Solar Power
This training reviews how solar power will contribute to a clean and stable electric grid. This training is part of a series of trainings on achieving a clean electric grid and some of the main technologies that will get us there.
Background on solar power
Most of the solar power we generate comes from photovoltaic (PV) systems. A solar PV cell uses semiconductor materials like silicon to convert sunlight to electricity using the photovoltaic effect. Solar panels can be deployed in a “distributed” fashion in places like rooftops and parking lots, or in large and more cost-effective “solar farm” arrays (a.k.a. “utility-scale solar”).
A less common source is concentrated solar-thermal power (CSP). This approach uses a vast array of mirrors that direct sunlight to a single receiver. The receiver is usually composed of a tower containing a fluid like molten salt or water. The heated fluid can then be used to power a heat engine like a steam turbine. But since solar PV is far cheaper and more ubiquitous than CSP, we’ll focus on the former in this training.
How solar power supports a clean and stable electric grid
Once a solar array is installed, it produces essentially no climate pollution (aside from the energy needed to maintain and eventually decommission the system). The solar cells simply soak up sunshine and turn it into clean electricity.
Solar PV costs have fallen dramatically in recent decades. It now costs 85% less than just a decade ago. In fact, utility-scale solar PV is now the cheapest source of new electricity in the U.S. on average (see the FAQ below for more on cost comparisons). As a result, planned solar projects are planned to expand solar capacity operated by the electric power sector 38% this year (from 95 gigawatts (GW) at the end of 2023 to 131 GW by the end of 2024). Overall, solar energy still accounts for just under 4% of all electricity generated in the U.S., but a significant percentage in several southwestern states, as the map below from Lawrence Berkeley National Lab illustrates.
Issues with solar power
The primary issue with solar power lies in its intermittency and variability — it can only generate electricity when sunlight reaches the solar cells. That means the amount of energy solar panels can provide is reduced during cloudy weather and is essentially zero at night. This issue can be alleviated through a variety of approaches, including by coupling solar panels with energy storage systems, complementing them with firm power sources (i.e. geothermal power, hydroelectricity, nuclear power, and bioenergy and gas with carbon capture), spreading out wind and solar farms (which often produce peak power at different, complementary times) over large geographic areas connected by long-distance transmission lines, and implementing electricity demand response.
Siting solar panels also requires a significant amount of land area. But the 2021 Princeton Net-Zero America report estimated that in total, deploying the needed amount of solar panels to reach net-zero emissions would require less than 0.5% of total U.S. land area. That’s only about one-hundredth as much land as is devoted to agriculture, and less than five times the land area of American golf courses. The land use issue can also be somewhat alleviated by combining solar panels with other uses, like installing them on rooftops and parking lots, or on farms with crops that thrive in the shade that the panels provide (an approach called “agrivoltaics”).
Sometimes local opposition can block the installation of solar facilities. In 2022, local governments rejected 80 solar projects. This opposition is often catalyzed by anti-renewable energy groups, based on a mix of legitimate concerns about land use and misinformation about the environmental and health impacts of solar panels. This local opposition can be countered by other local residents expressing their support for solar projects.
Another concern is that as of 2021, China was involved in more than 80% of solar panel component manufacturing. The U.S. put tariffs on Chinese solar panels in 2012 due to accusations that they were receiving unfair subsidies and using forced labor. The Inflation Reduction Act provided incentives for companies to develop domestic solar supply chains, but in the meantime those tariffs are a topic of ongoing debate and raise the cost of solar power in the United States.
How much could solar power contribute to a clean and stable electric grid?
According to the Princeton Net-Zero Report, in 2050 the U.S. will need 9 to 39 times more solar power than today in order to reach net-zero emissions depending on the scenario. That’s between 637 and 2,700 gigawatts (compared to about 70 gigawatts in 2021), accounting for between 26% and 42% of America’s total electricity generation in 2050.
The large range depends on a variety of factors. For example, how much total electricity is needed, which depends on how much each sector of the economy electrifies, how fast we can install new solar panels, and how much electricity demand is met by other technologies.
Other FAQs
What about claims that solar panels are bad for the environment?
Every item we use requires raw materials that need to be mined and manufactured into a final product. Solar panels particularly need silicon and copper, and those minerals have to be mined and made into solar cells. These activities have environmental and carbon footprints.
But those impacts are vastly less than those from the fossil fuel energy they will replace. For example, nearly 8 billion tons of coal were mined, and over 4 billion tons of crude oil were extracted from the ground in 2020 alone globally. For comparison, the World Bank estimates that a pathway to meet the Paris targets would require less than 3.5 billion tons of minerals in total over the next three decades.
To generate energy from fossil fuels we have to burn them and then extract more from the Earth in a never-ending cycle. Conversely, the minerals to make a solar panel only have to be extracted once, and then most of the materials can be recycled. Solar panels do contain some metals like lead that can eventually leach out if they are disposed of in a landfill instead of being recycled.
Additionally, technological developments will probably reduce the environmental impact of future solar panels.
How much energy can we get from distributed solar?
Installing distributed solar panels on places like rooftops and parking lots has the benefit of producing clean electricity right where the demand is located. It thus reduces the need for long-distance transmission lines. But by lacking the economies of scale that come from big solar farms, distributed solar is more expensive and there’s less space to install it.
As a result, the Princeton Net-Zero Report estimates that in 2050, about 33% of U.S. electricity will come from utility-scale solar compared to just 5% from distributed solar. Both are important, but utility-scale solar is expected to play a larger role in a decarbonized economy due to its size and cost advantages.
How do solar costs compare when including energy storage?
Comparing costs between different energy generation technologies is a challenge. Because solar energy is variable, by itself it can’t fully displace a consistent on-demand “dispatchable” source of energy like fossil fuels or clean firm alternatives. But because the U.S. does not yet put a price on carbon pollution, fossil fuel energy doesn’t reflect the additional costs associated with its climate damages.As our deployment of solar energy ramps up, it can simply begin to displace some of the generation from more expensive alternatives. For example, fossil fuel power plants could run less often during the day and provide backup during cloudier weather and at night. But as solar power becomes a significant percentage of the overall electricity supply, it will more often need to be combined with complementary technologies like energy storage to address the intermittency issue. One recent analysis found that even when including the cost of storage, solar energy is cheaper than many other sources like coal and nuclear, and on par with geothermal power.