Basics of electricity and photovoltaics


Foto de Social Income en Unsplash

This session is part of the process of the Community of Practice of passive infrastructure.

In this first session of lessons on solar power, we will learn about:

  • Basic concepts of field, force, resistivity
  • and charge flow in conductive materials
  • Concepts of power, voltage and electric current
  • Calculating the Watts-hour energy consumption
  • How photovoltaic panels work

For more info about the Lessons on Solar Power process, you can read more here:

You can also find out more about the Community of Practice in the meeting logs here:

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For these classes I am preparing references and taking advantage of every online resource that exists in this digital world.
One very important thing for us will be to create “temporary agreements” that because of the possible difference in previous knowledge that each one has, we will need these agreements to understand basic electricity and move on to better understand photovoltaic systems.

A first thing that I would like to leave you with is this picture that compares a photovoltaic system to a hypothetical rainwater collection system, which I created based on this great reference https://www.opensourcesolar.org/

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The most common thing when you think of electricity is shock; who has never had a shock? Whether it’s from touching a bare wire or from wearing synthetic clothing on a dry day.
But to understand what it is and how this electricity works we can start by thinking what this word means and where it comes from. The word comes from the Greek term ἤλεκτρον (ēlektron) or electron. And so the word electricity means a set of effects resulting from the presence of electrons.

And what would be the electrons?

At this point we need to make our first temporal agreement, we need to believe that everything that exists is made of atoms and electrons are part of atoms.

There is a lot of material on the Internet about what atoms are:

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Notes

Participants: Elektra, Henok, Hiure, Pepe, Sam, Yewo, Mano, Solomon, Dinesh, Shalini, Pablo (Bruna, Adriana, Baca, Nico, Nils, Mike)

Hiure will explain us about Electricity. Hiure is a physist but this kind of presentations is new to him. Everybody is welcome to ask question and to come forward, if things are unclear or not understandable…

The idea today is to talk about:

  • photovoltaic intro
  • electrictiy
  • meaning of voltage
  • meaning of current
  • resistence in electronic circuits
  • calulations of power
  • the funcioning of photvoltaic panels

Many new concepts will be talked about…our brain will make "temporary agreements" and then we come back for deeper understandings…

PART 1

Solar vs photovoltaic systems
…a solar system can also be a water heating system, a photovoltaic system is always about the production of electricity

What means photovoltaic

photo > light > sun
voltaic >voltage > electricity

…for a better understanding, let’s compare rainwater collector system with a photovoltaic system…(from opensourcesolar.org)

Rainwater collector system: easy to understand and relates to electricity basics (but also be careful with over-simplifying things)

RC System elements: collector, pipes, valve in, tank, valve out, sprinkler

PV System: PV panel, wires, charge controller, battery, LDV, load

…now let’s have a look what is in the wire. A first temporary agreement is to accept, that all in the world is made by basic building blocks called “atoms”.

Atoms are made of a central part (nucleus) and other parts moving around called electrons.

The worls electricity coms from electrons (part of the atomic building piece). A set of effects resulting from the presence of electrons (charge).

Electricity flows through a circuit. A simple circuit can be a battery wired to a lamp. Electrons flow, similar to rainwater in a pipe. In the battery there is force that pushes and pulls electrons. This force is called voltage. In a PV system the voltage is produced from sun light. Other basic concepts are current and resistance. And there is also an electric field. So let’s see the details.

What does voltage does: it pushes and pulls the electrons. It can also be used to send and receive binary information. A simily: let’s imagine 2 talks: the full one has more voltage the other less, so one with more potential flow, the other less. So voltage is a force to flow in “the pipes” and can turn on things. In other words, it is a difference in electrical potential energy per unit of charge between two points (or Joules per Coulomb).

What is current? The flow of electrons in your body (experienced as a shock). Compared to water: current is more o less flow. It is messured with amperes (the number of electrons flowing through a certain point per second).

What does resistance does: all material resist the flow of electrons. If you have a wire made by copper they flow is different compared to aluminium, due to their atomic structure. Using the water comparisons: the valve would be the resistance limiting the flow in the pipe. So resistence is the ability of material to slow or to stop the flow of electric current, messured by ohm.

In short:

Electrical power. what is this?

Electrical power is messured in watts: 1 watt = 1 joule / second

Power (P) = voltage (V) * current(C)

Example: cellphone connected to a 12v battery and the is a 0,5 A current. How much power is this?

We can also calculate the power consumtion per hour (Wh)

Example; A radio is plugged in and plays music for three hours. The radio says on the the back that it consumes 7W of power.

Wh = 7W * 3 hours
WH = 21 Wh

1. Q&A session

Q: Why are batteries messured in Amp hours?
A: Using the tank example: The amp hours help to calculate after how much time the tank (battery) will be empty, leaving the vault open.
A: For a battery, the normal voltage times ampere hours (roughly) equals watthours.

Q: What does LDV does? How does it protect the battery discharge?
A: The LDV is normaly inside the charge controller. The battery is different from a tank, since

PART 2

All the energy we have on earth comes from the sun. So how to controll the flow of electrons from the sun? Think again of the atoms, the building blocks. And we can combine different atoms, that make up for different materials,as for instance photovoltaic panels

How photovoltaic panels work?

If we take a closer look:

To make it easy: we have two different kind of materials in a solar pane, very similar but with a different atomic structure. Positive and negative charges are triggered when photons from the sun pall on the PV cells. Thereby voltage is created. The electrons are migrating, flowing…

Experiment: this lamp got burned because the voltage of the battery was to high. But if I put a resistance, then it protects my lamp. So in PV systems we also needs elements to protect the equipment.

For today this is the main idea and let’s do another feedback session:

Q: Are all solar panels photovoltaic?
A: Photovoltaic menas electricity generated from light. So it is a feature of all photvoltaic panels (but not all solar energy systems). Terms naming non-PV systems are: solar thermal colector, solar collector, solar panel (for water heating)

The next session will be about how to size, plan and protect solar systems.

Please post questions and ideas on communitynetworks.goup!

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Some solar pricing information from Zimbabwe The best solar system to buy in Zimbabwe - Techzim

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Recording is up:
https://videos.apc.org/u/apc/m/basics-of-electricity-and-photovoltaics/