Saturday, 2 May 2015

Energy storage and nuclear power

A couple of days ago, Elon Musk, the billionaire serial business creator, fronted a product launch at one of his companies - Tesla Motors.  Telsa is renowned for building high quality electric cars but this launch wasn't for a car: it was for batteries.  Elon was explaining how the battery technology originally developed for the Tesla cars will now be available to home owners and companies to provide electricity storage.  The news has naturally focused on the $3500 10kWh domestic battery pack, but I think the real killer is in the industrial, grid scale scalable storage that they are going to offer.  This is interesting enough for one un-named utility to already put their name down for 250MWh of capacity, and indeed its the industrial/utility side that analysts see as the major market.

Which got me thinking: how much solar/wind/etc generation and Tesla storage could you buy for, oooh, say the cost of EDF's proposed Hinkley Point C nuclear power station?  The estimated cost of Hinkley Point C keeps going up, but lets use the original EDF £16bn figure here.  Hinkley Point C is a 3.2GW station, so we need to try to match that using renewables for £16bn ($24.22bn at the current exchange rates).

Now first off I have to say that this is just me getting some ball park figures: its not an engineering analysis.  I just want to see if Tesla's batteries plus renewable generation can give us a stable base load power source to the National Grid that would look to the outside world as though a 3.2GW nuclear station were sitting there. To do this we'll need more than 3.2GW of renewable generation capacity: we not only have to match the nuclear station's peak output, but also fill the batteries so that we can also supply power at night and on calm, overcast days.  Lets assume that we want 3 days worth of energy in the batteries to cover these low generation periods to start with.

Now we don't know what cost Tesla's commercial utility scale power packs are going to be, but we do know that the residential 10kWh ones will cost $3500, or in other words $350 per kWh.  I would assume that an economy of scale kicks in when you're buying a huge amount of batteries for utilities that would reduce this $350 per kWh figure for the utility scale one.  Lets say it knocks $50 off the figure - yes, that's a wild, stab in the dark guess, but its seems vaguely sensible and conservative.  So we need three days worth of 3.2GW generation stored:

3 days x 24 hrs x 3.2GW = 230.4GWh = 230400000kWh

At my estimated $300 per kWh that will cost:

$300 per kWh x 230400000kWh = $69120000000 = $69.12bn.

Ah, that's blown the $24.22bn budget already, and we haven't even paid for any of the renewable generation yet - this is just the cost of 3 days of Hinkley Point C sized output storage.

Lets plough on though, and see what the final number is.  For large scale renewable power generation, the costs are falling (ie going the other way to nuclear!).  Large scale wind turbines cost $1.5m-$2m per MW of output.  Large scale solar farms cost ~ £1.6M ($2.42M) per MW if I've read the slightly confusing Solar Trade Association report right.  Lets pick $2M per MW as reasonable wet finger guesstimate of cost for both wind and solar then.

We need to generate more than 3.2GW though: we want to match Hinkley Point C's output when we're generating at our peak and have lots of excess generation capacity available then to fill up the Tesla batteries for the periods when its calm and dark.  Lets guess again and say that we need twice the generation capacity to do this.  We might need more, we might need less, but 6.4GW again seems like a reasonable first guess.

At our $2m per MW estimate of renewable generation costs, this 6.4GW will cost $12.8bn.  Well at least that bit is under the $22.42bn Hinkley Point C budget!

How much energy storage can we get for the $9.62bn difference?  At $300 per kWh estimate we get:

$9.62bn / $300 per kWh =~ 32GWh

So that's about 10 hours worth of storage if we're going to be sucking 3.2GW from the battery system. That's still not bad, but will it be enough to allow large scale solar and wind to challenge nuclear for base load power generation in a decarbonised Grid?  Some people think so, and the numbers will fall on the side of renewables+batteries if their cost trajectory keeps going down in the same direction whilst nuclear's costs keep rising.  It will be interesting to see how this plays out.