Energy Storage Part1

Part1

Energy Storage for Power Systems

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Contents

Introduction

Energy storage systems Mechanical Energy Storage

Chemical Energy Storage

Thermal Energy Storage (TES)

Conclusions

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Introduction

The variation of electricity demand over the days and

seasons causes a problem for the power plant

management and efficient work.

Examples of possible energy management methods:

Supply power peaks by interconnecting power netwroks that

might have different power demands on them.

Use newer and more efficient power plants for base-load

generation and use older less efficient plants for peak-power

generation

Use smaller, low capital cost less efficient power plants as

power peaking units

Add energy storage system.

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Introduction

Advantages of using energy storage

reduced energy costs;

reduced energy consumption;

improved indoor air quality;

increased flexibility of operation;

reduced initial and maintenance costs.

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Introduction

Some energy storage applications :

Utility. base-load electricity can be used to charge ES systems during evening or off-peak weekly or seasonal periods. The

electricity is then used during peak periods.

Industry. High-temperature waste heat from various industrial processes can be stored for use in preheating and other heating

operations.

Cogeneration. Coupled production of heat and electricity by a cogeneration system rarely matches demand exactly, excess

electricity or heat can be stored for subsequent use.

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Introduction

Some energy storage applications (cont..) :

Wind and run-of-river hydro. Conceivably, these systems can operate around the clock, charging an electrical storage

system during low-demand hours and later using that electricity

for peaking purposes. ES increases the capacity factor for these

devices, usually enhancing their economic value.

Solar energy systems. By storing excess solar energy received on sunny days for use on cloudy days or at night, ES

systems can increase the capacity factor of solar energy

systems.

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Energy storage systems

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Mechanical Energy Storage

Hydrostorage

Compressed air storage

Fly wheel

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Water is pumped upward

when excess electricity exist

Water is let down through

turbine when electricity is

needed

The efficiency of a pumped

water storage plant is about

50%

When the energy is needed,

the plant only needs 30 s to

reach 100% of its power

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Hydrostorage (Pumped energy storage)


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the overall efficiency of hydro pumped storage h as the ratio of the energy supplied to the consumer while generating, Egand the energy consumed while pumping, Ep.

h =Eg / Ep = g p

The energy used pumping a volume V of water up to height

h with a pumping efficiency p is

Ep=ghV/ p

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The energy supplied to the grid while generating with

generating efficiency g will be given by:

Eg=ghV g

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Compressed air storage Air is compressed during off-peak hours and stored in large

underground reservoirs, which may be naturally occurring caverns, salt

domes, abandoned mine shafts, depleted gas and oil fields, or man-

made caverns.

During peak hours, the air is released to drive a gas turbine generator.

The total cold start-

up time to full load

is normally 11 min,

but as short as 6

min in an

emergency


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Compressed air storage Application in gas turbine cycles


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Fly wheel A wheel of relatively large mass that

stores rotational kinetic energy.

Flywheels can have a significant

advantage in vehicles that undergo

frequent start/stop operations as in urban

traffic.

The quantity of energy stored in a

flywheel is usually small. One watt-hour

of energy is equivalent to 1.8 kg of mass

on a 2 m-diameter flywheel rotating at

600 rpm

It is used for energy storage for smal

periods of time


Chemical Energy Storage

Electrochemical Batteries

Hydrogen

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Electrochemical Batteries

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Hydrogen storage characterstics A fuel for electricity and/or heat production in fuel cells

or combustion engines.

Powering transportation devices, in addition to being a

chemical commodity.

Hydrogen can be stored more easily and transported

more inexpensively than electricity

Hydrogen is less advantageous than electricity in terms

of production costs.

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Hydrogen Storage Technologies An expensive highpressure tank in which the steel is

100 times heavier than the hydrogen stored.

Refrigerated, vacuum-insulated dewar system which is

both expensive and energy consuming.

Absorbing hydrogen in metallic powders, forming

hydrogen metallic compounds (metal hydrides) which

can be decomposed by the application of heat,

releasing hydrogen

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Hydrogen Production The raw material from which most hydrogen is likely to

be produced in the future is water

A significant amount of hydrogen is already produced

by the electrolysis of water

In a perfectly efficient electrolytic cell, 94 kWh of

energy is needed to produce 28.3 m3 of hydrogen (at

atmospheric pressure)

Most electrolysis cells operate at energy efficiencies of

about 6075%

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Hydrogen Production Water can be decomposed directly by thermal energy,

but the temperature required for a reasonable yield,

approximately 2500C, is not readily available from nuclear reactors or other thermal sources.

Water can be decomposed also through a

thermochemical process which is a series of chemical

reactions. However, it need temperatures of 900C or higher.

Research is ongoing to utilize heat at significantly

lower temperatures (approximately 500C), like the copper chlorine cycle.

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Energy Storage Part1