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Doubts over the Eraring Power Station closure

When Origin Energy announced recently that it planned to close its 2922-megawatt (MW) Eraring Power Station, the largest coal-fired power plant in the country accounting for 20% of NSW's generation capacity, the NSW Government said it would underwrite the construction of a 700 MW battery by the time Eraring ceases to operate in August 2025.

However, in the words of Chief Brody of Jaws fame who said, "You’re gonna need a bigger boat", surely NSW is "Gonna need a bigger battery."

Measuring energy and capacity

To begin, we need to clarify two important power industry measures. First, there is 'capacity'. The typical rating measure for power stations, it is the maximum output of electric power able to be produced at a point in time. For example, Eraring has the capacity to generate a maximum 2922 MW of power at a given instant.

Second, there is the measure of 'energy', which is the amount of power output over a period of time, measured in watt hours (Wh). The annual output rating of Eraring therefore being 25,596 gigawatt hours (GWh), (2922 x 8760 hours in a year/1000), 1 GW = 1000 MW. Energy is the usual power rating for batteries (or energy that can be stored), therefore talk of "construction of a 700 MW battery" is obscure, as it does not indicate the period of time the battery can continuously supply 700MW of power.

In reality, power plants will never deliver full capacity over an entire year, for reasons such as energy demand, and planned outages for maintenance. This is where 'capacity factors' come in. An annual 'capacity factor' is the actual output measured over a year, as a percentage of the theoretical maximum output.

Required battery capacity

In the five years to the end of 2021, the average annual output out of the Eraring plant was 16,012 GWh. That is, an average capacity factor of 62.5% (= 16,012 / 25,596), which is the equivalent of 1828 MW continuous power generated (1828 = 0.625 x 2922).

Suppose then that to replace Eraring, continuous power rounded up to 2000MW will be needed in future. And assume that Eraring will be replaced with solar power plus battery storage, so that when the sun is shining, the solar plant produces 2000MW continuously at full capacity. What size battery will be required?

Assume also that on average, there are 10 hours of full sun per day, therefore battery storage will be needed for the remaining 14 hours. Meaning 14h x 2000 MW = 28,000 MWh of output storage required. The battery will also need to be charged daily when the sun is shining, so an additional 28,000 / 10 = 2800 MW of continuous power generation will be necessary. To deliver 2000MW all day every day will therefore require a power plant capacity of 4800 MW, and 28,000 MWh of battery storage.

Making up for cloudy days

But of course, these numbers assume continuous sunlight in the daytime hours, day in day out. The power plant’s generating capacity and necessary battery storage blows out considerably in the event that the sun doesn’t shine.

To demonstrate, suppose we have one full cloudy day every three days. One day without the sun shining requires additional storage of 24 hours times 2000 MW, which equals 48,000 MWh. With two full days of sunshine before the cloudy day, that means 20 hours are available to generate the 48,000 MWh needed for one full cloudy day. That is, an additional 2400 MW of generating capacity required. So we are now up to a generating capacity need of 7200 MW, plus storage of 76,000 MWh across probably multiple batteries, to ensure continuous supply of 2000 MW of power.

Now sometimes there will be more than one cloudy day in a row, including partial cloudy days, and at other times, more than two days of sunshine between cloudy periods. So there will be occasions when the additional generating capacity will not be enough, and times when it will be too much. Such is the unpredictability of sunshine. Add in the fact that batteries don’t actually fully charge or discharge, and the numbers here are understated.

Similar calculations could be undertaken for wind generated energy, but being even more volatile than solar, would imply an even greater amount of generating capacity and storage required.

Clearly these calculations are simplistic, but they serve to give an order of magnitude, and highlight the inadequacies of the battery proposal, and the uncertainty that surrounds the intermittent nature of weather-dependent energy sources.


Tony Dillon is a freelance writer and former actuary. This article is general information and does not consider the circumstances of any investor.


Tony Dillon
March 25, 2022

Appreciate the comments, thanks.

With some comments, just to clarify, the intention of the article was not to suggest that a battery could in part be a substitution for a reduction in energy generation. To the contrary, it was intended to show the opposite.

