In this section, I’ll lay out why decarbonization of the US power grid matters, provide a high-level overview of the current situation and economic trends, and then address why such a proper solution to the problem has high complexity.
1.1 Doom and Gloom: Why Reaching Zero Carbon Matters
In October 2018, the Intergovernmental Panel on Climate Change (IPCC) published a special report on the impact of a global average temperature rise of 1.5°C over pre-industrial levels [i]. The message wasn’t pretty. It mentioned “hot extremes in most inhabited regions”, with an increase of the extreme temperatures in the mid-latitudes by about 5 degrees Fahrenheit. It discussed “increases in frequency, intensity, and/or amount of heavy precipitation in several regions” alongside “the probability of drought and precipitation deficits in some regions”. It predicted that sea levels could rise by somewhere just under a foot to over two-and-a-half feet by 2100 (with every four inches representing 10 million people exposed to related risks). The report discussed how 1.5°C represented the possibility of a climate “tipping point” of sorts – beyond 1.5°C, dangerous feedback loops would start to enter the picture [1]. Should the ice sheets in Antarctica or Greenland become unstable, it could result sea levels rising several yards over hundreds to thousands of years. The report touched on ocean acidification leading to species loss and extinction (and amplifying other effects). All of the doom-and-gloom contained in a world 1.5°C hotter than pre-1750 was succinctly summarized by the report with “[c]limate-related risks to health, livelihoods, food security, water supply, human security, and economic growth are projected to increase with global warming of 1.5°C”.
As bad as the 1.5 degree threshold may sound, it’s a almost a goal at this point. The world is likely to hit the 1.5 degrees warmer sometime between 2030 and 2052, and we’re already at 1 degree of temperature increase. Achieving a 1.5 degree path with a limited amount of “overshoot” (temporarily crossing the 1.5 degree line before retreating back) would require reducing our global emissions by 40-60% between 2010 and 2030, and hitting global net-zero emissions sometime around 2050 (give or take 5 years). All of this “would require rapid and far-reaching transitions in energy, land, urban and infrastructure (including transport and buildings... unprecedented in terms of scale”. For energy and electricity use specifically, the report notes a need to both electrify energy end use faster (i.e. use electricity for more processes where we currently use fossil fuels), cut back substantially on coal and natural gas use for electricity generation, and implement more carbon capture and storage (CCS). There is a small nugget of hope for this transition, however: the IPCC notes that “…political, economic, social and technical feasibility of solar energy, wind energy and electricity storage technologies have substantially improved over the past few years… These improvements signal a potential system transition in electricity generation.”
Figure 1: Model Pathways to 1.5 degrees of Warming [ii]
Which brings us to the US. If a global clean energy and electricity transition is to have any shot at success, it will have to include the US. In 2019, the US produced about one-seventh of global energy-related emissions [iii]. In 2018, the US emitted 6,677 million metric tons of CO2 equivalent [2], and the electricity sector accounted for 27% of these emissions [iv]: roughly 1,800 million metric tons of CO2 equivalent [3][v], or roughly the equivalent from burning 10 million railcars’ worth of coal [4]. While overall emissions from the US power grid have fallen by 27% from their peak in 2007 [vi], estimates for the social cost of pollution related to US electricity production (i.e. the costs not directly paid by emitters, perhaps in the form of reduced air quality or premature deaths) just in 2011 are $147B [5]. We’re already paying the cost for pollution from the electricity sector; the damaging effects aren’t just in the future.
1.2 Achieving a Zero Carbon Economy Requires Electrifying (Perhaps) Everything, and Cleaning up the Electricity Sector
The electricity sector in particular is presented with a unique demand on the road to net-zero: because it enables other industries and sectors to decarbonize, it must more rapidly decarbonize in order to not delay the overall decarbonization path. In other words, the electricity sector acts as a sort of bottleneck to the decarbonization of other sectors.
