Batteries & Emissions

Let’s talk about greenhouse gas emissions. No, not from coal and gas — I mean the lifecycle emissions of clean energy.

Source: NFCRC

From production of raw materials, construction and maintenance, to decommissioning, all energy sources are responsible for some emissions. Even solar (45 gCO₂-e/kWh), wind (12 gCO₂-e/kWh), and wave energy (8 gCO₂-e/kWh)… hydro may be more than we realised because of rotting drowned vegetation and other factors. Nuclear needs a lot of materials, but this is easily balanced out by the sheer energy density of uranium, so its overall lifecycle emissions still come out about 12 gCO₂-e/kWh.

Source: Lyon Solar

What if we don’t want to backup solar or wind with fossil fuels, and instead use storage? It’s a popular idea. Well, the first thing to realise is that this isn’t done at grid-scale anywhere — not how we imagine it, as “storage taking the place of conventional backup to supply power at night or in calm weather”. In countries like France, pumped hydro storage stores cheap supply overnight to meet lucrative daytime peaks. Even new large-scale batteries in California are set up to work the same way. This is called arbitrage and it’s the most profitable function of storage on the grid.

We also need to recognise that a) special double-ended dams can’t just be built wherever, and b) it is most certainly lithium ion (Li-ion) battery systems which are the most deployable storage capacity. Recent market research puts most Li-ion production in China — nearly three times as much as is produced in the US, in fact. There are currently serious concerns regarding the supply chains for the critical materials in modern batteries — lithium, cobalt and graphite — covered in this excellent article. Additionally, Li-ion systems will need replacing as frequently as every ten years.

But back to emissions. Yes, Li-ion emits over the course of its full lifecycle. There hasn’t been much work done on this, but what there is challenges the assumption that swapping fossil fuels out for batteries in a solar- or wind-powered grid will really count as deep decarbonisation. A presentation by Stanford researchers provides a visual guide for the lifecycle emissions we might achieve using Li-ion and other battery technologies.

Source: Barnhart et al. Solar PV plus Li-ion storage emissions intensity is indicated by the yellow line.

Deciphering the curious log scale, it’s pretty clear that by adding Li-ion batteries, solar has roughly quadrupled up to about 200 gCO₂-e/kWh. If the Stanford numbers are anything to go by, this is what we’re actually going to get; there’s a lot of both solar and Li-ion batteries planned all over the world. And when you think about it, this isn’t so counter-intuitive. The batteries are extra material in the system but don’t create any extra energy, only shift what is generated by solar to times when it’s more useful. More technology for the same energy output.

Source: Wang et al. Applied Energy 2016, 184, 873–881

But wait — this is assuming the emissions of the US, while we know most Li-ion will be produced in China. A recent article in Applied Energy put Chinese electricity emissions at 1,170 gCO₂-e/kWh to the US’s 720 gCO₂-e/kWh: about 1.6 times as emissions intensive.

A hypothetical solar-powered country relying on mass-produced Li-ion batteries to fill the dark gaps may be responsible for substantially more than 200 grams of CO₂-equivalent for each kWh it consumes — chillingly, all while considering itself clean, green and decarbonised!

On the face of it, we’re not going to drive emissions from electricity down to zero if the supply system we build is stuck in triple-digits.

Source: Solarcity

We need a better idea of the lifecycle emissions of these modern, high-purity-material storage devices. Maybe with further analysis it won’t be so bad. Maybe capacity will improve, lifespans will lengthen, and more materials will be recycled. Maybe it can be managed or minimised as part of a more diverse grid supplied by more renewables and nuclear. And hopefully the predominant producer — China — will continue decarbonising its energy supply. But if carbon-free is the goal, we can’t pretend to have a free lunch. We can’t just assume batteries don’t have emissions.

Next: A Message from Ontario

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