What is a photovoltaic system and how it works

With the cost of energy increasing, a photovoltaic system can represent an immediate cost but an investment for the future. Here is a guide with all the basic information to understand how to install a system, how much it costs and how much it can make.

Energy prices, in the last period, have grown by 300% and the first very high bills are starting to arrive. No one can say if (and when) the situation will return to normal, however it is good to look forward. The future that is painting before us sees a home that is even more connected, and therefore even more demanding in terms of consumption despite efficient appliances. Added to this is a car that, in the next few years, will use electricity instead of fuel to travel.

If consumption increases and the cost per kilowatt hour also increases, it is good to think about how to try to limit one of these two parameters, or both.

Globally, massive investments are being made in renewable and clean energy sources, with an eye to photovoltaics and wind power, but today even small consumers are starting to look with interest at photovoltaic systems as a solution to save . They do it for two reasons: the first is that thanks to the incentives, and we are not referring only to the infamous 110%, it is possible today to buy a complete system with a considerable saving, the second is that with the  Condominium Reform a family or an individual condominium can install a photovoltaic system for its own use both on a property of the individual and on the common parts.

This means that a person could also decide to install a system on the roof of the condominium after having communicated it to the administrator and after having explained to the assembly how he intends to do it. The assembly can request changes to the project but cannot deny using the common parts in order to install a photovoltaic system, as long as the same possibility is guaranteed to the other condominiums. Translated it means that a person cannot use the entire roof, but can use part of it for the installation, leaving others the possibility of carrying out a similar installation. This is easy in condominiums with few units, a little more complex in larger ones.

We have created this article to dispel some myths about photovoltaics and give some general indications on this type of system.

What is a photovoltaic system and how it works

The name itself says it: a photovoltaic system is a system where electricity is produced using the sunlight. The central element is the photovoltaic panel, which is placed side by side with other panels to compose a string. Each single panel is made up of a series of modules and each individual module contains several cells, which represent the element capable of converting the photons of solar radiation into energy.

The semiconductor used today for the production of cells is silicon, and the principle by which electricity is produced is not very complex: when photons hit the surface of the cell, one part is reflected and therefore lost, another part is dispersed underneath. form of heat while a last part, the one that triggers the “reaction”, is absorbed by the electrons in the atomic structure of the semiconductor allowing them to start flowing, producing an electric current.

This direct current is then converted, not without a loss, into alternating current by an electronic component, the inverter, thus finally becoming available for consumption.

A solar panel illuminated by the sun continues to produce energy which is immediately available and must therefore be consumed . But what happens when there is no load capable of consuming the energy that is constantly produced by the plant?

Today there are two ways to manage the energy produced in excess, that is the one that is not consumed: the first is to exploit a system called “exchange on the spot” while the second is to have a storage system , essentially a lithium battery (or more than one) that store the excess energy produced by a photovoltaic system and make it available in the bands where the photovoltaic does not produce. The on-site exchange is similar to a battery, indeed, it can be considered a virtual battery: it allows the user to transfer to the electricity distribution network a quantity of energy that is not consumed immediately, and then withdraw it later, when needed. All with the addition of a contribution that allows to amortize the cost of the same system.

Tesla Powerwall is one of the most popular domestic batteries

Are there any differences between the various panels? Isn’t it advisable to take the most powerful ones?

The first myth about solar panels to dispel is the fact that it pays to take more “powerful” panels so you need less. In reality, the panels with a higher power value are also thicker and heavier panels, and are often not considered for installations on the roofs of homes because they could give more problems than benefits. A home panel must be light to facilitate assembly – they weigh about 20 kg each – small and easy to handle and above all efficient.

Today the main differences between the different panels on sale mainly concern three parameters: the first is aesthetics, the second is efficiency and the third is the guarantee.

Aesthetics have an impact, and not a little, on the cost: there are panels with very simple frames that clash on the roofs, others that, thanks to the black coating and the black cells, are even slightly more efficient in terms of capturing light and reflected light. .

LG’s solar panels, black

Red solar panels that blend in with the tiles

There are also colored panels, for example red, which are suitable for some areas where landscape constraints prevent the installation of panels that can visually disturb a scene, however, in addition to being very expensive, these panels are also inefficient.

The second value is efficiency, performance. To understand what is meant by efficiency, you must first pass from the power which is indicated in kWp, or peak kiloWatts: with this value declared by the manufacturers we mean the maximum power that a panel can generate in standard conditions, which have been set in a radiation equal to 1000 W / m², at a temperature of 25 ° C and an AM1 value equal to 1.5. AM1 indicates the density of solar radiation hitting the earth’s ground at noon on a totally cloudless day.

We are moving forward under conditions that are unlikely to occur in a real situation, all values ​​that come out of the laboratories. The performance of a panel tells us what the percentage of solar radiation will be in this “perfect” day converted into energy by our panel , and usually the values ​​are around 19 – 21%. We are therefore faced with very similar panels for the various manufacturers, and although there are differences they are not so obvious: there is no panel that, for the same size, generates double the energy.

The third parameter is perhaps the most interesting one because it is the factory guarantee that the manufacturer recognizes not only on manufacturing defects but also on energy production . A solar panel is based on an exchange that leads to a deterioration of the components used in the junction of the cells and this means that over the years the amount of energy it can produce will drop more or less uniformly. Although the average lifespan of a panel is estimated to be several tens of years, after 25 years of use the panels can lose 15% to 25% in efficiency. Precisely for this reason it is good to look at panels for which the manufacturer guarantees an acceptable production for at least 25 years.

I have decided that I want a photovoltaic system, what solutions do I have?

