By Sam Clamons
Editor’s Note: This article contains numerical estimates compiled from various research articles. It was reviewed by three climate experts: Casey Handmer, Paul Reginato, and Jonathan Burbaum. Their notes are recorded in the footnotes. Our full dataset and calculations are available for download. We hope this will be a useful starting point for much deeper discussions.
Modern biotechnology is powered by sunlight. Light-gobbling algae, both natural and engineered, are harvested and squeezed for biofuels or dried and pressed to make shoes. We use sugarcane and sugar beets — essentially autonomous, self-replicating, solar-powered biofactories — to mass-produce sugar. That sugar, along with hydrolyzed yeast, form the basic media used to grow genetically engineered E. coli, yeast, and other microbes that make various medicines and foods. At some point in the supply chain, nearly every bioengineered product either is a solar-powered plant or derives its energy from one.
Sunlight is an exquisite energy source. It’s abundant, renewable, and cheap to access. Its consumption produces no greenhouse gasses or toxic byproducts. However, “renewable and abundant” is not the same as “infinitely abundant.” Wildlife, agriculture, and solar electricity generation all use sunlight, too. In principle, all of these processes compete for photons. A joule absorbed to synthesize plastic precursors in an algae can’t also be used to feed a tree or charge a cell phone.
Fortunately, there is a lot of sunlight to go around. While humanity might be forced to make trade-offs between wild plant life and food for humans in the future, it won’t be because we run out of sunlight.
To get a sense of where sunlight goes, we can compare the sunlight inputs to our most sunlight-intensive industries — solar power and agriculture — to the sunlight used by wild organisms, while also accounting for the photons that do nothing but heat the ground or bounce right back into space. These numbers are important enough that scientists around the globe have put effort into estimating them. Just note that these are estimates rather than direct measurements, and they vary between sources. Collectively, these estimates give us an order-of-magnitude picture of Earth’s sunlight budget.
Solar power generation is relatively easy to account for. The Energy Institute’s 2025 Statistical Review of World Energy estimates that humanity’s solar industry currently soaks up sunlight at a rate of approximately 1,200 gigawatts (GW), of which about 240 GW is usefully converted to electricity. If we were to expand our solar capacity to match current global electricity demand at the same conversion efficiency, that absorption would balloon to about 18,000 GW.
What about human agriculture? Figuring out the total amount of sunlight used by humans worldwide is no easy feat, but several groups have attempted it. One somewhat dated but thorough example from 2007 comes from Helmut Haberl and his six co-authors at Klagenfurt University, who use a combination of global crop yields published by the Food and Agriculture Organization and land-use estimates based on satellite imagery. They estimate that human-managed crops, wood, and grazing land together fix about 8 billion metric tons of carbon each year. We can convert carbon mass to stored energy using the energy content of glucose, which comes out to about 1,700 GW. We must also adjust this number upward by 30 percent to account for the increase in agricultural production since 2007.
Different plants convert sunlight to sugar at different efficiencies. A theoretical-best-case estimate comes out to about 10 percent efficiency. This estimate begins with successfully-absorbed photons and ends with final accumulated biomass (for C3 plants, those that use the Calvin cycle for carbon fixation and make up the bulk of plant productivity worldwide) to arrive at 22,000 GW of sunlight absorbed — pretty close to the amount of sunlight required for current global electricity needs.
Determining nature's use of sunlight is more complicated. Natural ecosystems are massively more complex and diverse than agricultural fields, so any estimate of natural photosynthesis will come with large error bars. Nevertheless, there have been rigorous attempts.
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