Fossil fuels have been formed during hundreds of millions of years and consist of only a very small portion of the solar energy earth has received during that time. So, in a way you could say fossil fuels are renewable, although the pace of renewability is extremely slow. If we should use fossil fuels in the pace they were created, they would only contribute to a very small fraction of the energy we use. We over exploit these sources and that by the time they will be more and more expensive to exploit.
A theory was launched some time ago saying that at some time the use of oil will reach a peak. That happens when supplies are so scarce and expensive to explore that consumption decreases. Some industry experts predict that we are very close to that event already. See, for example, the link.
It is quite clear that sooner or later oil, gas and coal will pass its peak production capacity and then decrease in availability. When this occurs we must be ready to meet the ever increasing energy needs with new sources of more rapidly renewing energy. The cost benefit of developing alternative sources of energy is said to be when oil hits the $80 per barrel mark. Oil hit this level in late 2006 and has only dipped below this level for short periods of time since.
Availability of fossil fuels will eventually decrease but that is not the only worry with using fossil fuels. During combustion it is inevitable that carbon dioxide is produced. Coal gives off the most CO2, oil somewhat less and gas least per energy unit produced.
The figure below shows emission by type of user.
As can be seen the production of electricity produces the largest amount of CO2 of any energy consumer group. This is due to the fact that coal fired power plants are the largest producer of electricity in the world. Other big generators, which also contribute to CO2 emissions, are gas fired and diesel power stations.
The figure below shows the proportion of different types of electric generation.
About two thirds of all electricity in the world is generated by fossil fuels. If we look at new production it is encouraging, however, that wind power is increasing very rapidly, as is hydroelectric power. The latter has been made possible by new technology developed to transfer electric power by High Voltage Direct Current (HVDC). See more below.
Coal fired power plants are very big facilities. In several places around the world tests are being undertaken to capture and store the carbon dioxide that is generated. The idea is that the CO2 could be pumped back into geological formations in the ground and be kept there for a very long time. Should this succeed, a big part of the electricity could be produced without emitting CO2 into the atmosphere. Coal is the fossil fuel that will last the longest. Most sources talks about one hundred to several hundred years’ worth of coal yet to be exploited. This would give us time to develop alternative energy not based on fossil sources.