There is an ongoing effort to find materials that can be used as alternatives to fossil fuels. These materials need to store energy in a stable form that is easily transported from one place to another. This is a challenge that is much easier said than done.
Fuels made from biological materials, such as algae based biofuels or biodiesel produced from animal fats or vegetable oils, are renewable energy sources. In addition to being renewable, they burn cleaner and more efficiently, reducing the pollutants released into the atmosphere. Issues with this alternative source include negative impact on water resources as well as sustainability at large production scales.
Nuclear reactors can create energy for human use, but with risk. An accident could cause a leakage or explosion of radiation, resulting in serious damage to human life and health.
Hydroelectricity, another source of energy, mostly uses the energy stored in water that is blocked by a dam. Hydroelectric plants can be very effective and they do not directly produce carbon dioxide which reduces pollution. Unfortunately, among other issues, the dams can destroy fish and wildlife habitats.
Despite difficulties with finding alternatives, more and more research is being done and other fuel sources are constantly being refined and improved.