It helps to understand the nomenclature of the different scopes of emissions. Scope 1 emissions can be directly attributed to an organization, business, or sector: this refers to “the direct burning of fossil fuels in generators, facilities, and vehicles” [vii]. Scope 2 emissions refers to purchased energy that wasn’t directly generated, such as electricity, and Scope 3 emissions refers to emissions further up-and-down the value chain. While much more complex than Scope 1 and Scope 2, it can be loosely thought of as including the emissions associated with suppliers and customers. As a household-level example, Scope 1 emissions come from the gasoline we fuel our cars with, the generators we run during a power outage, or the natural gas we use for cooking. Scope 2 emissions are the emissions incurred to produce the electricity we used. Scope 3 emissions come from the products we use and make in our home – paper towels, beef pot roast, our clothing. The beef pot roast we have for dinner wouldn’t have been consumed without us; therefore we’re responsible for the emissions.
Figure 2: Three Scopes of Emissions, for a Federal Agency [viii]
For many industries with currently high Scope 1 emissions, the path to decarbonization relies on shifting Scope 1 emissions to Scope 2 emissions, and relying on clean electricity to negate Scope 2 emissions. Transportation represents a fairly high-profile example: in 2018, transportation accounted for 28% of US greenhouse gas emissions, over half of which was due to passenger cars and trucks [ix]. While the barriers to electrification may be high for airplanes, ships, or Class 8 long-haul trucks towing tens of thousands of pounds, barriers to electrifying passenger vehicles are much lower, and electric cars have being steadily increasing adoption rates across the world. Such electrification can be driven by shifts in consumer perceptions on economics, performance, and practicality [x]. Replacing a gasoline-powered family vehicle with an electric one shifts emissions from Scope 1 to Scope 2, and as the power grid relies more on zero-carbon sources, the overall emissions impact of an electric vehicle falls further.
For heavy industry, a similar shift will have to occur. Industry produced 22% of 2018 US emissions (not including Scope 2, which the EPA attributed to the earlier 28%) [xi]. Most of the 22% came from Scope 1 emissions, though a similar strategy of electrifying equipment to shift Scope 1 emissions to Scope 2 emissions presents a key opportunity for driving sector decarbonization. If heavy industry shifts toward more electric equipment, then that equipment’s carbon footprint is essentially linked to that of the power grid. Clean up the power grid, and the equipment is also cleaned up automatically [6]. For heavy industry, electrification also represents a potential economic benefit, with some use cases benefitting from higher performance and lower total cost of ownership [7][xii].
For transportation, industry, and other sectors, shifting Scope 1 emissions to Scope 2 emissions through electrification has two benefits for decarbonization: (1) electrification tends to bring with it increased energy efficiency, which immediately lowers overall emissions, and (2) the amount of carbon emitted per unit of energy consumed isn’t fixed and has steadily decreased in the US over the past 15 years [8][xiii]. Indeed, Sterchele et al. find that “the more ambitious the climate protection targets are, the faster the required transition from a fossil fuel-based demand to a demand dominated by electric technologies, i.e., the consumption sectors get progressively electrified” [9][xiv].
Estimates of the overall energy that we can save by electrifying everything are around the 45% mark [xv]. In other words, transitioning current fossil-fuel-based demand to electricity would reduce the total amount of energy that we consume in the first place, mostly due to higher the efficiency inherent to electrification (e.g. electric cars are more efficient than gasoline cars, on a miles-per-unit-energy basis) and to the lack of energy spent in the fossil fuel supply chain – extraction, refining, transportation, etc.
However, a reduction in energy isn’t a reduction in electricity. The upshot is that we need to vastly scale the power grid if we are to increasingly electrify more and more sources of energy demand. Furthermore, to achieve real progress toward zero-carbon, we’d have to not only transition existing electricity generation sources to zero-carbon ones, but also ensure that new capacity that’s built is also zero-carbon.
