Waterproofed...

Waterproof solar cable is a MYTH. At least while speaking about the DC string cables. This has not been an issue at the early time of photovoltaic market. It has changed together with the boosting floating PV projects. So what needs to be taken into consideration?

How it all begun?

At the time, when EN50618, resp. IEC62930 standards were defined, nobody would even think of the PV cable to be exposed to water. It was not an issue. It was important for the cables to be flexible. Insulation should be robust enough to withstand a common mechanical stress. It can′t contain halogen or any other poisonous substances. And to be temperature and UV resistant.

Now comes the hidden devil. In order to replace halogen, there need to be other substances which fulfill the function of flame retardancy. Those substances are based on inorganic mineral flame retardant basis. Such substances have one weakness. They are highly hydroscopic! This means that in a long-term perspective, it absorbs the humidity (water) like a sponge! It is the main reason, why solar cables are NOT intended to be permanently submerged in the water!

Water RESISTANT vs. Water PROOF

Many people don′t recognize it., There is a huge difference between those two definitions. In principle, all polymeric materials are not humidity proof. Some of them might perform better than other ones when exposed in the water. However, it is not a question IF, but WHEN. Sooner or later the cable will fail. Therefore, it is important to distinguish between being waterproof or water-resistant. The construction of those cables is very different.

In order to guarantee waterproof properties, there needs to be a metal-based barrier as one of the insulation layers of the cable. Wire armoring, metal tape or any sort of paper/foil tapes are worth anything, but not the waterproof properties!

Wait a minute! We talk about the flexible string cables, right? So it is not possible for a string cable to be flexible, if one of its insulation layers shall be a hermetically closed metal tube, right? This has only one conclusion:

PV String Cables are not waterproof. It is technically not possible.

The next question is obvious. How differs the water-resistant cable then? Each manufacturer has a different approach to this topic. Some of those have a realistic base, some of them are covered with a mesh of marketing. And quite a few of them serve you nothing else than a lie.

Water-resistance has many faces. It depends on the use. Each cable (or any other component) is classified based on different schemes. As far as the solar DC string cables are concerned, the best what has been so far achieved is the 德国莱茵TüV集团 standard 2Pfg 2750/09.20. The basement of this standard has it′s origin in the UL44 standard which is taking into consideration the water/humidity exposure. However, the testing sequences of the 2Pfg norm are significantly boosted and the requirements are truly challenging. Reaching this certification is paramount for floating PV, as well as conduit burial cables, or any exceptionally wet/humid environment (marine).

AD8 - Magic Formula

It is unbelievable, how many companies tend to hide behind the AD8 statement. For easier imagination, let me to summarize the terminology for you.

AD1 - Negligible: Limited chance for water exposure

AD2 - Water drops: Water drops (rain) might occur

AD3 - Spray: Water droplets falling to the cable surface in an angle of 60° or more

AD4 - Splash: Occurrence of splash water is possible

AD5 - Jet: Water jets possible

AD6 - Waves: Occurrence of waves is possible

AD7 - Immersion: Occasional partial or total flooding

AD8 - Submersion: Permanently under water

Seeing the above logics, it is very obvious that the flexible PV string cables can′t be thrown to the AD8 category, as this one is reserved for subsea cables, which have a totally different construction and parameters. Those are just about anything, but not flexible. AD8 means nothing else than waterPROOF. You already noticed in the previous paragraph that the criteria for waterproof cables do not match with the structure of flexible string cable.

Now comes the tricky point. There is no standard or test sequence which would evaluate, test and certify the classification of any cable with a relevant AD criteria. The ADx is a self-declaration of a manufacturer, which does not need to be confirmed by any 3rd party authority. In other words - it is up to you, whether you trust the cable manufacturer or not. It is up to you to decide whether you accept the risks associated or not.

Main take-away

• Using standard, commonly used solar cables on installations with a long-term water exposure is not recommended, as the common cables are hydroscopic.
• There is a big difference between water-resistant and water-proof. Pay attention!
• No matter what, avoid permanent exposure of the cable in the water. Using water-resistant cables (certified with the 2Pfg 2750/09.20) will help you to eliminate accelerated ageing (in other words unexpected expenses) of the array.
• Using water-resistant cables is not only for floating PV projects. It is also highly advisable for cables buried in pipes & conduits, or cables used in marine environment.
• Water-proof flexible PV string cable does not exist.
• AD8 flexible PV string cable does not exist.

Stay Tuned

Next month′s newsletter will focus on using red, blue, white, green, yellow and any other color on PV cable. Subscribe & follow. Safeguard your PV investment!