After being manufactured, wind and solar technologies can generate energy without direct emissions and, as such, would appear to be a simple solution to our energy challenges. However, even though adding some wind and solar to the grid can be valuable, forcing the grid to rely 100% on wind and solar is very risky.
Every energy technology has its pros and cons: Fossil fuels have drawbacks, notably their emissions, their need to be extracted them from the Earth, and their wastes; but, they are very reliable and have a very high density energy, so they require very little land use. Wind and solar can generate energy without direct emissions or the need for fuel to operate; however, they are intermittent – relying on the weather, which we all know is something you do not rely on. They also have low energy density – requiring enormous land use, high costs, significant infrastructure requirements, and they rely on fossil fuels for their construction. These lesser known facts are highlighted in the documentary “Planet of the Humans”, directed by Jeff Gibbs, with Michael Moore as the executive producer.
An important point that is often overlooked is that the drawbacks of a technology become more apparent the more the technology is used. The negative impacts of fossil fuels are noticeable because we heavily rely on them: they supplied 81% of the world’s energy and 64% of the world’s electricity in 2018 . The negative impacts of wind and solar have not been obvious, largely because they have had such limited impact: they supplied 2% of the world’s energy and 7% of the world’s electricity in 2018 . If we were to try to rely on wind and solar for all the energy that we get from fossil fuels, their drawbacks would be much more obvious and severe. Let’s explore this topic more.
Wind and solar power plants rely on intermittent sources of energy that vary with the weather. We cannot control the weather, so we cannot control the output from wind and solar power plants. As a result, even though we can sometimes get sufficient energy from them, wind and solar alone cannot guarantee us energy all the time, especially during extreme weather events (e.g. storms, extended freezes, heat waves) – when we need them the most. When only modest amounts of intermittent wind and solar are on the grid, intermittency is manageable, as the dispatchable sources (fossil and nuclear) can supply energy when wind and solar are unable to. However, at 100% wind and solar penetration, the full capacity of the grid would be intermittent with no dispatchable energy support. This would drastically increase the risks of grid outages and insufficient supply. Adding excess wind and solar capacity alone will not solve the problem, as it is only a matter of time when the weather pattern will prevent any amount of wind turbines and solar panels from producing meaningful amounts of energy, for example: very low or very high wind speeds outside of the wind turbines’ operating range will result in minimal generation from wind farms ; at night and during times of heavy cloud cover, the output of solar farms is negligible as well. And there are times of year when low or high winds occur at night or during cloud cover.
Intermittency management strategies such as industrial scale battery storage have been proposed to facilitate 100% wind and solar. While this solution to decarbonization is theoretically possible, it is not practical or cost effective. According to the Clean Air Task Force, if the California Internal System Operator (CAISO) were to supply its entire 2018 demand with 50% wind and 50% solar, surplus energy generated during the peak summer season would need to be stored for use during the winter, when both wind and solar generation is low. To store all of this energy would require a battery system with 35,946,633 MWh of storage capacity; this is approximately 14% of California’s annual electricity demand (Figure 1) .
To gain further perspective of the impacts of intermittency, if one were to attempt to capture all of the surplus energy generated under this scenario during the periods of highest wind and solar peak, the Clean Air Task Force estimates that “you would need a storage system equivalent in instantaneous capacity larger than the generating capacity of the entire U.S. electric grid” .
Figure 1: California energy surplus and deficit in CATF 2018 50% Wind, 50% Solar scenario 
Wind and solar have the potential to generate a lot of energy at times when conditions are just right. However, these conditions do not reliably occur, so generation will seldom be at that magnitude. But the battery system must capture all of the surplus wind and solar energy produced, so it will need to be able to match that maximum capacity, even if it is only for short spurts. These requirements for storage size and charge/discharge capacity result in the need for a massive battery system. Manufacturing such a large system will be very expensive, and will have significant environmental impacts due to the necessary mining of huge quantities of raw materials, notably lithium and cobalt.
Replacing existing fossil fuel power plants and constructing wind and solar farms will also incur significant costs. Examining the cost impact of wind, solar, and batteries for California, the Clean Air Task Force predicts energy supply costs will increase exponentially as wind and solar penetration approaches 100% when battery systems are installed to support them: $57/MWh at 60%, $389/MWh at 80%, and $1,402/MWh at 100% wind, solar, and batteries  (Figure 2). By way of comparison, it costs about $30/MWh from coal.
