Humans Biased Toward Biology and Against Robots
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Stated another way:
100% sunlight—non-bio-available-photons-waste-47% leaving-->
53% (in 400—700 nm range) --30%-of-photons-lost due to incomplete absorption leaving-->
37% (absorbed photon energy) --24%-lost-due-to-wavelength-missmatch-degradation-to-700 nm-
28.2% (sunlight energy collected by chlorophyl) --32%-efficient-conversion-of-ATP-and-NADPH-
9% (collected as sugar) --35-40%-of-sugar-is-recycled/consumed-by-the-leaf-in-dark-and-photo-
5.4% net leaf efficiency
net efficiency of a leaf at 25°C is about 5%
many plants lose most of the rest of this doing things like growing roots
most crop plants store ~0.25% to 0.5% of the sunlight in the product (corn kernels, potato starch,
sugar cane is exceptional in several ways to yield peak storage efficiencies of ~8%.
Photosynthesis by D.O.Hall & K.K.Rao says that photosynthesis increases linearly up to about
10,000 lux or ~100 watts/square meter before beginning to exhibit saturation effects. Thus, most
plants can only utilize ~10% of full mid-day sunlight intensity. This dramatically reduces average
achieved photosynthetic efficiency in fields compared to peak laboratory results.
Real plants (as opposed to laboratory test samples) have lots of redundant, randomly oriented
leaves. This helps to keep the average illumination of each leaf well below the mid-day peak
enabling the plant to achieve a result closer to the expected laboratory test results using limited
Only if the light intensity is above a plant specific value, called the Compensation point the plant
assimilates more carbon and releases more oxygen by photosynthesis than it consumes by
Cellular respiration for it´s own current energy demand.
Algae and other monocellular organisms
From a 2010 study by the University of Maryland, photosynthesizing Cyanobacteria have been
shown to be a significant species in the global carbon cycle, accounting for 20–30% of Earth's
photosynthetic productivity and convert solar energy into biomass-stored chemical energy at the
rate of ~450 TW.. In addition, 25 Gigatons of carbon annually were sequestered from
cyanobacteria alone, more than the 8.67 gigaton release from fossil fuels worldwide in 2008.
According to the cyanobacteria study above, by simple math, this means the total photosynthetic
productivity of earth is between ~1500-2250 TW, or 47,300-71,000 exajoules per year. Using this
source's figures of 178,000 TJ of solar energy hitting the Earth's surface , see also Earth's
energy budget, suggests that the total photosynthetic efficiency of the planet is 0.84% to 1.26%.
Efficiencies of Various Biofuel Crops
Popular choices for plant biofuels include: Oil Palm, Soybean, Castor Oil, Sunflower Oil, Safflower
Oil, Corn Ethanol, and Sugar Cane Ethanol.
An analysis[original research?] of a proposed Hawaiian oil palm plantation claimed to yield 600
gallons of biodiesel per acre per year. That adds to 2835 watts per acre or 0.7 watts per square
meter . Typical insolation in Hawaii is closer to 5.5 kW-hrs/square meter/day or 230 watts .
For this particular oil palm plantation, if it delivered the claimed 600 gallons of biodiesel per acre
per year, would be converting 0.3% of the incident solar energy to chemical fuel. Total
photosynthetic efficiency would include more than just the biodiesel oil, so this 0.3% number is
something of a lower bound.
Contrast this with a typical photo-voltaic installation , which would produce an average of
roughly 22 watts per square meter (roughly 10% of the average insolation), throughout the year.
Most crop plants store ~0.25% to 0.5% of the sunlight in the product (corn kernels, potato starch,
etc.), sugar cane is exceptional in several ways to yield peak storage efficiencies of ~8%[citation
Ethanol fuel in Brazil has a calculation that results in: "Per hectare per year, the biomass
produced corresponds to 0.27 TJ. This is equivalent to 0.86 W per square meter. Assuming an
average insolation of 225 W per square meter, the photosynthetic efficiency of sugar cane is
0.38%." Sucrose accounts for little more than 30% of the chemical energy stored in the mature
plant; 35% is in the leaves and stem tips, which are left in the fields during harvest, and 35% are
in the fibrous material (bagasse) left over from pressing.