The photovoltaic on board. A practical guide to choosing the plant for your boat.
Now photovoltaics are increasingly present on our boats, when it comes to making a purchase but you are uncertain about the power, the technology to choose and how to build the plant.
Whether you’re a sailor or a motorcyclist, during the round or the bathroom, you’ll surely have woken up with a buzzer that reminded you to set in motion to recharge your batteries.
If you did not have a charge management system, however, you may have over-discharged the batteries with a consequential decrease in the life of the same and, in some cases, with a much bigger problem in the absence of a battery dedicated only to the engine: “how to I’m going to start now?”
Even if you’ve always been aware of the charge management, it’s certainly not pleasant to stay at the bottom with an engine running for several hours to recharge the batteries.
This article is intended to be a practical guide to choosing an environmentally friendly and above all efficient way to recharge batteries that is precisely photovoltaic.
Let’s start by talking about what are the first questions you are facing.
What technology do I choose?
In this article it will fly over what are the adaptations that some boaters make that install on their boats panels made for civil use that once on board degrade quickly and have very low efficiencies.
The state-of-the-art, today offers for nautical flexible photovoltaic panels and very high efficiency walkable that can be installed in various ways and that adapt to all needs: zip, tear, tenax, eyelets, structural double adhesive etc. etc.; we will refer the analysis of these fasteners methods to a later article.
We will postpone the analysis of these fasteners methods to a later article.
With regard to the technology to choose the first dilemma you have is: Monocrystalline or Polycrystalline?
Unfortunately, if you ask the panel builders, you will have conflicting answers and this is related to the fact that everyone pushes (for purely commercial reasons) on one product or another.
The fundamental difference lies in the cell production technique that decrees its performance: polycrystalline cells are in fact produced with the scraps of monocrystalline cells and therefore have lower yields.
Currently for good Italian or European manufacturing panel, we arrive at efficiencies of 22.5 for monocrystalline cells and about 16 for polycrystalline cells: this means that at the same exposure a polycrystalline cell for its nature and design it is required to produce at least 6 less energy.
Efficiency is one of the key aspects of choosing the panel, don’t be attracted by the power…
In fact, a photovoltaic module transforms into electricity,the solar energy that radiates on the surface of the same: the parameter of choice must therefore be efficiency but also compactness.
For example, a panel with 100watt efficiency and an area of one square meter produces the same energy as a panel with 10-inch efficiency with a power of 200watts and two square meters of surface area.
Moreover, the powers declared by the manufacturers are peak powers difficult to reach in our latitudes: the average production of a good quality panel is in fact 60-80 of its power.
To make the performance of the panel worse, however, further aspects such as orientation contribute, which in boating may not be the optimal one since very often a boat at the bottom in the course of a day will repeatedly vary its own Direction.
A further problem arises from this last reflection.
How do I orient my panel? What area should I mount it in?
In fact, from all the studies carried out, it has been noted that as orientation and exposure change, firstly a monocrystalline panel is always more efficient than a polycrystalline and that the horizontal position is also preferable to all other locations.
There’s no point in standing behind the Sun and always moving the panel… in fact, throughout the day the horizontal position is the one that wins over the others in terms of the energy produced.
The thing that needs to be paid the most attention is the shadow areas: it seems strange but even a single cell in the shade can significantly change the performance of the individual panel; you have to think of a photovoltaic panel as a series of light bulbs: what happens if one of the bulbs (shadow cell) stops working?
There are, however, panels made on an Italian patent that are designed in the logic of ensuring as much as possible the operation of the panel even with some cells in shadow or faults; Again, the operation of the panel is significantly reduced, even reaching 50 of the optimal operation, but it is definitely an added value…
Another question you’ll surely have asked yourself is:
“Besides the panel what do I need?”
At the heart of the system, in addition to a good panel, is definitely the Charge Regulator of which everything has been said and written; The regulator is tasked with turning the panel’s non-constant voltage current into current with correct voltage for the charge of its battery pack.
There are essentially two types of Regulators on the market: PWM and MPPT.
Now all retailers only decant MPPTs because they are regulators who can charge the battery pack at any voltage of the photovoltaic module; on the other, these regulators are very expensive and negatively affect the initial cost of the system.
What you need to know though is that an MPPT regulator is really useful only when the nominal voltage of the panel is very different from that of the battery pack; For example, 16V panel and 12-24V batteries or 8V panel and 12-24V batteries.
For modules with nominal turns very close to that of the battery pack, however, PWMs also work well (we talk about 5 percent loss of charge compared to MPPTs) compared to an initial cost of 50 less than a regulator MPPT of the same power.
In both cases, the regulator will make a full charge as it does with a normal charger.
We can therefore summarize that the following aspects will have to be taken into account for the charge controller:
- The Number of cells in the panel must be managed by the controller.
- The open circuit voltage of the panel must be appropriate.
- It must be equipped with a management system for overheating the panel.
- It must be equipped with a management system for overturning the panel.
- The maximum power managed must be at least 20 times higher than the panel’s.
- It must have a specific charging program for the battery in possession (open pot batteries, AGM or Lithium have different charging programs).
- Presence of the temperature probe to allow the recharging to be compensated against the ambient temperature.
- It must be equipped with a short-circuit protection system.
Finally, the question you’re sure to be asking yourself:
“How much power do I need?”
Below is a summary table that will allow you to guide you to the best choice and will guarantee you full autonomy provided that your fully charged battery pack allows you to spend an entire night in the clear.
As a rule, given the great benefits of using the panels in the boat, I always recommend that you have at least a 75-95 watt panel since the cost of the charging regulator in this case would be pretty much the same.
The installation of a single photovoltaic panel is a very simple operation and can be carried out by anyone with a minimum of dexterity and practicality in the on-board system.
The most complex part is the wiring since the positive and negative cable coming from the panel, must be brought as close as possible to the batteries near which the charging controller should be installed.
The batteries remain to be connected to the regular with two other cables, one negative and the other positive. The advice is to never exceed the meter in length for this type of connection and in doubt the section of the cable to be used applies the rule: “the more double the better…”
For the cable section, however, you can ask directly to the retailer who is usually able to sell you both the cable and the connectors needed to connect panel and regulator.
Usually you prefer not to do any interruption of electrical cables and to use a red cable for the positive and a black one for the negative (as is required by the legislation).
I also recommend using, at least for the outside, UV and weather-resistant cables, use the same cable even in the boat if they do not pass the entire route inside ducts or corrugated pipes.
Some regulators also have an additional output referred to as Load. They are programmed outputs to power small utilities such as twilight bulbs: of course at night or even during the day if the user absorbs more than the panel produces the current will be taken directly from the batteries to which the regulator is connected; this option is usually overlooked for nautical use.
The last tip I leave you is: if you have been attracted by the eye-catching price of the Chinese panels under the house let it go.
You would bring home a product of poor quality that at best will be a dead weight on board, at worst it will pose a danger to you and your boat for consequential dangers of short circuit and fire on board.