1.3 Where we are Now
The United States encompasses a large landmass with incredibly varied terrain. As a result, it may not be too surprising that there is no one “national grid”, such as the one the United Kingdom built to service the entire island of Great Britain – geography represents a fundamental barrier to this task. Nevertheless, many regions and smaller grids connected together into three “interconnects”, which serve as larger grids themselves. Thus, the “US grid” can be thought of as three grids: (1) the Western Interconnect, which services the area west of the Rockies, (2) the Texas Interconnect, which serves the majority of Texas, and (3) the Eastern Interconnect, which services the area east of the Rockies (except Texas) [xvi]. Interconnections are themselves aggregations of smaller networks of generators and transmission lines. They help provide resiliency and stability in a system where, at any given microsecond, power generation must match up with power consumption [10]. If a power line or a generator were to fail, another transmission line or generator could essentially pick up the slack while repairs are made. However, these grids are mostly separate – there’s very little capacity to share electricity from any of the interconnects to any other. Thus, a power plant failure in Texas couldn’t be overcome with extra capacity from a plant in New Mexico, though an outage in Charlotte could be indirectly aided with capacity from Chicago. To give a sense of scale, in 2016 peak demand for the Western Interconnect was around 140 GW, 70 GW for the Texas Interconnect, and 450 GW for the Eastern Interconnect [xvii] (see Appendix A1 for a discussion of power vs. energy and common units). To avoid backouts, each grid needs to have enough electricity generating capacity to cover these peak demand scenarios.
Figure 3: Interconnections of the US Power Grid [xviii]
On the generation front, there’s roughly 1,100 GW of summer utility-scale capacity across the country [xix] (energy demand peaks in most of the US occurs in the summer, so it’s important to measure how much capacity is available then, and utility-scale ignores smaller-scale generation sources like rooftop solar). 67% of summer capacity comes from fossil fuels, nuclear provides about 9% of capacity, and 13% of capacity comes from wind and solar. Power isn’t the same as energy, however, so there isn’t a one-to-one relationship between sources of capacity (power) and sources of electricity (energy). For example, nuclear power plants tend to constantly be producing electricity, whereas solar panels can’t produce 100% of possible power at every instant throughout the day (due to the natural cycle of the sun, along with weather patterns). A plant’s capacity factor defines how much electricity a plant produces as a percentage of how much that plant could produce, if it were running at nonstop full capacity [xx]. For all of 2019, nuclear power plants had a capacity factor well over 90%, solar had a capacity factor around 25%, and natural gas plants averaged 57% [xxi]. Thus, we’d expect nuclear to produce more electricity than its share of generating capacity, and solar to produce less.
From the energy perspective, the US produced just over 4,100 TWh of electricity in 2019. Fossil fuels accounted for 63% of the electricity produced, nuclear provided about 20%, and renewables made up the remaining 18% [11]. Breaking apart the renewables category, 7% (of the total electricity production, not of the renewables share) comes from wind, another 7% from hydropower, and solar takes up 2%. Biomass, geothermal, and other sources round out the remainder [xxii]. While the snapshot doesn’t sound encouraging, the trends certainly can be.
Figure 4: US Electricity Production, 2000-2020 [xxiii]
Wind and solar electricity production have grown at an exponential rate over the past decade, driven by increasingly improving economics. In 2000, wind produced 5.6 TWh of electricity, and grew to 17.8 TWh in 2005 (3.2x in 5 years), 94.7 TWh in 2010 (5.3x in 5 years), 190.7 TWh in 2015 (2x in 5 years), and over 300 by 2019 (1.6x in 4 years). From a capacity standpoint, wind capacity grew from 2 GW in 2000 to 104 GW in 2019. Solar is practically out of the picture until 2007, when growth began – in 2007, solar produced 0.6 TWh of electricity. Four years later in 2011, solar had tripled in production to 1.8 TWh. In 2015, solar accounted for 24.9 TWh (13.8x in 4 years), and in 2019 solar generated 72.2 TWh of electricity (2.9x in 4 years) [xxiv]. The slowdown in growth on a multiplicative-factor basis is mostly due to the near-irrelevance of wind and solar electricity at the turn of the century, though it hides the fact that the two are growing on an absolute basis at breakneck speed. Solar’s capacity has grown from less than a GW to 37 GW in 2019 [xxv]. These capacity expansions are the result of large investments in building out renewable electricity capacity – in the 2010s, wind investment in the US alone totaled $165B, while solar investment was even higher at $211B [xxvi]. This incredible growth and investment contrasts against the stagnation of hydropower and nuclear electricity, which have had stable shares of electricity generation and much less investment.
