr

Cost of Power Produced $/kW Is this a correct formula? Does this make sense for energy storage?

Levelized Cost of Energy LCOE LCOE is equivalent to the cost of energy stored. If LCOE is larger than cost of Energy purchased, energy storage business fails. Government incentives are important. But is that all? LCOE doesn’t tell you everything you need to know!

Conclusions Both power and discharge time are very important for an energy storage system. Batteries are capable of very short to intermediate discharge times Very suitable for demand peak shaving and frequency regulations. Pump-hydro and CAES are suitable for high power, long discharge time. Relatively longer ramp time, limits these systems to longer respond time applications. Efficiency is important only if it is worth it. Cost, Cost, Cost!!!

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