water + sunlight (= heat) = steam

how much heat energy can we collect from the sun with an energy absorber of 1 square meter surface area, and how much water can we convert to steam with this energy?

recall that most populated places around the earth receive at least 5 Kilo-Watt-hours (KWh) of energy per day, on average, over every square meter, provided the energy collector’s surface is pointed square at the sun at all times

5 KWh = 5 KW*60*60 seconds = 18,000 KW-second  = 18,000 KJ = 18 MJ (Mega Joule)

recall, it takes 315 KJ to heat 1 litre of water from 25 deg C to 100 deg C

315 KJ = 315 KW-sec = 315/(60*60) = 0.09 KWh

and 2260 more KJ to convert all of 1 litre of boiling water into steam

2260 KJ = 2260/(60*60) = 0.63 KWh

(and while we are at it, 1 KJ = 0.00028 KWh and 1 KWh = 3600 KJ = 3.6 MJ)

it takes 2575 KJ (315 + 2260), same as 0.72 KWh (0.09 + 0.63) KWh to convert all of 1 litre of water at an initial temperature of 25 deg C, into steam

if a 1 square meter energy absorber were pointed square at the sun all day, it were a sunny and cloudless day, in an ideal world, where all of the 5 KWh (or 18 MJ) of incident sunlight as energy were collected without losing one whit, and all of this collected energy were once again, without any waste what-so-ever, ideally used to convert water, all of it, from a starting temperature of 25 deg C into steam, we’ve steamed up 7 litres of water

(5 KWh/0.72 KWH per litre or 18,1000 MJ /2575 MJ per litre)

in summary:

1 square meter, 5 KWh (or 18 MJ), ideal world, 7 litres of 25 deg C water -> steam



About Vishwa Narayan

who can live without water? drinking water for all is my goal, through Theertham, a not-for-profit organization i founded and registered in Texas. you can reach me at drvishwanarayan@yahoo.com
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