On the fossil-fuels side of electricity, there’s been a massive shift away from coal and toward the use at natural gas. Coal once dominated the US electricity sector, with an absolute annual peak of 2,016 TWh produced during 2007. This represented 48.5% of all US electricity production that year. In 2019, coal produced 966 TWh of electricity, or 23.5% of US electricity production that year [xxvii]. The past 12 years have seen coal’s share of the electricity production shrink to half of what it was previously, despite only a ~1% drop in total electricity consumption. It’s immediately worth noting the contrast in scale to solar and wind. The drop in electricity production from coal was 5.5x the amount of wind energy produced in 2019, and almost 15x the amount of solar energy produced in 2019. Despite rapid growth in renewables, the scale wasn’t yet there for renewables to displace coal at a national scale. That came from natural gas. In 2007, it accounted for 897 TWh of electricity production; by 2019 it represented 1,582 TWh, (making up for 65% of coal’s decline). Today, natural gas accounts for 38.5% of US electricity production, making it the dominant source of electricity.
The rise of natural gas is largely a function of lower prices, both for construction and operation. After a peak in 2008 at $9.26/1000 cubic feet, a US fracking boom in shale gas led to prices for natural gas for electricity producers falling steeply [12]. Prices dropped nearly 50% the next year and have continued a steady downward trend since then. In 2019, the price for natural gas reached below $3 [xxviii]. Natural gas combined cycle plants also benefitted from low capital costs, high efficiencies, and fast construction times [xxix]. Coal-fired power plants are no longer competitive, and the last new coal plant to be built within the US was in 2015 [xxx].
For the most part, economics is what drove the shift in electricity generation sources. Electricity is a commodity; neither your toaster nor the power lines carrying power across the country can tell the difference between electricity generated from a solar panel or a coal plant. As a result, electricity functionally has the same selling price, regardless of source [13]. Profits, therefore, almost entirely depend on cost, and no metric captures cost of electricity better than the Levelized Cost of Electricity (LCOE). Windmills and solar panels are different from a natural gas or nuclear power plants since they have functionally zero marginal costs. Unlike nuclear or natural gas power plants that must keep buying fuel, once a windmill or solar panel is built and the upfront cost is paid, there’s little cost to the owner beyond general maintenance. The LCOE essentially represents the total costs paid for a generator (including interest, tax credits, maintenance, fuel, etc.) divided by the amount of electricity produced [xxxi].
From this LCOE perspective, renewables are the cheapest [14] source of electricity available in the US. The EIA estimates that solar’s LCOE is around $33/MWh, before tax incentives, for new plants entering service in 2025, compared to $34/MWh for onshore wind, $37/MWh for natural gas, and $40/MWh for hydroelectric plants [xxxii]. Furthermore, both wind and solar have been getting steadily cheaper over time as production and installations have grown [15] – from 2015 to 2020, the cost of wind electricity fell 5% annually, while the cost of solar electricity fell 11% annually [xxxiii], as shown in the graph below:
Figure 5: LCOE of Wind and Solar Electricity, 2009 – 2020 [xxxiv]
That cost advantage means that solar and wind should be built out at an increasingly rapid rate – the explosive growth discussed earlier is only the early stages of wind and solar electricity being competitive in certain regions. As solar and wind become more competitive in more regions, an acceleration in deployment is likely. In 2019, wind, solar, and natural gas accounted for 46%, 18%, and 34% (respectively) of planned capacity additions during the year, while coal, natural gas, and nuclear accounted for 53%, 27%, and 18% (respectively) of planned capacity retirements [xxxv]. Cheaper sources are winning out, at the expense of older, more expensive ones.
Figure 6: Grid Additions and Retirements: From Coal to Renewables and Natural Gas [xxxvi]
1.4 How far do we need to go to get to a 100% Zero-carbon Power Grid?
One of President Biden’s campaign targets was to achieve a zero-carbon power grid by 2035 [xxxvii]. That’s an ambitious goal, one that will require considerable effort and resources to be even potentially feasible. Different forecasts produce different estimates of how much capacity the power grid will need in the future. These numbers vary due to differing assumptions in energy efficiency, the speed of electrification of other sectors, and the presence of net-zero policies. Predicting the future is hard – especially when that future is 30 years out – but these estimates can provide a helpful guide for how much capacity the grid will need.
