(From our GLD October 2018 newsletter)
Battery Power for the UK

By Julian Hawins

There has been a lot of hype recently about using batteries for grid storage, to overcome two key limitations of wind and solar power: intermittency and non-dispatchability. So, how practical is this?

Rechargeable batteries use reversible electrochemical processes to store and supply electric power. Capabilities:

• Size ranges from tiny to very large. (Sizes in common use range from tiny watch batteries to grid storage such as Tesla's "Hornsdale Power Reserve" in South Australia.)
• Easy and convenient to use. (No mechanical components or combustion required.)
• Moderate energy density. (Up to about 0.5 MJ/kg, compare up to 50 fuel for diesel fuel, 20 for consumable food, 0.05 for supercapacitors, 0.3 MJ/kg for water in a 100m high dam).
• Cost is competitive for small devices, less so for large storage (batteries are fairly modular, so cost increases roughly in proportion to size; some other technologies have major economies of scale).
• High efficiency of recovery (can be up to about 90%, compare around 80% for pumped storage, 40% at best for chemical fuels both created and burned efficiently).
• Reasonable lifetime, but not huge. (Well cared for batteries tend to lose capacity after thousands of cycles, but quick charging/discharging can wear them out quickly. Pumped storage could potentially last for centuries with regular maintenance and replacement of parts.
• Very rapid response to events - can be in milliseconds.

Limitations:

• Current technology probably won't support huge storage at reasonable cost. (Hornsdale power reserve battery stores 129 megawatt-hours (460 GJ) of energy, (about 25 minutes' peak output of the nearby wind farm). Compare Dinorwig pumped-storage hydroelectric scheme in Snowdonia's 9,100 megawatt-hours (33,000 GJ or 33 TJ).
• Limited supplies of key minerals such as lithium could limit use on a very large scale.
• Self-discharge rate of several percent per month when not in use, also can be damaged by leaving completely discharged.

The one thing they can definitely be used for is to handle short term fluctuations in power. The South Australia battery has already switched in once to a response to a coal-fired power station failing hundreds of miles away, mitigating the resulting impact, and has provided much of the state's normal frequency control.

But what about longer term storage? That depends on the timescale.

Time-shifting means capturing solar power in the day and using to satisfy peak power needs in the evening, ultimately overnight. Some people are already doing this, and it is potentially financially viable if you have existing solar power, due to the difference between what you pay to buy electricity from the grid, and what you will be paid for electricity supplied to the grid. This isn't necessarily for everybody, and mainly helps in the summer rather than winter. Also, it's not clear that this is practical on a UK-wide level, at least with current battery technology.

Inter-day storage is also possible, capturing power on windy days to tide us through low levels of wind. Given the timescales over which weather varies, it's reasonable to plan for storing a week's electricity to provide reasonable security of supply. In the UK about 330 TWh of electricity are produced in a year, that's about 1 TWh per day, or 7 TWh (= 7,000 GWh) per week. So 1 week's electricity would require about 50 000 big Tesla batteries, or 700 Dinorwig pump storage systems, to store it.

Some people have proposed intra-seasonal storage. One recent assessment of using batteries to store power in California's summer to use in the winter came up with a cost estimate of 2.5 trillion dollars.

The UK has most wind energy in the Winter and slightly more at night, balancing out solar power over a period of weeks, and providing more power in the seasons when we need it most. So, the inter-day storage assessment is more relevant for us than for countries in mid latitudes relying mainly on solar power, where time shifting from summer to winter could be needed.

Could new technology solve this? There's a lot of research being done, and it wouldn't be surprising if costs halve in the next twenty years. A big drop, say by a factor of twenty, would be a bit more surprising, though an increase in maximum number of cycles would spread the cost over a longer period.

But don't be down-hearted about this. The above estimates suggest that batteries aren't, on their own, a quick, easy and cheap solution. It doesn't mean that there isn't a solution: there are a lot of good (and some less good) options available, and batteries will be a useful part of the mix.

Explanatory references

https://en.wikipedia.org/wiki/Energy_density#Extended_Reference_Table - energy densities and recovery efficiency.

https://en.wikipedia.org/wiki/Hornsdale_Wind_Farm#Hornsdale_Power_Reserve

https://en.wikipedia.org/wiki/Dinorwig_Power_Station

https://www.technologyreview.com/s/611683/the-25-trillion-reason-we-cant-rely-on-batteries-to-clean-up-the-grid/ - cost of relying on batteries for inter-seasonal storage.

https://reneweconomy.com.au/tesla-big-battery-outsmarts-lumbering-coal-units-after-loy-yang-trips-70003/ - the big battery helps to keep the lights on after a traditional power station trips out suddenly.

https://en.wikipedia.org/wiki/Energy_in_the_United_Kingdom - total UK electricity production. total electricity generation of 335.0TWh (2014) works out at just under 1 TWh per day.

