The unit used in discussing global energy issues is usually the quad (Q). The quad equals one quadrillion (1015) BTUs of energy. One Q of energy is equal to the energy produced by 33 nuclear power plants in a year, or the energy content of 10,000 supertankers of oil, 400,000 rail cars of coal or 28 billion cubic meters of natural gas.
The global energy consumption today is about 400 Q. It comes from oil (35%), coal (25%), natural gas (20%), wood/biomass (10%), nuclear (7%), and from renewable sources, such as hydro power (3%). The global energy consumption is rising at a yearly rate of 20 Q and is expected to reach 600 Q by 2020.
|FIGURE 1: GLOBAL ENERGY CONSUMPTION|
Click image to enlarge. Data: NASA 1999
As shown in Figure 1, the total fossil fuel reserves of the globe are estimated to amount to 75,000 Q.
Between 1950 and 2000, the global energy consumption increased from 100 to 400 Q. The total energy consumption (red line) is rising at a higher rate than the fossil-fuel availability (solid blue line). The fossil envelope (dotted blue line) describes the probable consumption curve of the accumulated fossil energy on the planet. It projects a maximum yearly production rate of 700 Q at around 2050 and the elimination of this energy supply by the year 2200.
Besides of the exhaustible nature of fossil fuels, their use also releases 25 million tons of carbon dioxide yearly into the atmosphere. It is estimated that the resulting global warming damage will consume as much as 20% of the global GDP by 2020 even if we do not consider the potential cost of “energy wars.”
It is for these reasons that conversion to the inexhaustible and clean “solar-hydrogen” energy is recommended. In this series, I will discuss a) the availability of the required solar energy; b) the methods and efficiencies available to convert solar energy to electricity; c) the technology to convert that energy into liquid hydrogen for storage distribution; d) the costs; and e) the steps needed to quickly and without wars or disruptions convert our global economy to solar-hydrogen.
Solar Energy Requirement and Availability
The amount of solar energy produced by a unit area of solar collector (m2) is called “insolation.” Insolation changes with the weather, the time of day, the orientation of the collector and the insolation in the particular area of the globe. High insolation areas on the five continents are noted on the right of Figure 2 below. The insolation during a clear March day in Daggett, Calif., is shown on the left.
If we assume that this is an average day for the year, and if the collector is provided with a tracking mechanism that points it toward the sun, the total yearly energy received per square meter of collector area is slightly less than 4,000 kilowatt-hours.
|FIGURE 2: HOT SPOTS|
Insolation variation in March in Daggett, Calif. (top), and areas where insolation exceeds that of Daggett, Calif. (bottom).
Today, the per capita energy use ranges from1,000 kWh/yr in Africa to 16,000 kWh/yr in Canada. Therefore, if the collection and conversion system is assumed to be 10% efficient, and the solar energy is collected in a high insolation region, the per capita collector area required to meet the total energy needs of the globe would range from 2.5 m2 for people living in Africa to 40 m2 in Canada.
On the same basis, the collector area required to meet today’s total energy use of mankind can be estimated to be about 3% to 5% of the area of the Sahara. Assuming that the yearly solar energy collected by each square meter of collector area is 3,000 kWh, knowing that a square kilometer (km2) is a million square meters, and that each kWh equals 3413 BTUs, the collector area needed to collect each Q is 100 km.
Land occupies 150 million km2, the oceans occupy 361 km2. Therefore the Sahara covers 1.6% of the total surface area of the globe. Including the oceans, the total high insolation area on the planet is more than 25 times that of the Sahara. Therefore to collect the global energy use today, 40,000 km2 needs to be covered. Because the Sahara’s area is 9 million km2, 4.44% of its area would need to be covered.
Naturally the total area of high insolation on earth is much larger than that of the Sahara, and solar energy can be collected not only on solid ground, but also on floating islands in the oceans.
Next time, I will discuss the methods available to convert this solar energy to electricity.
|About the Author|
Béla Lipták, PE, process control consultant, is editor of the Instrument Engineer’s Handbook, and former chief instrument engineer at C&R (later John Brown). He is a recipient of ISA’s Life Achievement Award (2005) and member of the CONTROL Process Automation Hall of Fame (2001).