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

2. 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

3. 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.

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

5. 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).

6. 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

7. 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).

8. 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

9. 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.

10. 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)

11. 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

12. 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)

13. 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. 13

14. GREEN TRANSPORT This? ……….. or this?

15. GREEN TRANSPORT 15

16. 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.

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

18. “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

19. 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 !