Sydney trigen? Try again with renewables | RenewEconomy

Sydney trigen? Try again with renewables

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Why bring a polluting gas plant back into central Sydney when you can get a better emissions result with renewables and aircon upgrades?

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Since the industrial revolution, when cities became dirty places, we have been removing pollution from their streets and neighbourhoods.

We’ve seen old central coal plants closed down and replacements built hundreds of kilometres away.

Stricter and stricter vehicle emissions standards have been enacted to reduce local pollution and improve the health, wellbeing and happiness of city dwellers.

So why would you choose to then bring a gas power plant back into the centre of the city, where it will release large quantities of health-damaging nitrogen oxide?

A subsidiary of Origin Energy and the City of Sydney have done a deal to start rolling out trigeneration (“trigen”) gas generators in the most heavily populated urban area of Australia.

Trigen is being touted as the new clean, decentralised system for generating power. You might hear about its fabulous efficiency, or the potential to burn renewable bio-gas in future, but when you remove the spin, it’s just re-packaged fossil gas.

But our concern is not just that it’s not renewable, or the nitrogen oxide gases, among other pollutants, that will damage respiratory health. As it turns out, trigen’s carbon emissions and energy efficiency aren’t that great either.

Comparing apples with apples

The City of Sydney compares its trigen plan to burning coal in existing plants. It actually would have been more accurate to compare it to the grid average, which is lower (because it includes some gas and hydro, in particular).

But that’s not our main point. Its easy to look better than the coal-dominated status quo, but it would have been fairer if they compared it to other possible efficiency upgrades with similar capital expenditure and energy costs.

That way we can also see what the “opportunity cost” is for going with trigen, as compared to the benefits and opportunities of other options we could take.

In our view, the alternative upgrade options to trigen would centre around an energy efficiency program upgrading existing building chillers (airconditioning). The upgraded chillers could be powered by a new, conventional gas-fired power plant out of town, or (preferably) by new renewable electricity generation.

Following is our comparative survey of these two options, which highlight the weaknesses of the trigen case.

How efficient?

The council claims that reciprocating engines burning gas between 7am-10pm will be 42 per cent efficient in creating electricity; and of the remaining waste heat, 25 per cent equivalent of the gas’ original energy will be delivered to buildings in the form of heating and cooling, using an old-fashioned absorption chiller.

This claim adds up to 67 per cent of the total energy that was in the gas to start with being delivered in useful form to residents and businesses.

However, 3 per cent of the electricity generated is used to pump water around the 40km-long hot water network. This would not be necessary in a non-district heating/cooling system, such as our alternative scenario.

A further 6 per cent of the original energy is lost using an absorption chiller for creating chilled water, as these only run with a Co-efficient of Performance (COP) of 0.7; that is, 0.7 times the input energy is delivered.

So despite using 67 per cent of the energy in the gas, the system is only really 58 per cent efficient at delivering energy service to customers.

Today’s average Sydney city building chiller plant has a Co-efficient of Performance (COP) of 2.5 – that is, 2.5 times the energy in the electricity is delivered as pumped heat. Compare this to COP 0.7 for absorption chillers.

Modern chillers are heat pumps: they concentrate the ambient heat. Their energy use is from compressing and pumping to supply or remove heat, not from creating it.

At COP 2.5, current chiller plant is only drawing on 40 per cent of its delivered energy from grid electricity while the other 60 per cent is the renewable, ambient heat it harvests.

So here’s the clincher: delivering 19 per cent of the gas’ energy for heating and cooling (as shown in the City of Sydney report) only displaces that 40 per cent of building heating/cooling which is currently generated by grid electricity; 40 per cent of 19 per cent is 7.5 per cent, which is the equivalent energy needed to run today’s chiller plant and deliver the same heating and cooling as the trigen scenario.

What would a standard alternative look like?

So what if we were to burn the gas in a modern “best performance” combined cycle gas turbine (CCGT) plant outside town instead? This is just “business-as-usual” that is already in use in much of the world, yesterday’s answer to coal’s high carbon emissions.

According to General Electric such a plant would achieve 55 per cent efficiency (55 per cent of the gas energy converted to electrical energy).

According to Marginal Loss Factor data from the Australian Energy Market Operator (AEMO), delivering electricity from a remote generator to a large building in Sydney would lose no more than 5 per cent of the electricity in transmission and distribution.

This means that, including transmission losses, a CCGT plant out of town would be 52.25 per cent efficient at delivering electricity into a city building (95 per cent of 55 per cent).