The National Renewable Energy Laboratory (NREL) published the Electrification Futures Study in 2018 indicating ~4,700 TWh of electricity demand in 2050 under a business-as-usual approach, ~5,650 TWh under a “Medium” scenario (which involves some easily accomplished electrification), and ~6,500 TWh under a “High” scenario (where a more aggressive electrification approach is taken). The same study estimated that national peak demand could reach 838, 997, and 1114 GW under the business-as-usual, Medium, and High scenarios respectively [16][xxxviii]. The “High” scenario implies a kind of transformative growth in electrification (though not necessarily broad enough for a net-zero society), and the numbers imply a ~70% increase in capacity for the power grid (both in terms of energy and power).
Another estimate by Jacobson et al. [xxxix] uses a first-principles approach to determining a “goal” grid size: first, they forecast total energy use in 2050 by country (using data from the IEA and EIA), and then examine the effect that 100% electrification would have. After obtaining a 45% estimate on overall efficiency improvements [17], they estimate that total, end-user electricity use (i.e. the amount of electricity that actually reaches homes, businesses, and industry) is ~11,300 TWh [18]. Assuming a 5% transmission loss [xl], that means the US would need to produce ~11,900 TWh [19] of electricity each year. For comparison, in 2019, the US delivered [20] ~3,700 TWh of electricity to consumers. Therefore, we’d need to grow the power grid by roughly 200% [21] in order to cope with such a transition – and to make the grid zero-carbon, all existing and all new generation would need to come from nuclear, wind, solar, and other zero-carbon sources. That 45% is a critical assumption – if the overall savings are a more conservative 35%, we’d need to bolster the size of the grid by about 260% [22] to support a net-zero transition.
Regardless of whether the NREL study or the Jacobson et al. study turns out to be more accurate, we’ll need to vastly expand renewable electricity production. Considering that zero-carbon sources didn’t even produce 40% of the electricity the US used in 2019, transitioning to a zero-carbon grid within 15 years is quite the moonshot [23]. It isn’t a straightforward solution – merely scaling up the existing power grid by adding more wind and solar capacity won’t cut it.
1.5 Reliability Concerns from Variable Renewable Energy’s Intermittency and Seasonality
Intermittency and seasonality are two crucial issues with wind and solar that create reliability issues, on different ends of time scales: intermittency raises a minute-to-minute or day-to-day issue, while seasonality represents a more annual problem.
Wind and solar belong to a class of electricity sources called Variable Renewable Energy (VRE) – essentially, the output from these sources of electricity is hard to reliably predict. We can estimate, on average, the amount of electricity that a wind turbine or solar panel will produce in a specific location (given historical weather data, for example). However, there’s little control we get over the output on a second-by-second level. Generators fueled by nuclear or fossil fuel sources are controllable; operators can turn them on or off as they see fit. A wind turbine or solar panel, however, may produce different amounts of electricity from one minute to the next (e.g. due to cloud cover) or one day to the next (e.g. due to a weather system passing through the area, creating cloudy conditions for a few consecutive days), which creates an issue for grid operators. For example, a windy/sunny day may be followed by a calm/overcast one [24]. At any given instant, supply must match demand, which is difficult to accomplish given the high intermittency from wind and solar if these sources account for a large percentage of the grid’s generation capacity.
A slightly different issue that nevertheless manifests itself on a similar scale is a phenomenon referred to as a “duck curve” [xli]. In an area with sizeable market penetration of rooftop commercial/residential solar (which is “behind-the-meter”, in that electricity generation occurs at the consumer site and thus affects how much power the user draws from the grid in the first place), the amount of power demanded drops during the daytime as solar panels begin producing energy. At night, however, electricity use ramps up quickly: both due to solar panels no longer producing behind-the-meter power, and also as “gross” [25] power demand rises (e.g. when people come home from work and begin cooking and running the laundry). This in turn creates a need for higher grid infrastructure flexibility, as generators need to be able to shut down during the day and restart to meet the evening demand. Intermittency issues can be mitigated by deploying energy storage systems and spreading generation across a wider variety of geographies [26][xlii].
