Solar and Wind Power: Overview of the Key Advantages & Challenges
Solar and wind power evoke a wide range of emotions. The emotions are based on the perceived benefits and drawbacks of the technologies. This article provides a realistic overview of the key advantages and challenges of solar and wind power.
Background
In case of solar power, semiconductor materials such as silicon are used to convert sunlight to electricity. In case of wind power, wind turbines are used to convert the energy in wind to electricity. These technologies are very different from fossil fuel power technologies such as natural gas power and coal power. In case of fossil fuel power, natural gas or coal is burned to produce heat energy which is then converted to electricity.
The contribution of solar and wind power to global electricity was trivial until a couple of decades ago (Figure 1)¹. But it has increased very rapidly in recent years.
The global share of solar and wind power was about 14% in 2023².
Key Advantages
The first advantage of solar and wind power is the massive availability of sunlight and wind. The sunlight or solar energy received by earth in just one and half hours is comparable to the energy consumed by the global population in a year³.
What about wind? There is enough wind energy to supply over five times our yearly global energy consumption⁴. So, in theory, the potential for solar and wind power is extremely high.
The second advantage is that the lifecycle greenhouse gas emissions from solar and wind power are very low (Figure 2)⁵.
Obviously, this is a critical advantage from the viewpoint of addressing our climate challenge.
The costs of solar and wind power have decreased markedly in recent times. This leads to the third advantage.
Solar and wind power have a low levelized cost of electricity or LCOE. This metric is often used to compare the costs of the different technologies in the power sector. LCOE includes the upfront cost and operating and maintenance costs of the power technology over its lifetime. I must make an important note here. The LCOE costs of solar and wind power do not provide the complete picture. More about this later in the article.
The fourth advantage is that solar and wind power do not emit pollutants during operations. This is because unlike fossil fuel power, solar and wind power do not burn fuel to produce electricity.
Solar and wind power are attractive solutions to address climate change because of these major positives.
Key Challenges
But solar and wind power also have some major challenges. I will spend more time discussing the challenges because this discussion is more complex.
The challenges of solar and wind power arise from two crucial facts about their sources.
· Sunlight and wind are very dilute sources of energy.
· Also, they are intermittent sources because sunlight and wind are not available as and when needed.
Let us first consider the challenge associated with the dilute nature of solar and wind energy.
Metrics such as energy density and power density provide information about how dilute the energy source is⁶. Based on any reasonable metric, solar and wind energy are more than a thousand times dilute compared to fossil fuels.
We will review the case of solar power as an example. Earth receives massive amounts of sunlight. But the amount of sunlight received per unit area is small⁷.
This makes it challenging to capture the sunlight. Why? Because it is difficult to harness energy from an extremely dilute energy source. For example, it is very difficult to fish in a large lake that only has a few fish.
The dilute nature of the energy sources leads to two specific challenges for solar and wind power.
Solar and wind power require far more critical minerals than fossil fuel power technologies. This large need for critical minerals is the first challenge.
Critical minerals are those that are required for important applications and have a risk of supply disruption⁸. Example applications are high technology devices, defense applications and energy technologies.
Solar power requires sixteen times more critical minerals compared to fossil fuel power per unit of electricity produced over the life of the power plant⁹𝄒¹⁰. Onshore wind power requires twelve time more critical minerals, while offshore wind requires fourteen times more.
This is not a problem right now. But the large need for critical minerals can become a serious challenge when the use of solar and wind power is increased massively. I have discussed this in an earlier article.
The land requirements are also much higher for solar and wind power. This is the second challenge.
A utility scale solar power plant requires over hundred times more land than a natural gas power plant to produce the same amount of electricity per year¹¹. A utility scale wind power plant requires several hundred times more land than a natural gas power plant.
The power plants are usually built near high population centers to improve economics and minimize electricity losses. Land access can be an issue near highly populated regions. This will be especially the case when the use of solar and wind power is massively expanded. I have discussed details in an earlier article.
