Storage.ppt

8/14/2019 Storage.ppt

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EE535: Renewable Energy:

Systems, Technology &

Economics

Energy Storage


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Introduction to Storage

Energy storage is the conversion of energy to other forms so that it may

be used at a later stage when required.

Industrial scale energy storage technologies are measured in terms of

their power output (MW) and their capacity (MWh).

The most common type of energy storage is Spinning Reserve where

power plants operate at a level slightly below the point where they begin

to produce power. This allows them to react quickly to large swings in

demand.

The spinning reserve is the extra generating capacity that is available byincreasing the power output of generators that are already connected to

the power system. For most generators, this increase in power output is

achieved by increasing the torque applied to the turbine's rotor.


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Comparing Storage Technologies

Most Important factors

Cost & Return on Investment

Efficiency

Cycles

Influential Factors

Response Time (milliseconds to hours/days) Energy Density (Size and Space Requirements)

Environmental Impact

Charge Time


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Intermittent Wind Supply

Wind is not a controllable energy

source, it is either blowing or it

isnt and this power is distributed

to the electricity grid regardless of

whether it is needed or not.

The grid cannot store energy sopower plants have to match the

demand in real time.

Often several power plants will

operate in Spinning Reserve

mode during periods of high wind

output to cater for the inevitable

drop in wind.www.inference.phy.cam.ac.uk/withouthotair/c26/page_187.shtml

Yearly, Bi-Monthly & Monthly Wind Output (MW)


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Typical 7 day Winter Demand profile (Saturday/Sunday generally lowest)

Wind Output for same time period has no correlation to demand

Issues with excess wind generation between 12.30 AM6AM

Source: Eirgrid


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Storage TechnologiesFlywheel Energy Storage

Flywheels are mechanical devices

which accelerate a rotor to a very

high speed, storing the energy as

rotational energy.

These devices are most suitablefor high utilization applications as

their efficiency decreases in

proportion to their use.

Suitable for short term lulls in windgeneration output (1-5min)

Rated for > 100,000 cycles

Used in F1 racing cars (0.1kWh,4.6Wh/kg)

http://www.upei.ca/~physics/p261/projects/flywheel2/flywheel2.htm


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Storage TechnologiesFlow Batteries

Flow Batteries allow energy to be

stored in two solutions existing at

different electrochemical

potentials.

All the energy is stored in the

electrolyte solutions so that thecapacity is determined by the size

of the electrolyte tanks

The system power is determined

by the size of the fuel cell stacks

which can be arranged in

series/parallel as required.

Suitable for daily lulls in wind

generation output (< 12hours)

Rated for > 10,000 Cycles

http://www.netpowertech.com/e_menu_page.aspx?bid=4&id=10


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Storage TechnologiesPumped Storage

Pumped storage is one of theoldest energy storage methods.

During the night cheap electricity

is used to pump water into the

upper reservoir.

It is then released during the day

and peak times when it is morevaluable.

Additional features such as

frequency regulation and black-

start capabilities.

Pumped storage installations arecapable of providing power for

extended periods, from hours to

several days.

Rated for > 30 years

www.hk-phy.org/energy/alternate/hydro_phy/images/pump_storage.gif


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Establishing Volume of Water Required

When designing a pumpedstorage facility for a given capacity

the two most important factors are

water volume and height.

If the height is doubled, only halfthe water volume is needed for the

same power capacity.

Volume =

Where p is the density of water, g isacceleration due to gravity, h is the

height drop and is the efficiency of

the turbines/pumps.

sec/gh

Power

Top Reservoir

Lower Reservoir

Pumps/TurbinesEfficiency ()

Elevation/Head (h)

Volume &

Density (p)


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Example

A pumped storage facility is proposed for construction in thewest of Ireland to store excess power generated from wind

farms in the area. A potential location has been identified with a

head height of 250m between the upper and lower lakes. The

latest Siemens turbines with an efficiency of 90% will be utilised

in the construction.

What volume of water is required to store 12GWh ?


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Solution

36

3

3

9

9

106.19)(

)3600)(5437()(

5437sec/

)2207250(

1012sec/

)9.0)(250)(81.9)(1000(

1012sec/

sec/

mxtotalVolume

mtotalVolume

mVolume

xVolume

xVolume

gh

Power

Volume


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Proposed Storage Techniques

Electric Car Grid Tie

Current generation electric vehicles are capable of storing from 5kWh

up to 30kWh of capacity. Suggestions have been made that this

capacity could be made available to the grid in conjunction with smart

metering.

Hydrogen Production

The process of extracting hydrogen from water is currently very

inefficient . Energy from renewable energy sources could be used to

create hydrogen and store it until it is needed for power generation or

for vehicle fuel.

Super Capacitors These devices can be used for storing small amounts of electrical

energy in applications where hundreds of thousands of cycles would

be common. Areas such as regenerative braking in vehicles with

many stops/starts are suitable for these devices.


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Turlough Hill (Wicklow Mountains)

4x73MW Turbines

292MW for 5 hours

Head ~280m

Provides:

Load levelling

Peak Shaving

Frequency Regulation Black Start capability

Running since 1974

http://www.esb.ie/img/2.3.1_Turlough-Hill_800x600.jpg e

Documents

Storage.ppt