How does solar photovoltaics work?

Renewables

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The irruption of renewable energies has gone hand in hand with the utilisation of the sun, but do you know how solar photovoltaics works and how it reaches your home?

The sun, that incandescent ball that occupies our sky and around which practically all the human cultures have revolved, revolve and will revolve (literarily and literally speaking). A cultural and religious veneration that, far from being banished by an increasingly less mystical humanity, is now being harnessed scientifically through energy. And the fact is that this 4,6-billion-year-old star –barely an adult compared to the age of other stars– is vital for life on earth (we do not think it is necessary at this point to explain why) but also for the production of clean, sustainable and inexhaustible energy: solar photovoltaics. Thus, in just a few decades, we have gone from living with our backs to the sun –from an energy point of view– to experiencing a photovoltaic fever in which we are beginning to take advantage of the potential of our sun to generate electricity. But have you ever wondered how photovoltaic solar energy works? Well, today we’re going to enlighten you with it; get your suntan lotion on and let’s get started.

Perhaps the first and most necessary thing is to clarify what photovoltaic solar energy is. This type of energy is obtained by converting the sun’s radiation into electricity thanks to the so-called photoelectric effect, which basically consists of the emission of electrons (which will later become electricity) as a result of electromagnetic radiation falling on a material, in this case the photovoltaic cells located on the surface of the photovoltaic panels, regardless of their size and technology. These, in turn, have a series of layers of electricity semiconductor material, either silicon or other materials, covered by a glassy film that allows solar radiation to pass through and minimises energy loss, although currently the maximum efficiency is 20% in the most advanced installations. In this way, the sun’s rays that remain inside are “trapped” inside the photovoltaic plate thanks to the generation of an electric field that runs through an electric circuit that is transferred through the electrical installation.

We already have our beloved solar rays, whose intensity will determine – within the capacity limits of our installation – the power we will be able to generate, trapped in our electrical circuit thanks to the “magic” of science. Now it’s time to turn them into real electrical energy that we can use.

Well, as the “trapped” photons release electrons, they generate more and more electricity through the circuit of the photovoltaic plate, which cannot take advantage of all the electrons generated and redirects them back to the so-called negative panel so that they can re-enter the process at a later stage. Thus, this cyclical process allows the production of what we know as direct current, which is stored in batteries to be subsequently converted into alternating current (the one we consume at home) thanks to the work of the second main protagonist of our explanation: the voltage inverters.

These inverters are key, as without them it would be impossible to take advantage of photovoltaic solar energy. Thus, the work of these devices matches the current of the energy to that which we can find in any socket in a house thanks to the conversion from DC to AC. The explanation for this need for current conversion is that direct current, as its name suggests, offers a regular flow that runs in a mono-directional manner, while alternating current works thanks to a constantly changing power and direction. In this way, inverters change the direction of the direct current from constant to alternating current, so that we can take advantage of it for our domestic use, as it is much easier to adapt the specific voltage of our electrical appliances to alternating current.

Well, it is at this point that, in order to continue with the explanation, we need to look at the types of photovoltaic installations that exist. Basically, we can divide them into two main groups:

  • Grid-connected photovoltaic systems
  • Off-grid photovoltaic systems
  • Let’s look at the differences in operation and what other elements come into play to ensure their use.

Grid-connected solar photovoltaics systems

These types of installations, whether they are self-consumption installations (those that we install in our private homes to supply ourselves with “free” energy) or a power plant (a large installation that generates photovoltaic solar energy and distributes it to different consumers), are interconnected with the large electricity grid; allowing the grid to be fed with the surpluses (in the case of self-consumption) and production (in the case of power plants).

It is at this point that we must differentiate between domestic and central installations, mainly due to the number of elements that come into play to ensure their correct operation.

  • In domestic installations, electrical energy, once it is in alternating current, passes to batteries from where it is consumed by our electrical appliances or stored waiting to be consumed. In turn, surplus energy is sent through the public electricity grid for use by consumers.
  • In photovoltaic power plants, the process is much more complex because, once the electricity is generated, it has to be fed into the grid, where it begins a very interesting journey to its consumption.

Thus, once the electricity generated passes through the inverter, it has to pass through a key element in the whole process: the transformation and distribution centre. This device raises the voltage, increasing efficiency and reducing energy losses, so that it can be transferred to the grid, which transports the electricity to the points of consumption.

As the electricity approaches the consumption points, it passes through the substation to reduce its voltage so that it can be used.

Off-grid solar photovoltaics systems

This second classification is the least common, but very much present in sectors such as agriculture, as well as in remote or difficult to access locations. Basically, these are installations that operate in what are known as “energy islands” to meet the energy demand of autonomous installations. Thus, these types of photovoltaic installations, which are much simpler in terms of operation as they do not require more switchgear as they are not connected to the main electricity grid, can act as electricity generators for lighting, for irrigation systems in plantations or as support for other generation systems such as diesel generators.

To do this, and returning to the point where the energy has already passed through the solar panel and is safely stored in our battery, these installations require another extra element that differentiates them in terms of operation: the regulators. This element basically functions as a protection system for the battery against electrical overloads or possible inefficient or irresponsible uses of the accumulated energy. In this way, the batteries, well protected, dump the energy on the autonomous electrical network (wiring and domestic/agricultural/industrial installation) and the latter makes use of it. It’s as easy as that.

Solar photovoltaics: sustainable and cheap

Until recently, the debate on photovoltaics, as with other sources of renewable energy generation, was a heated one. The clouds that threatened to cover the sunny “photovoltaic sky” were nothing more than doubts about its own viability as an energy source. Like any technology, photovoltaic paid the toll of a cost overrun in its initial phase which, after several years demonstrating its versatility, it has managed to overcome thanks to technological maturity and a sustained decrease in installation prices.

Thus, just two years ago, a milestone in the history of solar photovoltaics occurred when the International Energy Agency (IEA) published its annual World Energy Outlook 2020 report in which it ruled that solar energy is not only competitive and efficient, but is “the cheapest electricity in history” –that’s nothing. The key to this is the cost of capital for solar power projects, which allows solar power to be produced at a price of less than $20 per megawatt hour, which is one of the reasons why funding bodies look favourably on the provision of capital for the development of new solar projects due to its high profitability.

Today, photovoltaic power generation capacity has reached the psychological barrier of 1,000 GW thanks to the contribution of an excellent 2021 in which 168 GW of capacity was added to the global electricity grid. This is attested to by SolarPower Europe‘s Global Market Outlook for Solar Power report, which also notes that this is the ninth consecutive year in which the PV industry has broken its annual installation record. A trend that is expected to be repeated in 2022, when forecasts point to solar power installations exceeding 200 GW for the first time.

How does electricity reach the house?

It’s ten o’clock at night, it’s the middle of winter and it’s 8 ºC outside. You hardly notice it. In front of your TV set, you are enjoying the comfort of your electric radiator. Meanwhile, you charge your mobile phone and you hear in the background the dishwasher doing the dirty work while you are resting. It is the “miracle” of electricity at home. This everyday scene is brought about by electricity. And although it may seem completely normal to us, it is not as simple as it may seem.

For electricity to reach our homes safely, energy must be generated and transported. It must also be transformed and distributed. All of this through a complicated tangle of substations, electrical transformers, distribution centres and networks. In an underground labyrinth of which we know nothing.

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