Alternative options are available to eliminate the land challenge. Rooftop solar and offshore wind do not require any land. But rooftop solar and offshore wind are far more costly in many regions. For example, in the United States, rooftop solar is over two times more costly per unit of electricity produced compared to utility scale solar¹². Also, offshore wind is two and half times more costly than onshore wind¹³.
Residential solar has a markedly higher cost because of its tiny scale. Residential solar systems produce small amounts of electricity. In contrast, utility-scale power plants produce electricity on a very large scale. Consequently, a utility-scale power plant has an advantage of economy of scale. Economy of scale refers to the principle that large-scale production often has a lower cost per unit produced as compared to a small-scale production¹⁴.
Next, we will review why discussing costs of solar and wind power is not straight forward.
The intermittent nature of sunlight and wind leads to a major difference between how electricity is supplied by the different power technologies. Fossil fuel and nuclear power can supply electricity when we need it. The supply from these power technologies does not depend on the weather conditions.
On the other hand, solar power can supply electricity only when there is sunlight. Wind power can do so only when the wind is blowing.
Why is the nature of electricity supply so important? Because our society has stringent electricity needs. We need continuous electricity for certain applications at our homes, industries, and other facilities. For other applications we need electricity in short bursts. The demand for electricity fluctuates with time. Our current lifestyle is possible because the electrical grid can supply electricity to meet our 24X7 demand. Operators control the supply of electricity such that it matches the demand every second, every minute and every hour and day of the year.
Solar and wind power have inherent challenges to meet out 24X7 electricity demand. Why? Because operators cannot control the output from solar and wind power. Weather controls their output. There is uncertainty associated with solar and wind power. Also, the electricity output can vary dramatically because the amount of sunlight and wind can vary hour-to-hour, day-to-day and season-to-season.
This has important implications. Solar and wind power produce high amounts of electricity during certain times, for example when the sunshine and wind are at their peak. But at certain other times, when there is low sunlight and wind, they produce very little electricity. Moreover, the low sunlight and wind conditions can extend from many hours to weeks. Think about the cloudy and calm days that all locations experience from time to time.
This means that solar and wind power cannot be used to meet 24x7 electricity demand without the use of supporting technology options. A high share of solar and wind power in the electricity mix requires the extensive use of supporting options such long duration energy storage, back-up generators and massive electrical grid upgrades and expansions. These options are not cheap and add substantially to the electricity costs. For example, the long duration energy storage is very expensive¹⁵𝄒¹⁶𝄒¹⁷.
The costs of the supporting options must be included when discussing high share of solar and wind power. The levelized cost of electricity (LCOE) metric, that we discussed earlier does not include such costs. Efforts are underway to decrease the costs. But there is a limit to such cost reductions. I will discuss the future costs of electricity in a net zero world in my next article.
Currently, many regional electrical grid systems have a 10% or higher share of electricity from solar and wind power¹⁸. Next, we will review how these systems adapt to the deficiencies of solar and wind power.
Each grid system has some level of flexibility, i.e., the ability to do more than which is typically required.
For example, excess capacity or redundancy is required for the time-periods when some power plants are unable to generate electricity because of operating or other issues. Such flexibility is needed to maintain a high reliability of the system during periods of stress. The deficiencies of solar and wind power are accommodated by using the existing flexibility of the grid system.
Several adjustments are needed during the time-periods when the output from solar and wind is too high or too low. One example is to import or export electricity from and to the neighboring regions. Another example is to curtail or decrease output from solar and wind power during peak periods. A third example is to increase or decrease the output from existing dispatchable power plants.
Such adjustments typically cause a sub-optimization of the system, i.e., they have a negative impact overall. This is expected considering that these adjustments are made to adapt to the inherent deficiencies of solar and wind power. A price must be paid for the inherent challenges of solar and wind power.
