POWER MANAGEMENT FOR SUSTAINABLE ENERGY SYSTEMS Graham Town Electronic Engineering Macquarie University.

OVERVIEW The need for Sustainable energy systems 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

ENERGY 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.

ENERGY 2010 CO2 emissions are mainly from burning fossil fuels for: Electricity generation (coal) Transport (oil) 4

PROBLEMS WITH FOSSIL FUELS 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).

PROBLEMS WITH FOSSIL FUELS 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

ENERGY OPTIONS TO 2050+ 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).

ENERGY OPTIONS TO 2050+ 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). 8

PRACTICAL 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.

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)

SOLAR CELL ARRAY CHARACTERISTICS 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

SOLAR CELL ARRAY CHARACTERISTICS 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)

ENERGY STORAGE TECHNOLOGY Many different technologies available, different characteristics 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. http://www.mpoweruk.com/performance.htm http://www.batteryuniversity.com/parttwo-34.htm 13

GREEN TRANSPORT This? ……….. or this? http://www.gizmag.com/lexus-hybrid-bicycle-concept/14938/

GREEN TRANSPORT http://www.gizmag.com/lexus-hybrid-bicycle-concept/14938/ 15

ENERGY 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

POWER TECHNOLOGY Will follow same evolutionary path as wireless communication technology (i.e. to smaller, more mobile systems) 17

“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

CONCLUSIONS 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 !