We talked before about roofs and condominiums, but in reality today we can also start with something smaller. There are simple photovoltaic systems consisting of a panel to be mounted on the balcony railing or on the wall. We are faced with solutions that cost just over 300 euros and make it possible to produce about 400 kWh of energy in a year, as much as a refrigerator consumes.

The real system, however, is the one installed on the roof, and in this case we are talking about systems ranging from 2 kWp to 6 kWp . To give an idea of ​​the overall dimensions with current technologies, a 2 kWp system requires about 10 square meters of roof, while a 6 kWp system requires 30 square meters of roof which can also be managed in blocks, they do not necessarily have to be contiguous.

An average family can install up to 6 kWatt, because in Italy beyond this threshold it is necessary to adapt the electrical system passing from single-phase to three-phase. There is no technical reason, pure bureaucracy: in other countries it is also possible to install 10 kW systems with a single-phase meter.

How much you save with a photovoltaic system

It is safe to save, but it is not easy to establish in advance how much you can save because it depends on many factors. The first aspect is related to the orientation of the house: the solar panels should be installed to the south, trying to maintain a perfect perpendicularity with the sun. However, if you do not store excess energy in a storage, you could also decide to orient slightly east or west to take advantage of the early hours of the day or enjoy unbalanced production in the second part of the day.

To understand how much it is possible to produce with a photovoltaic system, a beautiful tool developed by the European Union is available, the PVGIS , which by indicating the address, the type of plant and the orientation is able to estimate what will be the annual production taking also take into account various atmospheric factors.

The system obviously does not take into account shadows caused by tall trees or even particular seasons, and it is evident that a winter where it almost never rains, without clouds and without fog, makes a plant perform better than it can if the sky is perpetually covered. .

A 6 kWp peak power plant in Milan has an annual production of about 8000 kWh, which becomes about 9000 in Rome and almost 10000 in Catania.

However, we must not think that photovoltaics alone can solve every problem and reduce the bill to zero, and this is true both in the case of systems with storage and in the case of systems without storage. A family with photovoltaics must necessarily change its habits trying to make the most of self-consumption: washing machines, dryers and dishwashers, to name some of the appliances that are used “spot” and which have significant consumption, must be used when the system is producing energy and not in the evening, when the system does not produce.

For this reason, the possibility, via app, to manage smart appliances by turning them on remotely or, with automation, when the electricity is free because it comes from the sun is convenient.

How much does a photovoltaic system cost

Despite the processor crisis and the increase in prices, some manufacturers have told us that in recent years photovoltaic systems have not suffered a drastic increase in prices as has happened for other sectors, also drugged by the various bonuses.

The cost of a 2 kW system starts from approximately € 6,000 installed and can reach € 16,000 in the case of a 6 kW system., price which also includes the project, labor and inverter. Thanks to the 2020 decree, today it is possible to give 50% and immediately benefit from the discount on the invoice, and this makes a system much more affordable: it ranges from 3,000 euros to 8,000 euros installed. The addition of a storage battery today represents an important cost, 10 kWh cost about 8,000 euros and it is a price that is really difficult to amortize. For this reason, as long as there is, it is good to take advantage of the exchange on the spot that works practically like a battery and above all does not wear out. The battery can always be added in the future, when prices change, and above all you can also use the car parked and connected to the network as a battery for the home at night.

We are facing an important cost, but usually it is possible to pay back the investment in about 6/7 years . However, if we calculate the cost of current energy and the incentives, today it could be possible with a good exploitation of self-consumption to return the investment even after 5 years.

Solar panels also require little maintenance: they are resistant to hail and strong wind, and thanks to the rain they can be cleaned. Only in the case of installation in dusty areas, for example near fields, may require annual maintenance to clean the surface. In the magazine of Evolvere, a company of the Eni group that has installed over 10 thousand  small photovoltaic systems throughout the country in recent years, there is a complete guide  that explains why atmospheric agents should not represent a concern and a brake on the installation of a photovoltaic system.

Problems related to installation

The main obstacle related to the installation of a photovoltaic system is related to the actual installation. The biggest fear is that cable ducts may appear in the house, and masonry work may be required. In reality , the installation of a photovoltaic system today is quite simpleand the companies that install them take care of everything, including any energy regulations. If the cables that carry the direct current to the inverters must have a large section to avoid losses due to distances, after converting the direct current into alternating current the cable that reaches the meter is of small section and usually passes through the normal corrugated part of today’s homes. The only elements to put in the house are batteries and inverters, which are often placed in technical rooms, closets or even in the boxes if you can.

Installation is not a problem for the user, although it is good that the user makes sure that the work is done in a workmanlike manner: in this period, also thanks to the various bonuses, many jobs could be done in a hurry and bad and it is good therefore to choose the company carefully. The time required for installation is a few days.

This is intended to be an introductory and not necessarily super in-depth article on a topic that we believe is of great interest, especially in a period where the cost of energy is growing but the devices we have permanently on at home are also growing. Precisely for this reason, in the coming weeks we will deal with other issues related to energy efficiency in the home, and we will also see how the storage systems work and how they can be combined with any plans that provide free energy at night, energy that can also be used for ” charge the batteries ”. We will also closely follow the installation of a photovoltaic system and a storage system, and we will see how to organize a “smart” home that can maximize self-consumption thanks to connected appliances and home control hubs.


by Abdullah Sam
I’m a teacher, researcher and writer. I write about study subjects to improve the learning of college and university students. I write top Quality study notes Mostly, Tech, Games, Education, And Solutions/Tips and Tricks. I am a person who helps students to acquire knowledge, competence or virtue.

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