07 Jul Transitioning to Utility-Scale Renewable Electricity Storage
Transitioning to Utility-Scale Renewable Electricity Storage: An Introduction to Decision Analysis By: Nate Pajka
Utility companies in the United States are faced with incredible pressure to meet increasing electricity consumer demand in real time. The stark reality of electricity generation is that more electricity must be generated than what is sold because significant amounts of energy are lost as heat in transmission and distribution (“Electricity Generation, Capacity, and Sales,” 2020). In 2018, there were over 153 million electricity customers in the US, and they consumed almost four billion megawatt (MW) hours of electricity, which amounted to $406 billion in total revenue (“SAS Output – Summary Statistics US,” n.d.). Over the past ten years, these totals have been steadily increasing, and as a result, utility companies must lean on their most efficient means of generating electricity in the current political and economic climate if they plan to meet demand. In 2019, fossil fuels (natural gas, coal, and petroleum) accounted for 63% of total electricity generation, while renewable energy sources only accounted for 17% (“Electricity in the US,” 2020). Data from 2018 indicates that fossil fuel electricity generation led to the following levels of harmful greenhouse gas (GHG) emissions that year: over 1.87 billion metric tons of carbon dioxide (CO2), over 1.57 million metric tons of sulfur dioxide (SO2), and over 1.48 million metric tons of nitrogen oxides (NOx) (“SAS Output – Summary Statistics US,” n.d.). To curb these emissions, the US could develop utility-scale generation and storage of electricity through renewable energy sources that are far less harmful to the environment and public health. However, the use of fossil fuels as a source of energy generation is so ingrained in US culture, history, economics, business, and politics that this level of change is often met with strong opposition.
The Transition to Renewable Electricity Sources
Before discussing the processes of clean generation and storage of electricity, it is necessary to understand the importance of transitioning from the current system revolving around fossil fuels to one relying upon renewable energy sources. In 2019, natural gas was the highest electricity generation source in the US by a significant margin, accounting for 38% of electricity generation (almost 1.5 billion MW hours) via steam and gas turbines (“SAS Output – Summary Statistics US,” n.d.; “Electricity in the US,” 2020). The consumption level of natural gas is increasing, as other fossil fuel consumption levels decline (“SAS Output – Summary Statistics US,” n.d.). Natural gas is considerably less polluting than other fossil fuels, as it produces 117 lbs. of CO2 per million British Thermal Units (MMBtu) as opposed to 200 lbs. per MMBtu by coal and 160 lbs. per MMBtu by oil (“Natural gas and the environment,” 2019). However, methane is the primary component of natural gas, which is far more efficient at trapping radiation than CO2 and therefore has a 25 times greater negative impact on the atmosphere, pound for pound, than CO2 (“Overview of Greenhouse Gases,” n.d.). In 2017, natural gas and petroleum systems accounted for 31% of total US methane emissions (ibid.). Natural gas also significantly affects the environment during the exploration and extraction processes. Vehicles disturb vegetation on drilling lands, vegetated areas around well sites are cleared and leveled to make room for drilling activities, the drilling activities and machinery themselves emit pollutants, laying natural gas pipeline is extremely invasive, and natural gas that companies cannot transport or sell is burned at the drill site (flaring), releasing CO2, carbon monoxide, SO2, NOx, and many other compounds (“Natural gas and the environment,” 2019). Hydraulic fracturing, or fracking, has become a popular technique to extract natural gas because it is a cost-efficient process that grants access to previously unattainable reserves (ibid.). However, this process is extremely detrimental to the environment, especially in the communities surrounding the drill site. The process requires large amounts of water, creating a scarcity of the resource in nearby areas (ibid.). Hydraulic fracturing liquid also contains hazardous chemicals that, when released into the surrounding soil and water sources, contaminates (ibid.). The wastewater produced from the fracking process contains high levels of contaminants, as well, which must be treated properly to ensure that it is not released into the surrounding area (ibid.). Injecting this wastewater into the subsurface around the drilling area is a common means of disposal, but this method has the potential to create small earthquakes (ibid.). Finally, natural gas can be released during the drilling process, introducing harmful methane emissions into the atmosphere (ibid.).
