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What is the cheapest form of energy storage?

Author: Evelyn

Mar. 07, 2024

168 0

Tags: Energy

As the global consciousness shifts towards sustainable practices, the demand for renewable energy has never been more pronounced. The urgency to mitigate the environmental impacts of conventional energy sources has propelled the exploration and adoption of renewable alternatives. This brief overview will delve into the growing significance of renewable energy and the pivotal role it plays in addressing the challenges posed by climate change.

With the specter of climate change looming, the imperative to transition from fossil fuels to cleaner and more sustainable energy sources has gained unprecedented momentum. Governments, industries, and individuals worldwide are recognizing the need to reduce carbon emissions and embrace environmentally friendly alternatives. Renewable energy, encompassing sources like solar, wind, hydropower, and geothermal, stands at the forefront of this transformative shift.

The growing importance of renewable energy is underscored by its inherent ability to harness power from the natural elements without depleting finite resources or emitting harmful pollutants. This transition not only addresses environmental concerns but also fosters energy security, reduces dependency on fossil fuels, and opens new avenues for technological innovation.

Introduction to the Concept of Solar Energy Storage

Within the realm of renewable energy, solar power emerges as a beacon of promise. The sun, an abundant and perennial source of energy, can be harnessed through photovoltaic cells to generate electricity. However, one of the challenges associated with solar power is its intermittent nature, dependent on weather conditions and daylight availability. Introducing the concept of solar energy storage becomes paramount in addressing this intermittency, ensuring a consistent and reliable power supply even when the sun is not shining.

In the subsequent sections, we will delve into the various facets of solar energy storage, examining the different methods, efficiency considerations, and cost-effectiveness, with the ultimate goal of identifying the most pragmatic solutions for a greener and economically sustainable future.

What is Solar Energy Storage?

Harnessing the power of the sun through solar panels has revolutionized the energy landscape, but the intermittent nature of sunlight poses a challenge for a consistent power supply. Solar energy storage addresses this challenge by capturing excess energy generated during peak sunlight hours and storing it for use during periods of low or no sunlight. This section explores the definition, significance, and various methods employed in solar energy storage.

Solar energy storage refers to the process of capturing and storing excess energy produced by solar panels for later use, ensuring a continuous and reliable power supply. The significance of solar energy storage lies in its ability to address the intermittency of sunlight, enabling a seamless integration of solar power into the broader energy grid. This not only promotes energy independence but also contributes to grid stability and reliability.

Solar energy storage systems play a crucial role in maximizing the utilization of solar power, allowing users to access electricity even when the sun is not shining. This capability is particularly essential for residential, commercial, and industrial applications, where a consistent power supply is imperative for daily operations.

Brief Explanation of Different Methods:

Storing Solar Energy Without Batteries

One method of storing solar energy without batteries involves the use of solar thermal technologies. In solar thermal systems, excess energy is used to heat a fluid, such as molten salt or water, which can then be stored in insulated tanks. This stored thermal energy can be converted back into electricity when needed, providing a continuous power supply.

Another approach involves using compressed air energy storage, where excess energy is used to compress air and store it in underground reservoirs. During periods of low sunlight, the compressed air is released, driving a turbine to generate electricity.

Storing Solar Energy in Batteries

Battery storage is a widely adopted and versatile method for storing solar energy. During peak sunlight hours, excess energy generated by solar panels is stored in batteries for later use. Lithium-ion batteries are commonly used due to their high energy density, efficiency, and relatively low maintenance requirements. These batteries provide a reliable and scalable solution for residential, commercial, and utility-scale applications.

Additionally, lead-acid batteries and emerging technologies such as flow batteries and solid-state batteries are also being explored for their potential in solar energy storage, offering different combinations of cost, performance, and sustainability.

Types of Solar Energy Storage Systems

Effective solar energy storage involves a diverse array of technologies, each with its unique strengths and applications. In this section, we provide an overview of various solar energy storage technologies, encompassing battery-based systems, thermal energy storage, pumped hydro storage, and flywheel energy storage.