So at this stage, our alternative is a little less efficient than trigen’s 58 per cent. But we’re not finished yet.

The latest, most efficient heat recovery chillers achieve an impressive COP 6.5 – so we can more than halve the current electricity demand for cooling by going from COP 2.5 to COP 6.5 chiller technology.

This option uses 138 gigawatt hours (GWh) of electricity for heating and cooling. This almost exactly matches the 135GWh that is used just pumping water in the trigen plan.

As a bonus, our chiller upgrade would reduce the peak electricity demand in the city by about half, since most of this demand is from air conditioning. This would reduce energy bills, lowering transmission/distribution loss factors (all of which are higher during peaks), and reduce carbon emissions.

The CCGT option would also give a benefit out-of-hours (10pm-7am every day) when the City’s trigen would be idled due to economic reasons; and during summer peaks, when the old (currently existing) chiller system will be required to run, drawing more power to supplement the trigen system.

Comparing those percentages again

Just 3.5 per cent of the annual energy used for the CCGT gas plant would deliver the same amount of heating and cooling as the City of Sydney’s Tri-gen proposal, if we upgrade the chillers as well.

With the central CCGT plus central chiller-upgrade option we end up with the equivalent of 73 per cent of the energy contained in the fossil gas delivered as useable energy: 52.5 per cent plus the performance multiplier of the new chillers.

This is well ahead of the real end use energy in the City of Sydney’s Trigen option, and even ahead of their claimed efficiency. The extra percentage gain in our scenario is not waste heat from burning gas, but just harvesting renewable heat.

If all these percentages are confusing, the diagram below illustrates the relative quantities of energy used (and wasted) from the different scenarios, all of which deliver the same output in terms of useable energy.

Burning 20% less gas

Our example CCGT option delivers the same amount of electricity, cooling and heating to city buildings as the trigen proposal, with only 80 per cent of the amount of gas burned.

The Sydney trigen proposal will consume 17,000TJ (Terajoules) of gas per year. This is the equivalent of 86 average days of current gas supply from the Moomba gas field.

Moomba is Sydney’s main fossil gas field now, but in the future the supply will increasingly include coal-seam gas. Our calculations exclude the latest damning research on fugitive emissions, ie gas leaks – a significant problem, especially with coal-seam gas, but beyond the scope of this analysis.

With gas use comes high and volatile fuel prices, and increasingly, land degradation. This land impact could be from coal-seam gas production on prime agricultural land, or in the future, by jacking up demand for land-hungry biogas production.

As we move to renewable energy, biofuels will be needed for our industrial economy: steel production and other chemical processes; range-extending motor vehicles; and operating other specialist plant and agricultural machinery. We shouldn’t divert them to jobs that can be done by other means.

Let’s just skip the gas options

The sensible course of action would be to to bypass dirty fossil gas within the city, and upgrade chilling plant instead, taking advantage of renewable ambient heat: the city’s greatest renewable resource.

And then the city should bypass the gas age altogether.

A 100 per cent renewable option to supply the annual electricity demand of the upgraded building chiller plant could be supplied with wind and solar power.

The city could commission a dedicated 330MW wind farm in the region, and 660MW of photovoltaic solar panels for the other half.

The solar panels could be installed in the City of Sydney and two or three of the neighbouring municipalities with just 130,000 5kW rooftop systems. It’s not that much: Australia currently has over 700,000 rooftop solar systems on private residences alone.

We would achieve 1042GWh annually from each of these sources, assuming a fairly common 35% capacity factor for wind, and 18 per cent capacity factor for solar.

Which road shall we take?

100 per cent renewable energy will of course reduce carbon emissions to zero. But renewables come in smaller units. You don’t have to build the whole replacement all at once.

What if we built just enough renewables to reduce emissions by the same amount as the trigen plan? It turns out we would have to supply just 39 per cent of the energy from renewables, if we also go with the building chiller upgrade.

That way Sydney will be well on the road to 100 per cent renewables and genuine energy efficiency, instead of a costly and dirty detour through gaslands. It’s Clover Moore’s choice now on which road she wants to steer Sydney down.

Beyond Zero Emissions will be releasing a special Sydney Buildings plan in July to coincide with the release of the Zero Carbon Australia Buildings plan.

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  1. Alastair Leith 8 years ago

    Well argued Matthew, good to see BZE kicking goals from square inch of the forward arc!

