The Trouble with Energy Storage

Energy Storage - The Holy Grail for intermittent electrical generators.

Reading the tweets and articles from the wind and solar industries (and their avid followers) you could be forgiven for thinking that large scale energy storage was a done deal. Something that just needed the bureaucrats in Westminster or Berlin or Washington to rubber stamp.

Sadly though, large scale wind/solar energy storage is not only not a done deal it is not even on the horizon. Even if it was it would still be very far from being a “solution” to intermittent and dilute electrical generation. But more on why that is in a later post.

First of all lets be clear about what I mean by energy storage.

In a way, all current thermal generation and hydro depend on “energy storage” The difference between energy storage at (say) a coal plant and a wind farm is that the coal plant stores its energy pre-generation (i.e. as raw fuel) whereas a wind turbine has to convert its energy into a non-electrical form after excessive generation in order to store it. So the wind turbine has to convert its excess energy into some form of fuel to be stored for later use. The coal plant simply does not use the fuel until it is needed.

(by the way I am using coal plant here because it is a good comparator – not because I am a fan of coal generation – I prefer nuclear)

Typically the front runners for renewable energy post generation fuel storage revolve around two technologies:

1. Pumped hydro (pumping water up hill into a reservoir)
2. Or as is the fashion - in some form of Battery.

Pumped Hydro.

Pumped hydro is an old and proven technology. It existed a long time before the current wind/solar obsessions. Originally pumped storage facilities ( like Dinorwig in Wales) were built to store energy when the price was low (typically at night) and then sell that stored energy at peak demand (when prices were high). Using this model, pumped hydro works very well. It is a profitable and very worthwhile addition to the Grid.

But things change when you try and use it to store excess solar and wind energy. You essentially break the pumped hydro economic model, especially with solar PV. (See Speigel Online article here )

You have to buy in energy when prices and demand is high while sacrificing your profitable market as well. Then you then have to sell on when prices and demand is low.

It does not work. Even if you created some subsidy regime to support this broken model, the number of potential pumped hydro sites are very limited anyway.

But at least, individual pumped hydro sites can store relatively large quantities of electricity.

Although UK pumped hydro could not deliver the energy quickly enough to actually take over the whole UK grid, they do hold enough energy to power the entire UK grid for about 1 hour. 

While that may not sound much, it is overwhelmingly better than any form of battery storage.

When we get to battery style storage the practicality and price viability of large scale energy storage falls off a very high cliff.

Batteries

The biggest battery in Europe is in Leighton Buzzard in the UK. It can store 10MWh of electricity. It could (say) store half the output from a single small 10MW wind farm running at maximum output for two hours. It cost £20 Million. An average UK demand is around 30GWh. So this single battery would power the entire UK grid for about 1.2 seconds.

OK, you may say – let us distribute/duplicate it and use a cheaper technology After all why not have a cheaper 10MWh battery for every (say) 5 wind turbines? You know - Spread it out a bit.

Lets look at the (arguably) most viable and cost effective large scale battery technology available today – Vanadium Redox flow batteries.

(Incidentally - this is VERY clever technology and has many potential applications – I am not knocking the technology – only the application) .

Flow batteries store the energy in the electrolyte. The consequence of this is that theoretically the only limitation to the their storage capacity is the amount of electrolyte you can to store. 

Currently Vanadium Redox batteries store about 20 Wh per litre of electrolyte. So for 10MWh you need to store around 500,000 litres of highly corrosive Sulphuric Acid based electrolyte.

Lets say technical innovation decreases that by a factor of 10. You would still need to pump/store/process 50,000 litres or nearly 100 tonnes of electrolyte. 

That is for 10 MWh. Or 1.2 seconds of nationwide supply.

So, why not just store more electrolyte? Simple eh?

But remember, this stuff is lethal. It is massively corrosive and is a liquid. Then remember this is one SMALL wind farm.

Multiply that by thousands of wind farms. Then avoid killing anyone or regularly risking massive environmental pollution. That really is a challenge!

Of course there are other technologies (Lithium-ion being the other main and more expensive player) but whatever you look at, the problems of large scale energy storage are immense. They are effectively intractable.

Remember, what I have discussed above is the LATEST and most promising technologies. On Twitter people often eulogize about lead-acid batteries or compressed air, but really their capabilities are far below pumped hydro or flow batteries.

But Tom Murphy on his appropriately named blog Do The Math has done a very good analysis of a theoretical (USA) National Lead Acid Battery and its practicalities On this Link

A very interesting post on the EROEI (Energy Returned On Energy Invested) on  storage with RE has been written by John Morgan  On This Link

Large scale post generation energy storage is not viable.

Bit even worse – not only is it not viable, it is also potentially very, very (and appallingly) dangerous.

But more on that in another post.

(Here I am not considering issues with charge/discharge rates, resource availability or lifetime cycle expectancy – they all just make things worse)