Overview of Various Storage Technologies

  • Battery-Based Systems: Battery-based systems are among the most prevalent and versatile solutions for solar energy storage. Lithium-ion batteries, commonly used in electric vehicles and renewable energy applications, have gained prominence due to their high energy density, efficiency, and relatively long lifespan. These batteries store excess solar energy during periods of sunlight and release it when demand exceeds the solar generation. Other battery technologies, such as lead-acid batteries and emerging options like flow batteries, offer different trade-offs in terms of cost, performance, and environmental impact.
  • Thermal Energy Storage: Thermal energy storage systems store solar energy in the form of heat. This category includes technologies like molten salt storage, where concentrated solar power systems use mirrors to focus sunlight on a receiver, heating molten salt to high temperatures. This stored heat can be used to generate steam and drive turbines, producing electricity when needed. Thermal energy storage is known for its extended storage durations and ability to provide continuous power, even after the sun has set.
  • Pumped Hydro Storage: Pumped hydro storage is a well-established and widely used form of energy storage. Excess electricity is used to pump water from a lower reservoir to an upper reservoir during times of high energy availability. When electricity demand increases, water is released from the upper reservoir to the lower reservoir, passing through turbines to generate electricity. Pumped hydro storage is valued for its large-scale capacity, rapid response times, and ability to store energy over extended periods.
  • Flywheel Energy Storage: Flywheel energy storage systems store energy by spinning a rotor (flywheel) at high speeds and converting kinetic energy into electricity when needed. Excess solar energy is used to accelerate the flywheel, and when electricity demand rises, the kinetic energy is converted back into electricity. Flywheel systems are known for their quick response times and ability to provide short bursts of high-power output.

Understanding the characteristics and applications of these diverse storage technologies is crucial for tailoring solar energy storage solutions to specific needs, whether at a residential, commercial, or utility scale. In the subsequent sections, we will delve into the advantages, limitations, and considerations for each type of solar energy storage system, aiding in the selection of the most suitable technology for various applications.


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What is the Most Efficient Way to Store Solar Energy?

Efficiency is a paramount consideration in selecting a solar energy storage method, impacting both the economic viability and environmental sustainability of renewable energy systems. This section conducts an analysis of efficiency across different storage methods, discusses factors influencing efficiency, and aims to identify the most efficient and cost-effective solutions.

Analysis of Efficiency in Different Storage Methods

Battery-Based Systems:

Battery systems exhibit high round-trip efficiency, indicating how effectively stored energy can be retrieved. Lithium-ion batteries, for example, often achieve efficiencies above 90%. However, it's essential to consider factors like self-discharge rates and degradation over time, which can affect overall efficiency.

Thermal Energy Storage:

The efficiency of thermal energy storage depends on the specific technology used. Molten salt storage systems, prevalent in concentrated solar power applications, can achieve high efficiencies due to their ability to store and release heat effectively. However, thermal losses during the storage and conversion processes can impact overall efficiency.

Pumped Hydro Storage:

Pumped hydro storage systems are known for their high round-trip efficiency, often exceeding 80%. The efficiency is influenced by factors such as the elevation difference between reservoirs, turbine and pump efficiency, and losses in the water conveyance system.

Flywheel Energy Storage:

Flywheel systems offer rapid response times and high-power output but may have lower round-trip efficiency compared to some other technologies. The efficiency is influenced by factors such as frictional losses and energy losses due to air resistance.

Discussion on Factors Influencing Efficiency

  • System Design: The design of the storage system, including the components used and their configuration, can significantly impact efficiency. Well-designed systems maximize the conversion and retrieval of stored energy.
  • Technology-Specific Considerations: Each storage technology has its unique characteristics that influence efficiency. For instance, battery efficiency may be affected by the choice of electrodes and electrolytes, while thermal storage systems are influenced by the insulation and heat transfer mechanisms.
  • Temperature and Environmental Conditions: Temperature plays a critical role in the efficiency of many storage technologies, especially batteries. Extreme temperatures can affect the chemical reactions and overall performance, influencing efficiency.
  • Cycle Life and Degradation: The longevity of the storage system, including the number of charge-discharge cycles it can endure before degradation, is crucial. Systems with longer cycle life often offer better long-term efficiency.

Identifying the Most Efficient and Cost-Effective Solutions

Selecting the most efficient and cost-effective solar energy storage solution requires a holistic consideration of various factors, including initial costs, maintenance requirements, and the specific energy needs of the application. While lithium-ion batteries are widely used for their high efficiency, other technologies may offer better suitability for certain applications or economic advantages over time.

What is the Cheapest Form of Energy Storage?