    How long did it take BZE to prepare that analysis? Given that SCC has full time staff and very well paid consultants to do this kind of work how on earth did they arrive at Trigen. I met a co-gen/tri-gen salesman at a lunch a few weeks ago and he was claiming tri-gen can be up to 95-98% efficient. Your analysis doesn’t show those kinds of efficiencies that’s for sure but it does show how they can compare apples to oranges when making comparisons.

    • Conrad Townsend 8 years ago

      Governments, councils, developers and other bodies around the world are arriving at Trigen, and more importantly, district energy or centralised heating and cooling systems. The reason is not purely for carbon emission savings but for demand management.

      The Electricity Network operators around Australia are currently spending $45billion maintaining and upgrading electricity networks (poles and wires) to meet an increasing peak demand, while actual electricity use is stabilising or even reducing. This cost is greater than the entire NBN project which runs over 15 years. Money that could be spent on renewable energy.

      By having embedded generation of electricity, heating and cooling meeting peak building demands, the need to upgrade electricity networks is abated. Doing using low carbon energy generation is ‘two birds with one stone’.

  2. Liam 8 years ago

    Well done Matthew for this peice of work poking at the holes in the City of Sydney Trigen plan.

    Just a few clarifications / issues:
    – The most efficient air cooled CCGT available is 50% thermal efficiency sent out when located in Australia – not 55%.
    – My understanding is that the absorbtion chillers in the Trigen Master Plan are assumed to be 80% efficient -not 70% – and that heat losses from network were assumed to be 10%
    – Are chillers with a COP of 6.5 commercially available at a scale of a single building? My understanding is that these systems are only this efficient at precinct scale and would require a cooling network.

    Even with these changes the overall conclusions around whole of system efficinecy would not be different.

  3. Ben Courtice 8 years ago

    95-98% efficiency for trigen would have to include some interesting assumptions, I’m sure. Perhaps in a very cold climate, where all the waste heat could be used simply for building heating, it may approach that? When you want to run chillers, as Australian office buildings primarily do, year round – I think you should have told him he’s dreaming!

  4. Matthew Wright 8 years ago

    This is one of the documents that actually has some data in it put out by the City of Sydney for readers to analyse.

  5. John Davis 8 years ago

    Tri-gen has always worried me. The sales pitch always tells us it is efficient because the waste heat is used for heating or cooling. They never mention the half year in spring and autumn when all we need is fresh air. Heating and cooling are not always needed. So the waste heat is indeed wasted.
    That leaves a big hole in the efficiency calculations.

    As well as that, they are using gas, which has problems, and they are using small generators, that can never be as efficient as a power station.

  6. Matthew Wright 8 years ago

    I think my 55% efficiency call for regular operation of a new build CCGT is reasonable.

    See: Siemens Combined Cycle Gas Turbine (CCGT) plant at 61% efficiency. (air cooled)

    • Liam 8 years ago

      I’d be skeptical about thermal efficiency figures used by Siemens and GE on their websites. They typically quote thermal efficiency as generated, not as sent out, and for performance in the Northern Europe climate, not in NSW.
      Still, happy to be proven wrong.

      • Matthew Wright 8 years ago


        I am inclined to agree with you, though 61% gross efficiency would highly likely equate to 52-55% net here. Also rejecting heat becomes less of an issue as the efficiency rises.

        Likewise the city of Sydney is using a highly optimistic 42% efficiency figure for the reciprocating engines – straight out if the marketing brochure.

        In any case I am showing the chasm in performance so we can choose a better path. The same emissions output at 61% existing NSW grid avg, 39% renewables and Heat Recovery Chiller upgrade inc

  7. Concerned 8 years ago

    One problem, you will need to back up your renewables with fossil fules during winter.
    Also the renewables will need to be subsidised, and even then I can not see commercial premises paying such a high price of 25 to 30 cents a KW.(look at the BZE proposal for South Australia)
    The Sydney scheme will stand on it’s own two feet, and provide the required efficienies.
    ” COP 0.7 for absorption chillers”, that is incorect, depending on the configutation it can reach 2.5 as you well know.
    In addition , the concept is running in London at the projected efficienies.
    Very skewed article.

    • Concerned 8 years ago

      sorry .07 to 1.8

    • Ben Courtice 8 years ago

      Renewable subsidies? So maintaining a duplicate energy distribution network for gas is not costing anything?

      And coal mining receives no government subsidy or assistance? In fact the assistance in the form of rebates, subsidies etc to fossil fuels dwarfs that to renewable energy.

      The other point about renewables is that BZE are planning for a system that does not need backup in winter. In the meantime, Matt’s proposal will provide the same amount of energy per year.