The second most prevalent source of electricity generation in the US in 2019 was coal, which accounted for 23% of electricity generation (over 1.1 billion MW hours) via steam turbines (“SAS Output – Summary Statistics US,” n.d.; “Electricity in the US,” 2020). The coal mining process is extremely invasive and has considerable negative impacts on our environment. Surface or strip mining is carried out mostly in Wyoming, and accounts for 63% of all mining activities (“Coal and the environment,” 2020). In the Appalachian Mountains, coal is extracted via mountaintop removal and valley fill mining, which is executed by removing mountain tops with explosives (ibid.). These processes permanently alter the landscape, while the streams and rivers below or nearby are blanketed with rock and dirt (ibid.). Water flowing out of these rock-filled valleys often contain pollutants which are carried downstream, harming aquatic life (ibid.). Abandoned underground mines can pose a serious threat, as well. They are prone to collapse, affecting the land and potentially the livelihoods of those living above (ibid.). They also leak acidic water which can drain into nearby groundwater (ibid.). Methane gas, called coalbed methane, often concentrates in underground mines, and has the potential to explode (ibid.). Coal mining and abandoned mines account for a sizable share of US GHG emissions, as they comprised 9% of total US methane emissions in 2017 and just under 1% of total US GHG gas emissions (ibid.). Of course, the burning of coal is also incredibly harmful to the environment. Harmful emissions resulting from coal combustion includes: SO2, which contributes to acid rain and respiratory illnesses; NOx, which contribute to smog and respiratory illnesses; particulates, which contribute to smog, haze, respiratory illnesses and lung disease; CO2, which is a harmful GHG gas; mercury and other heavy metals, which cause neurological and developmental damage in humans and other animals; and fly ash and bottom ash, which are harmful residues that often leach into groundwater (ibid.).
Petroleum, the final fossil fuel commonly used in the generation of electricity, accounted for less than 1% of electricity generation (about 25 million MW hours) in 2019 (“SAS Output – Summary Statistics US,” n.d.; “Electricity in the US,” 2020). However, petroleum is a high producer of CO2 emissions, as 45% of US energy-related CO2 emissions resulted from petroleum fuel combustion in 2018 (“Where greenhouse gases come from,” 2019). Much like natural gas extraction, exploration and drilling for oil disrupts vegetation and necessitates clearing and leveling of the area around the drill site (“Oil and the environment,” 2019). Fracking is a common technique used to extract oil, which has similar negative environmental impacts to those discussed for natural gas. Perhaps the most notable negative environmental impact of oil are spills. Oil spills contaminate soil and water and may cause devastating explosions or fires (ibid.).
While not a fossil fuel or a renewable energy, nuclear power accounted for 20% of electricity generation (over 807 million MW hours) in 2019, making it the third most prevalent source (“SAS Output – Summary Statistics US,” n.d.; “Electricity in the US,” 2020). Nuclear power reactors do not directly produce carbon emissions, but mining and refining uranium and constructing the metal- and concrete-adorned plants require extreme amounts of energy which is harnessed via fossil fuels (“Nuclear power and the environment,” 2020). Though the risk is minimal given safety redundancies and government oversight, a nuclear reaction taking place at a nuclear power plant has the potential to cause widespread and severe air and water contamination (ibid.). Perhaps the most pressing and prevalent environmental concern associated with nuclear are the resulting radioactive wastes (ibid.). While intense regulations seek to protect people from this nuclear waste, it can remain harmful to humans for thousands of years (ibid.). Spent reactor fuel rods are considered high-level radioactive, and as of today, the US has no definitive location to store these rods (ibid.). Relying on nuclear power with no safe storage options for these spent rods could lead to a surplus of dangerous radioactive material for which the US has no formal plan to deal with. This may increase risk level to the environment and to humans if a solution is not found and we continue to generate waste at the current rate.