As the world seeks sustainable energy solutions, the cost-effectiveness of solar energy storage systems becomes a pivotal factor in their widespread adoption. This section conducts a cost analysis of different solar energy storage systems, evaluates initial setup costs and maintenance expenses, and aims to identify the most budget-friendly options for diverse applications.

Cost Analysis of Different Solar Energy Storage Systems

1. Battery-Based Systems:

  • Lithium-Ion Batteries: The cost of lithium-ion batteries ranges from $200 to $300 per kilowatt-hour (kWh). Prices have been decreasing steadily over the years due to advancements in technology and economies of scale.
  • Lead-Acid Batteries: Lead-acid batteries are generally less expensive, with costs ranging from $100 to $200 per kWh. However, they may have shorter lifespans and lower efficiency compared to lithium-ion batteries.
  • Emerging Technologies (Flow Batteries, Solid-State Batteries): Costs for emerging battery technologies can vary widely, but they are generally higher than those for established lithium-ion and lead-acid batteries. As technology matures and production scales up, costs are expected to decrease.

2. Thermal Energy Storage:

  • Molten Salt Storage: The cost of molten salt storage is influenced by the specific concentrated solar power (CSP) system used.  Costs can range from $20 to $50 per kWh of storage capacity. The upfront infrastructure costs for CSP systems using molten salt can be substantial.

3. Pumped Hydro Storage:

  • The cost of pumped hydro storage varies based on factors such as the size of the facility and the terrain. Large-scale pumped hydro storage projects can have costs ranging from $100 to $500 per kWh, with much of the expense associated with constructing reservoirs and hydraulic structures.

4. Flywheel Energy Storage:

  • The cost of flywheel energy storage systems can range from $500 to $1,000 per kWh. Flywheel systems typically have higher upfront costs due to precision engineering requirements but may have lower maintenance expenses.

Evaluating Initial Setup Costs and Maintenance Expenses

Initial Setup Costs:

  • The cost of setting up solar energy storage systems includes the purchase and installation of components such as batteries, inverters, control systems, and associated infrastructure. Battery-based systems, especially lithium-ion batteries, often have higher initial costs.
  • Pumped hydro storage involves significant construction expenses related to reservoirs, turbines, and pump stations.
  • Thermal energy storage requires specialized equipment for capturing and storing heat, contributing to initial costs.
  • Flywheel systems require precision-engineered components, impacting their initial setup costs.

Maintenance Expenses:

  • Maintenance costs vary among different systems. Battery-based systems generally have lower maintenance requirements, while pumped hydro storage may incur maintenance expenses related to mechanical components and water conveyance systems.
  • Thermal energy storage systems may require periodic inspections and maintenance of heat capture and release mechanisms.
  • Flywheel systems may have lower maintenance requirements compared to some other technologies.

Identifying the Most Budget-Friendly Option

The choice of the cheapest way to store solar energy depends on the specific context and requirements of the project. Lithium-ion batteries are often favored for their versatility and decreasing costs, but other technologies like pumped hydro storage and molten salt storage can be more cost-effective in certain situations. As technology evolves and markets change, it's essential to stay informed about the latest developments in the energy storage sector.


  1. How Long Can Solar Energy Be Stored?

While there are differences in battery types, a standard solar battery can store energy for one to five days.

2.   How to Store Solar Energy at Home?

The approach that is most commonly used for storing solar energy in residential systems is by far the use of batteries. A chemical reaction occurs among the battery's constituent parts when solar energy is introduced. This reaction stores the energy. When the battery is depleted, the reaction is reversed, enabling current to flow out of the battery.

3.   Is it worth storing solar energy?

The importance of solar storage to you may change if you utilize a lot of grid electricity. If you want to get as much of your energy usage off the grid as possible, solar storage is a fantastic alternative for lowering your dependency on the power grid.


Determining the cheapest way to store solar energy involves considering a range of factors, including the initial cost, efficiency, lifespan, and maintenance expenses of various storage technologies. While lithium-ion batteries have dominated the market with their proven track record and decreasing costs, emerging technologies like flow batteries, compressed air energy storage, and thermal energy storage present promising alternatives. The optimal choice depends on the specific requirements of the application, geographic location, and available resources.

