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POWER MANAGEMENT POWER MANAGEMENT FOR FOR

SUSTAINABLE ENERGY SYSTEMSSUSTAINABLE ENERGY SYSTEMS

Graham Town

Electronic Engineering

Macquarie University.

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OVERVIEWOVERVIEW

• The need for – decreasing reliance on fossil fuels

– increased reliance on sustainable sources of energy

– efficiency in energy conversion and use

• Sustainable energy systems– source, storage, load, power management…

• Efficiency in sustainable energy systems– solar cells, wind turbines, batteries, converters

• Integrated circuits for – power conversion & management

– energy harvesting

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ENERGY 2010ENERGY 2010

• Fossil fuels (oil, coal) are main source of energy in modern society.• Advantages: high energy density (45MJ/kg, approx. twice ethanol)

relatively easy to transport safely, easy to use.

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ENERGY 2010ENERGY 2010

• CO2 emissions are mainly from burning fossil fuels for:

– Electricity generation (coal)

– Transport (oil)

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PROBLEMS WITH FOSSIL FUELSPROBLEMS WITH FOSSIL FUELS

1. A finite (non-renewable) resource – esp. oil/petroleum– maximum rate of production - “peak oil” - occurred in 2008

– current rate of usage greater than rate of production• at current rates oil will run out around 2050

Campbell, “Petroleum and People”, Pop’n and Environ.,24, 193 (2002).

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PROBLEMS WITH FOSSIL FUELSPROBLEMS WITH FOSSIL FUELS

2. CO2 emissions causing environmental change

– Global warming caused by greenhouse gases in atmosphere

climate change, extreme weather events, etc.

– Ocean acidification caused by absorption of CO2

potential threat to marine food chain

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ENERGY OPTIONS TO 2050+ENERGY OPTIONS TO 2050+

1. Reduce fossil fuel usage i) for the environment, ii) to make resource last longer

To use less energy (esp. for transport, heating/cooling)…. • reduce population and/or living standards increase energy efficiency

Campbell, “Petroleum and People”, Pop’n and Environ.,24, 193 (2002).

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ENERGY OPTIONS TO 2050+ENERGY OPTIONS TO 2050+

2. Replace fossil fuels with sustainable energy sources (i.e. no compromise to the needs of future generations)

– Nuclear energy

– “Renewable” (naturally replenished) sources of “green” (unpolluting) energy• solar• wind• wave & tidal• hydropower• biomass• geothermal

– Energy harvesting

International Energy Agency, “Key World Energy Statistics,” p6 (2009).

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PRACTICAL ENERGY MATTERSPRACTICAL ENERGY MATTERS

• Available on demand?• e.g. solar power not available at night, wind power often variable

• Storage? (if not available on demand)• e.g. thermal, mechanical, chemical, electrical

• Transport? (if source and load not colocated)• e.g. electrical, chemical

• Efficient conversion (for storage, transport)• e.g. chemical electrical (e.g. battery)• e.g. thermal mechanical (e.g. steam turbine)• e.g. mechanical electrical (e.g. wind turbine)• e.g. electrical electrical (e.g. DC-AC, DC-DC converters ~95% efficient)• conversion efficiency particularly important for harvesting small amounts of

energy from the environment (ambient light, vibrations) for mobile devices.

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POWER SYSTEM MANAGEMENT POWER SYSTEM MANAGEMENT

• Any electric power system has a source, load, and usually storage• Each of the components have a preferred operating point

– e.g. maximum power point (V and I for max. power transfer)

– e.g. charge/discharge rate for max. lifetime

• Power management is req’d to maximise system performance, especially in energy harvesting (ambient sources: small, variable)

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SOLAR CELL ARRAY SOLAR CELL ARRAY CHARACTERISTICSCHARACTERISTICS

• For a given irradiance, the power extracted from a solar cell (or uniform array) depends on the voltage across it, up to a maximum – the maximum power point, or MPP

http://www.innovativesolar.com/images/File/BSE_What_is_MPPT.pdf

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SOLAR CELL ARRAY SOLAR CELL ARRAY CHARACTERISTICSCHARACTERISTICS

• The MPP varies with irradiance, temperature, etc.• Arrays of cells are often used to boost voltage or current

– BUT shadowing of any cells in array can cause large reduction in avail. power

• Need smart and efficient power conversion & combining

Organic (polymer) solar cell array fabricated and characterised by the author at St Andrews University (2009)

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ENERGY STORAGE TECHNOLOGYENERGY STORAGE TECHNOLOGY

• Many different technologies available, different characteristics

http://www.mpoweruk.com/performance.htm

http://www.batteryuniversity.com/parttwo-34.htm

Longevity of lithium-

ion as a function of charge and discharge

rates.

A moderate charge and discharge puts less stress on

the battery, resulting in

a longer cycle life.

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GREEN TRANSPORTGREEN TRANSPORT

This?

……….. or this?

http://www.gizmag.com/lexus-hybrid-bicycle-concept/14938/

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GREEN TRANSPORTGREEN TRANSPORT

http://www.gizmag.com/lexus-hybrid-bicycle-concept/14938/

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ENERGY HARVESTINGENERGY HARVESTING

• e.g. “wireless switch” technology The effort made in pushing the switch powers a small and efficient wireless transmission system to activate remote equipment

• e.g. power generators in your shoes The act of walking generates electricity by flexing a piezoelectric material embedded in a shoe, e.g. to charge a battery for mobile communication, etc.

http://www.inhabitat.com/wp-content/uploads/rollers1.jpg

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POWER TECHNOLOGYPOWER TECHNOLOGY

• Will follow same evolutionary path as wireless communication technology (i.e. to smaller, more mobile systems)

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““POWER SUPPLY ON A CHIP”POWER SUPPLY ON A CHIP”

• Research sponsored by local company, Sapphicon Semiconductor– Only IC manufacturer in Australia

– Silicon-on-sapphire CMOS platform• Transparent sapphire substrate low loss, high speed, efficient heat x’fer• Better than standard CMOS for power management and energy harvesting

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CONCLUSIONSCONCLUSIONS

• We need to change energy usage patterns develop different sources of energy use available energy more efficiently

• Integrated electronics provides reliable, low cost, and compact technology for efficient energy conversion and utilisation smart management of power systems…

and the battery on your mobile phone will last longer !