The total amount of energy in an isolated system does not, cannot, change. ... We can gain energy (again, through chemical processes), and we can lose it (by expelling waste or emitting heat).but the initial energy came from The Singularity:

According to the laws of thermodynamics and conservation law, energy cannot be created or destroyed. That begs the question of how energy started out then and where it came from. The answer lies in understanding the singularity in the Big Bang Theory.

Introduction:
The principle that states energy cannot be created or destroyed is known as the law of conservation of energy. It is a fundamental concept in physics and is derived from the first law of thermodynamics. This law states that the total energy of an isolated system remains constant over time.

Energy Transformation:
While energy cannot be created or destroyed, it can be transformed from one form to another. This is evident in various everyday phenomena. For example, when we burn wood, the chemical potential energy stored in the wood is converted into heat and light energy. Similarly, when we plug in an electrical device, electrical energy is converted into other forms such as light, heat, or mechanical energy.

The Big Bang Theory:
The origins of the universe and the initial source of energy can be traced back to the Big Bang. According to the Big Bang theory, the universe began as an extremely hot and dense point, often referred to as a singularity. At this point, all the energy and matter in the universe were concentrated in this tiny, infinitely dense region.

Expansion and Distribution of Energy:
Following the Big Bang, the singularity rapidly expanded, causing the distribution of energy and matter throughout the universe. As the universe expanded, the energy spread out and transformed into various forms such as light, heat, and gravitational potential energy. This energy has been continuously transforming and redistributing over billions of years.

Nuclear Fusion and Stellar Energy:
Stars, such as our sun, play a crucial role in the generation of energy. In the core of stars, a process called nuclear fusion takes place, where lighter atomic nuclei combine to form heavier nuclei. This fusion releases an enormous amount of energy in the form of light and heat. This stellar energy is then radiated into space and becomes available for other processes.

Conclusion:
In summary, while energy cannot be created or destroyed, it can be transformed from one form to another. The initial source of energy can be traced back to the Big Bang, which resulted in the expansion and distribution of energy throughout the universe. Processes such as nuclear fusion in stars also contribute to the generation of energy. The concept of energy conservation is a fundamental principle in physics and has wide-ranging applications in understanding the workings of the universe.