As technology continues to evolve and economies of scale drive down costs, the landscape of solar energy storage is likely to undergo further transformations. Government incentives, research and development efforts, and market competition will also play crucial roles in shaping the future of affordable and sustainable energy storage solutions. In the pursuit of a cleaner and more sustainable energy future, ongoing innovation and collaboration across various sectors will be key to unlocking even more cost-effective and efficient ways to store solar energy.

The world’s best solar power schemes now offer the “cheapest…electricity in history” with the technology cheaper than coal and gas in most major countries.

That is according to the International Energy Agency’s World Energy Outlook 2020. The 464-page outlook, published today by the IEA, also outlines the “extraordinarily turbulent” impact of coronavirus and the “highly uncertain” future of global energy use over the next two decades.

Reflecting this uncertainty, this year’s version of the highly influential annual outlook offers four “pathways” to 2040, all of which see a major rise in renewables. The IEA’s main scenario has 43% more solar output by 2040 than it expected in 2018, partly due to detailed new analysis showing that solar power is 20-50% cheaper than thought.

Despite a more rapid rise for renewables and a “structural” decline for coal, the IEA says it is too soon to declare a peak in global oil use, unless there is stronger climate action. Similarly, it says demand for gas could rise 30% by 2040, unless the policy response to global warming steps up.

This means that, while global CO2 emissions have effectively peaked, they are “far from the immediate peak and decline” needed to stabilise the climate. The IEA says achieving net-zero emissions will require “unprecedented” efforts from every part of the global economy, not just the power sector.

For the first time, the IEA includes detailed modeling of a 1.5C pathway that reaches global net-zero CO2 emissions by 2050. It says individual behaviour change, such as working from home “three days a week”, would play an “essential” role in reaching this new “net-zero emissions by 2050 case” (NZE2050).

Future scenarios

The IEA’s annual World Energy Outlook (WEO) arrives every autumn and contains some of the most detailed and heavily scrutinised analysis of the global energy system. Over hundreds of densely packed pages, it draws on thousands of datapoints and the IEA’s World Energy Model.

The outlook includes several different scenarios, to reflect uncertainty over the many decisions that will affect the future path of the global economy, as well as the route taken out of the coronavirus crisis during the “critical” next decade. The WEO also aims to inform policymakers by showing how their plans would need to change if they want to shift onto a more sustainable path.

This year it omits the “current policies scenario” (CPS), which usually “provides a baseline…by outlining a future in which no new policies are added to those already in place”. This is because “[i]t is difficult to imagine this ‘business as-usual’ approach prevailing in today’s circumstances”.

Those circumstances are the unprecedented fallout from the coronavirus pandemic, which remains highly uncertain as to its depth and duration. The crisis is expected to cause a dramatic decline in global energy demand in 2020, with fossil fuels taking the biggest hit.

The main WEO pathway is again the “stated policies scenario” (STEPS, formerly NPS). This shows the impact of government pledges to go beyond the current policy baseline. Crucially, however, the IEA makes its own assessment of whether governments are credibly following through on their targets.

The report explains:

“The STEPS is designed to take a detailed and dispassionate look at the policies that are either in place or announced in different parts of the energy sector. It takes into account long-term energy and climate targets only to the extent that they are backed up by specific policies and measures. In doing so, it holds up a mirror to the plans of today’s policy makers and illustrates their consequences, without second-guessing how these plans might change in future.”

The outlook then shows how plans would need to change to plot a more sustainable path. It says its “sustainable development scenario” (SDS) is “fully aligned” with the Paris target of holding warming “well-below 2C…and pursuing efforts to limit [it] to 1.5C”. (This interpretation is disputed.)

The SDS sees CO2 emissions reach net-zero by 2070 and gives a 50% chance of holding warming to 1.65C, with the potential to stay below 1.5C if negative emissions are used at scale.

The IEA has not previously set out a detailed pathway to staying below 1.5C with 50% probability, with last year’s outlook only offering background analysis and some broad paragraphs of narrative.

For the first time this year, the WEO has “detailed modelling” of a “net-zero emissions by 2050 case” (NZE2050). This shows what would need to happen for CO2 emissions to fall to 45% below 2010 levels by 2030 on the way to net-zero by 2050, with a 50% chance of meeting the 1.5C limit.

The final pathway in this year’s outlook is a “delayed recovery scenario” (DRS), which shows what might happen if the coronavirus pandemic lingers and the global economy takes longer to recover, with knock-on reductions in the growth of GDP and energy demand.

