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.
Here’s a new tab with functioning buttons..

–	Measured solar impact: Watts per square metre	–
Loss from Direct	Attenuators	Gain from Indirect
11%15%20%25%30% %	Scattered	0% %
0.5%1%1.5%2%2.5%3% %	Ozone	0% %
1%2%3%4%5% %	Upper Dust Layer	0.3%1%1.5%2% %
6%7%8% %	Air Molecules	0.1%0.5%2% %
1%4.5%6%7.5%5% %	Water Vapour	0.1%0.5%1% %
0.5%2%3%4%5% %	Lower Dust Layer	0.2%2%4%5.5%7% %
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?