How Efficient is the Sun for Growing Plants? Turns out, not very efficient!

One myth that exists about the sun is that it emits the optimal wavelengths and intensities in the color spectrum that a plant needs to thrive. The reality is the sun is actually pretty inefficient for plant growth but its free and there's a lot of it. Here's a small excerpt from wikipedia which explains the how plants use the suns energy. 

"The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao:[6]

Starting with the solar spectrum falling on a leaf,
47% lost due to photons outside the 400–700 nm active range (chlorophyll utilizes photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)
30% of the in-band photons are lost due to incomplete absorption or photons hitting components other than chloroplasts
24% of the absorbed photon energy is lost due to degrading short wavelength photons to the 700 nm energy level
68% of the utilized energy is lost in conversion into d-glucose
35–45% of the glucose is consumed by the leaf in the processes of dark and photo respiration

Stated another way:
100% sunlight → non-bioavailable photons waste is 47%, leaving
53% (in the 400–700 nm range) → 30% of photons are lost due to incomplete absorption, leaving
37% (absorbed photon energy) → 24% is lost due to wavelength-mismatch degradation to 700 nm energy, leaving
28.2% (sunlight energy collected by chlorophyll) → 32% efficient conversion of ATP and NADPH to d-glucose, leaving
9% (collected as sugar) → 35–40% of sugar is recycled/consumed by the leaf in dark and photo-respiration, leaving
5.4% net leaf efficiency.

Many plants lose much of the remaining energy on growing roots. Most crop plants store ~0.25% to 0.5% of the sunlight in the product (corn kernels, potato starch, etc.)."


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