Absorption needed by scaling efficiency to world’s electricity demand: 1.8TW
Plants mainly convert sunlight (energy inside photons) into sugar. Theoretical best-case efficiency estimate is 10%, about 22TW of absorbed sunlight.
Another way to estimate total sunlight energy is to measure total amount of carbon captured, and convert the energy content of glucose.
A better way to estimate total sunlight absorbed is to look at chlorophyll fluorescence satellite measurements that directly converts to GPP (Gross Photosynthetic Productivity).
Different part of earth’s bio-ecosystem absorb carbon differently. Majority is C3, grasslands (and crops) is C4. Desert uses CAM (water efficient photosynthesis). Ocean tend to use carbonate CO2 rather than dissolved.
Satellite measurements can’t estimate amount of photosynthesis inside the ocean.
Measure dissolved O2
estimate carbon absorption by tracing carbon isotope
fluorescent measurement to estimate concentration of chlorophyll
Human captured solar output: 1200GW is 11% of total human-agriculture photosynthesis: 22000GW, and 1% of all of sunlight captured by anthropogenic earth (solar, crops, forest, ocean).
All of sunlight captured by anthropogenic earth is 0.1% of total incoming sunlight on Earth. Most of that is absorbed as “heat”, or isn’t captured to extract its utilisable power.
Earth is absorbing 0.6W/m2 out of 340W/m2 of incoming sunlight.
Agriculture is vastly inefficient in its resource usage. Takes up about 45% of arable land, only captures about 10% of total human-controlled sunlight, and uses majority of potable water.
Questions
How is total sunlight received by earth calculated? Does it factor in other factors out of human reach, like clouds?
What are C3/C4 plants?
C4 plants have adaptations that allow them to photosynthesise is absence of oxygen. But C3 plants are more abundant due to favorable climate (low temperature for majority of earth’s life) and high CO2 concentration.