Climate change

May 6, 2010

Santos chief’s gassy vision Part 2 – is gas almost as good as nuclear?

This is part 2 of an analysis of some recent public statements by Santos CE David Knox. If you haven’t already done so, read this first.

In Part 2, I address the following statement:

One thing I would note about advocates of nuclear is that they often ignore natural gas and its role in power generation. Often, they gloss over the existence of gas and simplistically abbreviate the debate to one of ‘if renewables fail, then we have to go nuclear’ as was reported in last week’s Advertiser. Gas already delivers close to 70% of the carbon intensity reduction that a shift from coal to nuclear would achieve in eastern Australia, but at far less expense and with none of the sociopolitical challenges. In short, the real competitor to nuclear power in Australia will be natural gas.

Is this claim credible? Let’s crunch the numbers, working from first principles.

For simplicity, I’ll compare the most efficient gas technology (combined cycle gas turbines; CCGT) and Generation III nuclear power (thermal reactors — the type of reactor that will be most commonly deployed over the next few decades).

First, consider the greenhouse gas intensities. I’ll derive numbers here from the recent meta-analysis in Energy by D. Weisser (2007). These include upstream and downstream emissions, so are more conservative than the optimistic figures Knox gives for gas in his talk, which only considers operating stage emissions (aside: these are zero for nuclear):

Coal = 950 to 1,250 kg CO2eq / MWh
CCGT = 440 to 780 kg CO2eq / MWh
Nuclear = 3 to 24 kg CO2eq / MWh

Next, consider Australia’s current electricity demand. As noted here, this is 250,000 GWh per year. Of this, 78% comes from black/brown coal, 15% from gas, and 7% from hydro (see Garnaut Review). So, switching from coal to gas, or coal to nuclear, involves replacement of ~200,000 GWh of electricity per year (23 GWe average).

First, based on Weisser’s review, 200 TWh of coal-fired electricity should generate 190 – 250 million tonnes (Mt) of CO2eq. If this coal-fired electricity was to be entirely replaced by CCGT, it would result in 88 – 156 Mt of annual emissions from power generation (an 18 to 65 % reduction [incorporating the full range of uncertainty given by Weisser’s figures]). If the coal was instead replaced by nuclear, it would be 1 – 5 Mt (a 97.5 to 99.8 % reduction).

Alright, let’s take the best-case scenario for gas, and the worst-case for nuclear and coal. In this case, nuclear results in a reduction of 245 Mt of CO2eq. Gas results in a reduction of 162Mt of CO2eq. On this basis, gas would result in a 65 % of the reduction that a shift from coal-to-nuclear would achieve. That’s the absolute best-case scenario for CCGTs (the worst case is just 18 % of what nuclear could achieve).

However, looking at it another way, in this best-case scenario for CCGTs, Australia’s cumulative yearly GHG emissions from the electricity sector would be 17 times greater than if we went for nuclear (88 Mt vs 5 Mt). Food for thought.

But look again at what Knox actually says:

Gas already delivers close to 70% of the carbon intensity reduction that a shift from coal to nuclear would achieve in eastern Australia

Already? I don’t think so. From the above figures, gas generates roughly 37 TWh of electricity per year. Since most of this comes from steam and open cycle turbines, the upper bound on emissions intensity for CCGT of 780 kg CO2eq / MWh  is more appropriate here. On this basis, gas currently saves ~20 Mt per year. A shift from coal-to-nuclear would save ~245 Mt.

Okay then, let’s look at it from another angle. Australia’s total GHG emissions inventory from the energy sector (fuel combustion + fugitive emissions from electricity, transport etc.) in 2007 was 408 Mt (see table above). What if we use this as the reference point? We can easily work out that if our current gas-fired electricity had instead been supplied by coal at the high emissions intensity level, this figure would have been closer to 428 Mt. On this basis, gas already results in about a 5 % reduction in our energy-sector carbon intensity. A full nuclear replacement of electricity only) would drop this to closer to 160 Mt — a 60 % reduction (prior to replacement of transport fuels etc.).

Sorry Santos, but I just can’t make your strange gassy claim work. (A prize to any of my readers who can!).  It simply doesn’t stack up and I suggest you don’t repeat it in public in the future. Indeed, I conclude that natural gas is already doing very little to mitigate our carbon intensity, and even a massive wholesale switch to CCGT for electricity generation would be nowhere near as effective in cutting emissions as a dash to nuclear. Nor is gas a medium- or long-term solution for energy security, as I explained here.

So, I’m left to reiterate the following statement — now hardened with the above analysis:

The UK is now paying dearly for their dash for gas, following the coal mine closures of the 1980s. Their once-abundant North Sea fields are rapidly depleting. Again, Australia should take note of this warning. We must not go down the natural gas-for-coal substitution route. It would be long-term economic suicide. Also, gas is a carbon-based fossil fuel, releasing 600kg of carbon dioxide per megawatt hour. Unlike the situation for uranium power, the electricity price is strongly tied to the fuel price for gas. A spike in the gas price means big jumps in power prices. Cheap uranium energy is a much more secure proposition. Gas is best reserved to meet occasional peak power demands, not baseload needs.

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