The calculations for 50,000 big Tesla batteries, or 700 Dinorwigs are my own, dividing 1 week's electricity generation by the capacity of Hornsdale and Dinorwig respectively. They are intended to indicate the size of the problem, not to show it can't be solved.

There has been a lot of hype recently about using batteries for grid storage, to overcome two key limitations of wind and solar power: intermittency and non-dispatchability. So, how practical is this?

Rechargeable batteries use reversible electrochemical processes to store and supply electric power.

Capabilities of rechargeable batteries:

• Size ranges from tiny to very large. (Size range in common use from tiny watch batteries to grid storage such as Tesla's Hornsdale Power Reserve in South Australia.)
• Easy and convenient to use. (No mechanical components or combustion required.)
• Moderate energy density. (Up to about 0.5 MJ/kg, compare up to 50 fuel for diesel, 20 for consumable food, 0.05 for supercapacitors, 0.3 for water in a 100m high dam).
• Cost competitive for small devices, less so for large storage (batteries are fairly modular, so costs near linear; some other technologies have major economies of scale).
• High efficiency of recovery (can be up to about 90%, compare around 80% for pumped storage, 40% at best for chemical fuels both created and burned efficiently).
• Reasonable lifetime but not huge. (Well cared for batteries tend to lose capacity after thousands of cycles, but quick charging/discharging can wear them out quickly. Pumped storage could potentially last for centuries with regular maintenance and replacement of parts.
• Very rapid response to events - can be in milliseconds.

Limitations:

• Current technology probably won't support huge storage at reasonable cost. (Hornsdale power reserve 129 megawatt-hours (460 GJ) compare Dinorwig pumped-storage hydroelectric scheme in Snowdonia 9.1-gigawatt-hour (33 TJ).
• Limited supplies of key minerals such as lithium could limit use on a very large scale.
• Self-discharge rate of several percent per month when not in use, also can be damaged by leaving completely discharged.

The one thing they can definitely be used for is to handle short term fluctuations in power. The South Australia battery has already switched in once to a response to a coal-fired power station failing hundreds of miles away, mitigating the resulting impact, and has provided much of the state's normal frequency control.

But what about longer term storage? That depends on the timescale.

Time-shifting means capturing solar power in the day and using to drive peak power needs in the evening, ultimately overnight. Some people are already doing this, and it is potentially financially viable if you have existing solar power, due to the difference between what you pay to buy electricity and what you will be paid for electricity supplied to the grid. This isn't necessarily for everybody, and mainly helps in the summer rather than winter. Also it's not clear that this is practical on a UK-wide level, at least with current battery technology.

Inter-day storage is also possible, capturing power on windy days to tide us through low levels of wind. Given the timescales over which weather varies, it's reasonable to plan for storing a week's electricity to provide reasonable security of supply. In the UK about 330 TWh of electricity are produced in a year, that's about 1 TWh per day, or 7 per week. That equals about 50,000 big Tesla batteries, or 700 Dinorwigs.

Some people have proposed intra-seasonal storage. One recent assessment of using batteries to store power in California's summer to use in the winter came up with a cost estimate of 2.5 trillion dollars.

The UK has most wind energy in the Winter and slightly more at night, balancing out solar power over a period of weeks, and providing more power in the seasons when we need it most. So, the inter-day storage assessment is more relevant for us than for countries in mid latitudes relying mainly on solar power, where inter-seasonal storage could be needed.

Could new technology solve this? There's a lot of research being done, and it wouldn't be surprising if costs halve in the next twenty years. A big drop, say by a factor of twenty, would be a bit more surprising.

But don't be down-hearted about this. The above estimates suggest that batteries aren't, on their own, a quick, easy and cheap solution. It doesn't mean that there isn't a solution: there are a lot of good (and some less good) options available, and batteries will be a useful part of the mix.

Explanatory references

https://en.wikipedia.org/wiki/Energy_density#Extended_Reference_Table - energy densities and recovery efficiency.

https://en.wikipedia.org/wiki/Hornsdale_Wind_Farm#Hornsdale_Power_Reserve

https://en.wikipedia.org/wiki/Dinorwig_Power_Station

https://www.technologyreview.com/s/611683/the-25-trillion-reason-we-cant-rely-on-batteries-to-clean-up-the-grid/ - cost of relying on batteries for inter-seasonal storage.

https://reneweconomy.com.au/tesla-big-battery-outsmarts-lumbering-coal-units-after-loy-yang-trips-70003/ - the big battery helps to keep the lights on after a traditional power station trips out suddenly.

https://en.wikipedia.org/wiki/Energy_in_the_United_Kingdom - total UK electricity production. total electricity generation of 335.0TWh (2014) works out at just under 1 TWh per day.

The calculations for 50,000 big Tesla batteries, or 700 Dinorwigs are my own, dividing 1 week's electricity generation by the capacity of Hornsdale and Dinorwig respectively. They are intended to indicate the size of the problem, not to show it can't be solved

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