The need for the suboptimal adjustments increases as the share of solar and wind power increases¹⁹. I will discuss California as an example. The share of solar and wind power has increased rapidly in California, from less than 5% in 2010 to over 30% in 2023²⁰𝄒²¹. The need to curtail electricity has also increased rapidly.
The amount of electricity curtailed from solar and wind power has increased from a trivial amount in 2010 to over 2.5 billion kWh in 2023²².
How much is this curtailed amount? Over 60 countries in the world use less electricity than this per year²³. The African nation Chad, which has a population of 18 million, uses only a tenth of the electricity curtailed by California²⁴.
Solutions to decrease the curtailment are available and California will use these in the coming years. But the solutions are not cheap. They will add to the overall cost.
The costs associated with the adjustments that are required to adapt to the deficiencies of solar and wind power are not included in the LCOE metric. This means that the LCOE metric only provides partial costs for solar and wind power.
The U.S. Energy Information Administration (EIA) lists solar and wind power in a separate category to prevent direct LCOE comparisons between the different power technologies²⁵. Solar and wind are listed as resource constrained technologies. While fossil fuel and nuclear power are listed as dispatchable technologies.
Extreme views versus Facts
Currently we are amidst an unfortunate clash of extreme views about solar and wind power. Proponents of solar and wind power only focus on the advantages of solar and wind power. They ignore or downplay the challenges and the related implications. On the other end, detractors mainly focus on the challenges of solar and wind power.
Such extremes views are leading to confusion about the path forward. For example, some people now believe that solar and wind power are perfect solutions to address climate change and no other solutions must be considered. Others believe that solar and wind power cannot provide reliable electricity and should not be used. The extreme views, which are driven by emotions, are making it more difficult to address climate change.
A robust approach is to focus on the facts. These inform us that solar and wind power are important solutions to address climate change. Facts also inform us that the inherent challenges of solar and wind power should be carefully considered when developing a path forward. I will discuss one such path in an upcoming article.
Summary
Solar and wind power have several important advantages. They are powered by almost limitless sources. They produce low greenhouse gas emissions and can produce low-cost electricity. They do not use fuel to produce electricity and so do not emit pollutants during electricity production.
The challenges arise from the dilute and intermittent nature of sunlight and wind. Solar and wind power require far more land and critical minerals than fossil fuel technologies. They produce high levels of electricity during certain periods and low levels during some periods. Because of the variable and uncertain nature of the output, solar and wind power can provide low-cost electricity only when their share in the electricity mix is low to moderate. Even so, the true cost is more than the popularly discussed LCOE costs. This is because the LCOE costs do not include the costs arising from the suboptimal adjustments of the existing system.
The suboptimal adjustments are required to adapt to the inherent deficiencies of solar and wind power. At high global shares of solar and wind power, it will be essential to include expensive supporting options such as long duration energy storage, backup power and a massive grid upgrades and expansions.
Extreme views are making it difficult to use these options efficiently to address climate change. Overall, the facts show that solar and wind power are important technologies to address climate change. But it is important to consider their challenges when developing energy policies to address climate change.
References & Notes
[1] U.S. Energy Information Administration. International Data. Electricity generation.
