The Battery Powered Future
As renewables become cheaper than fossil fuels, new battery technology means renewable power grids are closer than ever.
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In this week’s newsletter we discuss batteries and energy storage. We start with recapping why renewable sources aren’t viable without energy storage. Then we’ll break down some of the leading energy storage methods, including lithium-ion batteries, flow batteries, and hydro pumped storage and their role in building the renewable grids of the future.
The transition to renewable energy is critical for our planet’s survival, and as the price of sources such as solar and wind drops exponentially, the prospects for greener economies look more and more promising. However, to be truly functional, the power grids of the future need a way to store all this renewable energy and turn it into a reliable source of power. Because of this, just as much as solar and wind, our green future needs batteries.
The Renewable Renaissance
To understand why batteries are vital, we need some background on the rapidly changing mix of energy sources. Ever since the industrial revolution, the majority of our energy needs have been met by fossil fuels. Coal became widespread once the English realised that it was more effective than burning wood at driving the newly invented steam engine. As the steam engine gave way to the combustion engine, oil came to dominate the energy landscape and the world entered the petroleum age. Currently, about 60% of US energy production is from fossil fuels. Globally, that number is 84%.
Unfortunately, fossil fuels are not good. Their combustion produces pollution and they only form when organic matter is crushed underground by immense pressure for millions of years. So unless we are willing to wait for that long, fossil fuels are not sustainable. This is why we need alternate renewable energy sources, such as geothermal, hydro, wind, and solar.
Renewables have made incredible progress over the past decade, highlighted by the incredible cost reduction in sources such as solar and wind . Wind has declined by as much as 2x and solar by closer to 10x. Renewables are now cheaper than fossil fuels. The end of fossil fuel dominance seems to be in sight.
So… problem solved? Not quite.
Although solar and wind are now economical, that isn’t enough. Fossil fuels can be stored and used whenever they are most needed. This way, energy production can be changed to match fluctuating demand. This is called load balancing. On the other hand, solar and wind only produce electricity when the sun shines or the wind blows, which might not be when energy demand is at its peak. Just by themselves, solar and wind plants might not be able to load balance and meet energy demand. This is a basic requirement, so without the ability to store energy for future use, renewables can never be the basis for our power grids.
The Potential (Energy) of Batteries
Batteries are the missing link to this puzzle. With batteries that efficiently store the energy produced by renewables, we can build viable power grids. Just as fossil fuels stored the sun’s energy captured via plant photosynthesis, batteries store the sun’s energy captured via solar cells and wind farms. Batteries are essentially the oil barrels of the renewable future.
The fundamental principle of batteries is that they convert electrical energy into potential energy. As the name suggests, if something has potential energy that means it has the capacity to do something useful in the future, which is exactly what we want from a battery.
Lithium-Ion Batteries
The design that dominates currently is the lithium-ion based chemistry. Invented by Nobel laureate Akira Yoshino in 1985, Li-ion batteries are used in all types of electronic applications.
The basic components are:
A negatively charged anode made of carbon in the form of graphite.
A positively charged cathode made of a metal oxide such as cobalt oxide.
Lithium atoms/ions which move back and forth between the anode and cathode during charge and discharge.
A separator between the cathode and anode that lets only lithium move through.
All these parts are contained in the electrolyte, a liquid that allows ions to move freely back and forth between the cathodes.
To see how this works, first let’s assume the battery is in its fully charged state. This means that all the lithium is in the carbon anode. Because of quantum mechanics, lithium atoms really want to give up one electron and become lithium ions. Similarly, cobalt ions in the cobalt oxide really want to accept electrons. The natural resolution is for the lithium to give up its electrons to the cobalt, and this force is what causes the electrons to move.
The separator makes sure that the electrons cannot just go directly to the cobalt, so the only path available is via the load connected to the battery. This way, the electrons must go through the load and deliver electrical energy on their way to the cobalt. The energy the electrons deliver wasn’t created from nothing. It is the converted form of the electrical potential energy between the cobalt and lithium atoms.
As more electrons accumulate on the cobalt cathode, it increasingly becomes more negative. This attracts the positive lithium ions from the other side and since the separator is permeable to lithium ions, they can go through. Now, the electrons, lithium ions, and cobalt oxide form lithium cobalt oxide on the cathode. Once all the lithium and electrons have transferred to the cathode and the carbon anode is exhausted, the battery is dry.
