Is it time to say goodbye to a unit or two at Tarong?

The rate of solar penetration in Queensland is simply mind-blowing. Every day, I read of a new project. So with all of this new capacity coming on, do we still need all of the State owned coal plant?

The first response to this question is, ‘we need power at night’. This is, of course, true; however, the evening peak need not be supplied by the State owned coal assets.

In a previous blog, I described how the combination of large scale solar and aero-derivative gas turbines, working in concert, provide firm, reliable power throughout the day and over the evening peak (at a very low average carbon intensity). Battery storage and pumped hydro also offer, feasible alternatives as firming capacity (we could immediately make better use of Wivenhoe Pumped Storage, for example).

In a future Queensland, with substantial solar capacity on-line, we will shortly be faced with a significant oversupply of daytime power. As a State, we can choose to do nothing; or we can choose to facilitate this change by ‘making space’ in the daytime market for more solar, by removing some of the State owned, high carbon intensity generation capacity from the system.

There is no shortage of enthusiasm to invest in the Queensland power sector, and no shortage of enthusiasm to invest in low carbon firming capacity. The NEG (National Energy Guarantee) and a free market will allow the private sector to respond, given sufficient notice.

I am not talking about the sudden removal of 1400 MW from the system, I am suggesting a staged, planned and well announced withdrawal, one unit at a time, in a manner that will allow the private, low carbon sector, to respond.

So, why Tarong? Tarong is the oldest of the State owned coal plant still in service. Unit 1 was commissioned in 1984, making it thirty-four years old. Tarong is a sub-critical plant, meaning that its steam temperatures and pressures are lower than modern coal plant, and therefore its efficiency (and hence carbon intensity) is a bit lower. Leave the newer, supercritical, Tarong North running for longer as it is more efficient and has lower carbon intensity.

Old steam plant, does not respond well to cycling (frequent changes in load or start stop cycles), as thermal fatigue propagates micro-cracks in the various metal components used in the plant. This means that, as daytime supply increases (and daytime prices drop), the State will be given the choice of either increasing its maintenance spend, or staying on-line at steady load, uneconomically, during periods of low prices (and also pushing out new entrants with lower carbon solutions).

Curtailing generation at Tarong will also have the added benefit of reducing water demand the in Burnett and Wivenhoe catchments. Freeing up this water capacity for agricultural and other uses (such as making hydrogen).