Is ‘clean coal’ power the answer to Australia’s emissions targets?


Lynette Molyneaux, The University of Queensland

As Australia’s energy debate heats up, some politicians are calling for cleaner and more efficient coal power stations to reduce greenhouse gas emissions.

Energy Minister Josh Frydenberg told ABC radio on Tuesday that “ultra-supercritical coal-fired power plants actually drive down the carbon footprint by up to 40%”.

And last week Resources Minister Matt Canavan referenced a report, as yet not released by the Department of Industry, Innovation and Science, which claims that Australia can meet its carbon emission targets by replacing existing coal generators with ultra-supercritical coal generation.

So, is this a reasonable strategy to reduce Australia’s emissions?

Cleaner coal

Australia’s coal generation fleet is ageing and needs replacing. Two-thirds of the 25 gigawatts in operation (after Victoria’s Hazelwood power station is retired this year) is more than 30 years old, according to ACIL Allen’s generator report. By 2025 a further 18% of the fleet will be more than 30 years old.

That means that in 2025 a mere 4GW of our existing coal power will still be considered adequately efficient. This is important because efficient generation affects not only how much generators are paying for fuel, but also carbon dioxide (CO₂) emissions.

Modern coal power plants feed pulverised coal into a boiler to combust. Tubes in the boiler walls then absorb the heat and the steam generated in these boiler tubes turns the steam turbine and generates electricity.

The difference between subcritical, supercritical and ultra-supercritical boilers is in the steam conditions created in the boiler. Supercritical and ultra-supercritical boilers are often referred to as high-efficiency, low-emissions technologies.

Ultra-supercritical power stations are designed to operate at higher steam temperature and pressure. This improves efficiency, and has been made possible by new materials that can cope with higher temperatures.

Ultra-supercritical coal power stations operate under steam conditions above 593-621℃ and 28.4 million pascals (a measure of pressure). You can find further detail in this report.

Using higher temperatures means greater efficiency, producing more electricity using less coal. Australia’s most efficient coal power station, Kogan Creek, is able to convert 37.5% of the gross energy, or calorific value, of coal into electricity. Hazelwood converts only 22%. The remaining energy is lost as heat.

By comparison, ultra-supercritical coal stations are able to convert up to 45% of the gross energy of coal to electricity.

Advanced ultra-supercritical coal generation is expected to convert over 50% of the gross energy of coal to electricity, but the expensive alloys required to accommodate the very high temperature requirements make the plants very expensive. Before advanced ultra-supercritical coal plants can be deployed, new design changes like this will first need to be tested and evaluated in pilot implementations.

Reducing fuel use reduces emissions. Hazelwood’s reported CO₂ emission intensity from 2014-15 was 1,400kg of greenhouse gas for every megawatt-hour of electricity it produced. Kogan Creek emitted 831kg per megawatt-hour.

The greater efficiency of ultra-supercritical generators can reduce emissions intensity to 760kg per megawatt-hour for black coal. Advanced ultra-supercritical generators can reduce emissions even further. Upgrading or replacing Victoria’s brown coal generators to ultra-supercritical would reduce emissions intensity to 928kg per megawatt-hour.

So greenhouse gas emissions can be reduced if ultra-supercritical generators replaced Australia’s old, inefficient coal generators.

But is it enough?

The problem is just how much CO₂ emissions can be reduced. Emissions from coal power are the largest contributors to Australia’s total emissions.

In 2013-4, coal generators emitted 151 million tonnes of greenhouse gas, generating 154 million kilowatt-hours of electricity. Details can be found here. This is 29% of Australia’s total emissions in 2013-14 of around 523 million tonnes. (Transport contributed around 18% to total emissions.)

Let’s assume the current fleet of power stations is operating at 80% capacity, considered to be an economic optimum for coal power. This would generate 176 gigawatt-hours of electricity and 165 million tonnes of emissions. This allows for a 14% increase in consumption of electricity by 2030, which is likely given projections of population and economic growth.

If we then replace the entire 25GW, both black and brown, with ultra-supercritical generation, according to the assumptions included in the Australian Power Generation Technology Report, emissions would total 139 million tonnes. This would represent a 16% reduction in coal emissions, but a mere 5% reduction in Australia’s total emissions in 2013-4.

And then we would have those ultra-supercritical power stations for the next 30-40 years, incapable of reducing our emissions further as global targets tighten.

If Australia were to wait until advanced ultra-supercritical coal power is tested and trialled, then we could speculate that emissions from coal generation could reduce by a further 10% to 124 million tonnes. This would be a more promising 25% reduction in coal emissions, but still only a 7.7% reduction in Australia’s total emissions.

Understanding Australia’s emission reduction target

Australia’s emission reduction target for 2030 is 26-28% below 2005 levels.

Emissions in 2005 were 594 million tonnes. Australia’s climate target would require emissions to reach around 434 million tonnes in 2030, a reduction of 160 million tonnes.

If coal power stations were to reduce emissions by 26-40 million tonnes through a shift to ultra-supercritical generators, then Australia would still be a very long way from meeting its committed targets.

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The only way shifting to ultra-supercritical coal power could meet Australia’s 26-28% climate target is if carbon capture and storage (CCS) were applied.

