Is Solar Energy Actually Renewable?

What is solar energy?

Solar energy is radiant light and heat from the sun that is harnessed using a range of technologies such as solar heating, photovoltaics, and concentrated solar power. Solar panels, also known as photovoltaic panels, convert energy from the sun into electricity. They are made of semiconducting materials which absorb sunlight and convert it into a flow of electrons, generating direct current (DC) electricity.

When sunlight hits the solar panel, the absorbed photons knock electrons free from the atoms in the panel, allowing current to flow. An inverter then converts the DC current into alternating current (AC) electricity that can power homes, businesses and the local utility grid. This process of converting light directly into electricity is called the photovoltaic effect.

Solar energy is considered renewable because the sun will continue burning for billions of years. As long as the sun shines, solar panels can produce electricity. The amount of sunlight that arrives at Earth’s atmosphere provides more than 10,000 times the energy required to power the planet. Solar energy is abundant, inexhaustible and clean.

Citation: https://www.sunrun.com/how-does-solar-energy-work

The renewable debate

Solar energy is often referred to as a renewable energy source because it relies on the sun, which will continue emitting energy for billions of years (1). However, some argue that solar power is not truly renewable due to the materials and processes required to manufacture solar photovoltaic (PV) systems (2).

Those who claim solar is not renewable point to the mining and materials required to produce solar panels and other system components. Solar PV cells rely on certain rare earth metals and silicon that must be extracted from the earth through mining operations (3). Panels also utilize aluminum, glass, and plastics that require fossil fuels for manufacturing. Some experts argue that since solar relies on the extraction of non-renewable resources, the technology cannot be considered truly renewable (2).

Furthermore, the manufacturing process for solar PV cells and modules generates carbon emissions and toxins that can impact the environment. Life cycle analyses estimate that manufacturing accounts for around 15-20% of a solar panel’s overall emissions (4). The use of fossil fuels and chemicals in mining, purification, and fabrication suggests solar is not as “clean” or sustainable as often claimed when considering the full lifecycle impacts (3).

Sources:

(1) https://www.energybrokers.co.uk/news/net-zero/is-solar-energy-really-renewable

(2) https://www.johnlocke.org/is-solar-energy-really-renewable-is-it-free/

(3) https://www.carolinajournal.com/opinion/solar-energy-neither-renewable-nor-free/

(4) https://www.nrel.gov/docs/fy13osti/56487.pdf

Solar energy resources

The sun produces enormous amounts of energy through nuclear fusion reactions in its core, where hydrogen atoms fuse into helium [1]. In fact, the sun produces 380,000,000,000 terajoules of energy every second [2], which is far more than humanity’s current and future energy needs. The sun is able to produce such vast amounts of energy because it contains over 99% of the solar system’s mass. The sun’s immense gravity produces the pressure and temperature required to sustain fusion reactions that release energy according to Einstein’s famous equation E=mc2. While solar energy will remain abundant for billions of years, it represents only a tiny fraction of the sun’s total energy output that reaches Earth. Even so, the amount of solar energy striking Earth in one hour could meet the world’s energy needs for an entire year if properly harnessed.

Lifespan of solar panels

Solar panels typically have a lifespan of 20-30 years before they start generating noticeably less energy and need replacing (1). The key metric used to measure lifespan is called the “degradation rate”, which refers to the slow decline in energy generation capacity over a solar panel’s lifetime. Most solar panels lose around 0.5-1% of their power output per year. After 20-25 years, most panels will have around 80% of their original capacity. While solar panels can still function past their warranty period of around 25 years, at some point it makes sense to replace them with newer, more efficient models for optimal energy production (2). Proper maintenance and cleaning can help maximize the lifespan of solar panels.

Some factors that affect solar panel lifespan include panel technology, climate and weather conditions like temperature swings, humidity, and hail, as well as physical damage from events like storms. High-quality solar panels made with robust materials and advanced engineering can typically last longer. Location also plays a role, with harsher conditions causing more wear and tear. With regular inspections and care, solar panels can keep functioning for 20-30+ years in many areas before replacement is warranted.

Sources:
(1) https://www.energysage.com/solar/how-long-do-solar-panels-last/
(2) https://www.igs.com/energy-resource-center/energy-101/how-long-do-solar-panels-last

Recycling solar panels

While solar panels can last over 30 years, eventually they need to be replaced as their efficiency declines. Historically, recycling methods for solar panels have been limited. One report found that around 80% of solar panels are disposed of in landfills. However, new and improved recycling processes are being developed.

Traditional glass-based solar panels can be recycled by separating the frame, junction box, cables, and film layers. The glass, silicon, and silver can then be repurposed. New polymer-based panels require chemical recycling methods to separate the plastic layers. Recycling companies like Veolia are investing in advanced solar panel recycling technology and facilities.

