Scene: It is Christmas. Joe and Peter are happy - both have received gifts from Santa Klaus. They are impatient to meet each other and to show their presents.
Joe receives many presents because he got good results at school. Among all these gifts, he especially likes the construction kit with a small electric motor to make a carousel. The carousel has to be constructed from a lot of metallic parts and screws. In the box is also a small solar PV panel that will provide the electricity to run the electric motor.
Peter opens a large package containing a Formula 1 loop and 2 small formula 1 cars with electric motors. The loop is made of plastic plates that provide the speedway. Every plastic plate has two channels in the middle that assure the guidance of the small cars on the loop. There are also two consoles for two players that can remotely increase the speed of the cars on the loop…

Now, both children, separately in their houses, are enjoying chocolate bonbons and oranges, but tomorrow they will meet to play with the new toys brought by Santa Klaus during last night. Both of them are going to bed and dreaming about tomorrow.

It is still dark outside, but the children are already awake. Each of them waits with impatience for the day to start, to have breakfast and to meet each other.

Joe: Mum, can I invite Peter to our home to build my construction kit now?

Mother: Peter’s already called and proposed to meet in his house because he’s got a very nice large Formula 1 loop with two racing cars. I told him that you’d go to him after the breakfast. Joe is very impatient to leave.

Peter has finished breakfast and has already started to put the loop plates together on the carpet in his room when somebody is ringing at the door. Its Joe - the construction kit in his right hand.

Both of them start to excitedly examine eachother's toys. Somebody is ringing at the door. Its Paul who’s come to say hello to Peter’s parents and is very glad to see the kids together. Joe and Peter are keen to capture Paul to look at their toys. Paul apologises to Peter's parents and goes with the kids.

Paul: What do we have here? A Formula 1 race loop, and a construction kit with solar PV panel. That’s extraordinary. We can make an interesting combination because I also have in my pocket a solar PV panel of the same shape and capacity as yours. Your loop is powered by electric batteries? We can feed each racing car with solar PV panels.

Peter: Is it better to use PV panels than electric batteries?

Joe: I believe that PV panels are better than batteries because they are not discharging themselves like the batteries.

Peter: What do we do if there is no light, do the PV panels still produce electricity?

Joe: No. But you have lamps in your room, so we can use those if there is no sunlight, for now.

Paul: Well done boys. Let’s investigate more! Paul takes some electric accumulators and electric batteries out of his pocket. He also takes out a small PV panel exactly the same shape as the one in the construction kit. Let’s see how the PV panels and electric batteries work and, if you want, we can talk a bit about electric accumulators.

The camera is focusing on the tools, the batteries, accumulators and PV panels.

Peter: we can see what is written on them. Some of them have a label indicating that they are rechargeable. Yes! This makes the difference: the accumulators can be recharged and the ordinary batteries get thrown out after they are discharged.

Joe: I’ve seen a young man throwing the discharged batteries from his Walkman on the ground in the park. I told him that the batteries must be collected and not disposed together with ordinary waste; because batteries are hazardous waste.

Paul: The batteries are producing electricity as result of a chemical reaction between a base and the electrodes. The accumulators are somehow similar. There are many types of accumulators - the oldest and the most known one is the lead plates and acid accumulator.
A battery is a device that stores energy and makes it available in an electrical form. Batteries consist of electrochemical devices such as one or more galvanic cells (or, more recently, fuel cells). The first possible evidence of batteries in history are the Baghdad Batteries from sometime between 250 BCE and 640 CE. The modern development of batteries started with the Voltaic pile developed by the Italian physicist Alessandro Volta in 1800. The worldwide battery industry generates 48 billion dollars in sales annually (2005 estimate).
Lead-acid batteries (or accumulators), invented in 1859 by French physicist Gaston Planté, are a type of galvanic cell and are the most commonly used rechargeable batteries today. They also represent the oldest design with one of the worst energy-to-weight ratios, although the power-to-weight ratio can be quite good. Also, the energy-to-volume ratio is good compared to other types of batteries. They are cheap and can supply high surge currents needed in starter motors. Every reasonably modern car uses a lead-acid battery for this purpose. They are also used in vehicles such as forklifts, in which the low energy-to-weight ratio may in fact be considered a benefit since the battery can be used as a counterweight.
Lead-acid car batteries consist of six cells of 2 V nominal voltage. Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV) oxide (PbO2) in an electrolyte of about 37 % w/w sulphuric acid (H2SO4). Modern designs have jellified electrolytes. In the discharged state both electrodes turn into lead sulphate and the electrolyte turns into water. (This is why discharged lead-acid batteries can freeze.)
But let’s see how the PV panel works.

Joe: a PV is made of semiconductor materials that have the property of transforming the light waves into electricity. Generally, to build solar PV panel silicone crystals are used.

Paul: A solar cell, or photovoltaic cell, is a semiconductor device consisting of a large-area p-n junction diode, which in the presence of sunlight is capable of generating usable electrical energy. This conversion is called the photovoltaic effect. The photovoltaic effect was discovered in 1839 by French experimental physicist Alexandre-Edmond Becquerel. He observed that certain materials would produce a small current when exposed to light. Light is comprised of packets of energy called photons. When light hits the p-n junction of a semi-conductor the absorbed photon energy releases an electron from the n-type region and moves it to the p-type filling a hole and creating a current. The field of research related to solar cells is known as photovoltaics.
Solar cells have many applications. They are particularly well suited to, and historically used in, situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth orbiting satellites, handheld calculators, remote radiotelephones and water pumping applications. Solar cells (in the form of modules or solar panels) on building roofs can be connected through an inverter to the electricity grid in a net metering arrangement.

Paul: That’s it. So PV cells are producing electricity without any noise, vibration or moving parts. They present a lot of advantages however the downside is the very high costs. Generally, the PV panels (that are formed by several solar cells) are used together with electric accumulators, in order to store the electricity produced during the daytime. This way the electricity can be used during the night.

Peter: Now we know the differences between electricity sources, what do you say to feed our racers with electricity from solar PV panels?

Paul: We will need only four pieces of insulated wire to make the connections between solar PV panels and the racers.

The three people are making the connections and then they are testing the installation. It works perfectly. The only thing to remember is not to stay between the light source and the PV panels.

The boys start playing. They are glad and say that next summer they will play outside with the Formula 1 racing loop. They really like the idea of a contest of solar automobile builders in their school.