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| Fig. 1: Price of photovoltaic panels over time, measured in 2019 dollars per watt. (Image Source: K. Bailey, after Sodhi et al. [1]) |
As worldwide energy demand and concern about climate change both grow each year, there has been further development of renewable energy resources, such as solar and wind power, to supplement and potentially replace fossil fuels in the future. Over time, the cost of solar energy has been decreasing, making it a more competitive alternative to fossil fuels. Measured in 2019 US dollars, the cost of solar energy decreased from $2 per watt in 2010 to less than $0.50 per watt in 2019. [1] The cost has been decreasing with the help of improvements in manufacturing processes and government subsidies. [1] Fig. 1 shows the steady decrease in prices of photovoltaic panels over time. While solar energy becomes more attractive as prices decrease, solar panels require sufficient surface area available to work. Let us make a simplified calculation to estimate the theoretical area of solar panels needed to meet worldwide energy demand.
In order to estimate the area of solar panels needed, we start with the worldwide energy consumption value from 2021: 595.15 EJ. [2] We then divide this number by the solar constant, 1366 W m-2, which is the energy flux from solar radiation at the top of Earth's atmosphere. [3] Taking the solar panel efficiency o be 14% and assuming that one place on Earth receives approximately 12 hours of daylight per day, we find that the area of solar panels needed to be the sole source of energy worldwide is [3]
| 5.9515 × 1020 J
y-1 1366 W m-2 × 3600 sec h-1 × 24 h d-1 × 365 d y-1 |
× | 1 0.14 |
× | 24 h 12 h |
= | 1.97 × 1011 m2 |
As a comparison, a radius of R = 6378 km for the earch gives a surface area of the Earth of [3]
| 4πR2 = 4π × (6.378 × 106 m)2 = 5.11 × 1014 m2 |
This means that solar panels would have to cover roughly 0.04% of Earth' surface. The surface area of land on Earth is about 29% of the total area or 1.48 × 1014 m2. [3] Therefore, solar panels would have to cover about 0.13% of land area on Earth.
While some may be encouraged that the area required represents a small percentage of Earth's surface area, this estimation has many limitations. First of all, the number I used for the total energy for the world is a carbon-based fuel equivalent value. [2] Instead of adding the amount of renewable energy used, BP adds the amount of fossil fuel energy that would be required to generate that same amount of electric energy, taking average power plant efficiency into account. [2] Thus, the number I used in this calculation is larger than the actual amount of energy consumed worldwide in 2021, and this makes my area estimate larger. In addition, the solar constant I used is likely larger than the amount of solar radiation that would actually reach the solar panels due to factors such as latitude, angle of the sun, and energy losses as solar radiation travels from the top of the atmosphere to the ground. Ignoring these factors makes my area estimate smaller. The amount of daylight experienced per day is location dependent and varies at different times of the year, so 12 hours per day may not be an accurate estimation when taking these factors into account. Overall, the amount of energy generated using solar panels depends on location, so it is an important factor in deciding where to use solar energy. In general, solar panels will generate the most energy in locations with the most direct sunlight, often in hot, dry locations. In all, solar panels can be an effective renewable energy source.
© Kathleen Bailey. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] M. Sodhi et al., "Economic Lifetimes of Solar Panels," Procedia CIRP. 105, 782 (2022).
[2] "BP Statistical Review of World Energy 2022," British Petroleum, June 2022.
[3] R. L. Jaffe and W. Taylor, The Physics of Energy (Cambridge University Press, 2018).