While the environmental footprint of energy sources has already been the subject of several studies and therefore it is mapped quite well, the footprint of energy storage is often forgotten. Since energy storage is a key ingredient for the mass expansion of renewable energy sources (RES), we feel it is important to consider both of their ecological footprints. Will renewables paired with storage beat fossil fuels with carbon capture technology when it comes to emissions? Let's find out!

What do we know about them?

In recent years, batteries have been studied mainly in connection with the rising popularity of electric vehicles (EV). Thanks to that, today, we know quite a lot about their raw materials, especially lithium and cobalt.

The vast majority of lithium comes from Australia, the USA, China and Latin America. More than half of the world's known reserves are located in the Atacama Desert area – one of the driest places in the world. To extract one ton of lithium they use about 1.5 million liters of water. Even though there are some other, more gentle mining methods, they are not yet able to compete price-wise. But lithium extraction has its negative impacts in other areas as well. In China, it contaminates rivers almost regularly, and US researchers have found the footprints of the lithium processing site in fish caught 240 km downstream.

Cobalt is not an angel either. Around 65% of the world’s production comes from one single country - the Democratic Republic of Congo. Local miners often use only simple tools without any protective equipment. Sometimes even their bare hands. And unfortunately, child labor is also often the case. And what about nickel, another material used to produce batteries? Its reputation isn’t any better when it comes to the environment and human health.

Battery manufacturers are aware of these problems, but because of the concentration of raw materials in just a few places around the world, their hands are often tied. The good news is that many of them have already managed to significantly reduce the use of cobalt and emissions from battery production. In November 2019, the Swedish IVL released a report according to which during the past two years, the CO₂ emissions have been halved, ranging from 59 to 119 kg CO₂ per kWh of battery capacity. The lower value shows emissions released by the extraction and transport of raw materials and assumes that only renewable energy was used for the production of batteries. The higher value considers using solely the energy from fossil fuels. The mean value is, therefore, 89 kg CO₂ per kWh of battery capacity.

Life cycle carbon footprint

However, this mean value is not enough. To compare and add it to the footprint of RES, we need to identify the carbon footprint of the whole battery life cycle. Robert Rapier, the US chemical engineer, calculated this in his FORBES article. The calculations were for the famous and currently the largest battery storage in the world – the Hornsdale Power Reserve in Australia built by Tesla. For our estimation, we will use Robert’s method. It may look quite complicated at times, so if you are not too curious about the details, feel free to skip to the results.

CALCULATION:

Robert Rapier used the data from the Product Environmental Footprint Category Rules (PEFCR), which indicates, for Li-ion batteries, the energy efficiency of 96% (as 4% energy is lost during charging and discharging), and a lifetime of approximately 400 charge cycles. After 400 cycles, the battery capacity drops below an acceptable limit of 60%. For our calculation, we consider the average value of the battery capacity which is 80% of the initial value.

As many professionals in the field confirmed, the value of 400 charge cycles was significantly underestimated. Tesla, a company behind the Hornsdale Power Reserve, has recently patented a battery that should easily exceed 4,000 charge cycles. We will base our calculation on the value from the batteries which are already being manufactured. Specifically, the one that guarantees 1,500 cycles and which Elon Musk uses in the Tesla Model 3. The Australian battery is used to store power from the 100 megawatts (MW) Hornsdale Wind Power Station with 129 megawatt-hours (MWh) of energy storage, meaning:

129 MWh x 0.8 (80%) x 1500 (cycles) = 154,800 MWh

The received value is the amount of energy we get back from the battery and represents 96% of the energy we used for charging it. During the battery’s life cycle, we would, therefore, need 161,250 MWh of energy to charge it. According to IPCC, the carbon footprint for wind energy is 11 g CO₂ per kWh, or 11 kg CO₂ per MWh.

11 x 161 250 = 1 773 750 kg CO₂

To this result, we have to add the carbon footprint of the battery, which is 89 kg CO₂ per kWh. With the energy storage capacity of 129 MWh, this is 11 481 000 kg of CO₂, which together gives us 13 254 750 kg of CO₂. However, to get a value comparable to the carbon footprints of other energy sources from our previous article, we need to divide this result by 161,250 MWh of electricity (as all of the produced wind energy is used to charge the battery).

RESULTS:

The carbon footprint of the energy produced by the wind power plant and stored in the battery is 82.2 g CO₂ per kWh. For photovoltaic panels, this would be around 116 g CO₂ per kWh. Both are still significantly lower than emissions from coal and gas power sources with carbon capture technology (220 and 170 g CO₂ per kWh, respectively).

The second life of a battery

Many batteries can be safely used even after their capacity drops below the acceptable limit (determined as 60% of their original capacity), and from the economic point of view, it makes no sense to replace them immediately with new ones. In the context of battery energy storage systems (BEES), one of the options is to use the old batteries from electric vehicles. For one simple reason – for the electromobility, the decreasing capacity of the battery represents a serious problem for the vehicle’s range. Therefore, upcycling can extend the life of an EV battery by up to a third and reduce its costs per kWh by half – to around $150. In addition to the price, giving the battery a second life will also reduce its total carbon footprint. According to Circular Energy Storage, London's research and consulting firm, up to three-quarters of EV batteries can be reused.

Once the batteries are no longer suitable even for energy storage, it is time to recycle them. As of today, only a handful of large-scale batteries have reached this stage of their life cycle, so the impact of their recycling is still hard to define. But even considering the negative effects of the extraction of their raw materials, we expect it to be significantly more favorable to both nature and people. With the ever-increasing share of recycled raw materials in the production of new batteries, along with the higher share of RES in the energy mix, the environmental footprint of batteries will only keep dropping.

And this is great news! Because greener and distributed energy production is exactly what we are pursuing at FUERGY. If you are interested in more information in this area, feel free to follow us on our social media or subscribe to our newsletter.

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