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Energy and Environment

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Md. Mizanur Rahman MEng(Sweden), PhD (Finland), CEng Chartered Energy Engineer (EI, UK) Certified Energy Manager School of Mechanical Engineering Universiti Teknologi Malaysia Email: mizanur@mail.fkm.utm.my

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• Energy demand is not constant

• Present energy systems contain inherent flexibility capabilities

• Existing flexibility mostly on supply side

• Energy demand and supply matching requirement • On spatial and time (x, y, t) variations

• Critical for the electric system

• Modern energy technologies integration requires energy flexibility strategies

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• Flexible demand • Storage • Electric Vehicle EV, ICT • Smart Grids • Electricity markets

• Co-generation (CHP) • Electricity-to-Thermal

E2T • Electricity-to-Gas E2Gas • Vehicles-to-Grid ,V2G,

For modern Energy integration

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Solar electricity generation

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The main technologies involved in electrical energy storage are

• Batteries (with different configurations and materials) • Compressed air • Flywheels • Superconductors • Supercapacitors • Pumping hydropower

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• Compensate for temporary loss of production of generating unit.

• Fulfil commercial obligation of pre-sold energy supply/avoid penalties

• Add value to supply peak hours

• Ratio between peak & average power often reaches a value of 10 leading to over-dimensioning of production & transmission equipment (peak)

• Resulting gains due to storage systems need to secure a return on of the double conversion chain

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About 3 %

of global generation capacity.

Source: http://www.iec.ch/whitepaper/pdf/iecWP-energystorage-LR-en.pdf 10

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(Sodium–Sulphur)

• Commonly called CAES (compressed air energy storage) and turbine generates electricity from the expansion of the compressed air

• It is expected to cover energy more than power demands. • Store compressed air (45–70 bars) from excess power from the grid to

produce electricity.

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• CAES technology consumes 40% less energy than conventional natural gas turbines, since in these two-thirds of natural gas is consumed to compress air for the combustion process, which is already obtained with CAES

• The first commercial CAES system was a 300,000 m3 natural gas cavern and 290MWunit built in Huntorf, Germany in 1978, reaching 42% efficiency

• Only another plant exists in McIntosh, Alabama (USA). Connect a 100-MW wind farm and a 268-MW CAES unit

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• MIT, USA constructing concrete spheres on the seabed close to off-shore wind farms. • The spheres 31 m in diameter • Be placed about 350 m deep. • The surplus electricity from offshore wind would be used to pump out the sea water

storing air in them. • When power is required, sea water would penetrate moving a turbine and generating

electricity. • These spheres would be able to deliver 5 MW for 4 h and could have a durability of 40

years.

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• Rotating (30,000–40,000 rpm) high mass cylinder

• Suspended by magnetic bearing

• Operates in vacuum to improve efficiency

• Connected to a generator to produce electricity

• Cover more power than energy demands

• The main advantages of the flywheel

• Minimum maintenance requirements

• long life and inert behavior to environmental conditions.

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• High power flywheels are highly developed and applied in aerospace and UPS systems.

• The losses in stand-by are less than 1 %

• Transition from 0 to 100 % power output is achieved in less than 5 ms.

• The world’s largest flywheel (in operation since 1985) consists of six disks having each a diameter of 6.6 m and a thickness of 0.4 m.

• One disk weights over 107 t, and during charging (6 min), the rotating speed is increased from 70 % of its limit to 100 % with a thyristor system of 19 MW.

• Energy discharge time is approximately 30 s, supplying up to 160 MW of power

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• These devices are also known as superconducting magnetic energy storage systems (SMES).

• Energy is stored in the magnetic field created by a flow of electric current in a superconducting coil.

• The coil wires cooled below the critical temperature to reach the superconducting properties.

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The magnetic energy stored by a coil carrying a current is E= 0.5 L I2 Where, E = energy (J) L = inductance (H) I = current (A)

• Charging is conducted by converting AC from a power network into DC

• Excites the superconducting coil.