Figure 2:See graph title for description (“Electricity in the US,” 2020).
In 2019, renewables accounted for only 17% of electricity generation in the US (over 270 million MW hours), which is up 4% from 2015 and 7% from 2010 (“SAS Output – Summary Statistics US,” n.d.; “Electricity in the US,” 2020). Last year, wind power generated more electricity than any other renewable energy, accounting for 7% of total electricity generation and 42% of all renewables (“Electricity in the US,” 2020). Wind turbines convert wind energy into electricity, and therefore do not release emissions that can harm the environment. As a result, wind turbines generate clean energy that would have been otherwise generated by fossil fuels, thereby leading to a net decrease in carbon emissions. In 2018, the electricity generated from wind turbines offset near 200 million tons of carbon pollution, or 43 million cars worth of CO2 emissions (“Wind Power Benefits,” n.d.). Wind turbines also created $9.4 billion in public health savings in 2018 by significantly reducing air pollution (ibid.). Perhaps the most advantageous trait of wind farms is that they leave 98% of land undisturbed, allowing for the land on which they are situated to be used for other important purposes (ibid.). Hydropower also generates 7% of total electricity in the US, but 38% of all renewable energy generation (“Electricity in the US,” 2020). Like wind power, hydropower releases no carbon emissions to the atmosphere, and it offsets the burning of 4.4 million barrels of petroleum per day worldwide (“Hydroelectric Power,” n.d.). It is also one of the most flexible and easily accessible forms of energy production, as accumulation reservoirs can respond immediately to changes in electricity demand (ibid.). This makes hydropower an enticing option to generate energy for peak and intermediate load generators, which have historically used natural gas and petroleum inefficiently. Most other forms of renewable energy are intermittent (wind slows, clouds block the sun, etc.), but hydropower can be stored and used when needed which is more efficient and economical (ibid.). This feature also means the price of hydropower is extremely stable as it is not subject to market fluctuations and developments are considered long-term investments (ibid.). Hydropower plant reservoirs can also be used for irrigation, drinking water, or water table reserves, efficiently using the space and resources (ibid.). Solar power only generated 2% of total electricity in the US in 2019 (“Electricity in the US,” 2020). Generating solar power does not release any carbon emissions and if the US achieves a 27% solar share of total electricity generation by 2050, it could reduce power-sector GHG emissions by 10% and save up to $252 billion in total costs and $167 billion in health and environmental damages (“Benefits of Achieving High Penetration Solar,” n.d.). It is important to note that solar power is accompanied by some negative impacts, as land must be cleared to make room for solar farms and toxic chemicals and materials are used to make photovoltaic cells (“Solar Energy and the Environment,” 2019).
Figure 3: See graph title for description (“Electricity in the US,” 2020).
Utility-scale Generation and Storage of Electricity
In order for a power plant generator to be considered utility-scale, it must have at least one MW of total electricity generating capacity (“Electricity Generation, Capacity, and Sales,” 2020). To balance and meet electricity demand immediately, operators of the electricity grid require that power plants produce and introduce the correct amount of electricity to the grid at all times (ibid.). There are three main types of generators used to do this: base load, peak load, and intermediate load (ibid.). Base load generators supply much of the minimum load of the electric grid, running continuously throughout the day, producing at a constant rate (ibid.). Nuclear power is the most popular base load generator energy source because it is inexpensive and inflexible to load changes, but geothermal, biomass, and hydropower are commonly used for similar reasons (ibid.). Peak load generators are designed to help meet electricity demand during periods when consumer demand is at its highest (ibid.). These generators are typically fueled by natural gas and petroleum and are inefficient and costly to operate (ibid.). Intermediate load generators provide demand response during periods between peak and base load, making them the most prevalent type of generator (ibid.). Natural gas is the typical fuel source for this generator type, as it is best suited for handling constant changes in load (ibid.). There are additional categories of electricity generators that exist on a smaller scale. Intermittent renewable resource generators rely on solar and wind power when they are available to produce electricity (ibid.). Distributed generators are connected to the grid, but primarily provide electricity generation for individual buildings (ibid.). They can even generate more than the building uses, and the surplus can be sent or sold back to the grid (ibid.). Presently, some states require that utilities use more renewable energy sources and they provide financial incentives for them to do so, which has increased the prevalence of these types of generators.