  8. Concerned 8 years ago

    Sorry COP .7 to 1.8

  9. Brendan Dow 8 years ago

    Hi Matthew,

    I think it is important to concede that this is a fantastic project and despite it not being as green or innovative as you might wish, it is certainly a move in the right direction.

    How about giving credit for the City of Sydney for having the ticker to set a benchmark for others to better in the not too distant future?

    • Ben Courtice 8 years ago

      I think it only looks great because we’re starting from such a terribly low point with the Australian electricity grid’s coal reliance. In terms of opportunity cost, it’s pretty terrible. It’s great greenwashing PR for the gas industry, though.

  10. Matthew Wright 8 years ago


    This is a terrible project, it will cost a lot more (When taking into account the absorption chillers which the City of Sydney has failed to cost) than going 39% Wind Power and upgrading the existing building chillers to the latest energy efficient chillers.

    For the same carbon emission outcome we can have a 39% renewable option on the way to 100% renewables or we can go dead end gas with carbon lock in for a higher price.

    • Concerned 8 years ago

      Mathew if you think this is true, do you think those undertalking the project are silly?
      Perhaps they actually know what they are doing.
      You seem to obsess when the word “gas” is mentioned.

      • Ben Courtice 8 years ago

        I think being “obsessed” with gas, in this sense, makes good sense.

        Gas is highly polluting, all the more so as we go into unconventional sources like fracking and so forth. It’s also competing directly with renewables to be the next generation of our electricity generators.

        We’ve half cooked the planet with coal, do we want to finish it off with gas?

      • Alastair Leith 8 years ago

        Silly is your word nameless ‘Concerned’. In the meanwhile Matthew states his case with reasoned argument and some data. If you don’t consider AWG climate change an issue I guess anyone devoting their life to arresting the dire situation might seem obsessed, to others they are an inspiration, as Matthew Wright is to many who care about more than selfish pre-occupations.

  11. Sean 8 years ago

    the only side benifit i could see to a trigen system is that the cooling loop could be hooked up to OTEC

  12. Conrad Townsend 8 years ago

    I agree that the GHG intensity of high efficiency electric chillers running off gas or renewables are competitive with absorption chillers running off waste heat, and also that the goal is to move to fully renewable electricity. Is a local council actually able to build a renewable energy facility elsewhere and use it? It’s a National Grid after all, or at least state based. They would need a retailer to purchase the electricity via the grid. So no different from just buying electricity, which may not make an actual difference in the current regulatory conditions, with the MRET set target of 20% by 2020. The GHG emission intensity of the gird would reduce, and it would be double counting to say the local government is also reducing its emissions.

    Local Governments cannot control the policy regarding renewable penetration in the national grid. Especially our dense cities, that have no space or ability to install the type of renewable energy required capacity required to meet such huge energy demands in CBD’s. It’s worth noting that the CoS have a substantial renewable energy master-plan also.

    As it stands, gas fired reciprocating engines produce electricity at about half the carbon intensity of the NSW grid. The GHG emission reductions are there. It is not a distraction from renewables. Renewables can, and hopefully will continue to develop nation wide at the same time. But it is a sensible move for a local council, for one CBD, compared to using grid electricity or the building by building trigeneration systems.

    A major part of Precinct Trigeneration and District Energy projects is providing heating and cooling thermal networks that link up the heating and cooling demands of large energy guzzling buildings. It’s energy collaboration for large property owners in the CBD, and lots of innovation can come from it. Once the buildings are connected to centralised heating and cooling via underground insulated thermal networks, the heating and cooling can be provided by the least GHG emitting method. When more renewable electricity is available, and grid GHG intensity goes below gas fired electricity, heating and cooling can be produced by using renewable electricity. Additionally, waste heat can often come from industry, which is normally rejected into the air or waterways, so sees zero additional GHG emissions.

    Peak electricity is primarily driven by heating and cooling, and it will always be difficult for renewable electricity to match generation with demand at these times. When a city is linked up to centralised heating and cooling, the central plant rooms can contain heating and chilling stores that charge when renewable electricity is available, and dispatch when the buildings need it. Just look to Scandinavia who are building huge thermal stores to provide heating and cooling to their cities to supplement their move to renewable energy.

    Is precinct trigeneration and district energy in Australia distracting from, or blocking the development of renewable electricity?

    Or is the better question, is 100% renewable electricity possible without district energy including thermal storage in our CBD’s?

