Let’s say you become tired of having to eat all the time and would like to spend

Question

Let’s say you become tired of having to eat all the time and would like to spend your days just lying in the sun. And let’s imagine you found a way to cover your skin with algae, and that all the reduced carbon products they produce are absorbed through your skin and are available for your respiration. Make some assumptions about your surface area and assume a photosynthetic efficiency of 1% and noontime incoming photosynthetically-active radiation of 400 W/m2. Calculate what percentage of your daily energy needs you could satisfy this way.

Explanation / Answer

As per the question let's assume we are getting sunlight for 8 hours in the days with intensity of photosynthetically-active radiation of 400 W/m2 (we will get more sunlight but I have compensated that by taking the noontime incoming photosynthetically-active radiation)

Hence we will get 400 W/m2 for 8 hours i.e. we will be getting 3,200 W/m2 of photosynthetically-active radiation in a day.

As per various data the average body surface area for adult men is 1.9 m2.

Therefore an adult man will receive photosynthetically-active radiation = 1.9 x 3,200 W

Therefore an adult man will receive photosynthetically-active radiation= 6,080 W

1% of this = 6,080 x 0.01 = 60.8 W

For 8 hours this will eaqual to 60.8 x 8 x 60 x 60 = 5,253,120 w

We know 1 calorie = 4.1868 Ws (watt-second)

As average man need 2,500 calorie per day i.e. = 2,500 x 4.1868 = 10,467 Watt per day = 10,467 x 24 x60x60

= 904,348,800 w

Therefore percentage of daily energy needs satisfied by photosynthetically-active radiation = (5,253,120/904,348,800) x 100 = 0.58 %

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