These article originate from my contributions to Energiris, a Belgian citizens’ cooperative committed to accelerating the energy transition. As part of our mission to inform and raise awareness among both co-owners and the general public, we regularly publish educational content on topics related to sustainable energy.
The original articles were published in French and Dutch, reflecting the multilingual context of our cooperative. By sharing them here in English, I also wish to reflect my personal commitment to a more sustainable and better-informed society.
What does a photovoltaic installation consist of?
We will take the example of a house, which is familiar to our cooperative members, but the main components are the same for all types of installations.
In order to convert sunlight into electricity that can be used in the building and/or fed back into the electricity grid, two main elements are required:
- Photovoltaic panels, usually installed on the roof of a building (but other types of installation exist), are made up of photovoltaic cells that convert the energy contained in light1 to produce direct current.
- An inverter that converts direct current into alternating current, which can be used by electrical appliances in the building (such as the fridge, television, a lamp, etc.).
Finally, the entire system is connected to the electricity distribution network via one or two electricity meters2 belonging to the network operator, in order to feed in any electricity that is produced but not consumed by the building, or to draw the electricity required for your consumption if the panels do not produce enough (at night, on rainy days, etc.).
The following elements can also be added:
- A monitoring system that analyses and/or optimises the performance of the installation while monitoring it from your phones, tablets and computers.
- A battery energy storage system, allowing the electricity produced to be stored and released when needed. Adding a battery will require the addition of a regulator to control the charging and discharging of the batteries and optimise their service life.
How a photovoltaic cell works
As mentioned above, photovoltaic panels are made up of cells that convert the energy contained in light3 to produce direct current.
A photovoltaic cell is a semiconductor device made of silicon crystals. It consists of a ‘P-type’ layer with “missing” electrons (called holes) and an ‘N-type’ layer with excess free electrons. When the two types of material are bonded together and exposed to sunlight (direct or indirect), electrons are ‘ejected’. This is called the photoelectric effect. A charge imbalance exists between the two semiconductor layers. If both sides of the cell are connected to a charge or wires, the electrons can flow through the wires to the other side of the cell, producing an electric current created by the exchange of electrons.
The voltage produced by a single solar cell is approximately 0.6 V. A photovoltaic panel consists of several cells connected in series to produce a higher voltage.
Construction of a solar panel
As we have just seen, a panel consists of a series of photovoltaic cells connected in series to produce a higher voltage. But these cells are not simply ‘placed on the roof’. They are assembled on a rigid frame to form a usable module.
The panel will consist of:
- an aluminium frame, a rigid structure that houses the sandwich structure
- tempered glass, facing the sun and allowing its rays to pass through while protecting the highly fragile cells. This is the side that faces the sun.
- Just below the glass are the photovoltaic cells, connected to each other by conductive plates or wires. The cells are encapsulated in a transparent resin. This resin ensures watertightness and thus protects the cells from moisture, oxidation and the development of mould, which could impair the functioning of the panels and reduce their efficiency.
- Finally, there is a polymer back plate that protects the rear and houses a box for connections.
Influence of latitude and seasons
In direct sunlight, one square metre of the Earth’s surface at the equator receives up to 1,000 W of energy per day, without clouds. However, not all latitudes receive the same amount of solar energy. At a latitude of 50°4, the power is approximately 610 W per m².
The further away from the equator, the more panels a photovoltaic installation will need to produce a given amount of energy. This means that a panel will be smaller at the equator than on a roof in Brussels.
The calculation of the surface area of solar panels needed to power a building must therefore take into account the latitude at which the photovoltaic installation will be used.
The seasons also have an impact on the amount of solar energy reaching the Earth’s surface. In the northern hemisphere, a photovoltaic cell will produce more energy during the months of June to August than during the months of December and January.
This is due to a number of factors, such as:
- The days are shorter in winter and longer in summer.
- The sun is lower in the sky during the winter months.
- The winter months are more prone to cloud cover.
- In areas where it snows, a fixed installation will produce less energy when the panels are covered with snow.
This does not, of course, render photovoltaic installations unusable in our latitudes, but it will have an impact on the number of solar panels required for a given power output.
The problem of shaded areas
One of the enemies of photovoltaic installations is shade, which reduces electricity production since photovoltaic cells need light to generate energy. Shade can be partial or total. If a panel is partially shaded, this can lead to a drop in solar energy production for the entire system. If a panel is completely shaded, it will not produce any solar energy at all.
To overcome this problem, various technical solutions can be used, such as:
- By installing micro-inverters, photovoltaic modules can be managed independently, limiting or reducing power losses in a module due to shade or technical failure.
- Optimisers, installed on photovoltaic panels, monitor their output in real time and optimise their production by searching for the maximum power point (MPPT).
- The use of solar panels equipped with bypass diodes. These diodes ensure that the electricity produced by the cells that are always exposed to the sun continues to flow through the panel, even if some of the photovoltaic cells mounted in series on the panel are in the shade.