The motivation for the article was to provide clarity to often confusing reports in certain sections of the media. Where for example with the Eraring closure, stating that a 700MW battery was to be built on the closure of a 2922 MW plant in the same sentence, confuses power with energy. The 700 MW is the power the battery can provide, but says nothing about its stored energy. We can calculate the energy the power plant can supply from such a statement, but not the battery’s. Some of the reporting would have us believe that batteries will somehow provide some cover for closing off a coal plant’s capacity. Clearly that’s not the case, which is what my simplified numbers tried to show.

And I wanted to make the point that batteries can only store energy, not generate it. Typically such mega batteries will deliver their energy in a matter of hours before needing to be recharged.

More emphasis needs to be placed on the role of batteries in stabilising grids, rather than covering for reduced capacity.

March 26, 2022

Unfortunately Tony, we need more clarity. Sure you have given a lesson that W (power) and Wh (energy) are not the same. However the idea that a battery is designed to replace a power station is flawed, as such you cannot calculate the battery size. Most of your article is dedicated to performing this calculation and highlighting the issues of intermittent generation. The Australian Energy Market Operator (AEMO) has some great resources for learning about the energy transition that will occur. Look for the integrated system plan, they model the firming support (battery/hydro/gas) for the grid after the coal generators choose to close down.

March 26, 2022

Hear hear Tony!
It's wonderful to have an actuarial study done of this proposed impending disaster.
I've been into the Eraring turbine hall and to think that a 700 MW battery will replace the 4 x 660 MW gensets humming away just beggars belief.
It is also apparent to me that commentators below have no idea of the energy requirements of industry. My own personal experience of both concrete casting and food manufacturing is that both electricity and gas are consumed on colossal scales.
For instance, when curing the modest, circa 3 - 4 tonne tunnel segments for a desalination plane intake and outlet tunnels, we used a modest 5 tonnes rated steam boiler. That is, it could steam 5 tonnes or 5,000 liters of water per hour into steam at 150 psi (tph), continuously. To do this, I personally measured the gas consumption at the meter, and it was 1 cubic metre (1,000 litres) of gas every 40 seconds!!
And 5 tph is a quite small steam boiler.
When in food manufacturing, we had 2 boilers; 1 x 11 tph and 1 x 6 tph. And we were a modest niche producer, annual turnover ~ $50M. We are now burning 3.4 cubic metres every 40 seconds!
Electricity consumption, while it was not in my remit, was equally huge. Consider, for example, when 40,000 litres of raw canola oil arrived at an ambient temperature of 30 Celsius and for cold filtering it has to be first refrigerated to -5 Celsius. That's some refrigerator and a lot of power!
I have quickly come to the conclusion that the proponents of alternatives to base load thermal power are having delusions. Do they really think that a car can be started with a AA battery or two? A 9V lantern battery then, surely.
Madness, and I for one, am not walking gaily off the cliff...

March 27, 2022

There are not 10 hours of full sun per day. The vast majority of solar farms are fixed panels which means for much of the early morning and much of the late afternoon you get very little production. On a good summers day you might get the equivalent of between 5-6 hours, if you aggregate the many hours of reduced production. In winter it is proportionately worse.

March 24, 2022

To put all this debate into perspective: "The energy consumption by the Ethereum blockchain has increased from an estimated 14.81TWh per year in January of last year to 112.4 TWh at the time of writing.
The spike, which is about 658%, places Ethereum’s power consumption at the same level as the Netherlands."

March 24, 2022

We need look no further than the UK to see where we might be heading re energy security. This morning their power generation was: Gas 60%, Nuclear 19%, biomass and coal 6%, Wind 2%, Hydro 1%, batteries nil. The UK power supply is a mess, but they are connected to Europe with a big extension cord, and are increasing their nuclear capacity!

March 24, 2022

Shutting down any coal fired power stations is a pipe dream, try and do any major manufacturing without coal, you're dreaming if you think a battery can suffice at any time.

March 23, 2022

Well of course Tony, but I wonder how many reading here are prepared to understand the huge import of your comment's calculations ?

Mark Buchanan
March 23, 2022

"Climate change delusion & the great electricity ripoff" published by professor Ian Plimer explains in great detail where we are headed. Get rid of the aluminium smelters will keep the lights on for a few more years. There won't be much left of industry to destroy so lets just continue to dig stuff out of the ground and grow our agriculture business. When the lights do go out then we will see some action !!