Electricity storage systems and facilities store electricity generated during off-peak periods and provide it during periods of high demand (ibid.). In this way, storage systems can assist in smoothing prices, as they can sell electricity during periods of high demand to dilute the market and drive down costs. These systems are especially relevant for intermittent renewable resource generators given that the sun is not always shining, and the wind is not always blowing. If wind turbines and solar panels are generating high amounts of energy in off-peak periods, efficient electricity storage is useful to ensure this energy is saved and deployed in times where it can be used to complement a stressed grid. There are a number of electricity storage systems that are active in the US reliant upon renewable energy sources. The largest source of electricity storage in the US is pumped storage plants for hydroelectric power (Mayes, 2019). Water is pumped into reservoirs during off-peak periods when energy is cheap, then, when demand is high, the water flows downhill and through hydroelectric generators at a dam (ibid.). However, in 2018, the total generating capacity of pumped storage (in GW) was less than one third of the amount of conventional hydroelectric capacity in the US (ibid.). California alone accounted for 17% of the national total as no projects have been online since 2012 to construct new plants (ibid.). These pumped storage plants cost much more to construct than a typical hydroelectric plant and the process of pumping water uphill incurs additional operational costs (ibid.). Solar thermal storage is another option that has been utilized in the US to store electricity. This technology consists of a concentrating solar power (CSP) system which reflects the sun’s rays into a receiver creating heat, and therefore, energy that can be saved for later (“Concentrating Solar Power,” 2013). More recently, the US has been developing and advancing the technology of batteries, which have been pivotal in the storage of intermittent renewable resource energy (ibid.). Operating utility-scale battery storage power capacity has more than quadrupled from the end of 2014 (214 MW) through March 2019 (899 MW) (ibid.). Fortunately, utility-scale battery storage has had government support, as state-level policies have made it possible for this technology to grow (ibid.). The Golden Valley Electric Association’s battery energy storage system in Alaska and the Vista Energy storage system in California are the largest utility-scale battery storage sites in the US and provide a combined 80 MW of power capacity (ibid.). If the technology continues to grow as anticipated, this amount of energy storage will be tripled by 2023 (ibid.). The most pressing and obvious issue with electricity storage systems is that they consume more energy than they store, so they exhibit net negative energy generation balances (“Electricity Generation, Capacity, and Sales,” 2020). Pumped hydro systems incur considerable operational costs to pump water uphill and non-hydro systems lose energy through conversion and storage leaks (ibid.).
Given the information presented above, it is abundantly clear that developing utility-scale renewable energy storage to meet electricity demand would lead to widespread environmental and public health benefits. Each renewable energy technology releases zero to minimal GHGs throughout the manufacturing, implementation, and operational process. By converting to more widespread renewable energy, the US would reduce GHGs emissions tremendously as the burning of harmful fossil fuels to generate electricity would be replaced by non-emitting sources. Additionally, the US would realize significant economic and efficiency benefits, as market fluctuations could be mitigated via an ever-present energy source that is harnessed naturally. That being said, the current capitalistic system is highly dependent on fossil fuel usage to function and a transition to renewables would face serious political opposition. Also, given the intermittency of many of these technologies and the inability for electricity storage to generate positive net energy balances, the science and efficiency has not reached a point at which utility-scale energy storage is possible.
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