Figure 7: The Duck Curve [xliii]
Figure 8: CA Solar Electricity Production by Hour [xliv]
At a larger scale, seasonality refers to patterns in electricity production over the course of a year. Solar panels produce may more electricity in the summer (when days are longer) than in the winter [xlv]; wind turbines tend to produce more electricity during the spring and less during the back half of the summer – in California, for example, wind power has an average capacity factor of over 40% during the late spring months and below 20% during the winter [xlvi]. The pacific northwest region of the US has less variation in wind seasonality, but capacity factors dip below 25% from September through January, and reaches around 35% from March through June. For solar, the US produced about 10 TWh of solar electricity in July of 2020, but only just above 5 TWh in December of 2020 [xlvii]. A true zero-carbon grid can’t just have enough capacity for spring days when wind and solar electricity generation is plentiful and overall electricity demand is low; reliability requires the grid being able to match supply with demand even during periods of cloudy and cold/hot of days (when electricity usage peaks to keep homes warm/cool and when generation is weakest). Seasonality can be mitigated with capacity overbuilding – though due to lower utilization of the overbuilt capacity, such generation is inherently less profitable.
Figure 9: Wind Capacity Factors Vary by Region and Season [xlviii]
The rest of this thesis attempts to answer the question of how we get from eighteen hundred (million metric tons of annual emissions) to zero, given the hurdles that we know of (especially seasonality and intermittency). A variety of proposed solutions exist, each of them tackling one piece of the puzzle – reliability, new generation capacity, energy storage, etc. I’ll discuss those solutions, explore some scenarios that combine those solutions, and then discuss some policies that could be enacted to accelerate the transition to a bigger, better power grid. However, it’s worth noting that specifics are difficult to come by – estimating exactly how much of any one solution we’ll need is foolhardy and pointless – we can’t really know exactly how much energy storage we’ll need, or how much excess capacity we’ll need to build. In the end, getting to a fully decarbonized power grid is going to require an all-of-the-above approach, as frustratingly nebulous as that may be.
[1] https://www.mckinsey.com/business-functions/sustainability/our-insights/climate-math-what-it-takes-to-limit-warming-to-1-point-5-degrees-c mentions a few of these: “If we lose our forests, which would happen at higher-climate-change levels, that will cause more global warming… similarly, losing ice cover warms the Earth. And so the global warming that is leading to the ice loss could then drive further global warming.”
[2] This means that other emitted gases (e.g. methane, nitrous oxide) were converted to CO2 emissions using the 100-year Global Warming Potential. Some gases also have different rates of affecting the climate: for example, methane warms the atmosphere much more than carbon dioxide does over 20 years than it does over a 100 year timescale. More information is available at https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
[3] For some perspective, annual global emissions from all sources are roughly around 50 gigatons (or 50,000 million metric tons) in CO2e – this entire paper is focused on roughly three-and-change percent of global annual emissions.
[4] A railcar holds about 200,000 pounds of coal. Readers interested in other conversions for more intuitive units can find various conversion factors at https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references.
[5] I use a Value of a Statistical Life of $8.3 million, and inflation adjust the author’s estimate from 2011 to 2020 using https://www.bls.gov/data/inflation_calculator.htm. See Appendix A2 for a more thorough discussion on the costs of externalities associated with electricity production.
[6] This is ignoring the emissions associated with production of that equipment, which aren’t necessarily zeroed out through a zero-carbon power grid.
[7] It’s worth noting that not all industrial processes are currently at a stage that’s ripe for electrification; some, such as the manufacturing of cement or steel, are going to be more tricky to decarbonize.
[8] In 2005, the US produced 606 grams of CO2-equivalent emissions for each kWh of electricity generated. In 2018 (the most recent year for which I could find all the necessary data), that figure dropped to 431 g CO2e / kWh – a 29% drop. This hasn’t just been driven by renewables – it’s also due to all forms of generation becoming more efficient, and coal-fired power plants being replaced natural-gas ones.
