Solar Power Technology

Coal is found practically on every continent and subcontinent. It is found buried deeply in the ground or under the seabed, or close to the surface. Coal characteristics vary widely according to its biological origin (forests, low growing vegetation, swamps, animals) and geological history (age, overburden, temperature, pressure). Thus, the chemical and physical characteristics of coal are also highly variable, such as the content of moisture, minerals (ash), sulfur, nitrogen, and oxygen; heat value; hardness; porosity.

The variability from coal to coal is clearly evident. For example, the carbon content varies from 62.9% for North Dakota lignite (a relatively young coal) to 93.9% for Pennsylvania anthracite (a relatively old coal). The sulfur content varies from 0.7% to 3.4% by weight, and the higher heating value (HHV) varies from 7070 Btu/lb (16,430 kJ/kg) for North Dakota lignite to 13,620 Btu/lb (31,650 kJ/kg) for Pittsburgh seam bituminous.

Because of the widely varying characteristics of coals, it is difficult to estimate the precise energy reserves residing in the world’s coal deposits. The world total coal reserves are estimated at 1.037E(12) metric tons. About one-half is bituminous and anthracite coal, whereas the other half is subbituminous and lignite coal. Assuming that the averageHHVof bituminous and anthracite coal is 12,500 Btu/lb (29,050 kJ/kg), and that of subbituminous and lignite is 8200 Btu/lb (19,055 kJ/kg), the world’s coal reserves have a total heating value of about 24,000 Q.

The 1995 world coal consumption amounted to a little more than 93 Q/y. If the present consumption level were to continue into the distant future, the world coal reserves would last about 250–300 years. However, if coal consumption keeps increasing at a rate of 0.8%/y (see Section 2.3), the lifetime of the world’s coal reserves would be only about 140 years.

The countries where the world’s major coal reserves are found are (in percent of the total) United States (26), former Soviet Union countries (25), China (12), Australia (10), Germany (7), South Africa (7), Poland (4), and other countries (9).

In addition to the above reserves, coal may be found in yet unproven reservoirs. Unproven reservoirs are called resources.6 Some estimates place the coal resources at about 140,000 Q.

The resources could supply the present consumption rate for about 1500 years. The resources are mainly located in China, the former Soviet Union countries, the United States, and Australia. However, the resources may be located at great depth under the ground or under the continental shelves. The cost of exploiting these resources will certainly be much greater than that of the reserves.