Coal is becoming scarce in many countries and more expensive here; its price has about doubled in the past year. It is our main source of electricity. In about 15 years the world may hit a peak in its production, and this combined with the fact that natural gas-–the secondary source of electricity generation--simultaneously will be at or past its peak, poses a threat to our supply of electricity.

I'm wondering where you get this figure. Is it just because of the current coal shortages we are experiencing??

There are a number of studies that indicate that coal production may peak in about 15 years. Chris Vernon has summarized some of them in this post.

Heading Out has argued that these studies may forecast a quicker end to coal than will really be the case. He believes that the decline in production in many cases occurred because cheaper (and/or better) alternatives became available. The forecasting method misses the fact that if the alternatives are no longer available, people may go back to these sources, and they will again become economic.

Coal prices are very much higher now than they were in the recent past. At one time China was an exporter; now it is an importer. There are many other countries that would like to increase the amount of coal they burn, since oil is very expensive. Prices have risen because demand is much greater than supply. This is one story talking about the higher prices.

We use a great deal more oil than coal. When there is a shortage of oil, there is pressure to ramp up coal to compensate. In practice, it doesn't really work, though. It is almost impossible to increase the amount of coal available for export very quickly. One needs to be able to extract more coal from the ground; then one needs railroad cars, barges, and ships to transport the coal on. Some exporters have recently had difficulty for a variety of reasons. South Africa has recently reduced its coal exports because it needs more internally.

OTOH it is possible Peak Coal could arrive before 2023-the studies summarized do not appear to clearly account for increased consumption caused by oil depletion and decreased oil exports.