Last updated April 9, 2019 at 5:40 pm
An imperfect but practical mix of renewable and conventional power sources is essential if the world is to reduce carbon dioxide emissions in a timely manner, says Australia’s Chief Scientist.
The cliffs of Cape Grim tower over the breaking waves at the north-western tip of Tasmania. Perched above is a research station that collects samples of the most pristine air in the world, carried by the prevailing westerlies thousands of kilometres across the Indian Ocean.
The message these samples carry is grim indeed. Every year since recording began in 1976, the carbon dioxide concentration has risen. I’ve often looked eagerly at the graph, hoping to see the downturn in the slope resulting from the adoption of national and international agreements to reduce emissions. It’s not there. Instead, the slope of the graph is now steeper than ever.
Our planetwide efforts to reduce carbon dioxide emissions are not working. One reason is that the task is much bigger than most people can fathom. The world runs on energy and civilisation depends on it. The existing energy supply system is enormous and replacing it with low-emissions alternatives is a journey that will take decades rather than years.
But perhaps the biggest problem is that we have no sound roadmap for how to get there. Some would block the path altogether, by denying the problem. Others unintentionally slow the journey, by seeking perfection.
‘Perfection is not the way to success’
As an engineer, I can tell you that pursuing perfection is not the way to achieve success. Design a perfect bridge and the expense will mean that it never sees the light of day. What bridge designers do is optimise for the key parameters of safety and cost over an expected lifetime.
A perfect world would indeed run on solar and wind electricity, supplemented by batteries, pumped hydroelectricity, compressed air and stored hydrogen as energy reservoirs for the dark and windless intervals. But the reality is that right now solar and wind provide only 6% of our worldwide electricity needs and storage systems are collectively a drop in the ocean.
If we were to close down all the coal fired electricity generators in the next ten or twenty years, we could try to replace them through a massive commitment to building solar and wind, but it is difficult to conceive that we could build enough storage in that timeframe. Without this storage there would be electricity shortages and the political backlash that slows the path to the perfect world.
So wherein lies the possible but imperfect solution?
To support the adoption of larger quantities of emissions-free solar and wind generation it will be necessary to supplement them with conventional electricity sources such as natural gas fired electricity or catchment hydroelectricity (in which rainwater falling in large catchment areas fills massive dams fitted with generators).
However, in Australia we haven’t built a large-scale catchment hydroelectricity system for more than fifty years and the likelihood of building more in future is slim. Geothermal, wave and tidal generation, and coal fired electricity with carbon capture and sequestration are not ready to operate at the scale we need.
Although nuclear electricity can operate at scale, it is politically fraught and too slow to construct in many countries. Biofuels can also operate at scale but they are controversial because it is not clear to what extent they lower emissions and scaling up takes away land and water needed for food production and forests.
The role of natural gas
That leaves natural gas. Not perfect – but very good. The carbon dioxide emissions from modern natural gas generators are only 40% of the emissions from the very best modern coal generators. They have another advantage over coal in that their output can be ramped up and ramped down very quickly. This means that they only have to operate when solar and wind generation cannot meet demand, making their overall contribution to emissions even lower.
In the US, driven by low domestic prices, the use of natural gas has grown dramatically, in many cases displacing coal, with the result that energy-related emissions there have fallen 15% since the increase in natural gas production began in the mid 2000s.
Natural gas generators are compact, high capacity and in a mature stage of their design cycle. We can build them as quickly as needed to support increased variable solar and wind electricity generation.
If we could agree to utilise our abundant natural gas to support the roll out of more wind and solar electricity, while managing local environmental concerns about natural gas production and accepting that it is very good rather than perfect, we would be able to lower emissions more quickly.
And at Cape Grim, the news would start getting cheerier.