[9] I’d recommend the NREL Electrification Futures Study (https://www.nrel.gov/docs/fy21osti/72330.pdf) to the reader interested in understanding how different levels of electrification affect the build-out of the US power grid.
[10] While energy storage is growing in size, the amount of energy that we could store in total currently represents very little of the electricity generated or consumed on any given day. This is the fundamental driver behind the need to perfectly balance supply and demand. Once energy storage capacities are far higher, it may be possible to overproduce electricity during one part of the day, and use the surplus to satisfy demand during a period of time when production may be lower. More on this later.
[11] These don’t add up to 100% due to rounding.
[12] You can see the explosion in production with the charts at https://www.eia.gov/energyexplained/natural-gas/where-our-natural-gas-comes-from.php.
[13] There are extra revenue opportunities in some markets for carbon-free power, though the general point holds true: there’s one electricity market settlement price.
[14] Since fuel costs and electricity produced can vary from place to place (e.g. solar panels will produce more energy in Arizona than in New England), accurate LCOE estimates can only be assigned to a particular technology in a particular region. Therefore, LCOE estimates are usually given either as a range (best-case to worst-case) or a capacity-weight average (the average LCOE, weighted by the size of the generators)
[15] Swanson’s Law is the name of this phenomenon for solar, though the more generalized version is called Wright’s Law, which basically relates a doubling in production to a percentage decline in cost (https://ark-invest.com/wrights-law/). Wright’s Law has been applied to multiple industries, though “experience curves” and “cost curves” are frequently applied to modeling the cost of renewable energy production and battery production.
[16] The “Medium scenario” involves electrification in transportation, heat pumps, and some industrial settings, and the “High scenario” involves a “transformational change” in the scope of electricity usage.
[17] This is the 45% figure mentioned earlier toward the end of Section 1.2. The 45.3% reduction comes from three sources: (1) 27.6% from higher efficiency in electrified processes (e.g. electric transportation, heat pumps for heating, etc.), (2) 10.9% from eliminating fossil-fuel infrastructure (e.g. procurement, transport, refining, etc.), and (3) 6.8% from further energy efficiency due to public policy. I later use 35% in what-if analysis as a more conservative reduction estimate by reducing the first two factors by 10% and eliminating the third altogether.
[18] Regrettably, Jacobson et al. publish energy use as an average annual load. This is obviously confusing, as the listed units are in GW, rather than actual units of energy, like GW-years. We convert their estimate of 1291.4 GWy to TWh as follows: 1291.4 GWy x (33.434 Quads / GWy) x (293.07 TWh / Quad) = 11,320. TWh
[19] 11320 TWh / 0.95 = 11916 TWh
[20] This figure is after transmission & distribution (T&D) losses on the power grid – there’s some level of inefficiency in transporting electricity on power lines; this figure accounts for that. We convert the source’s Quads figure to TWh as follows: 12.7 Quads x (293.07 TWh / Quad) = 3,722 TWh.
[21] (11320 – 3722) / 3722 = 204.1%
[22] With only 35% efficiency savings, the US grid would need to deliver (11320 / 0.55) x 0.65 = 13,378 Quads of electricity. (13378 – 3722) / 3722 = 259.4%
[23] It’s worth noting that while this may be a moonshot, it’s only one of many needed. Cleaning up and scaling the US electricity sector is, metaphorically speaking, a drop in the bucket of fighting climate change, since similar transitions will be necessary across the globe. As hinted at earlier, fighting climate change not only requires a change in the way we use energy (the electrification of buildings, industry, and transport) but also a revamp of how we use land (e.g. the agricultural and forestry sector) – exploring any of these topics could merit their own theses.
[24] https://www.cmu.edu/ceic/assets/docs/publications/working-papers/ceic-07-12.pdf provides actual data showing variation in energy production across multiple days at the resolution of minutes to seconds.
[25] “Net” load refers to the overall power consumption (load) at a given moment, after subtracting out VRE production (i.e. wind and solar). I use the term “gross” load to refer to the amount of load before subtracting out VRE production.
