The power of photovoltaics: how to save energy (and conversations)

 

It was a sunny day and i was on the plane, flying back to Italy from the Netherlands, to spend some days in Bergamo, my hometown.

The woman sitting next to me was staring at the seat in front of her  without saying a word. After a while she asked me: “Can you please tell me something? I hate flying and i am panicking. For me flying is definitely the worst… “

I don’t know why but in that moment the only thing i was able to think of, was the movie “Final Destination“ which was not a very good topic.

I looked out of the window searching for some ideas and i saw a big photovoltaic installation.

“ Can i talk about solar energy? “

“ Sure, anything is fine girl.”

“ Nice, get comfortable and listen to this story…”

 

Introduction

Photovoltaic panels convert solar energy in electricity through an apparently simple mechanism. The photovoltaic effect was discovered in 1839 by the french scientist Edmund Becquerel who put two electrodes in a conducting solution and realized that after illuminating one of them, a voltage was created. The first photovoltaic cells were made of selenium, but this material was not so efficient in terms of energy conversion. People passionate about photography might know that selenium is the material used for light sensitive cells in cameras.

Nowadays many photovoltaic panels are made of silicon, which is a semi- conductor. Semi-conductors are more conductive than insulators  (for instance wood) but less conductive than conductors (iron, copper).

 

How does it work?

A photovoltaic panel is made of several units, defined as cells. Each photovoltaic cell is made of two layers of silicon and some metallic plates. The silicon layers are treated with some chemicals: the upper layer is charged with phosphorus (negative charge) and the lower layer is charged with boron (positive charge). When the light hits the semi- conductor, electricity is produced. How is it possible?

When photons, the particles light is made of, hit the semi-conductor material, a first part of energy is reflected, a second part produces heat and a third part causes a movement of electrons from the atoms of the semi- conductor. In this way a current is created. Subsequently electrons reach the plates and are transferred to the electrical cables.

What is important to highlight is that photovoltaics produce energy in a continuous way, so electrons always travel following the same direction. The current used in all the electrical circuits present in ordinary buildings is alternate, which means that electrons change periodically their direction. In order to transform the continuous current  in alternate current,  an inverter is needed.

If during the day your photovoltaic system produces energy in excess, it is possible to share this surplus with the public electrical network. By doing this you will get some credits which will compensate the withdrawal from the public network necessary during the night, when the panels are not working.

Another option to save this surplus is the installation of  a storage system. The majority of the modern accumulation systems are based on the use of lithium ion batteries as they are more efficient and more long lasting than the “old” lead acid batteries.

 

Environmental impact

The good thing about photovoltaic panels is that they don’t need fossil fuels and that during the process there are no greenhouse gases emissions. However some problems arise during the panels production.

Indeed the manufacturing of some photovoltaic panels makes use of cadmium telluride, classified as toxic by the European Union (2011).

Furthermore the purification of silicon produces a very toxic compound,  silicon tetrachloride, as a by-product. At the moment some advanced processes capable of reducing the environmental impact are being tested, including the possibility of recovering some pure silicon from the by-product.

If you want to install a  photovoltaic system just make sure that you buy only certified panels from recognized insitutions  (for instance KIWA or IFI).

 

Future perspectives

The scientific interest about photovoltaics is increasing: there are some promising studies about the use of graphene which represents an alternative to silicon. Another interesting material is perovskite which showed a good power conversion efficiency.

Solar energy has a good potential and it represents a great turning point.  Unfortunately some manufacturers fabricate the panels making use of toxic compounds, taking advantage of the fact that in some countries  there is less control and that manpower is cheaper. This is all the wrong way round. In doing so, developing countries are just exploited in the name of renewable energy, but they will never benefit from it.

Of course there are a lot of positive examples to take inspiration from: this year in France O’ Mega1 has been created: it is a big photovotaic plant made of floating HDPE  modules and part of the project was payed through crowdfunding.

The Netherlands are also investing a lot in this technology: just a few days ago another floating photovoltaic plant was installed in Zwolle. According to the Netherlands Environmental Assessment Agency the total installed photovoltaic capacity will quintuple within 2030.

Usually we tend to associate the Netherlands to wind energy, which is of course a very popular  technology here, but not the only one!

If you want to know more about this take a look to the The Dutch PV portal ( or just ask me for some entertainment when you are traveling).

 

Giulia Ioselli