The chart below shows how the use of different energy sources changes under each of these pathways over the decade to 2030 (right-hand columns), relative to demand today (left).

Notably, renewables (light green) account for the majority of demand growth in all scenarios. In contrast, fossil fuels see progressively weaker growth turn to increasing declines, as the ambition of global climate policy increases, from left to right in the chart above.

Intriguingly, there are signs that the IEA has been giving greater prominence to the SDS, a pathway aligned with the “well-below 2C” Paris goal. In the WEO 2020, it features more frequently, earlier in the report, and more consistently through the pages, compared with earlier editions.

This is shown in the chart below, which shows the location, by relative page position, of each mention of “sustainable development scenario” or “SDS” in the WEOs published over the past four years.

Solar surge

One of the most significant shifts in this year’s WEO is tucked away in Annex B of the report, which shows the IEA’s estimates of the cost of different electricity generation technologies.

The table shows that solar electricity is some 20-50% cheaper today than the IEA had estimated in last year’s outlook, with the range depending on the region. There are similarly large reductions in the estimated costs of onshore and offshore wind.

This shift is the result of new analysis carried out by the WEO team, looking at the average “cost of capital” for developers looking to build new generating capacity. Previously the IEA assumed a range of 7-8% for all technologies, varying according to each country’s stage of development.

Now, the IEA has reviewed the evidence internationally and finds that for solar, the cost of capital is much lower, at 2.6-5.0% in Europe and the US, 4.4-5.5% in China and 8.8-10.0% in India, largely as a result of policies designed to reduce the risk of renewable investments.

In the best locations and with access to the most favourable policy support and finance, the IEA says the solar can now generate electricity “at or below” $20 per megawatt hour (MWh). It says:

“For projects with low-cost financing that tap high-quality resources, solar PV is now the cheapest source of electricity in history.”

The IEA says that new utility-scale solar projects now cost $30-60/MWh in Europe and the US and just $20-40/MWh in China and India, where “revenue support mechanisms” such as guaranteed prices are in place.

These costs “are entirely below the range of LCOE [levelised costs] for new coal-fired power plants” and “in the same range” as the operating cost of existing coal plants in China and India, the IEA says. This is shown in the chart below.

Onshore and offshore wind are also now assumed to have access to lower-cost finance. This accounts for the much lower cost estimates for these technologies in the latest WEO, because the cost of capital contributes up to half of the cost of new renewable developments.

When combined with changes in government policy over the past year, these lower costs mean that the IEA has again raised its outlook for renewables over the next 20 years.

This is shown in the chart below, where electricity generation from non-hydro renewables in 2040 is now seen reaching 12,872 terawatt hours (TWh) in the STEPS, up from 2,873TWh today. This is some 8% higher than expected last year and 22% above the level expected in 2018’s outlook.

Global electricity generation, by fuel, terawatt hours. Historical data and the STEPS from WEO 2020 are shown with solid lines while the WEO 2019 is shown with dashed lines and WEO 2018 as dotted lines. Source: Carbon Brief analysis of IEA

Global electricity generation, by fuel, terawatt hours. Historical data and the STEPS from WEO 2020 are shown with solid lines while the WEO 2019 is shown with dashed lines and WEO 2018 as dotted lines. Source: Carbon Brief analysis of IEA World Energy Outlook 2020 and previous editions. Chart by Carbon Brief using Highcharts

Solar is the largest reason for this, with output in 2040 up 43% compared with the 2018 WEO. In contrast, the chart shows how electricity generation from coal is now “structurally” lower than previously expected, with output in 2040 some 14% lower than thought last year. The fuel never recovers from an estimated 8% drop in 2020 due to the coronavirus pandemic, the IEA says.

Notably, the level of gas generation in 2040 is also 6% lower in this year’s STEPS, again partly as a result of the pandemic and its long-lasting impact on economic and energy demand growth.

Overall, renewables – led by the “new king” solar – meet the vast majority of new electricity demand in the STEPS, accounting for 80% of the increase by 2030.

This means they overtake coal as the world’s largest source of power by 2025, outpacing the “accelerated case” set out by the agency just a year ago.

The rise of variable renewable sources means that there is an increasing need for electricity grid flexibility, the IEA notes. “Robust electricity networks, dispatchable power plants, storage technologies and demand response measures all play vital roles in meeting this,” it says.