• By the effect of zero electrical resistance, energy storage is realized by circulating the persistent current through the circuit. In other words, electricity can be stored directly without energy conversion.

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• Only significant losses are produced in the rectifier/inverter process to pass electric current from AC to DC and vice versa.

• It is preferably applied to cover more power than energy demands.

The main advantages of these systems are • The short time between the charging and discharging (almost

instantaneous) • Very low energy loss in the charging and discharging process and • Absence of moving parts in the system main components. The largest drawback is price. Being implemented, primarily to provide ultra-clean electric power in industries that require it (microchips plants) or to stabilize the grid.

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• Most used type of energy storage facilities in electric power systems.

• The 100–400 MW and 1–2 GW class systems are the typical pumped storage power plants.

• Cover more energy than power demands.

• Composed by two water reservoirs, vertically separated

• pump water from the lower to the upper reservoir (pump mode) and vice versa (turbine mode)

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• The efficiency in the range 70–85 %

• Discharge times can range up to several days.

• Pumped hydropower plant consists of two to eight pump turbine units.

• Underground storage can also be used in wells and other cavities, with the

• Advantage of reducing controversies about direct impacts to human populations.

• Pumping sea or river water can be advantageous

(no need of a lower reservoir )

• Pumping sea water can attain up to 80 % efficiency because of the short waterway length, which reduces the hydraulic losses

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Pumped Hydro Storage

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Example:

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435-MW hydroelectric power plant, generating power to supply demand for electricity, or as a pumped storage facility

•

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Thermal Energy Storage (TES)

• Sensible Heat Storage (SHS): heating bulk material that does not change state (sodium, molten salt, pressurised water) during the accumulation phase.

• Heat is then recovered to produce water vapour

• Drives a turbo- alternator system

• Latent-fusion-heat (LHS): liquid-solid transition of material at constant temperature (sodium hydroxide/highly corrosive)

• During accumulation phase the bulk material -> solid state to liquid

• heat transfer between the accumulator and the exterior environment (heat transfer fluid)

• higher the heat/higher the concentration

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Thermal Energy Storage (TES) Sensible heat storage

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Water tight cisterns

• • Thémis station in France : Use of molten salt with solar panels Stores

40,000 kWh of thermal energy/ 1 day sunlight in 550 t of fused electrolyte

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-Hot water storage

-Off peak hours, HWS can

be obtained from a thermal

plant

-Condensation of the high

pressure steam from the

boiler or by tapping at low

temperature from turbine

outlet

-Thermal storage reservoir designed for 1000 kWh, 20m dia, 20m height for volume of 5000m3

Fig: sensible heat storage of electricity in a power plant

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More..

Chemical storage

Electricity capacitor

Energy Storage using Flow Batteries (FBES)

Fuel cells-hydrogen energy storage (FC-HES)

Small-scale compressed air energy storage (SSCAES)

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Capacity Characteristics

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Cost Characteristics

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Comparison of Technical Parameters

Source: http://www.eai.in/ref/ct/ees/ees.html

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Status of technology development

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R&D needs

Storage is the weakest link of energy domain, but is the key element for the growth of renewable energies

Need of improved technologies on short to mid-term

Lithium-ion batteries are very performent, expensive

Recycling and waste management of batteries

Life expectancy for lead batteries, weak link in isolated systems

Flow batteries, compressed air, super capacitors & flywheel to be made cost effective, reliable and efficient

2025: Pumped and compressed air storage systems

2040: It will be necessary to store electricity for several weeks &

months

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Group discussion

Discuss with your friends about the following issues (5 minutes)

1. Renewable energy are very intermittent in nature and non continuous..

2. Fossil fuels are depleting and emit huge pollutions..

3. For renewable sources, where there is demand there will be no supply..

4. Renewables, like Solar and wind, are not suitable for transportation fuels..

5. In future, liquid transportation fuels would be a challenge…

What do you suggest…? 33