You stand barefoot on the warm kitchen tiles, gazing out at the high鈥恟ises. You fill the kettle and while you wait for it to boil, toss yesterday鈥檚 teabag into the bin.
This may seem a pretty simple scenario; but behind the scenes, a vast framework of wasteful and polluting processes is at work. In big cities, the water in your kettle and the electricity to boil it may have travelled over 100km to reach you.
What toll is that cup of tea taking on the planet 鈥� and your wallet?
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Trigeneration 鈥� the simultaneous production of electricity, hot water and cold water from a single fuel source 鈥� is set to revolutionise the way we manage our resources. The technology isn鈥檛 new: Thomas Edison built the prototype system in 1882. But the green revolutionary potential of trigeneration is only now being realised.
Getting back to nature
At the moment, our cities鈥� resources are managed in linear, isolated systems 鈥� power and water coming in, waste going out. This is in stark contrast to the interconnected loops of natural ecosystems, where the output of one process forms the input of the next.
鈥淲e do everything to excess in Australia,鈥� says Vanessa Rauland, who is researching city decarbonisation at the Curtin Sustainability Policy Institute in Perth. 鈥淲e consume more resources and produce more emissions than almost anyone else in the world.鈥�
To get our urban metabolism under control, Rauland says we need to get back to nature: 鈥淲e need to move towards an integrated, circular system where resources are continuously recycled 鈥� just like an ecosystem. This is far more achievable at the local level.鈥�
In other words, cities need to 鈥榙ecentralise鈥� energy: instead of relying on a couple of large out of鈥� town power plants, we need to embed many small鈥恠cale ones in and around the city.
Cleaner, cheaper and more efficient than conventional technology, trigeneration is a perfect candidate.
Three鈥恌old benefits
Trigeneration works on the same basic principle as the coal-fire process that currently meets the staggering energy demands of most cities: water is boiled to create steam, which turns turbines to generate electricity.
But it is where the two technologies differ that trigeneration鈥檚 appeal lies. Instead of burning carbon-intensive coal (鈥渢he primary cause of climate change,鈥� says Rauland), trigeneration relies on low鈥恈arbon natural gas.
And where coal鈥恌ired plants waste two鈥恡hirds of the thermal energy they produce 鈥� as gas released into the atmosphere 鈥� trigeneration captures and recycles this excess heat.
Trigeneration鈥檚 hot water by-product can be used directly, to heat buildings or to drive absorption chillers to generate cold water, which can be used for air鈥恈onditioning.
It鈥檚 this on鈥恡he鈥恠pot recycling that gives trigeneration its 2.5 fold efficiency edge over coal-fire. 鈥淭he capture and use of waste heat means trigeneration achieves around 85% efficiency,鈥� says Rauland. 鈥淔or coal鈥恌ire, that figure is closer to 30%.鈥�
But herein also lies a major potential stumbling block for decentralised trigeneration. Without demand for hot and cold water nearby, trigeneration鈥檚 efficiency advantage is squandered.
鈥淎lthough trigeneration theoretically can work at any level, I can鈥檛 see this being feasible in our low鈥恉ensity suburban sprawl,鈥� says Rauland. 鈥淚t will only be economically viable in denser city centres.鈥�
Housing a mini power plant in your basement would also eliminate much of the transmission losses and substantial costs associated with bringing out鈥恛f鈥恡own power into the city.
Fuelling the future
But just how green is trigeneration; isn鈥檛 gas a fossil fuel? Although cleaner than coal, gas is still a non鈥恟enewable energy. In fact, its primary component, methane, is itself a more potent greenhouse gas than carbon dioxide.
This drawback could be overcome by perhaps the most exciting and cutting-edge aspect of trigeneration technology: its potential use of new鈥恮ave renewable and low鈥恈arbon fuel sources.
We鈥檙e talking about the untapped energy of waste; food scraps, agricultural biowaste, even sewage, can be recycled into synthetic gas, which could be fed into trigeneration plants.
One particularly impressive emerging technology, plasma arc gasification, blasts organic waste into its component gases at super鈥恏ot temperatures. This process, however, requires electricity 鈥� which seems somewhat counter鈥恜roductive 鈥� and isn鈥檛 yet an economically viable option.
Powering ahead
Meanwhile, gas鈥恌uelled trigeneration is already making an impact. A retrofitted network of trigeneration plants has transformed the Borough of Woking in the UK, reducing emissions by around 80% from 1990 levels.
Woking has also highlighted another major advantage of decentralised energy: the debilitating blackouts that plague our current systems could become a thing of the past.
Trigeneration pioneer Allan Jones, credited with the success of Woking and similar results in London, told a 2008 symposium audience: 鈥淲e鈥檝e had four national grid power cuts in the last couple of years. [In Woking] people were totally unaware there was a blackout.鈥�
When the City of Sydney was looking to reduce its emissions, it commissioned Jones to weigh up the available technologies. His consultancy group identified trigeneration as cheaper than large鈥恠cale renewable energies such as wind and solar.
Sydney is now aiming to meet 70% of its energy needs with trigenerated electricity by 2030. David Holden of sustainability analysis company Kinesis, who collaborated on the master plan, says he expects to see the first plants implemented next year.
And Sydney is not restricting the overhaul to electricity. It is also looking to simultaneously install decentralised water infrastructure. And remember that used teabag? An underground network of tubes to remove garbage at 70km/h is also on the table.
Several other Australian cities are moving to follow Sydney鈥檚 lead. It appears trigeneration is proving the catalyst for a radical transformation of the way we manage our resources.
But a few hurdles to decentralisation still remain.
鈥淲e are essentially completely redesigning the way we deliver energy to a city,鈥� says Holden. 鈥淪o it鈥檚 not without challenges.鈥�
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