Revised outlooks

The lower costs and more rapid growth for solar seen in this year’s outlook means there will be record-breaking additions of new solar capacity in every year from 2020, the IEA says.

This contrasts with its STEPS pathway for solar in previous years, where global capacity additions each year – net of retirements – have flatlined into the future.

Now, solar growth rises steadily in the STEPS, as shown in the chart below (solid black line). This is even clearer if accounting for new capacity being added to replace old solar sites as they retire (gross, dashed line). Under the SDS and NZE2050, growth would need to be even faster.

Annual net additions of solar capacity around the world, gigawatts. Historical data is shown in red while central outlooks from successive editions of the WEO are shown in shades of blue. The WEO 2020 STEPS is shown in black. The dashed line shows gross additions, taking into account the replacement of older capacity as it retires after an assumed lifetime of 25 years. Source: Carbon Brief analysis of the IEA

Annual net additions of solar capacity around the world, gigawatts. Historical data is shown in red while central outlooks from successive editions of the WEO are shown in shades of blue. The WEO 2020 STEPS is shown in black. The dashed line shows gross additions, taking into account the replacement of older capacity as it retires after an assumed lifetime of 25 years. Source: Carbon Brief analysis of the IEA World Energy Outlook 2020 and previous editions of the outlook. Chart by Carbon Brief using Highcharts

The story of raised outlooks for solar – thanks to updated assumptions and an improving policy landscape – is directly contrasting with the picture for coal.

Successive editions of the WEO have revised down the outlook for the dirtiest fossil fuel, with this year seeing particularly dramatic changes, thanks in part to a “structural shift” away from coal after coronavirus.

The IEA now sees coal use rising marginally over the next few years, but then going into decline, as shown in the chart below (red line). Nevertheless, this trajectory falls far short of the cuts needed to be in line with the SDS, a pathway aligned to the “well-below 2C” Paris target (yellow).

Historical global coal demand (black line, millions of tonnes of oil equivalent) and the IEA’s previous central scenarios for future growth (shades of blue). This year’s STEPS is shown in red and the SDS is in yellow. Carbon Brief analysis of the IEA

Historical global coal demand (black line, millions of tonnes of oil equivalent) and the IEA’s previous central scenarios for future growth (shades of blue). This year’s STEPS is shown in red and the SDS is in yellow. Carbon Brief analysis of the IEA World Energy Outlook 2020 and previous editions of the outlook. Chart by Carbon Brief using Highcharts

This year’s outlook makes particularly drastic changes for India, where the use of coal in electricity generation is seen growing far more slowly than expected last year.

In the STEPS, coal-fired power capacity would grow by just 25 gigawatts (GW) by 2040, the IEA says, which is 86% less than expected in the WEO 2019. Rather than nearly doubling in size from 235GW in 2019, this means that India’s coal fleet would barely grow over the next two decades.

Similarly, growth in the amount of electricity generated from coal in India is now expected to be 80% slower than thought last year, according to the IEA figures.

The IEA expects continued rapid retirements of old coal capacity in the US and Europe, which would by 2040 close 197GW (74% of the current fleet) and 129GW (88%) respectively.

Taken together, and despite a rapid expansion in southeast Asia, this means the outlook – for the first time – sees the global coal fleet shrinking by 2040.

Energy outlook

Taken together, the rapid rise of renewable energy and the structural decline for coal help keep a lid on global CO2 emissions, the outlook suggests. But steady demand for oil and rising gas use mean CO2 only flattens off, rather than declining rapidly as required to meet global climate goals.

These competing trends are shown in the chart, below, which tracks primary energy demand for each fuel under the IEA STEPS, with solid lines. Overall, renewables meet three-fifths of the increase in energy demand by 2040, while accounting for another two-fifths of the total. Smaller increases for oil and nuclear are enough to offset the decline in coal energy use.

Global primary energy demand by fuel, millions of tonnes of oil equivalent, between 1990 and 2040. Future demand is based on the STEPS (solid lines) and SDS (dashed). Other renewables includes solar, wind, geothermal and marine. Source: IEA

Global primary energy demand by fuel, millions of tonnes of oil equivalent, between 1990 and 2040. Future demand is based on the STEPS (solid lines) and SDS (dashed). Other renewables includes solar, wind, geothermal and marine. Source: IEA World Energy Outlook 2020 . Chart by Carbon Brief using Highcharts

The dashed lines in the chart above show the dramatically different paths that would need to be followed to be in line with the IEA SDS, which is roughly a well-below 2C scenario.