Trevor G
March 23, 2022

That’s alright, we can import our aluminium from China.

March 23, 2022

I have no wish to be unnecessarily critical given the good intentions of this article and the various commentators, but it and the comments are disturbingly naive. We have relied for many years on an east-coast grid and the various factors of baseload and peaking capacity, and supply and demand can only be modelled on a grid-wide basis. And that can only work if it is based on regional numbers aggregated up to the whole of grid. While I don't doubt that our energy regulator and generating and distribution companies have the combined capacity to do this, the ongoing negativity (or blind stupidity) of our current federal government towards renewables in general appears to have retarded progress for a decade. I suspect this will be another example where the ultimate solutions will be provided by state governments in collaboration with the regulator and corporations, and yet again the feds will be late to the party and largely irrelevant.

Trevor G
March 23, 2022

Perhaps the government should be considering nuclear energy if they insist on phasing out coal. I understand that the technology these days is much better with smaller reactors etc. We have the uranium and it ticks the net zero box. If we’re going to have nuclear subs than why not nuclear energy? Could be an interesting policy to announce before the election.

March 23, 2022

And remember on more thing that applies both to batteries and pumped hydro. Both a net consumers of electricity, meaning that it takes more energy to charge the battery or pump the water to the upper reservoir that what will be released as the battery is used, or the water let to flow out of the upper reservoir.

so, amongst all these maths and estimating, you have to add a factor for the loss of electricity that occurs simply from the storage (in a battery or reservoir) and re-generation of energy

The only thing that batteries and pumped hydro can do is work as a means of "balancing" supply (generation) and demand (usage)

March 23, 2022

Volvo's recent study compared Carbon Footprints of its fully electric XC40 Recharge and XC40 with an internal combustion engine (ICE), Depending on the source of electricity, it would take 86,000 Km of driving, for the European electricity generation mix, to breakeven. The emissions intensive manufacture of the EV's 70KwH battery is the primary cause, making the EV's manufacturing and refining stages 70% more CO2 intensive. Scaling up 70KwH to the grossly inadequate 700MwH Eraring battery may involve CO2 emissions equivalent to 10,000 Volvo EV batteries. For the suggested 76,000MWh battery, over 1 million Volvo EV batteries. That's a lot of real estate and a lot of emissions!

March 23, 2022

Correct the calculations are simplistic, as is your view of the electricity network. The battery is not designed to replace Eraring 1 for 1, but to add grid support. Spare capacity factor of other generators and new generation will pick up the slack.

March 23, 2022

This article conveniently ignores that not all renewable energy sources that will replace the Eraring capacity will be in the same place. Cloudy weather or non-windy weather is clearly an issue - that's why you don't build them all together. It shows why a grid wide solution is what is needed, not a narrow focus on individual plants etc.

That argument is a furphy if proper planning occurs - it isn't cloudy and non-windy in all parts of the connected grid at the same time. Never has been, never will. With a properly developed grid, it can be managed - and then the argument becomes nothing but an excuse for those wishing to keep us using dinosaur age fuel, rather then harnessing the free gifts bestowed by nature.

rod stephens
March 23, 2022

The other issue clearly overlooked is the time at night when there is the least demand on power. Electricity demand is not a constant.

March 23, 2022

Morning and evening are peak usage times with minimal assistance from solar.
Wind can be minimal in the morning (where I live a morning breeze is a rarity, but perhaps wind farms are different).
I suspect that storage will be the major supplier in the morning absent coal, gas or pumped hydro.

March 27, 2022

Your problem is that geographical distribution of generation means cost for trunking that power to where it is needed. Additionally you need to increase the number of renewable generators since your plan actually increases the probability that some part of the network is under cloud, I.e you are minimising the chances of major production losses by increasing the chances of some generation losses.

Believing that you can overbuild interconnects to somehow redirect production from everywhere cheaply is a rather typical fallacy. It’s not like plugging some double adaptors … even the interconnects we have built between the states are a balance between capacity and cost and they are currently a small fraction of total state energy demand, yet you surmise that we can do this across the entire rather dispersed renewable grid with the ability to trunk total energy demand due to weather conditions. It’s just not realistic when you actually do the engineering detail rather than hand-waving.


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