In the modern era, in which we live, the energy crisis is becoming one of the major challenges we face in our daily lives. There are many sources of energy, including more sustainable and greener ones such as renewable energy (e.g., wind and solar energy). However, the main source of energy remains soon to be depleted fossil fuels. According to the full report of BP Statistical Review of World Energy 2019, the total consumption of energy was equivalent to 13864.9 million tonnes of oil in 2018. However, only 561.3 million tonnes of oil equivalent, (4 percent of overall energy consumption), was consumed in the form of renewable energy .
The burning of fossil fuels leads to carbon emissions worsening climate change, which is another challenge we face besides the energy crisis. So, why do people still choose fossil fuels as the main source of energy but not renewables, even though renewable energy is cleaner, greener and more sustainable? One of the reasons is that renewable energy is mostly not as cost-effective as fossil fuels (Figure 1 ), despite the huge green taxes implemented by governments. Another reason why renewable energy is not widely used is its limitations connected to time and location.
“Over ten years, the application of large-scale energy storage would reduce more than 1 million metric tonnes of greenhouse gas emissions, equivalent to eliminating more than 200,000 cars from traffic, in Massachusetts”
Limitations of Solar Energy — “The Duck Curve”
Let’s explore the limitations of solar energy (one of the main renewable energy sources), in terms of time and location. There is a huge difference between the solar energy produced in London, United Kingdom, where the weather is mostly cloudy, and the solar energy produced in Los Angeles, California, United States, where the weather is mostly sunny. However, despite this difference, in both cities, the energy consumption is similar since they are both big cities with large populations.
It can be predicted that there will be a need for additional energy sources in London since its cloudy weather would reduce solar energy production. Solar energy production differs by time as well. While the solar energy production is greater in the mornings/afternoons and in summer/spring, it will be relatively less at night/in evenings and in winter/autumn.
Considering the daily routines of people nowadays, the energy consumption is relatively greater at night than in the morning, in which more solar energy is produced. When the solar energy supply is less than the consumption demands, mostly during evening and night, the additional energy supply is produced thanks to conventional ways (coal, gas, oil, etc.). On the other hand, in the mornings/afternoons, solar energy production exceeds the demand for energy. Hence, the inverse relationship between the consumption and production of solar energy depending on the time of the day actually creates a phenomenon called “the Duck Curve.”
The Role Of Energy Storage In Decarbonising Energy Systems
In accordance with the increasing global demand for energy, the supply of energy should increase. This will lead to new emissions of greenhouse gases if it’s in the form of burning fossil fuels. Even though renewable energy is becoming cheaper, it is not enough to replace it with fossil fuels due to the limitations mentioned above, supported with the Duck Curve. Hence, alternative energy storage solutions should be applied in order to decarbonize local energy systems.
Figure 3 from the Nature article titled “The role of energy storage in deep decarbonization of electricity production” represents how emissions are reduced with storage in California. This study shows that, despite the curtailment, which is “the reduction of output of a renewable resource below what it could have otherwise produced” , of one-third of the renewable energy, increasing renewables in California by 60GW will reduce carbon emissions by 72%.
However, in comparison to the zero-energy storage case, when energy storage solutions have been employed, the reduction in carbon emissions increases to 90%, and only 9% of renewable energy is lost. In Texas, where energy production is based less on renewable energy than in California, energy storage leads to a 57% reduction in emissions, and only 0.3% of renewable energy is lost. This illustrates that energy storage reduces greenhouse gas emissions more effectively when the energy stored is produced by renewable energy sources rather than fossil fuels . The study clearly illustrates that, in order to reduce carbon emissions, employing energy storage with renewables is more effective than only utilising renewable energy. It also highlights how storing renewable energy rather than energy obtained from fossil fuels is reducing more emissions.
Compared to other decarbonizing measures, employing energy storage solutions would be more cost-effective and easier to apply. According to Massachusetts Energy Storage Initiative Study’s report titled State of Charge, over ten years, the application of large-scale energy storage would reduce more than 1 million metric tonnes of greenhouse gas emissions, equivalent to eliminating more than 200,000 cars from traffic, in Massachusetts . Hence, implementing large-scale energy storage is easier and more cost-efficient than implementing other carbon emission-reducing measures such as reducing traffic. This shows another reason why energy storage has a significant role in decarbonizing energy systems.
Drawbacks Of Energy Storage & Alternative Energy Storage Solutions
Even though energy storage is known as a green technology, it can lead to an increase in greenhouse gas emissions if not deployed strategically. In the case in which fossil fuels are more cost-effective than renewables, energy storage might enable more fossil-fueled energy, thus, higher emissions. However, the most significant problem faced with energy storage is the energy loss that occurs when storing the existing energy. Even though the demand for energy does not change, more energy should be supplied and stored to meet the demand due to the loss of energy .
Figure 4.The map of storage CO2 emissions in United States 
Even when the energy loss is minimised, many energy storage technologies have short durations which is a serious limitation. Fortunately, some novel energy technologies could solve this problem with their higher duration :
Liquid Air: The generated energy is employed to liquefy air by cooling. When energy is needed, with exposure to waste heat, the stored liquid air is transformed into gas, which turns turbines to generate electricity .
Pumped Hydro: The basic principle of gravity is used to store the energy by pumping water from a low to a high reservoir in a dam. When water is released from the high reservoir to the lower part, its potential energy turns into kinetic energy, and energy is generated. Despite its low cost, one of the challenges it faces is the lack of sites to construct new pumped-hydro storage facilities since it takes a lot of space .
Flow Batteries: Through redox reaction, circulating liquid electrolytes in flow batteries are charged and discharged to store energy .
Underground compressed air: Generated electricity is used to pump compressed air into the underground, which works as a storage tank. When energy is needed, the pumped and pressurised air is released and the plant re-generates the stored energy .
Replacing fossil fuels with renewables is one of the better ways to reduce greenhouse gas emissions. However, due to the limitations related to time and space, renewables might not be the only energy sources used when not stored strategically. Storing over-generated renewable energy will reduce the reliance on fossil fuel energy; therefore, it will reduce the greenhouse gas emissions from burning fossil fuels. Consequently, it will benefit the decarbonization of energy systems by replacing energy from fossil fuels with stored renewable energy. The limitations of energy storage, such as the loss of energy can be minimised thanks to alternative energy storage solutions. Hence, while advocating the use of renewables, the governments should also support the technological developments in long-duration energy storage which will reduce emissions.
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[3.] Arbabzadeh M, Sioshansi R, Johnson JX, Keoleian GA. The role of energy storage in deep decarbonization of electricity production. Nature Communications. 2019;10(1).
[7.] Hittinger E, Azevedo IML. Estimating the Quantity of Wind and Solar Required To Displace Storage-Induced Emissions. Environmental Science & Technology. 2017;51(21):12988–97.
[8.](a href="https://www.greentechmedia.com/articles/read/most-promising-long-duration-storage-technologies-left-standing ">Spector J. The 5 Most Promising Long-Duration Storage Technologies Left Standing [Internet]. Greentech Media. Greentech Media; 2020 [cited 2022Jan3]. )
Damla Köse is currently an undergraduate student studying Chemistry at Imperial College London. She is from Izmir, Turkey. She aspires to be a researcher working on renewables, energy storage and nano-materials. She also has been an advocate of spreading STEAM education, especially to the children who lack basic needs of education, as the founder of The Hypatia Initiative and ACI STEAM Club.