    • Matthew Wright 8 years ago

      Two points, first point is that I’ve been overly generous in the above explanation and diagra as the Trigen system’s heating and cooling component has an annual capacity factor of just 50%.

      In other words if you take the 19% of heat and coolth that is provided by the 98C hot water distribution network it’s only running 40% capacity factor.

      Therefore the effective thermal efficiency of the system is actually 42% (Electric) + 9.5% (Hot Water and Absorption chiller coolth)

      Therefore the system has an annual thermal efficiency of 51.5% and a peak thermal efficiency of 58%.

      Pretty sad for something that is being touted as efficient.

      The capacity factor is so low due to minimal heating requirement in mid summer, minimal cooling requirement in mid winter and very little heating or cooling requirement in Autumn and Spring.

      Installing gas assets sends a signal, for exploration, extraction, pipelines, donations to political party, taxation regimes that create dependency and the list goes on. It’s like a cancer society can’t rid itself of.

      And gas is more polluting than coal when you take into account the 7-15% likely fugitive emissions by volume that are occurring at CSG and shale operations here and proven at sites around the globe.

      • Conrad Townsend 8 years ago

        You are touching on one of the advantages utilising waste heat to produce heating and cooling. If you have 10MW capacity of thermal energy, the same 10MW is available to service cooling in summer and heating in winter. As you suggest, as there is minimal heating demand in peak summer, all the waste heat can be used for cooling. So unless there is peak heating and cooling demand at the same time, it does not reduce the capacity factor by 50%.

        Additionally, it is unfair to compare capacity factors based on demand rather than availability (supply). The fact is, precinct trigeneration can supply electricity, heating and cooling when the buildings need it, unlike renewable energy which supplies electricity when wind and sun is available. Capacity is more relevant when demand exists, than just a blanket approach across 24 hours.

        The article is comparing precinct trigeneration to a large gas power station located somewhere near Sydney or renewable electricity generation in a nearby ‘region’, and a chiller upgrade programme. The fact is, a local council in the middle of a dense city cannot build, operate and sell electricity using a large gas power station or a regional renewable energy project.

        It is fairer to compare the precinct trigeneration approach to the current situation, which is a GHG emission intensive grid, rather than compare to 2 impossible projects. And this doesn’t even factor in the comparative costs of the options in the article.

        • Liam 8 years ago


          If the City convinces building owners to rip out their electric chillers and replace them with absorbtion chillers then they will have to size all trigen infrastructure to meet peak demand.

          If they don’t size the gensets and thermal network infrastructure to meet peak thermal demand, building owners will either need to keep standby electric chillers or large amounts of thermal storage to cope with very hot days.

          The capacity factor of the entire system will be well under 50%.

  13. Conrad Townsend 8 years ago

    Capacity factors have to be used in the correct context. They are typically used to compare solar and wind generation to other base load power sources, as the nameplate capacity is not a fair measure of generation capacity.

    Capacity factors are less relevant for projects that are servicing peak demand. For example, if a precinct trigeneration system is sized to service baseload demand (eg. typical daily heating/cooling, with back up boilers and chillers), it will have a higher capacity factor. However, if a precinct trigeneration system is sized to meet peak demands, it increases benefits like GHG emission and peak demand reduction. So capacity factor is a less relevant consideration when looking at systems designed to meet peak heating and cooling loads, and a high capacity factor can see other benefits diminished.

    Moreover, capacity factors look at the energy generation, not the whole system including chillers. If that were the case, the capacity factors of wind and solar would be reduced due to peak chillers sitting in buildings not being used during non-peak times.

    Availability factor may be a better comparison, where precinct trigeneration exceeds solar and wind.

    But if you must consider precinct trigeneration in terms of capacity factors, it will be reduced when there is a lack of heating and cooling demand in autumn and spring. Although buildings still do use heating and cooling during these times. But the capacity factor will not be reduced, as Matthew asserts in his comment, due to peak heating in winter and peak cooling in summer, as the waste heat can be utilised for either at this time. A 10MW system can provide 10MW energy at both peak heating and peak cooling times.

  14. Adam 8 years ago

    It seems there are quite a few assumptions made by all as to the drivers of this project.

    Why would city of sydney NOT pursue the BZE proposal? As someone mentioned I don’t think regional power station development (with gas and power connection all beyond their jurisdiction) would ever be palatable to the organisation on a number of levels.

    Perhaps they have their own self-sufficient sustainability objectives that also have geographic constraints.

    I don’t know myself although this BZE solution is purely technical which in reality is only a small part of the risk/scope pie.

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