Why are alternative resources important?
Alternative resources are important because we are running out of conventional resources and/or we want to minimize the damaging effects of conventional resources. Fossil fuels are a great example of this. We owe much of our development, especially the industrial revolution to the use of fossil fuels, such as coal, gasoline, diesel, natural gas, etc. These fuels are the dominant source of electricity and heating around the world. However, the combustion products of these fuels, especially carbon dioxide, are very harmful to the environment. Also, the quantity of these fuels is very limited and since they take a very long time to make, we cannot count on their sustained presence for more than a century or so (depending on their usage). Thus, we need alternative resources to replace them. Options such as nuclear power, solar power, wind energy, etc. have been studied and developed for (partial) replacement of conventional sources.
Hope this helps.