# Understanding the basics of electricity and photovoltaic

What is the difference between Volts and Amps? Kilowatts and kilowatt-hours?  What is the purpose of an inverter and a regulator? What is inside a generator?

#### The basics of electricity explained with water

To understand the fundamentals of electricity, it is important to understand and visualize its main parameters such as tension, intensity, resistance, power and capacity.

An analogy with water will help you understand them. In a given volume of water, there is a given number of water molecules, the elementary blocks that make up the liquid. Electrons can be compared with these molecules, as they also represent the equivalent elementary blocks in electricity. It is the movement water molecules that creates a flow of water, much like the movement of electrons creates electricity. Generating electricity therefore revolves around making the electrons move.

Let’s now picture a water mill, built on a river at the bottom of a snowy mountain.

• The taller and steeper the mountain is, the faster the flow of the river’s water will be. This difference in height between the top and bottom of the mountain, which leads to the flow of water, is called a difference in potential. In electrical terms, this difference in potential is called tension and is expressed in Volts (or “V”). Just like water flows from the top of the mountain to the bottom, the electrons move from “minus” to “plus” when they are in a closed circuit under tension.
• The warmer the mountain top gets, the the more water will melt and the more intense the flow of the river will be. In electrical terms, this is equivalent to what is called intensity, which is expressed in Amperes (also “Amp” or “A”). A river with a fast flow of water is as dangerous as a high electrical current!
• The water mill needs the flow of water to grind wheat and produce flour. In this analogy, the mill is equivalent to an electrical device (lightbulb, motor, computer…) which needs the flow of electrons to work. The wheel of the mill only turns if the water arrives with sufficient speed and strength, or in other words, with sufficient power. Similarly, the electrical power is expressed in Watts (or “W”). One Watt is the power carried by a 1 A flow of electrons under a tension of 1 V. One kilowatt (“kW”) is equivalent to 1000 Watts.
• If we place a rockin the middle of the river or otherwise try to block its path, the speed and trajectory of the water will be altered. This is analogous to the principle of resistance (which is expressed in Ohms). A resistor is an electrical component which introduces resistance in a circuit, and allows you to control the tension and intensity.

• It may be interesting to keep the water upstream before it reaches the water mill. This can be achieved with a dam or a water tank, allowing the flow of water to be controlled. This will even enable the mill to function after the snow has melted. These water reservoirs play the same role as a battery, which stores electrical energy so that it can be used when needed. The size of the reservoir is a direct analogy to the battery capacity which is expressed in Wh (watt-hour). A battery of 1 Wh is one which goes from empty to full by letting in or letting out a constant power of 1 W for an hour. A kilowatt-hour, often the most used unit of electrical energy, is nothing more than a thousand watt-hours.

#### The main components of a photovoltaic generator

A solar photovoltaic system made up of several components, each of which play a precise role. The ultimate objective is to convert the energy from the Sun into electricity, with a controlled tension, intensity and signal shape.

Let’s start with the key component of a photovoltaic system: the solar panel. A photovoltaic panel is made of numerous cells that enable a fundamental principle: the creation of a tension, and therefore the “presence of electricity”. In a nutshell, when the incoming rays of sunlight, charged with energy, collide with the cell, it creates a tension between one end of the cell and the other which forces the electrons to move. This is why it is more efficient to position the solar panel so that it is perpendicular to the solar rays: the “collision” creates more energy. Let’s bring back the previous analogy: the snowy mountain is itself the cell. The warmer it gets, the more snow melts and the more water flows downstream. The current generated in a photovoltaic system is proportional to the light flow received by all the cells (in other words, the sunnier it gets, the more electricity is generated) and this current takes the shape of direct current (commonly referred to as DC).

The electricity generated by a solar panel can be used directly, but since its electric current is highly variable (clouds, shadows…etc), it is often necessary to regulate it with the use of a battery. The battery is nothing else but a reservoir which stores electric energy until needed.

It is important to regulate the inputs and outputs of that reservoir (not filling it either too much or too fast and not emptying it too much nor too fast) to avoid damaging it. That is the role of a regulator. This component links the panels, the batteries and the power output (energy consumption). It allows an optimal combination between the direct energy coming from the solar panels and the energy stored within the batteries.

The electrical current can take the shape of a direct current (DC) or of an alternative current (AC). Besides the fact that electrical devices need a specific tension and intensity, they often need an electrical input in the form of alternative current. The inverter is the component that turns direct current, coming from the solar panels and batteries, into alternative current that can be used by most electrical devices.

In a nutshell, one can refer to this hydraulic analogy to understand the abstract principles that lie behind electricity, and in particular those of photovoltaic energy. As said by Einstein, the things you master can be explained in a simple way. At O’Sol, we master solar energy for you, and count on the simplicity and efficiency of our solar solutions. Our service and products will convince you, so do not hesitate to get in touch with us!