Posts Tagged ‘Battery’

Is a UK grid-scale battery feasible?

April 26, 2019

This is quite a technical article, so here is the TL/DR: It would make excellent sense for the UK to build a distributed battery facility to enable renewable power to be used more effectively.

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Energy generated from renewable sources – primarily solar and wind – varies from moment-to-moment and day-to-day.

The charts below are compiled from data available at Templar Gridwatch. It shows the hourly, daily and seasonal fluctuations in solar and wind generation plotted every 5 minutes for (a) 30 days and (b) for a whole year from April 21st 2018. Yes, that is more than 100,000 data points!

Wind (Green), Solar (Yellow) and Total (Red) renewable energy generation for the days since April 21st 2018

Wind (Green), Solar (Yellow) and Total (Red) renewable energy generation for 30 days following April 21st 2018. The annual average (~6 GW) is shown as black dotted line.

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Wind (Green), Solar (Yellow) and Total (Red) renewable energy generation for the 365 days since April 21st 2018. The annual average (~6 GW) is shown as black dotted line.

An average of 6 GW is a lot of power. But suppose we could store some of this energy and use it when we wanted to rather than when nature supplied it. In other words:

Why don’t we just build a big battery?

It turns out we need quite a big battery!

How big a battery would be need?

The graphs below shows a nominal ‘demand’ for electrical energy (blue) and the electrical energy made available by the vagaries of nature (red) over periods of 30 days and 100 days respectively. I didn’t draw the whole year graph because one cannot see anything clearly on it!

The demand curve is a continuous demand for 3 GW of electrical power with a daily peak demand of 9 GW. This choice of demand curve is arbitrary, but it represents the kind of contribution we would like to be able to get from any energy source – its availability would ideally follow typical demand.

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We can see that the renewable supply already has daily peaks in spring and summer due to the solar energy contribution.

The role of a big battery would be cope to with the difference between demand and supply. The figures below show the difference between my putative demand curve and supply, over periods of 30 days and a whole year.

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I have drawn black dotted lines showing when the difference between demand and supply exceeds 5 GW one way or another. In spring and summer this catches most of the variations. So let’s imagine a battery that could store or release energy at a rate of 5 GW.

What storage capacity would the battery need to have? As a guess, I have done calculations for a battery that could store or release 5 GW of generated power for 5 hours i.e. a battery with a capacity of 5 GW x 5 hours = 25 GWh. We’ll look later to see if this is too much or too little.

How would such a battery perform?

So, how would such a battery affect the ability of wind and solar to deliver a specified demand?

To assess this I used the nominal ‘demand‘ I sketched at the top of this article – a demand for  3 GW continuously, but with a daily peak in demand to 9 GW – quite a severe challenge.

The two graphs below show the energy that would be stored in the battery for 30 days after 21 April 2018, and then for the whole following year.

  • When the battery is full then supply is exceeding demand and the excess is available for immediate use.
  • When the battery is empty then supply is simply whatever the elements have given us.
  • When the battery is in-between fully-charged and empty, then it is actively storing or supplying energy.

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Over 30 days (above) the battery spends most of its time empty, but over a full year (below), the battery is put to extensive use.

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How to measure performance?

To assess the performance of the battery I looked at how the renewable energy available last year would meet a levels of constant demand from 1 GW up to 10 GW with different sizes of battery. I consider battery sizes from zero (no storage) in 5 GWh steps up to our 25 GWh battery. The results are shown below:

Slide15It is clear that the first 5 GWh of storage makes the biggest difference.

Then I tried modelling several levels of variable demand: a combination of 3 GW of continuous demand with an increasingly large daily variation – up to a peak of 9 GW. This is a much more realistic demand curve.Slide17

Once again the first 5 GWh of storage makes a big difference for all the demand curves and the incremental benefit of bigger batteries is progressively smaller.

So based on the above analysis, I am going to consider a battery with 5 GWh of storage – but able to charge or discharge at a rate of 5 GW. But here is the big question:

Is such a battery even feasible?

Hornsdale Power Reserve

The Hornsdale Power Reserve Facility occupies an area bout the size of a football pitch. Picture from the ABC site

The Hornsdale Power Reserve Facility occupies an area about the size of a football pitch. Picture from the ABC site

The biggest battery grid storage facility on Earth was built a couple of years ago in Hornsdale, Australia (Wiki Link, Company Site). It seems to have been a success (link).

Here are its key parameters:

  • It can store or supply power at a rate of 100 MW or 0.1 GW
    • This is 50 times smaller than our planned battery
  • It can store 129 MWh of energy.
    • This is just under 40 times smaller than our planned battery
  • Tesla were reportedly paid 50 million US dollars
  • It was supplied in 100 days.
  • It occupies the size of a football pitch.

So why don’t we just build lots of similar things in the UK?

UK Requirements

So building 50 Hornsdale-size facilities, the cost would be roughly 2.5 billion dollars: i.e. about £2 billion.

If we could build 5 a year our 5 GWh battery would be built in 10 years at a cost of around £200 million per year. This is a lot of money. But it is not a ridiculous amount of money when considering the National Grid Infrastructure.

Why this might actually make sense

The key benefits of this kind of investment are:

  • It makes the most of all the renewable energy we generate.
    • By time-shifting the energy from when it is generated to when we need it, it allows renewable energy to be sold at a higher price and improves the economics of all renewable generation
  • The capital costs are predictable and, though large, are not extreme.
  • The capital generates an income within a year of commitment.
    • In contrast, the 3.2 GW nuclear power station like Hinkley Point C is currently estimated to cost about £20 billion but does not generate any return on investment for perhaps 10 years and carries a very high technical and political risk.
  • The plant lifetime appears to be reasonable and many elements of the plant would be recyclable.
  • If distributed into 50 separate Hornsdale-size facilities, the battery would be resilient against a single catastrophic failure.
  • Battery costs still appear to be falling year on year.
  • Spread across 30 million UK households, the cost is about £6 per year.

Conclusion

I performed these calculations for my own satisfaction. I am aware that I may have missed things, and that electrical grids are complicated, and that contracts to supply electricity are of labyrinthine complexity. But broadly speaking – more storage makes the grid more stable.

I can also think of some better modelling techniques. But I don’t think that they will affect my conclusion that a grid scale battery is feasible.

  • It would occupy about 50 football pitches worth of land spread around the country.
  • It would cost about £2 billion, about £6 per household per year for 10 years.
    • This is one tenth of the current projected cost of the Hinkley Point C nuclear power station.
  • It would deliver benefits immediately construction began, and the benefits would improve as the facility grew.

But I cannot comment on whether this makes economic sense. My guess is that when it does, it will be done!

Resources

Data came from Templar Gridwatch

 


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