[2] EMBER. Electricity data explorer. https://ember-climate.org/data/data-tools/data-explorer/
[3] U.S. Department of Energy. Energy efficiency and renewable energy. How does Solar work? https://www.energy.gov/eere/solar/how-does-solar-work
[4] PNAS. Global potential for wind generated electricity. https://www.pnas.org/doi/10.1073/pnas.0904101106
[5] United Nations Economic Commission for Europe (March 2022). Lifecycle assessments of electricity generation options. https://unece.org/sed/documents/2021/10/reports/life-cycle-assessment-electricity-generation-options
[6] Energy policy, 123, 83, 2018. https://www.researchgate.net/publication/327239302_The_spatial_extent_of_renewable_and_non-renewable_power_generation_A_review_and_meta-analysis_of_power_densities_and_their_application_in_the_US
[7] U.S. EIA: Solar explained. https://www.eia.gov/energyexplained/solar/
[8] U.S. Geological Survey: Critical Minerals. https://www.usgs.gov/science/critical-minerals
[9] IEA Report, 2021. The role of critical minerals on clean energy transitions. https://www.iea.org/reports/the-role-of-critical-minerals-in-clean-energy-transitions
[10] IEA provides data based on capacity (per MW). But the capacity factor or availability of wind and solar power to generate electricity is lower than natural gas and coal power. Also, the life of solar and wind power is lower than natural gas and coal power. So, a solar or wind power plant with the same capacity as a fossil fuel power plant produces much lower electricity over the life. A more relevant approach is to compare the materials required per unit electricity produced by the power plants over the lifetime. I have converted the IEA data from materials required per capacity to materials required per unit electricity generated over the lifetime. I have used average data from IEA reports for the capacity factors and lifetimes. I have used the average of natural gas and coal power to represent fossil fuel power. https://www.iea.org/data-and-statistics/charts/average-annual-capacity-factors-by-technology-2018https://www.iea.org/reports/energy-technology-perspectives-2023
[11] Oakridge National Laboratory (2017): Environmental quality and U.S. power sector- air quality, water quality, land use and environmental justice. https://www.energy.gov/sites/prod/files/2017/01/f34/Environment%20Baseline%20Vol.%202--Environmental%20Quality%20and%20the%20U.S.%20Power%20Sector--Air%20Quality%2C%20Water%20Quality%2C%20Land%20Use%2C%20and%20Environmental%20Justice.pdf
[12] National Renewable Energy Laboratory (September 2022): U.S. Solar photovoltaic system cost and energy storage benchmark: Q1 2022. https://www.nrel.gov/docs/fy22osti/83586.pdf
[13] U.S. Energy Information Administration. Levelized generation costs (2023). https://www.eia.gov/outlooks/aeo/additional_docs.php
[14] Britannica. Economy of scale. https://www.britannica.com/topic/economy-of-scale
[15] U.S. Department of Energy. The pathway to long duration energy storage commercial lift off. https://liftoff.energy.gov/long-duration-energy-storage/
[16] Currently, the project cost of solar and wind power plant with just 12 hours of battery storage is five times more than the cost of a natural gas power plant to provide the same amount of annual electricity. The practical energy storage needs for most regions will be 24+ hours to many days. Thus, the project costs with current technology will be extremely high. Data for costs is from the following references. https://www.eia.gov/outlooks/aeo/assumptions/pdf/elec_cost_perf.pdf https://www.nrel.gov/docs/fy23osti/85332.pdf Green hydrogen is even more costly.
[17] Upfront cost of concentrated solar with thermal for only 12 hours of storage is also about five times more than natural gas power plants. This is the low-end cost. Energy storage that is substantially longer than 12 hours would be required for providing 24x7 electricity. https://www.iea.org/reports/projected-costs-of-generating-electricity-2020
[18] U.S. Energy Information Administration. International Data. Electricity generation.
[19] IEA: Projected costs of generating electricity 2020. https://www.iea.org/reports/projected-costs-of-generating-electricity-2020
[20] California energy commission. Total system electricity generation spreadsheet. https://www.energy.ca.gov/data-reports/energy-almanac/california-electricity-data/2021-total-system-electric-generation
[21] U.S. EIA. California. Profile analysis. https://www.eia.gov/state/analysis.php?sid=CA#49
[22] California ISO. Managing the evolving grid. https://www.caiso.com/about/our-business/managing-the-evolving-grid
[23] U.S. EIA data. Electricity. https://www.eia.gov/international/data/world/electricity/electricity-consumption
[24] World Bank data. Population of Chad. https://data.worldbank.org/indicator/SP.POP.TOTL?locations=TD
[25] U.S. Energy Information Administration: Levelized cost of new generation resources in the annual energy outlook 2022. https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf
