Although Tesla’s Powerwall battery storage is likely to be a disruptive force for electrical energy systems around the world, it is not going to supplant the major forms of electrical energy storage anytime soon, and is ill-suited to storing energy over longer timeframes such as between seasons.
When powering a modern economy, electrical energy comes with one major disadvantage – it requires that supply and demand must be balanced within strict limits at all times, as an imbalance will lead to voltage changes that can damage connected equipment and even the networks themselves. This challenge of network balancing has conventionally been managed by keeping the electricity “stored” in fossil or nuclear fuels until it is required.
This presents a storage problem for renewables, especially weather-dependent wind and solar. As we cannot hope to store the weather, we have to instead store the generator’s output, which is the electricity.
This is what Tesla’s Powerwall and the bigger Powerpack both intend to help with. At full capacity Tesla’s first Gigafactory is planned to produce batteries totalling 35 GWhe (gigawatthours electrical) each year. It’s an impressive figure – enough to power England, Scotland and Wales for about an hour.
However, to put this into perspective, Great Britain (Northern Ireland is counted separately) stores on average 800 times as much energy in its coal stockpiles alone. The chart below shows the total electrical energy equivalent stored in its coal stockpiles over the past two decades, with the amount stored tending to peak each autumn in preparation for an increase of electrical demand over winter. (The 2009 spike was partly caused by power plants stocking up on cheap coal after the financial crash). Over these two decades Great Britain has averaged just over 30,000GWhe of electrical energy stored this way.
GB electrical energy stored in coal stockpiles since 1995. Author's calculations based on DECC data, Author provided
Great Britain also has up to 32,000GWh of natural gas in long-term storage (which dropped from 41,400GWh earlier this year). While most is used directly for cooking or heating, the rest is consumed to make electricity. It’s tough to know exactly what proportion this is, since it’s difficult to apportion gas that came directly from storage as opposed to gas that came via liquified natural gas ships or through pipelines.
However if we estimated that 30% ends up in power plants with an efficiency of 50% then the electrical energy stored is around 4,800GWhe. Again, far more than Tesla’s Gigafactory annual 35GWhe output.
It’s even harder to tell how much energy is stored in Great Britain’s reserves of nuclear fuels of uranium and plutonium – the information is classified.
Fuels are Still Needed
These simple calculations show Great Britain remains overwhelmingly dependent on fossil fuels to store its electrical energy. The country needed nearly 800 GWhe of electrical energy in an average day last year, which suggests that batteries would have some way to go to supplant fuels, even for a day.
GB daily electrical energy demand in 2014. Own calculations; DECC data
This storage of vast amounts of energy in fossil fuels is typical of many modern economies as we have become accustomed to the flexibility that they allow us; they are able to decouple supply from demand by location as well as by time, and at a phenomenally low cost for storage.
Regardless of the falling price of batteries (Tesla’s or anyone else’s) they are always likely to be ill-suited to the long-term seasonal storage of thousands of GWhs of energy. Batteries are simply the wrong technology.
What is the Answer Then?
But the fuels we mainly rely on for electrical storage – coal and gas – are not ultimately sustainable, and contribute to increased CO2 emissions if burned without carbon capture. So if fossil fuels and batteries are not the answer to the seasonal storage of electricity – what is?
Carbon capture and storage holds out the promise of the continued use of fossil fuels, with all the fuel storage advantages this would allow. Additionally, fuels such as hydrogen or synthetic methane could be generated using low-cost, low-carbon energy and stored at scale too.
Comparison of Tesla’s 10kWh Powerwall with 4kg of coal. Powerwall image © Tesla, Author provided
A continued use of fuels isn’t necessarily competition for Tesla’s disruptive new battery packs; the two complement each other. They are different horses for courses, as not all energy storage is the same, and in the long run we are going to require both.
Tesla’s batteries aren’t about to take over the world just yet, especially if you count fuels as “energy storage”. But if the company goes on to produce a similarly disruptive force in the area of power-generated fuels, that really would be a gamechanger. Lets hope it or some other firm does soon – then we would truly have the components to decouple our economies from carbon emissions.