[26] While weather is correlated from one location to the next, that correlation decreases as the locations grow farther apart. Summing up all of the wind or solar resources on a grid across a variety of geographies may increase a grid operator’s ability to forecast electricity generation from those units, which in turns assists with balancing supply and demand. This might seem to contradict the earlier notion that a larger percentage of wind and solar makes it harder to balance the grid; even though solar and wind electricity generation may be more predictable, there’s still a larger percentage of the grid’s power that’s subject to variability: while solar power may be plentiful one day, it may be lower the next, though the grid must be able to reliably provide power under prolonger scenarios of cloudy weather.
Sources
[i] https://www.ipcc.ch/sr15/chapter/spm/
[ii] https://www.ipcc.ch/site/assets/uploads/sites/2/2019/02/SPM3a.png
[iii] https://www.iea.org/articles/global-co2-emissions-in-2019
[iv] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions
[v] https://cfpub.epa.gov/ghgdata/inventoryexplorer/#electricitygeneration/allgas/source/current
[vi] https://cfpub.epa.gov/ghgdata/inventoryexplorer/
[viii] https://www.epa.gov/greeningepa/greenhouse-gases-epa
[ix] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions#transportation
[xi] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions
[xiii] Emissions Data from https://cfpub.epa.gov/ghgdata/inventoryexplorer/#electricitygeneration/allgas/source/current, and Electricity Production Data is from https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php
[xiv] https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8386924
[xv] https://ars.els-cdn.com/content/image/1-s2.0-S2542435117300120-mmc3.pdf, page 45
[xvi] https://www.epa.gov/greenpower/us-electricity-grid-markets
[xvii] https://www.eia.gov/electricity/data/eia411/pdf/peak_load_2016.pdf
[xviii] https://www.eia.gov/energyexplained/electricity/delivery-to-consumers.php
[xix] https://www.eia.gov/electricity/annual/html/epa_01_02.html, Table 4.2
[xx] https://nuclear.duke-energy.com/2015/02/18/capacity-factor-a-measure-of-reliability
[xxi] https://www.eia.gov/electricity/annual/html/epa_04_08_a.html and https://www.eia.gov/electricity/annual/html/epa_04_08_b.html
[xxiii] https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php
[xxviii] https://www.eia.gov/dnav/ng/hist/n3045us3a.htm
[xxix] https://www.sciencedirect.com/science/article/pii/B9780857090133500018
[xxx] https://www.carbonbrief.org/mapped-worlds-coal-power-plants
[xxxi] https://www.eia.gov/todayinenergy/detail.php?id=35552
[xxxii] https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf, page 6
[xxxiii] https://www.lazard.com/perspective/levelized-cost-of-energy-and-levelized-cost-of-storage-2020/
[xxxiv] https://www.lazard.com/perspective/lcoe2020
[xxxv] https://www.eia.gov/todayinenergy/detail.php?id=37952
[xxxvi] https://www.eia.gov/todayinenergy/detail.php?id=37952
[xxxvii] https://joebiden.com/clean-energy/
[xxxviii] https://www.nrel.gov/docs/fy18osti/71500.pdf, page xiv (13 in the PDF for energy, 14 for power).
[xxxix] https://ars.els-cdn.com/content/image/1-s2.0-S2542435117300120-mmc3.pdf
[xl] https://www.eia.gov/tools/faqs/faq.php?id=105&t=3
[xli] https://www.energy.gov/eere/articles/confronting-duck-curve-how-address-over-generation-solar-energy
[xlii] https://www.nature.com/articles/s41467-020-18602-6
[xliii] https://www.bloomberg.com/news/articles/2021-03-11/california-s-solar-industry-is-getting-sunburned
[xliv] https://www.bloomberg.com/news/articles/2021-03-11/california-s-solar-industry-is-getting-sunburned
[xlv] https://www.iso-ne.com/about/what-we-do/in-depth/solar-power-in-new-england-locations-and-impact
[xlvi] https://www.eia.gov/todayinenergy/detail.php?id=20112
[xlvii] https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_1_01_a
[xlviii] https://www.eia.gov/todayinenergy/images/2015.02.25/main.png