By 2040, although oil and gas would remain the first and second-largest sources of primary energy, there would have been declines in the use of all fossil fuels. Coal would have dropped by two-thirds, oil by a third and gas by 12%, relative to 2019 levels.

Meanwhile, other renewables – primarily wind and solar – would have surged to third place, rising nearly seven-fold over the next two decades (+662%). The SDS sees smaller, but still sizeable increases for hydro (+55%), nuclear (+55%) and bioenergy (+24%).

Together, low-carbon sources would make up 44% of the global energy mix in 2040, up from 19% in 2019. Coal would fall to 10%, its lowest since the industrial revolution, according to the IEA.

Despite these rapid changes, however, the world would not see net-zero CO2 emissions until 2070, some two decades after the 2050 deadline that would be needed to stay below 1.5C.

This is despite the SDS including “full implementation” of the net-zero targets set by the UK, EU and most recently China.

(These targets would be only partially implemented under the STEPS, based on the IEA’s assessment of the credibility of the policies in place to meet the goals. For example, table B.4 of the report says that under the STEPS, there is only “some implementation” of the UK’s legally binding target to reach net-zero greenhouse gas emissions by 2050.)

Net-zero numbers

The NZE2050 “case”, describing a route to 1.5C, has been published for the first time this year, because the WEO team agreed “it was time to deepen and extend our analysis of net-zero emissions”, according to IEA director Fatih Birol, writing in the report’s foreword.

Over the past 18 months, major economies announcing or legislating net-zero emissions targets include the UK and EU. Most recently, China announced its intention to reach “carbon neutrality” by 2060. [Forthcoming analysis for Carbon Brief will explore the implications of this goal.]

Carbon Brief analysis of the last four WEOs shows that these developments – along with the publication of the Intergovernmental Panel on Climate Change (IPCC) special report on 1.5C in 2018 – have been accompanied by a significant uptick in coverage of these topics in the WEO.

Whereas the WEO 2017 used the phrase “1.5C” less than once per 100 pages, this increased to five uses in 2019 and eight uses per 100 pages in 2020. The usage of “net zero” is up from once per 100 pages in 2017 and 2018, to six in 2019 and 38 per 100 pages in this year’s report.

However, the NZE2050 case is not a full WEO scenario and so it does not come with the full set of data that accompanies the STEPS and SDS, making it difficult to fully explore the pathway.

This seems “bizarre”, says Dr Joeri Rogelj, a lecturer in climate change and the environment at the Grantham Institute at Imperial College London and a coordinating lead author of the IPCC 1.5C report.

The IEA already publishes lengthy annexes, with detailed information on the pathway for different energy sources and CO2 emissions from each sector, in a range of key economies around the world, under each of its main scenarios. (This year these are the STEPS and SDS.)

Rogelj, who last year joined scientists and NGOs calling for the IEA to publish a full 1.5C scenario, tells Carbon Brief that “all underlying data of the NZE2050 case should be made available with the same detail as the other WEO scenarios”.

Carbon Brief has asked the IEA for such data and will update this article if more details emerge. Rogelj adds:

“The main question, of course, is how the NZE2050 intends to reach its objective of net-zero CO2 emissions in 2050. Of particular interest here is how much and which type of CO2 removal [negative emissions] the scenario intends to use and how it intends to do so while ensuring sustainable development.”

The WEO devotes a full chapter to the NZE2050, with a particular emphasis on the changes that would be needed over the next decade to 2030.

(It also compares the pathway to those set out in the IPCC special report, saying that the NZE2050 case has a comparable CO2 emissions trajectory to the “P2” scenario, which stays below 1.5C with “no or low overshoot” and has relatively “limited” use of BECCS.)

The chart below shows how CO2 emissions effectively plateau to 2030 in the STEPS, remaining just below the level seen in 2019, whereas the NZE2050 case sees a decline of more than 40%, from 34bn tonnes (GtCO2) in 2020 to just 20GtCO2 in 2030.

The power sector contributes the largest portion of the savings needed over the next decade (orange wedges in the chart, above). But there are also important contributions from energy end-use (yellow), such as transport and industry, as well as from individual behaviour change (blue), explored in more detail in the next section.