The solar industry has also created recycling standards to prepare for the large volume of panels that will need recycling in the coming decades. While currently only 10-15% of panels are recycled, methods and capacity are rapidly improving according to industry analysis. Most experts expect recycling rates to increase dramatically within the next 5-10 years.

Mining required for solar

While solar panels do require some mined resources like silicon, the quantities needed are minimal compared to fossil fuels. Fossil fuels require continuous mining and drilling to extract coal, oil and gas from the earth. The National Energy Technology Laboratory estimates that a typical 500 MW coal facility requires over 13,500 acres of land to be continuously mined each year, producing over 125 million tons of coal annually [1].

In contrast, a large solar farm requires minerals like silicon, copper and glass, but only during the initial manufacturing stage. Once installed, a solar farm can generate clean electricity for decades with no need for further mining. Studies show the mining requirements per kWh for solar PV are hundreds of times less than fossil fuels [1]. While not completely free of mining impacts, solar’s upfront resource needs make it far more sustainable than continual fossil fuel extraction.

Energy Payback Time

The energy payback time (EPBT) refers to the length of time a solar panel must operate to generate the same amount of energy that was used to produce it. Most estimates find solar panels take 1-4 years to ‘pay back’ this energy cost of production ^[1]. The exact EPBT depends on the type of solar panel technology, where it is manufactured, and how much sunlight the region receives.

For example, a 2021 life cycle assessment of solar panels found mono-crystalline silicon panels have an EPBT of 2.7 years and thin-film panels have an EPBT of 1.1 years in Southern Europe ^[2]. This means it takes roughly 1-3 years for a solar panel to generate the equivalent energy that was used to produce it. After this break-even point, solar delivers a net energy gain over the many decades of its usable lifespan.

The EPBT is getting shorter over time as manufacturing becomes more energy efficient. Researchers predict the EPBT could reach 6-12 months for panels produced in the near future ^[3].

Emissions in manufacturing

While solar panels produce no emissions during operation, some emissions do result from manufacturing the panels. However, multiple lifecycle assessments show that the carbon footprint of solar energy is far lower than fossil fuels like coal and natural gas. According to an analysis by the National Renewable Energy Laboratory (NREL), life cycle greenhouse gas emissions from solar PV systems are similar to other renewables and nuclear energy, and are much lower than coal (NREL). Overall, NREL found harmonized greenhouse gas emissions estimates for utility-scale solar PV of 18-30 grams CO2 equivalent per kWh, compared to about 1000 g CO2e/kWh for coal (NREL).

While emissions are higher during manufacturing compared to the operation phase, solar panels offset far more emissions over their lifetime by displacing fossil fuel generation. According to EnergySage, solar panels offset their embedded carbon footprint, which accounts for manufacturing emissions, within just 1-4 years of operation. After that, solar panels continue displacing fossil fuel emissions for 20-30+ more years (EnergySage). So over the full lifecycle, solar results in a dramatic net reduction in emissions compared to fossil fuels.

Land Usage Challenges

Utility-scale solar power plants require a significant amount of land area. According to research, solar farms need around 5-10 acres per megawatt of installed capacity. To put this in perspective, a 200 MW solar farm would require 1,000 to 2,000 acres of land (source). This can present challenges for finding large, undeveloped plots suitable for utility-scale projects.

In contrast, rooftop solar panels utilize existing structures and do not take up additional land space. Rooftop solar allows otherwise unused rooftop area to generate clean electricity. Even though an individual rooftop system may have less capacity than a large solar farm, aggregating rooftop capacity across homes and buildings in a given area can produce meaningful energy contributions while preserving land resources (source).

Rooftop solar avoids land usage tradeoffs and environmental considerations associated with clearing new ground for utility projects. With rooftop solar, clean energy generation and land conservation goals can be achieved simultaneously.

Conclusion

Overall, solar energy is widely considered renewable despite some limitations and challenges. While solar panel manufacturing has some emissions and minerals need to be mined, the energy payback time is relatively fast. Solar panels can last 20-30 years, and most components are recyclable. While solar farms require large land areas, rooftop solar minimizes land usage. Compared to fossil fuels which will run out and continue emitting greenhouse gases, solar power is clean, renewable, and sustainable for the long-term energy needs of the planet.

However, solar isn’t perfect. The intermittent nature of solar makes energy storage a key challenge. Recycling infrastructure and processes need further development as well. There are also some emissions and land impacts from solar, so growth must be paired with thoughtful policies. Overall though, solar energy is predominantly renewable, especially compared to non-renewable fossil fuel sources.