Ultra-supercritical coal plants are expected to generate electricity at A$80 per megawatt-hour, according to the Australian Power Generation Technology Report. This is 45% more expensive than the average wholesale cost of electricity for 2015-16. If CCS is added, then the projected cost swells to A$155 per megawatt-hour, nearly three times last year’s wholesale cost of electricity.

These costs eventually get passed on to electricity bills, and it’s unlikely that consumers will be willing to see electricity prices rise that much.

Until we see more detail underpinning the current enthusiasm for “clean coal”, we’ll have to speculate on the assumptions of the report referenced by minister Canavan.

The Conversation

Lynette Molyneaux, Researcher, Energy Economics and Management Group, Global Change Institute, The University of Queensland

This article was originally published on The Conversation. Read the original article.

Changing climate has stalled Australian wheat yields: study


Zvi Hochman, CSIRO; David L. Gobbett, CSIRO, and Heidi Horan, CSIRO

Australia’s wheat yields more than trebled during the first 90 years of the 20th century but have stalled since 1990. In research published today in Global Change Biology, we show that rising temperatures and reduced rainfall, in line with global climate change, are responsible for the shortfall.

This is a major concern for wheat farmers, the Australian economy and global food security as the climate continues to change. The wheat industry is typically worth more than A$5 billion per year – Australia’s most valuable crop. Globally, food production needs to increase by at least 60% by 2050, and Australia is one of the world’s biggest wheat exporters.

There is some good news, though. So far, despite poorer conditions for growing wheat, farmers have managed to improve farming practices and at least stabilise yields. The question is how long they can continue to do so.

Worsening weather

While wheat yields have been largely the same over the 26 years from 1990 to 2015, potential yields have declined by 27% since 1990, from 4.4 tonnes per hectare to 3.2 tonnes per hectare.

Potential yields are the limit on what a wheat field can produce. This is determined by weather, soil type, the genetic potential of the best adapted wheat varieties and sustainable best practice. Farmers’ actual yields are further restricted by economic considerations, attitude to risk, knowledge and other socio-economic factors.

While yield potential has declined overall, the trend has not been evenly distributed. While some areas have not suffered any decline, others have declined by up to 100kg per hectare each year.

We found this decline in yield potential by investigating 50 high-quality weather stations located throughout Australia’s wheat-growing areas.

Analysis of the weather data revealed that, on average, the amount of rain falling on growing crops declined by 2.8mm per season, or 28% over 26 years, while maximum daily temperatures increased by an average of 1.05℃.

To calculate the impact of these climate trends on potential wheat yields we applied a crop simulation model, APSIM, which has been thoroughly validated against field experiments in Australia, to the 50 weather stations.

Climate variability or climate change?

There is strong evidence globally that increasing greenhouse gases are causing rises in temperature.

Recent studies have also attributed observed rainfall trends in our study region to anthropogenic climate change.

Statistically, the chance of observing the decline in yield potential over 50 weather stations and 26 years through random variability is less than one in 100 billion.

We can also separate the individual impacts of rainfall decline, temperature rise and more CO₂ in the atmosphere (all else being equal, rising atmospheric CO₂ means more plant growth).

First, we statistically removed the rising temperature trends from the daily temperature records and re-ran the simulations. This showed that lower rainfall accounted for 83% of the decline in yield potential, while temperature rise alone was responsible for 17% of the decline.

Next we re-ran our simulations with climate records, keeping CO₂ at 1990 levels. The CO₂ enrichment effect, whereby crop growth benefits from higher atmospheric CO₂ levels, prevented a further 4% decline relative to 1990 yields.

So the rising CO₂ levels provided a small benefit compared to the combined impact of rainfall and temperature trends.

Closing the yield gap

Why then have actual yields remained steady when yield potential has declined by 27%? Here it is important to understand the concept of yield gaps, the difference between potential yields and farmers’ actual yields.

An earlier study showed that between 1996 and 2010 Australia’s wheat growers achieved 49% of their yield potential – so there was a 51% “yield gap” between what the fields could potentially produce and what farmers actually harvested.

Averaged out over a number of seasons, Australia’s most productive farmers achieve about 80% of their yield potential. Globally, this is considered to be the ceiling for many crops.

Wheat farmers are closing the yield gap. From harvesting 38% of potential yields in 1990 this increased to 55% by 2015. This is why, despite the decrease in yield potential, actual yields have been stable.

Impressively, wheat growers have adopted advances in technology and adapted them to their needs. They have adopted improved varieties as well as improved practices, including reduced cultivation (or “tillage”) of their land, controlled traffic to reduce soil compaction, integrated weed management and seasonally targeted fertiliser use. This has enabled them to keep pace with an increasingly challenging climate.

What about the future?

Let’s assume that the climate trend observed over the past 26 years continues at the same rate during the next 26 years, and that farmers continue to close the yield gap so that all farmers reach 80% of yield potential.

If this happens, we calculate that the national wheat yield will fall from the recent average of 1.74 tonnes per hectare to 1.55 tonnes per hectare in 2041. Such a future would be challenging for wheat producers, especially in more marginal areas with higher rates of decline in yield potential.

While total wheat production and therefore exports under this scenario will decrease, Australia can continue to contribute to future global food security through its agricultural research and development.

The Conversation

Zvi Hochman, Senior Principal Research Scientist, Farming Systems, CSIRO; David L. Gobbett, Spatial data analyst, CSIRO, and Heidi Horan, Cropping Systems Modeller, CSIRO

This article was originally published on The Conversation. Read the original article.