Been a while since my last post - not much to write about amidst...

Been a while since my last post - not much to write about amidst the robust discussions.  I am on much firmer ground in this thread.  As it involves lithium batteries and possible lithium consumption (relevant to PLS), I trust the Moderators will allow it to stand.

I am very sceptical about the SA $M550 energy plan that includes 100 MW battery storage, a Government-owned gas generator and a privately owned gas generator with government contract.

Firstly, I assume 100 MW reported in the media is for an hour (100 MWh battery).  If so, then all that would do is reduce the load around the maximum demand on a given day by 100 MW out of say 2500 MW.  Big deal – that does not justify a $250M investment.  On the downside, the reduced demand would displace more gas-fired generation from dispatch, further reducing system inertia (see overview at bottom).

Secondly, what does adding two large gas-fired generators at a cost of hundreds of millions achieve?  There is a fair bit of gas fired generation in SA, but it does not run because gas is too expensive or scarce.  Wind farms receive a free kick because the network operator (AEMO) is required to take their supply whenever the wind blows and to add supply from elsewhere when it does not.  Supply from the interconnector is relatively cheap, so it generally operates flat out on medium to high demand days.  That leaves the gas generators being forced into a role of balancing supply and demand.  Sometimes that means accepting low prices just to run.  And they are penalized if they can’t run after bidding in (where is the penalty on wind farms if the wind suddenly drops?).

Adding more gas generation under contract to the SA Government further marginalizes existing generators.  Once they pull out, there is no backup if the new generators cannot run (for maintenance, leak repairs, transmission line outages, etc.).  It should make more sense to negotiate with existing generators and support measures to secure affordable gas supply.

Leading up to the worst storm in 50 years that caused a System Black in SA at the end of September, approximately 1900 MW of load was supplied roughly by 50% wind, 33% import from Victoria, and 17% by internal gas-fired generation (333 MW, according to AEMO reports).  This ignores embedded generation.  At least 500 MW of gas-fired generation was available but not called upon to run.  The rough sequence of events was –

1. Lines faulted, leading to voltage collapse (post-contingent flows on remaining lines become so high that the receiving end voltage is a fraction of normal)
2. For various reasons, wind farm output reduced by half (which increased import from Victoria)
3. The ac interconnector overloaded and tripped
4. This left (very roughly) 1900 (demand) – 400 (wind) – 500 (import via ac interconnection) = 1000 MW to supply the load (of which only 333 MW was contributing inertia).
5. The remaining inertia of the islanded SA network was too low to keep rate of change of frequency slow enough for under-frequency load shedding to operate
6. Frequency plunged until the lights went out

I would guess just 200 MW more of gas fired generation (this can easily be modeled) could have:

* reduced pre-contingent interconnector flow by 200 MW (more head-room to cope with overload),
* provided more voltage support within SA,
* reduced flows between terminal stations within SA (depending on which generators were scheduled on), and
* (even if the interconnector tripped) reduced rate of change of frequency enough to allow load shedding to operate.

Why did AEMO not schedule another 200+ MW ahead of a forecast 1 in 50 year storm?  Probably because dollars count more than energy security.  Engineers have built a fairly robust electricity network that could operate effectively if network controllers could occasionally over-rule the market systems.  Unfortunately, economists are telling politicians that “the Market will provide if only the market signals are not distorted by interference from engineers”.

Guess who politicians listen to?

I have only described the big SA black out.  Similar issues of economics “trumping” engineering have occurred several times to SA in the past 6 months.  The Australian Energy Market is broken – the physical system is GENERALLY not.


Notes on inertia

Newton’s First Law of Motion (the Law of Inertia) runs along the lines of - “A body in motion continues its motion until acted upon by an external force”.  In other words, it resists any attempt to change its velocity.  Rotational inertia is similar to linear inertia, except that the body in motion resists any attempt to change its rotational velocity.

An electricity system tries to run with frequency of 50Hz and voltages within a fairly tight range.  Rotating inertia helps to maintain frequency following disturbances and loss of generation, interconnectors or load.

Rotating inertia is created by steam, gas and hydro generators, from some older type induction generator wind turbines, and from synthetically derived inertia in newer wind turbines (IF provided – fitting it would reduce MW output for which the wind farm is paid).

It is also provided by rotating loads such as compressors, sewage pumps, air conditioning, rolling mills, mining equipment, escalators, food processing plants, printing presses, etc.

The rotating loads and generators rely on tightly controlled frequency (all sorts of horrible things start to happen to them - even during small deviations).  

Bigger loads of 10+ MW are NOT going to be supplied by batteries.  Batteries do not provide inertia for the system.  In fact, they tend to reduce it by displacing conventional generation.  In time, perhaps fancy electronics may allow batteries to produce synthetic inertia (can anybody tell us whether that is already the case, and provide a reference?).