What is the issue?Solar panels perform well when they are free of shade, or even in partial shadow, and the sun is directly above. However finding a position on a sailing vessel that will be continually optimised for light capture is unlikely.
To make matters worse a sailing vessel is highly space constrained, and large solar panels will easily encroach upon boat operations and crew comfort.
The best solution is to build a dedicated panel gantry so that the panels are clear of the deck and are in an area of relatively little shade. However this is an extensive piece of engineering, requiring some investment and specialist work, and it will dramatically alter the vessels aesthetics.
Why address this?Power on a seagoing vessel is a scarce resource and every available means of power generation needs to be absolutely maximised. This is particularly the case with solar panels which are a highly expensive investment, and a return on the investment is important. Yet the vessel must be liveable and the personal trade off’s need to be minimised.
How to address this?A simple and price effective solution is to attach the new solar panel to the back of the pushpit handrail. All this required was three standard pulpit rail mounting brackets that I attached to a stout sheet of aluminium bolted across the panel frame - best seen below with the panel folded down.
Photo: Michael Harpur
As seen above, I wanted the ability to fold it down out of harm's way and have some flexibility to raise it and lower it. This required some measure of support as the aluminium brace is positioned on the panel about a fifth of the way down so it could be hinged outboard and not intrude upon the cockpit area. To do this I needed some supporting structure to hold it aloft as seen below.
Photo: Michael Harpur
After considering several complicated stainless steel setups the simplest solution that worked the best was to use a PVC domestic water pipe. After cutting it down to two specifically measured pieces I simply ran a line inside the lengths that looped through a fixed bracket at the outer end of the panel. The sturdy pipes in triangulation provide an excellent supporting frame with a little give to provide some flexibility for those inadvertent bumps and knocks.
Photo: Michael Harpur
We took the power lead in through the top of the spare gas bottle locker which was immediately below. If this is not possible simply take the power cable down through the deck via installing deck plugs. This will enable the panels to be easily unplugged and removed if you are leaving the vessel in uncertain waters.
Using this simple system the solar panel could be turned out of the way when needed to be, and also flipped out to soak up the sun as required. The benefit of using the line for attachment is that it enabled us to tie it off at various levels along the post allowing the panel to be pivoting forward or aft. This allowed a helpful passing member of the crew to tune it into the sun to some extent. Although this tuning is only on one axis, which does not enable complete optimisation, it is still far better than completely fixed panels and can make a dramatic charging performance difference.
This very simple solution worked very well for us at a negligible cost. Incidentally, low-cost PVC piping is a very useful product to have aboard a vessel as it can underpin a host of solutions.
This could be done by attaching the stainless steel tube, which requires no modifications or specialised equipment for installation. Connect it directly onto the stern pulpit by sliding a clevis pin and split rings (should it need to be removed in an emergency) through the established lifeline eye. At the other end drill a hole through the stainless steel tube and fit it over the head of the stanchion post, again securing it with clevis pin and split rings. Grind and sand off all corners with a fine grade wet and dry paper so there are no sharp edges on the tube.
Once this is in place attach the solar panel to an oversized board. Heat affects the panel’s performance so it should be slightly raised by the board using washers as spacers to allow for free ventilation underneath. A half dozen or so one-inch ventilation holes beneath will help this cooling. Round the corners of the board and sand down all the edges, as being in the cockpit people will, in time, fall against the panel. Clamp the board to the rail with stainless steel U-bolts, and use wing nuts to easily adjust the requisite tension required to twist and hold them in place.
Photo: Michael Harpur
Solar panels only give their best when they can see the sun. An approach to mounting solar panels so as to extract every possible useful amp available is to fit them on a swivelling mount, which can be turned to directly face the sun. The above example has the panel fitted off the back end of the pushpit on a stainless steel 'T' post.
Image: Michael Harpur
This offers complete freedom to tune the panels directly into the sun for maximum performance, though it is worth considering strengthening the pushpit to take the extra load. Smaller panels can be handled by a universal joint, such as the Glomex four-way plastic aerial bracket sold as a bracket for a whip aerial. Swivel mounting and tuning the panels will make a dramatic difference to charging performance.
Photo: Link Solar Electric Group Co.,Ltd.
Another approach is to integrate flexible solar panels into a Bimini or spray dodgers as shown above - see video below. Or use large panels to create a Bimini as below.
Photo: Pauli Juppi
The problem about these latter two implementations is they are highly susceptible to shade. It is, of course, more than obvious that shade reduces solar panel power generation, but the effect of shade on a solar panel is much more than one might assume. For example, a typical solar panel rated at 12V nominal / 100W peak might produce 80W on a typical sunny day in a subtropical region at ideal temperatures. But where one would be forgiven for thinking shading 25% of the panel might reduce the panel's output to 60W, it actually drops it down to as low as 10W to 20W. This means that mounting panels where they are less subject to even partial shade during the course of the day is critical.
bimini on a Catalina 36
A final point that is worth considering when installing the panel is protecting the battery bank from solar panel discharge. When a solar panel is exposed to sunlight, the photon of sunlight knocks out the electron (-ve charge) of the solar cell and hence it acts as a source of electron and hence the source of current. Due to this release of the electron, the solar panel system is at a higher potential than the battery. This difference in potential between the solar panel and the battery leads to a flow of current from the solar panel to the battery.
But at night, or even partial light when the solar panel is shaded, the battery will eventually have a higher potential than the connected solar panel. There will be no flow of electrons from the solar panel and the solar panel will act as load start draining the battery creating a reverse flow. The amount of drain depends on the extent and duration of shading.
There are three typical areas where this form of discharge is prevented:
- • Integrated series diode in the panel - Most of the solar panels have a diode to block the discharge of the battery.
- • A series diode in the charge controller - This function facilitates a unidirectional flow of current from the solar panel to the battery blocking the reverse flow.
- • Fit a specific diode during the installation of the panel.
I have had problems with discharging despite having embedded diodes and a charge controller. Therefore, I can only recommend for peace of mind that a diode is inserted during installation to stop power floating back across the panel during the night. If you are wiring up more than one battery it is prudent to insert both diodes and fuses. If the problem is encountered the only solution is to disconnect the cables connecting the solar panel(s) to the battery every day before you go to sleep until it can be remedied.
Finally, I would suggest if you have flooded batteries to make certain there is plenty of water in the batteries before the solar panels get to work and monitor the charge carefully for a few weeks so you strike the balance between charge and consumption. See electrical power generation on a sailing yacht for more information.
With thanks to:Michael Harpur, Yacht Obsession.
Integrating solar panels into a Bimini
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