Solar Resource

The Solar Resource

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Satellite instruments, pointing directly at the sun, measure the intensity of the sunlight above the atmosphere as 1370W/m². This is called solar insolation. In combination the earth’s clouds, aerosols, atmosphere and surface reflect an average 31% of this sunlight, leaving 69% to be absorbed.
If you calculate how much solar energy the earth (with an average radius of 6378km) intercepts, this energy dwarfs all other available energy supplies. This immense power of the sun is often denigrated by the very limited conceptions of the fleeting fossil fuel industry but what is the real situation?

In only 24 hours the Earth intercepts solar energy which is equal to 3 times all the energy in all the oil there ever was.

In only 24 hours the Earth intercepts solar energy which is equal to 10 times all the energy in all the fissionable Uranium in Earth’s resources.

In only 24 hours the Earth absorbs solar energy which is equal to 2 times all the energy in all the oil there ever was.

In only 12 hours the Earth absorbs solar energy which is equal to all the energy in all the oil that’s still left and is harder to get.

In only 24 hours the solar energy absorbed by the Earth is equal to nearly 10,000 (9252) times all the fossil fuel, nuclear & hydro used by people in 24 hours.

The solar energy absorbed daily on the Earth’s deserts is equal to about 600 times the non-renewable energy that people use daily.

0.71% of the solar radiation reaching the Earth drives the wind, waves and currents.

Only 0.023% of the solar radiation reaching the Earth is photosynthesised into high energy organic molecules. The vast majority of this primary productivity is eventually metabolised by plants, animals and fungi. Only a very tiny fraction is fossilised.

All the oil there ever was, if spread evenly on the earth’s surface, would have formed a layer 0.54mm thick. All the oil that’s still left would form a layer the thickness of a jam tin lid (0.25mm).

If all the oil that was left in 2003 were divided evenly amongst the world’s population then, there would be 20,000 litres of oil for each person. Australians used 6.7 litre oil/person.day in 2003. So we would exhaust our allotment in 8 years, which occurs in 2011. [20,000 litres is a 2.7m cube – the size of a small jail cell.]

Seeing as we’re bathed in far more energy from above than there is in the ground below, let’s put together the information needed to replace fossil fuel burning.
One of sunlight’s important qualities is that its rays are almost parallel (within about ½ degree of angle or 31min of arc). This allows us to concentrate the sun’s rays into a small area where the intensity can produce quite high temperatures. High temperatures permit the conversion of a greater proportion of the sun’s energy into useful work (say via generating electricity). The 2nd law of thermodynamics gives the maximum possible efficiency of conversion.

Finding the Solar energy potential at your place. An excellent resource to help determine the quantity and quality of solar energy anywhere on the Earth’s surface is: NASA Surface meteorology and Solar Energy - Available Tables, which you can access from: http://eosweb.larc.nasa.gov/sse/
For the Latitude and Longitude that you enter, this excellent database gives you a comprehensive amount of information ranging from global and diffuse insolation on horizontal and tilted surfaces, direct normal radiation plus probable variations. The tables also supply wind speeds and much other meteorological data.
For instance if you wanted to assess the amount of energy supplied to a crop in Northern Rivers, NSW, Australia over a certain period then you would use the following table. (Note that Langly provides the insolation measurements in kWh/m².day but here I have converted it to MJ/m².day.)

Insolation on horizontal surface (MJ/m².day)

Lat -28.5 Lon 153	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
10 Year Average	24.1	21.5	18.9	14.9	11.7	11.1	11.8	15.1	19.5	21.6	23.6	24.1

And suppose you wanted to size a parabolic dish for the same district then you would use the “Direct Normal” table. (Where “Normal” means perpendicular to the surface)

Direct normal irradiance / Page method (MJ/m².day)

Lat -28.5 Lon 153	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Annual Average
10 Year Average	22.0	19.55	18.4	16.0	14.36	15.84	16.1	18.86	21.8	20.9	21.67	21.7	18.936

To calculate the size of the energy storage needed to carry you through low sun periods there are also tables that give you the minimum radiation for consecutive periods like 1, 3, 7, 14, 21, 30 days.

What is the destiny of the unreflected incoming solar radiation and the minor contributions to the Earth’s biosphere?
The table below gives you a good idea of the relative magnitudes of the major energy paths on the earth’s surface.
Power Budget for Earth’s Biosphere. All measurements in TerraWatt (TW or 10¹²J/s)

Input		Output
Input Source	Power	Output Source	Power
Solar Radiation	174000TW	Reflection	52000TW (30%)
		Heat	82000TW (47%)
		Evaporation & Precipitation	40000TW (23%)
		Wind, Waves & Currents	370TW (0.71%)
		Photosynthesis	40TW (0.023%)
Nuclear,Thermal, Gravitational	32.3TW	Heat radiation	32.3TW (0.018%)
Tidal	3TW	Heat radiation	3TW (.0017%)
Total In	174036TW	Total Output	174445TW (100.7%)

Rounding errors cause the 0.73% discrepancy.

As a comparison the rate of human use of energy (extrasomatic or outside the body ie not food) is currently 12.67TW. The human population consumes food at a rate of 0.75TW.

solar radiation graph

Sunshine Energy reaching the Earth in only 24 hours compared to the total Energy in the Earth’s remaining Fossil Energy “Reserves”

solar radiation graph

Sunlight energy: Nasa satellite readings of 1370W/m² outside the atmosphere, 30%reflected, 70% absorbed.
Fossil fuel reserves data from BP statistical review 2006. http://www.bp.com
Uranium reserve data from World Energy Council & World Nuclear Association
Humans use more than 400EJ/year of energy
World Nuclear Association http://www.world-nuclear.org/info/inf75.htm
World Energy Council http://www.worldenergy.org/wec-geis/publications/reports/ser/uranium/uranium

The Power of the Sun on the Earth

Alltogether 174000 TW is reradiated to space. 122000TW has been used in Earth processes (eg rain, wind). It goes to space as low quality longwave radiation (heat). The reflected 52000TW is high quality.		The Earth intercepts 174000 TerraWatts of quality Sunshine continuously

Output Power from the Earth to Space 174457TW (rounding errors)

Scale : 1mm = 1TW

High Insolation areas of the World

The orange areas = good places to install solar energy collectors

High Insolation