The energy in the universe exists in various forms, such as heat energy, light energy, and electric energy. When we say we “use” electric energy, we do not mean that we have destroyed, or lost, the energy. We mean that we have converted that electric energy into a more useful form of energy. For example, when we operate an electric lamp, we are converting electric energy into light energy and heat energy. We have used the electric energy in the sense that it no longer exists as electric energy, but we have not used up the energy. It still exists as heat energy and light energy. A light bulb converts electric energy into light energy and heat energy. Another familiar object that converts energy is the electric stove, which converts electric energy to heat energy. Changing electric energy to mechanical (rotational) energy with an electric motor is also a common conversion.

It takes a whole lot of energy to power the world as we know it. Annual energy consumption globally is estimated to be 580 million terajoules – equivalent to 13865 million tons of oil equivalents. Scientists have sounded the alarm on global warming for a long time. Still, in recent years the disturbances to our global climate have resulted in extreme weather events that have been impossible to ignore. For businesses looking to do their part through decarbonization, optimizing energy efficiency is one of the most cost-effective ways to go about it.

Energy efficiency is often reduced by devices and equipment being left on when not in use, charged while at full battery capacity, or otherwise drawing power from the electrical grid. For example - an older piece of equipment receives 500 joules of power to produce the equivalent of 100 joules of output; 100/500 = 0.2, or 20% efficiency.
A newer equipment version takes the same 500 - joule input to generate 400 joules of productive output; 400/500 = 0.8, or 80% efficiency — much better!
In some cases, the “wasted” energy will result in a byproduct that can be utilized, such as the heat generated by lamps that are primarily designed to illuminate. If we can’t capture that energy, it simply disperses itself and provides no benefit.

Voltage source

Ideal voltage source:
- It can provide a constant terminal voltage that is independent of the variations in its external circuit, Vab = Vs
- Its internal resistance, Rs = 0
- Its current depends on the variations in its external circuit

Real voltage source:
- It has a series internal resistance Rs, and Rs < RL
- The terminal voltage of the real voltage source is Vab = Vs - IRs