how much juice does the earth receive from the sun?

plenty, for our purpose of distilling salty or otherwise impure water into potable water

one square meter area pointed square at the sun (no tilt) outside the earth”s atmosphere receives about 1.35 kilo-watts of power from sunshine at any instant

this includes all wavelengths –  UV visible near-far IR. a sizable portion lies in the visible wavelengths of about 350 nm (deep violet) through 530 nm (bright verdant green) through 650 nm (deep dark red)

the atmosphere reflects some, absorbs some, and scatters some. this sunshine intercepted by a square meter at the surface of the earth is about 1 kilo-watt of power, provided it is noon time on a bright sunny day, and the surface is pointed square at the sun

this is enough power to run a small microwave oven

and when the sun is not at its zenith we receive less sunshine, during mornings and evenings

the amount of sunshine also depends on where we are on earth. at higher latitudes, the poles of the earth being an extreme example, depending on the seasons, we receive more sunshine (summer) or less (winter)

also, local weather matters as rainy cloudy very dusty places receive less sunshine

then there’s altitude, with higher altitudes receiving more sunshine as there is less of reflecting absorbing scattering atmosphere to traverse

we will ignore the changes due to natural variations in the sun’s energy output

so how do we find out the direct normal (pointed square at the sun) average energy received per day from the sun (i e insolation), for any given location? simple. look it up, for most locations, thanks to the people who have made these measurements

here’s a nice example from the book ‘power from the sun’ by William B. Stine and Michael Gever.


insolation at Dagett California

amount of sunlight received on a sunny day in March at Dagett, California


sunrise a little before 6 am and sunset a little after 6 pm. the curves peak, of course, at 12 noon. yellow = direct sunlight hitting our 1 square meter surface pointed square at the sun, maroon =  diffuse and scattered sunlight hitting the same surface, blue  = total sunlight hitting the surface = sum of the two

quoting from the book ‘this figure shows the variation of insolation over a full, clear day in March at Daggett, California, a meteorological measurement site close to the Kramer Junction’ (one of the largest solar thermal power plants in the world, at 354 MWp capacity). ‘The outer curve, representing the greatest rate of incident energy, shows the energy coming directly from the sun (beam normal insolation) and falling on a square meter of surface area which is pointed square at the sun. The peak rate of incident solar energy occurs around 12:00 noon and is 1,030 Watts per square meter’

Over the full day, 10.6 kilowatt-hours of energy has fallen on every square meter of surface area as represented by the area under this curve. that’s enough juice to run your 1 kilo-watt microwave for over 10 hours! on a bright sunshiny day. averaged over a year, and accounting for the few cloudy days there,  measurements over several years shows that on average 2725 kilo-watt-hours of energy fell on our 1 square meter surface on each year

averaging about 7.5 kilo-watt-hours per day, making Dagett one of the most sunny places on earth (which is why they built the Kramer Junction solar plant there)

of course, sunshine will vary over the seasons and the location. the poles receive the maximum amount of sunshine in summer. the equator receives near constant sunshine year round (ignoring effects due to clouds)

other places receive less sunshine than Dagett. Oslo, Norway receives 2.3 kilo-watt-hours-per-square-meter-per-day. Miami, Florida? 5.3. India? varies from 4 to 7 with about 1500–2000 sunshine hours per year, depending upon location

in summary:

many parts of the world receive an average of 5 kilo-watt-hours-per-square-meter-per day of energy from sunshine

and that is a lot of juice

like running your microwave oven non-stop for 5 hours…




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
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