Photovoltaic panel types

From the outside, the world of photovoltaic panels for residential use may seem rather linear. If we take a closer look, however, it is possible to see that there are several forks in the road to pass before arriving at the best possible choice. Understanding the different types and models of photovoltaic panels is not always that simple, especially for the non-expert. Therefore, to find the most advantageous solution, it is necessary to know what the market has to offer and to cross-reference this with your own needs, obviously taking your available budget into account.

Photovoltaic systems for residential use differ according to a range of criteria:

• the installation site, such as the roof or balcony;

• the presence or absence of grid connection, i.e. grid-connected or stand-alone;

• photovoltaic cell technology;

• the combination with storage systems.

Roof and balcony photovoltaics

As a rule, a residential photovoltaic system can be installed almost anywhere, but most systems are placed on the roof or on one of the balconies of the home.

The most classic installation uses the roof (flat or pitched) of detached ho]uses or apartment blocks. Roof-mounted photovoltaic systems can reach high power levels because several modules can be connected with the only limitation being budget and available area. 3 and 6 kW are the most common configurations. Depending on location, exposure and inclination, a 3 kW photovoltaic system produces between 4,000 and 4,500 kWh per year, enough to cover the consumption of a family of two to four people. In the case of an apartment block, both centralised and private systems can be placed on the roof: in both cases, apartment block meeting approval is required. Installation must be carried out by specialised technicians, after an inspection.

A balcony photovoltaic system has lower costs and simpler installation, but involves lower capacity. It is an ideal solution for those who want to reduce the impact of their utility bills with a low investment. This type of system can be installed on masonry balconies and railings of detached houses and consists of a panel, support structure, and a microinverter that converts direct current into alternating current. On average, a system of this type produces around 400 kWh per year and allows savings of 25% on the average household bill. Moreover, if space permits, several systems can be installed, preferably on balconies facing south. It does not require any administrative authorisation, but - if you live in an apartment block - prior notification will be needed. The application for grid connection is easy and free of charge, and activation takes place very quickly.

In the case of a so-called Plug&Play system, there is no need for a technician: you can install it directly on the balcony of your house or on the wall under a window. Simply connect it to the mains power via a dedicated socket and you have additional power of up to 340 W.

Stand-alone and grid-connected photovoltaics

Photovoltaic systems can be stand-alone or grid-connected. In the first case, these are known as stand-alone or island systems. This type is a good choice when the photovoltaic system is able to meet the entire energy demand of the house. For this to happen, however, it is essential for the system to be equipped with a storage system capable of storing the excess energy produced during daylight hours for use during the night.

Grid-connected plants, on the other hand, are connected to the power grid. On the one hand, this allows energy to be purchased from the grid when self-production is not sufficient to meet household needs. On the other hand, it is possible to sell, by feeding it into the grid, the energy surplus produced and obtain financial compensation.

Monocrystalline, polycrystalline and thin-film photovoltaics

From a technological point of view, photovoltaic panels can also be classified according to the type of photovoltaic cells used, which perform differently in terms of efficiency with different costs, as a result.

• Monocrystalline silicon module: this has an efficiency of 16-23% and is the most expensive. It has a simple appearance, is blue or black in colour, and can be used as a translucent cover, e.g. as an awning or garage roof;
• polycrystalline silicon module: this has an efficiency of 15-17% and is good value for money. It has a sparkling appearance and is more sensitive to cloud and sunlight;
• thin film module: this has an efficiency of 6-14% and is usually the cheapest. It has a dark, uniform appearance, can be very thin or flexible, and is less sensitive to high temperatures;
• hybrid module: this produces both energy and hot water. When combined with an unglazed solar thermal collector, it can be used for heating, domestic hot water production, basement heat regeneration or seasonal storage in large water tanks.

Photovoltaics with storage

As already mentioned, photovoltaic systems can be combined with a storage system. This improves the efficiency of the system because it allows any unused energy produced at times of maximum solar radiation not to be wasted. Generally speaking, these systems consist of a set of batteries or accumulators.

There are storage systems that coexist with the inverter (inverter with integrated battery) and others located outside, connected to the photovoltaic panels. In this case, we are referring to modular systems with external batteries.  A storage system is convenient when the greatest flexibility of use is desired and this is indispensable in stand-alone systems. The installation of a storage system involves a higher financial outlay than a simple photovoltaic system, but the costs are balanced by the increased efficiency that can even lead to a zero electricity bill.