The first law of thermodynamics states that: "The total energy of an isolated system is neither created nor destroyed, it remains constant".
Although the definition seems very technical and difficult to understand, there are numerous everyday examples that apply this thermodynamic principle.
We will use three examples:
A boy who throws a ball in the air.
Heat, energy and work, according to the international system of units is measured in Joules.
Conservation of energy in a balloon thrown into the air
Two types of energy are involved in this example: kinetic and potential.
A boy throws a ball into the air.
The moment the ball leaves your hands it has speed, therefore it has kinetic energy. It has not yet gained height, therefore it has no potential energy.
As he climbs he loses speed and gains height. It loses kinetic energy and gains potential energy.
When it reaches the highest point, it only has potential energy.
Finally it goes down again and the energies are reversed again.
Let's analyze how energy is transformed into a steam locomotive. We consider the locomotive as a thermodynamic system.
Initially all the internal energy of the system is internal energy of the fuel. Charcoal.
When combustion there is a change in energy, it is transformed into thermal energy.
All of this amount of heat is used to generate steam and power the engine's pistons. At this time, it is converted into mechanical energy.
When the engine moves, the locomotive moves. Get a speed. We now have kinetic energy.
In our example the locomotive is not an isolated system. Therefore there is heat exchange with the outside. In a steam locomotive there are many losses for example:
The smoke from combustion and the hot steam that escapes.
The friction between the different mechanisms generates negative work.
Friction with the tracks.
Friction with air.
The heat from the boiler that is transmitted to the air.
Conservation of energy in solar energy
So why is the performance of a solar panel not 100%?
All the solar energy that reaches the solar panel is transformed. But it is not all transformed into the same type of energy. Part of the radiation received by a photovoltaic module is converted into electricity.
However, another part is converted to heat, heating the panel; or it bounces back into the atmosphere.