Are photovoltaic tiles safe?

Instead of solar panels installed on roofs, tiles are already photovoltaic modules. This is the idea of photovoltaic tiles, an interesting product with many application possibilities. There are photovoltaic tiles of all types. Perhaps the most famous example is that of the American manufacturer Tesla.

We don't know whether the success (or fame) of Testa's tiles is due to the quality of the product or the eccentricity of Elon Musk, founder of Tesla Motors, who, in addition to manufacturing electric cars, is a shareholder in Solar City, one of the largest installers of US photovoltaic systems.

Recently, Tesla was involved in an imbroglio in the USA with Walmart, the largest supermarket chain in the USA. The reason? Fires in seven chain stores covered with photovoltaic panels. Although this unfortunate incident has nothing to do with the photovoltaic tiles manufactured by Tesla, the association of the accident with its photovoltaic tiles, which are the company's latest addition to the solar market and have received great interest from the public, is inevitable.

What are photovoltaic tiles?

It's simple. These are tiles covered with some type of photovoltaic device. The simplest case is conventional tiles on which crystalline cells (also conventional) are applied. What's new about this? There isn't much to say.

Instead of having photovoltaic modules on our roofs with 60, 72 or 144 cells (standard market numbers), we will have 100, 200, 300, thousand photovoltaic tiles individually equipped with a small number of crystalline cells. What you gain from this is just a large number of electrical connections and no advantage from the point of view of efficiency or practicality of installation.

An evolution of photovoltaic tiles with crystalline cells are tiles manufactured with thin films. This category includes tiles from Tesla and other manufacturers, such as the Chinese Hanergy, which we see in the figures below.

These types of tiles take advantage of the entire available roof area and can compete in efficiency and performance with traditional photovoltaic systems.

At the launch of Tesla's photovoltaic tiles, Jeffrey Brian Straubel, the company's CTO, stated that the success of the new product was due in part to Tesla's experience in manufacturing connectors for automotive applications.

“Many challenges were overcome through Tesla’s learning in validating and mass producing automotive connectors. We were able to solve complex design problems with in-house manufacturing, without outsourcing,” said Straubel.

In fact, good experience in the manufacture of electrical connectors is essential for the success of photovoltaic tiles. Photovoltaic tiles are like mini solar panels. The operating principle is the same as that of solar modules, whether crystalline or thin films.

Electrical connections

The central difference between the two technologies (modules x tiles) is the high number of connections to connect all the tiles on a photovoltaic roof. It is not necessary to have technical knowledge to imagine that the increase in the number of electrical connections may be accompanied by an increase in the number of problems.

Generally, the main reason for failures (and fires) in photovoltaic systems is poor contacts in the electrical connections and this will be no different with photovoltaic tiles. In photovoltaic systems, any small bad contact in an electrical connection can result in incalculable losses.

The root of the problem lies in the risk of generating electric arcs, since photovoltaic systems work under high voltages (typically around 900 VDC in residential or microgeneration systems) and direct currents with intensities of up to 10A. Any small bad contact can cause a fire. The reliability of electrical connections is fundamental to the success of photovoltaic tiles, as well as any other photovoltaic system, even those built with conventional modules.

MC4 Standard

There are manufacturers specializing in electrical connections for photovoltaic systems. The standard adopted worldwide throughout the photovoltaic market is known as MC4 (the initials refer to its original manufacturer, Multi Contact, today belonging to the Swiss group Stäubli).

Several manufacturers currently reproduce the MC4 type connectors, which are relatively compatible with the original MC4, distributed with denominations such as T4 and H4, for example.

The key to the success of photovoltaic tiles, so that they can compete with traditional photovoltaic modules, is the presence of good electrical connectors.

The connectors must preferably be of the MC4 type, standardized and adopted worldwide by the photovoltaic industry. Below we see an example of a photovoltaic tile that adopts the international MC4 standard.

What if the photovoltaic tile does not have MC4 connectors? Although this is very unlikely to happen, as photovoltaic system connections are globally standardized, care should be taken to ask the manufacturer about the safety of their connections:

• Are the connectors resistant to moisture or dust ingress?
• Are they resistant to oxidation and bad contacts?
• Are they compatible with the operating voltages of photovoltaic systems (1000 Vdc or 1500 Vdc), do they comply with standards NBR-5410 and NBR-16690?

If your photovoltaic tile manufacturer uses any type of connector that is different from MC4, ask questions. Connections for photovoltaic systems must meet the requirements of standard NBR-16690 (on photovoltaic electrical installations), which we highlight below:

Additionally, it must be considered that the electrical connector is just one of the items involved in the construction of a photovoltaic module or tile. There is still the presence of junction box, well known in conventional modules and also essential in solar tiles.

A junction box is necessary to safely make electrical connections between photovoltaic cells and the outside world. In addition junction box is useful for housing the diode bypass, which is essential in photovoltaic tiles, as well as in conventional solar modules. In the figure below, we see highlighted the junction box from Hanergy, where the diode is carefully housed bypass of the tile.

On the other hand, if your photovoltaic tile manufacturer does not employ junction box, leaving the diode bypass exposed, the metal contacts of the diode are exposed and can be touched by people or animals, posing a risk of electric shock and death, in addition to allowing the electrical contacts to oxidize, which will considerably reduce the product's useful life.

In response to the question that constitutes the title of this article, we can therefore state that photovoltaic tiles are as safe as any other photovoltaic module or device that has appropriate electrical connectors, that meet current technical standards and that do not pose a risk of electric arc, shock electrical, poor contact or premature oxidation of contacts. In summary, a good electrical connector is necessary for the safety of photovoltaic tiles.