These three wedges would contribute roughly equal shares of the extra 6.4GtCO2 of savings needed to go from the SDS to the NZE2050 in 2030, the IEA says.

The NZE2050 case would see low-carbon sources of electricity meeting 75% of demand in 2030, up from 40% today. Solar capacity would have to rise at a rate of around 300 gigawatts (GW) per year by the mid-2020s and nearly 500GW by 2030, against current growth of around 100GW.

CO2 emissions from coal-fired power stations would decline by 75% between 2019 and 2030. This means the least efficient “subcritical” coal plants would be phased out entirely and the majority of “supercritical” plants would also close down. The WEO says the majority of this decline would come in southeast Asia, which accounts for two-thirds of current global coal capacity.

Although nuclear would contribute a small part of the increase in zero-carbon generation by 2030 in the NZE2050, the IEA notes that the “long lead time of large-scale nuclear facilities” limits the technology’s potential to scale more quickly this decade.

For industry, CO2 emissions would fall by around a quarter, with electrification and energy efficiency making up the largest shares of the effort. More than 2m homes would get an energy efficiency retrofit during every month this decade, in “advanced economies” alone.

In the transport sector, CO2 would fall by a fifth, not including behavioural shifts counted below. By 2030, more than half of new cars would be electric, up from around 2.5% in 2019.

Behavioural changes

For the first time, this year’s outlook contains a detailed analysis of the potential for individual behaviour change to reduce CO2 emissions. (This is clear even at a simplistic level, with the word “behaviour” mentioned 122 times, against just 12 times in 2019.)

Behavioural shifts, such as cutting down on flights and turning down air conditioning, will play a vital role in achieving net-zero emissions, according to the report.

While the SDS calls for modest changes to people’s lifestyles, such as increased use of public transport, these choices only make up 9% of the difference between that scenario and the STEPS.

By comparison, in the NZE2050 these changes are responsible for nearly a third of the CO2 reductions relative to the SDS in 2030. 

The report includes a detailed analysis of estimated emissions savings from the global adoption of specific actions, including a global switch to line-drying laundry, slower driving speeds and working from home.

The authors estimate that 60% of these changes could be influenced by governments, citing widespread legislation to control car use in cities and Japan’s efforts to limit air conditioning in homes and offices. 

As the chart below shows, changes to people’s transport choices account for the majority of the emissions savings. Road transport (blue bars) accounts for more than half the savings in 2030 and significantly reducing the number of flights accounts for another quarter (yellow).

Around 7% of CO2 emissions from cars come from trips of less than 3km, which “would take less than about 10 minutes to cycle”, according to the authors. In the NZE2050 scenario, all of these trips are replaced with walking and cycling.

The report estimates that behaviour shifts could cut emissions from flying by around 60% in 2030. These include substantial changes, such as eliminating flights of less than one hour long, as well as reducing numbers of both long-haul and business flights by three quarters. 

Even so, due to the growth in aviation that is otherwise expected, total aviation activity in 2030 would still remain around 2017 levels in this scenario.

The remaining savings come from decisions to limit the use of energy in homes, such as turning both heating and air conditioning systems down.

Working from home has the potential to save emissions overall, as the reduction in emissions from commuting is more than three times larger than the increase in residential emissions.

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The report estimates that if the 20% of the global workforce who are able to work from home did so for just one day a week, in 2030 this would save around 18m tonnes of CO2 (MtCO2) globally, as the chart below shows. 

In fact, the NZE2050 scenario assumes that all those who are able to do so, work from home three days a week, amounting to a relatively modest 55MtCO2 savings.

Due to wider changes in the energy mix in NZE2050, the emissions impact of widespread home working is small when compared to the current situation, shown in the left-hand column, or STEPS in 2030, shown in the middle column.

While the report focuses on CO2 emissions from the energy system, it also alludes to the high levels of methane and nitrous oxide resulting from global agriculture and livestock farming in particular.

It notes that without shifts towards vegetarian diets it will be “very difficult to achieve rapid emissions reductions”.

The authors acknowledge that universal adoption of the proposed behaviour changes is unlikely, but suggest there are “alternative ways” in which such changes could combine to yield similar results. 

For example, though some regions may not introduce tougher speed limits, others might decide to cut driving speeds by more than the 7km/h suggested in the report.

Simon Evans was one of more than 250 external peer reviewers who read sections of the World Energy Outlook in draft form.

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