Originally Posted by
Jantar
The Ahuroa Gas Storage, built by Contact, can store up to 18 PJ of gas. To put that in terms of electrical storage, that is the equivalent of 1800 GWH of electrical energy and cost just shy of $400 M. So at first glance it looks like a cheaper option than Onslow. But that is not renewable, and it cannot be used to buffer intermittent generation as easily. Where it is used it is still only in a ratio of 1:1, not 1:2, so 2400 MW of fast start gas fired plant would be needed to do the same job as Onslow.
It also uses gas to run the compressors to feed the gas into the field, and uses more gas to heat the gas coming out of the ground. To recover that 18 PJ of gas actually requires buying 27 PJ of gas off the market between compressing and re-heating. Thus gas from storage being used as generation has a much higher marginal cost than gas purchased directly from the well.
Add in the Opex for gas fired plant and it becomes quickly obvious why electricity prices spike up to the hundreds of dollars per MWh even when there is no overall shortage. Opex for CCGT plant like at Huntly or Stratford is very high, around $40 per MWh plus fuel cost, while Opex for hydro plant is around $2 to $3 per MWh. Hydro fuel is nil for normal hydro plant, but will have a cost at Onslow.