Figure 2: The majority of battery storage capacity would be used for seasonal storage, very little (about 1%) of capacity would actually output electricity every day. Most of the battery capacity is only discharged a few times per year, but the annual levelized cost of that storage must be paid off throughout the year. The result is a very high cost per MWh for seasonal storage. The predicted MWh cost of a mixed energy system including firm (reliable) carbon-free sources is shown to the right of pure wind and solar 
Even with the assumption that capital costs will decrease by ~85% from their 2018 rates (~$500/kWh to $80/kWh), the capital cost of building a storage system capable of supporting 100% wind and solar for the California’s system is $2.9 trillion . This is greater than California’s 2019 real GDP of $2.8 trillion . Such high costs can deter the public from believing we can achieve carbon-neutral energy generation and will ultimate prove difficult to implement into policy.
Furthermore, even with the use of mitigation strategies, the intermittency of wind and solar presents insurmountable challenges at high penetration. According to a meta-study of 40 deep grid-decarbonization studies, assuming the U.S. were to upgrade to a sufficient amount of nationwide high-speed transmission lines, have a widespread deployment of battery storage, and have sufficient demand flexibility (through controllable electrical vehicle charging), an 100% wind and solar energy supply would still need to curtail the equivalent of 40% of annual demand, meaning 40% of the annual demand would be wasted .
On top of wasted electricity, wind and solar will also generates enormous solid waste as the turbines and panels reach the end of their useful lifetimes. Wind turbines (specifically the blades) are designed to have a lifespan of 20 years , and solar panels are expected to last approximately 30 years . Wind turbine blades, which contribute the most to wind power waste, are difficult to recycle, as they are made from a composite ; so, they must be disposed of, usually in landfills. According to research conducted by Cambridge University, the cumulative waste resulting from wind turbines is predicted to be 43 million tonnes by 2050, assuming wind energy will account for 17% of the world’s electricity demand . Solar panels are theoretically recyclable, but the process is much more expensive than putting them in landfills . According to the International Renewable Energy Agency, cumulative solar panel waste is predicted to be 78 million tonnes by 2050, assuming solar energy will account for 16% of the world’s electricity generation . Together, this waste is equal in mass to 40% of the plastic waste generated by all industrial sectors in 2015 (302 million tonnes) .
It is important that we recognize potential drawbacks of each energy technology in our efforts to sustainably meet the growing energy demand of our global society. We must find energy solutions that can mitigate our greenhouse gas emissions while supplying all people with reliable, clean energy with minimal impact on the environment.
While it is not practical to depend on wind and solar for 100% of our electricity, that doesn’t mean wind and solar cannot play an important role in our sustainable energy future, along with proper amounts of other low-carbon or carbon-negative technologies.
1 – “Data & Statistics.” IEA, 1 Jan. 2021, www.iea.org/data-and-statistics?country=WORLD.
2 – “How Do Wind Turbines Survive Severe Storms?” Energy.gov, Department of Energy, www.energy.gov/eere/articles/how-do-wind-turbines-survive-severe-storms#:~:text=The%20cut%2Din%20speed%20(typically,its%20maximum%2C%20or%20rated%20power.
3 – Cohen, Armond. “Re: SB 100 Joint Agency Report: Charting a Path to a 100% Clean Energy Future, Docket No. 19-SB-100.” Clean Air Task Force, 19 Sept. 2019, www.catf.us/wp-content/uploads/2020/01/CATF-Comments-SB100-Letter-1.pdf.
4 – “U.S. Federal State of California – Real GDP 2000-2019.” Statista, Statista, 20 Jan. 2021, www.statista.com/statistics/187834/gdp-of-the-us-federal-state-of-california-since-1997/#:~:text=In%202019%2C%20the%20real%20GDP,was%202.79%20trillion%20U.S.%20dollars.
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8 – Shellenberger, Michael. “If Solar Panels Are So Clean, Why Do They Produce So Much Toxic Waste?” Forbes, Forbes Magazine, 28 May 2019, www.forbes.com/sites/michaelshellenberger/2018/05/23/if-solar-panels-are-so-clean-why-do-they-produce-so-much-toxic-waste/?sh=ea8da23121cc.
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