Civilization, Energy and the Future

Solar Power

For the most part, our Sun delivers the same amount of energy to most places where humans live. One option for the future is to use photovoltaic cells to capture this energy and convert it into energy needed by humankind's technology. The following shows the challenges for this form of energy capture.


In the following table you can adjust the losses and gains that result from the passage of solar energy through Earth's atmosphere. As well, you can add a latitude effect. By clicking on the 'Update' button, you will see an estimate of the maximum amount of energy (total annual deposition) that the cells can capture.

 
Watts per square metre
 
Loss from Direct Attenuators Gain from Indirect
% Scattered %
% Ozone %
% Upper Dust Layer %
% Air Molecules %
% Water Vapour %
% Lower Dust Layer %
Resulting Loss Factor   Resulting Gain Factor
Resulting Black body Irradiance on and normal to the Earth's SurfaceWatt/m2
Cosine effect
Latitude [0-90)
Maximum DepositedWatts/m2  
Solar Collector efficiency% Maximum CollectedWatts/m2  
  Total Annual DepositionMJ/m2/a  

The above is the theoretical maximum amount of energy provided by the Sun. Yet, while solar power sites are becoming more common on Earth, their efficiency causes the actual power supply to be less as seen in the following table.


Place Irradiation
(kWh/m2/day)
Irradiation
(MJ/m2/a)
Power Production
(MWh/m2/a)
Power Production
(MJ/m2/a)
Daggett 7 9189 0.1988 715
Kramer Junction 7 9189 0.335 1207

The following table shows that solar energy is a worthwhile source of energy when considering our current usage. However, it comes at a cost. We can use the land to capture the energy form the Sun so as to feed our technology. Or, we can grow plants to capture the energy from the Sun so that we can feed our bodies. We can't do both.


Country Population Arable Land Primary Energy Consumption Consumption per person Consumption per square metre
    square metres Joules / annum MJ/person/annum MJ/square arable metre/annum
China 1306313000 1.39e12 82019500711720500000 62,840 59.2
USA 295734134 1.65e12 75440312577177000000 255,100 45.7
Sudan 37762842 1.61e8 40799009719500000 1,080 0.253
Turkey 69660559 2.3e8 1212301373884000000 17,400 5.27
Iceland 296737 7e7 162067000000000000 546,000 2315

Above table's data from Wikipedea (which sources World Fact Book) accessed 2010 December


By the year 20008, the total installed photovoltaic power on Earth amounted to 15,000MW (about 2.36e17 J/a). Consumption is about 4.74e20 Joules. Given the above factors, then we need about 4.74e11 square metres of photovoltaic collectors or about 3.1% of all the Earth's land area to replace the fossil fuels. As our population and energy use climbs, we need allocate more land area both for electrical energy for machines and more food energy for people. An interesting dilemma arises; do we feed ourselves, feed our machines or feed other living organisms? Is there space for all?


by Mark Foster Mortimer