We can recharge the battery by repeating this process in reverse. While the original process naturally releases electrical energy, this reverse reaction actually requires external energy as input. This comes from solar or wind farms and separates the lithium cobalt oxide back into cobalt oxide and lithium atoms. As the cobalt and lithium are separated again, the electrical potential energy between the lithium atoms and cobalt atoms is restored, and the battery is ready for use.
One major advantage of lithium batteries is that they are very energy dense. This means that they store a lot of energy in a small volume, which makes them ideal for applications such as phones and electric cars. Lithium-ion batteries have also been successfully deployed in grid-level applications, such as the 100 megawatt Hornsdale Power Reserve in Australia built by Tesla in 2017.
However, because lithium is so reactive, there is a risk of explosion if somehow the anode and cathode make direct contact and allow rapid discharge of the stored potential energy. Generally, lithium batteries are safe - it isn’t normal for your phone and computer to blow up - but there is an explosion hazard if the batteries are damaged.
Sourcing lithium and cobalt can also be tricky. Both elements are mostly sourced from only a handful of countries, and quite often mined in appalling conditions. 60% of cobalt supply comes from the Democratic Republic of Congo, a war torn and impoverished nation where child labour is common. Such conditions hardly make for robust supply chains. Because of this and other factors, lithium batteries can often be too expensive for large grid scale projects.
Flow Batteries
Many other exciting battery alternatives are currently under testing. One example is the flow battery, which is a modification on the lithium-ion battery.
Instead of the anode and cathode being fully contained in the battery housing, they are now stored in large tanks separate from the main battery. Since the cathode and anode are now liquids, they are called the anolyte and catholyte. These are pumped into the main battery volume, where an electron reaction similar to the one of the lithium battery occurs and releases energy to the load.
The amount of energy stored depends on the amount of chemical in the storage tanks. Since the tanks are separate from the actual battery, they could be made as large as possible so the energy stored could be very large also. This isn’t ideal for applications such as phones or cars, but it’s good for large scale power grid storage where space is not a limitation. Flow batteries also tend to present less of a fire/explosion hazard than lithium ion batteries.
However, like with lithium ion batteries, flow batteries could also face brittle supply chains. One common element in the catholyte and anolyte is vanadium, 60% of whose global supply is from one country - China. Given tensions today, it isn’t hard to imagine that vanadium supply chains might not be the most reliable. ESS, a company based in the US, is developing a flow battery based on more abundant materials such as iron. It is still in the early phases, but if it is successful this device could pose a genuine threat to the dominance of lithium ion batteries.
Pumped Storage
There are also energy storage solutions beyond batteries. One of the most well established of these is pumped hydro storage. Although batteries offer great promise for the future, pumped storage currently dominates energy storage, accounting for over 90% of global energy storage capacity.
Pumped storage works by having two reservoirs of water with one at higher altitude than the other. If there is low energy demand, surplus electricity from the grid is used to drive a pump and push water up to the higher reservoir. This way, the surplus electrical energy is stored as gravitational potential energy of the water. During high demand situations when the grid needs extra electricity, the stored water is allowed to fall down and drive an electrical turbine. Now, the stored gravitational potential is converted back into electrical energy and carried off by the grid. As with all energy storage solutions, there are pros and cons to be balanced with this approach. Pumped storage is a reliable method, which explains its widespread use. However, these plants are expensive to build and, unlike batteries, pumped storage only works in certain geographic locations with easily accessible high altitudes like mountains.
The progress that renewables have made over the past decade is incredible. With the sharp cost declines sources like solar and wind, renewables have finally become cheaper than fossil fuels. However, in order to be able to use them in the power grids of tomorrow, we need effective and economical batteries to solve the problem of load balancing.
Historically, pumped storage and lithium ion batteries have dominated energy storage. Pumped storage is currently the majority of global storage capacity, but can be built in only certain locations. Batteries offer a more flexible solution. The world’s first large scale battery storage project - Tesla’s 100 MW Hornsdale Power Reserve - is already built and uses lithium ion to supply power. However, lithium ion batteries have disadvantages such as safety and supply chain risks. They can also be expensive, which makes the battery space ripe for disruption. Many promising alternatives have appeared to take advantage of this, such as the flow battery. Although these aren’t a match for lithium ion quite yet, it appears to be only a matter of time till we find truly viable energy storage solutions for our power grids.
I love how you break this down! Great article