How the inverter works
As mentioned at the beginning of this article, the inverter converts the direct current from the photovoltaic panels into alternating current that can be used by electrical appliances in the building. It is a power electronic device usually consisting of electronic switches such as IGBTs, power transistors or thyristors. These switches are controlled electronically to modulate the source to obtain an alternating signal of the desired frequency. This signal is then filtered electronically to obtain a sinusoidal electrical signal that can be used by electrical appliances or fed into the electrical distribution network.
Inverters are critical and necessary components for photovoltaic installations, as the latter naturally produce direct current by capturing energy from the sun using photovoltaic cells, as explained above, while most electrical appliances operate on alternating current. Hence the need for an inverter to perform this conversion. They also have advanced features such as monitoring, power control and surge protection.
It should be noted that inverters must synchronise with the grid (same frequency, same phase) before the photovoltaic installation can supply its AC power.
How to size a photovoltaic installation?
The sizing of a photovoltaic installation depends on several factors such as electricity consumption, available surface area, orientation and inclination of the system, type of panel used, electrical connection, etc. It is important to size the installation correctly to ensure optimal performance.
There are several methods for sizing a photovoltaic installation. One method is to calculate the peak power of the solar panels. Peak power is the maximum electrical power that a solar panel can deliver under standard conditions. The efficiency of most solar panels is between 15% and 18%. To calculate the maximum capacity, you need to take into account the surface area of the solar panels, the efficiency coefficient and the amount of sunlight. Here are two formulas for calculating the power of the solar panels in an installation:
- Surface area (in m²) x efficiency coefficient (0.85) x 1,000 W/m² = Peak power (Wp)
- Energy (kWh) x efficiency coefficient (0.85) / Sunshine hours = Peak power (Wp)
It is important to understand that the power of a solar panel is expressed in peak watts (Wp) or peak kilowatts (kWp). 1 kWp corresponds to 1,000 Wp. The higher the number of kWp (the power of the solar panels), the more efficient the installation.
Another method is to size the installation based on electricity consumption. To determine the peak power required to cover a given production, the following formula can be used:
- Peak power to be installed = Consumption / (specific production of the site x correction factor) [kWh/year / (kWh/kWp x %) = kWp]
The technical service provider who will carry out the installation will be best placed to correctly size your installation.
References
- Institut Royal Météorologique, Rayonnement solaire global journalier, moyenne annuelle, https://www.meteo.be/fr/climat/climat-de-la-belgique/atlas-climatique/cartes-climatiques/rayonnement-solaire/rayonnement-solaire-global/annuel
- Khan Academy, Effet Photoélectrique, https://fr.khanacademy.org/science/physique-a-l-ecole/x6e8a541a302cdab5:physique-a-l-ecole-6e-annee-secondaire-2h/x6e8a541a302cdab5:physique-a-l-ecole-6e-2h-mecanique-quantique-l-atome-et-le-photon/a/photoelectric-effect
- Energie + , Ensoleillement, https://energieplus-lesite.be/theories/climat8/ensoleillement-d8/
- Kolantla, D., Mikkili, S., Pendem, S.R. and Desai, A.A. (2020), Critical review on various inverter topologies for PV system architectures. IET Renew. Power Gener., 14: 3418-3438. https://doi.org/10.1049/iet-rpg.2020.0317
- Vieira, Romênia & Araújo, Fábio & Dhimish, Mahmoud & Guerra, Maria Izabel. (2020). A Comprehensive Review on Bypass Diode Application on Photovoltaic Modules. Energies. 13. 2472. http://dx.doi.org/10.3390/en13102472
- Inverters: principle of operation and parameters | EME 812: Utility Solar Power and Concentration (psu.edu) : https://www.e-education.psu.edu/eme812/node/711
- Hernández-Callejo, L., Gallardo-Saavedra, S., & Alonso‐Gómez, V. (2019). A review of Photovoltaic Systems : design, operation and maintenance. Solar Energy, 188, 426‑440. https://doi.org/10.1016/j.solener.2019.06.017
Footnotes
- Photovoltaic systems do not use the sun’s heat. This is used by solar thermal systems, particularly for producing hot water.. ↩︎
- Dual flow meter or addition of a production meter known as a ‘green meter’. ↩︎
- Photovoltaic systems do not use the sun’s heat. This is used by solar thermal systems, particularly for producing hot water. ↩︎
- Belgium extends over 2 degrees of latitude, from 51°30′ at its northernmost point (Meerle) to 49°30′ at its southernmost point (Torgny). ↩︎
Beyond my role at Energiris, I place great importance on sharing knowledge. I have always considered education to be an essential tool for helping everyone better understand energy issues and the concrete solutions available to us. Sharing what I discover and making complex topics accessible to others is also my way of contributing to a fairer, more inclusive transition.