Adhesive advice for Solar panels

[Marco Flamingo]

I've been happy with my SNAD fasteners. No drilling through the cabin top, the panels are removable, and the panels are set off the cabin top surface. Mine have now been tested to 70 mph in high desert crosswinds, so I don't remove them for trailer travel. But if the panel is removed, the SNAD fitting is a good match to the gel coat and doesn't get in the way.

My procedure: attach female snap fittings to the back side of the panel. I used tiny stainless bolts with nylock washers, but pop rivets would work. Attach male SNADs to the snap fittings. Peel the paper off the adhesive and stick in place. I only used 4 SNAD fasteners, but more could be used, including one or two in the center to keep the flexible panel evenly offset from the curved roof. It takes a little fussing, but not as much as preparing to drill through your cabin top and then getting the holes sealed.

I thought I had a closeup picture in my folder, but I can't find it now.

Mark

[Pat Anderson]

Lots to think about here! I need to investigate SNAD and 1"x1" aluminum tubing with double stick tape to move my panels off the "wings" up to the roof so they can be flat to the sky. Now we do not have the Alaska Series, the panels need to move to the roof!

[Foggy]

The charge controller monitors the existing battery charge and delivers the
appropriate amps to charge the battery without over charging it. I get that.

When the battery is fully charged and the charge controller stops delivering
amps, save a few milliamps, what happens to the unused amps the solar panel
may be putting out at that time? Heat? Swelling? Explosion? Meltdown?

Ex: panel output is 3 amps, battery needs only 0.025 amp. Maybe there is a
market for a "save-your-amps" device?

Aye.
Grandma used to say, "It's possible to have too much of a good thing."

[Aurelia]

I believe the oldest of shunt controller designs did produce some heat to effectively burn off in certain overpower conditions but more modern PWM and MPPT types actually interrupt the circuit, allowing the panels to go to full open circuit voltage, and no amps are produced by the panels.

The only heat to worry about would be at the panels themselves in warmer climates, direct sun, and poor venting installations. Performance goes way down and the health of the panel is also at risk to some degree depending on type and construction.

A "save your amps" device would simply be a storage method for the power such as added battery capacity to charge, or it could be put to use more directly by consuming the incoming power for something useful so the cutoff voltage is not quite attained. When we are running the boat and I can see us nearing our peak charge, I am plugging in everything rechargeable we have to put that juice to use.

Phones, tablets, wireless speaker, hand vacuum using little inverter.... Those items will collectively pull over 8 amps if they are discharged significantly.

Greg

[thataway]

[Foggy]

Thanks, I got (part of) it. '' Open circuit voltage" = no amps flow to the battery
since the circuit is open (or in the water hose analogy, the nozzle is shut off and
no water comes out of the hose).

Still, the "open circuit" is located in the charge controller, right? But, in a small
panel without a charge controller, where is the open circuit located?

What is happening in the solar panel? How do the cells in the solar panel get
the message to stop making energy in sunlight when the voltage circuit is open
(the water pump should still be working creating increased pressure in the hose;
hence, swelling, explosion, etc)?

Trying to create a visual here... (maybe the analogy sucks).

Aye.

[Aurelia]

You need a closed path, or closed circuit, to get electric current to flow. If there’s a break anywhere in the path, you have an open circuit, and the current stops flowing — and the metal atoms in the wire quickly settle down to a peaceful, electrically neutral existence.

Within a charge controller, there is effectively a type of switch that opens the circuit, disconnecting the power from the boat loads. Without a load to consume it, power will not flow and nothing happens. The open circuit turns electrical power into only electrical potential which does nothing without a something consuming it.

A battery stores power while a solar panel produces it but they both have the same open circuit behavior. If there is no load on either, they do not transfer any power, anywhere. Literally nothing happens because they only have potential so long as the circuit is open.

Close the circuit with a switch, and power flows. A solar panel without any loads still has an open circuit voltage that you can measure with a voltmeter, but no load means no heat or action of any sort.

A solar panel without a load, is just a modest source of shade.

Greg

[Foggy]

Again Greg, thanks. That helps. I see "electrically neutral" and "electric
potential" when the circuit is open better now.

Aye.
Like Einstein said, "Nothing happens until something moves."

[thataway]

One other thing to remember about the trickle charge and topped off battery. With the small panels and no controller, there will be a diode to keep the battery from putting current back into the solar cells at night. This diode does drop the voltage by about half a volt. When the battery is fully charged, and there is essentially no current flowing--there will be an equilibrium between the battery voltage and the solar panel output. Since there is no voltage differential, no current flows. (Sort of "self regulates" This works fine if the solar panel is small. Lets say 2 watts for a typical group 27, 75 amp hour battery. If you have two of the 75 amp hour batteries, and it is hot (100* = 10% loss a month)--then 5 watts will be OK. If it is cold 40* to 50*, then you may only have 1.5% loss, a month, then 2 watts may be for for two batteries.

Now if Foggy has just two group 27 batteries--and a 80 watt panel, that is far more than needed for trickle charging, and a controller (best to have the MPPT) is essential.

On the other hand, 80 watts may not be enough to keep up with demands (depending on what he is running). Lets say that there is a refrigerator, and Foggy likes to anchor for several days, and not run his engines, or a generator to charge the batteries. He would be best served by the very least 100 watts, and probably best 200 watts. (The determining factors, assuming that it was only refrigeration and a few LED lights at night, would be both ambient temperature (how much run time for the refer, vs how much direct solar radiation hitting the panels.

Type of controller depends on temp: From Solarcraft site:
"An MPPT controller is better suited for colder conditions. As solar module operating temperature goes down, the Vmp1 increases. That’s because the voltage of the solar panels operating at their peak power point at Standard Testing Conditions (STC is 25C°) is about 17V while the battery voltage is about 13.5V. The MPPT controller is able to capture the excess module voltage to charge the batteries. As a result, a MPPT controller in cool conditions can produce up to 20 – 25% more charging than a PWM controller."

[Foggy]

Thanks, Bob

My current plan is an 80W (4.14 amps) and a 55W (3.2 amps) in parallel to
a PWM dual battery charge controller (10 amp max, automatic and smart)).
I'd like twin 80Ws but not space enough. More on controllers below.

Shading on solar panels is a power killer. Still have not determined whether a
small panel system (above) is better connected in parallel or kept separate for
the effects of shade (objects, clouds, etc). Greg thinks separate is the way to go
here. Also, apparently, shade on a single panel connected to others in series, is
a much worse draw down than if the panels were connected in parallel (?).

Below is my understanding level on PWM vs MPPT charge controllers.

SUMMARY (2 WEBSITES***) PWM v MPPT SOLAR CHARGE CONTROLLERS

PWM CHARGE CONTROLLER
* Smaller systems where MPPT benefits are minimal
* Requires heavier cable size for longer runs
* Solar array should match the battery voltages (12V for me)
* Solar array sized in amps (12 V panels in parallel)
* Better in warm solar cell temperatures (45* - 75*C = 113* - 167*F !!!)
[ Keep those panels cool? Why?]
* Less cost for small system


MPPT CHARGE CONTROLLER
* For higher power systems; 12V: few hundred Watts, 24V-48V: several hundreds of Watts
* Less efficient in low power applications (MPPT sweet spot = 170W or higher)
* Smaller cable sizes allowed in connections
* For full benefits, solar array voltage should exceed battery voltage
* Solar array sized in Watts (panels connected in series)
* Operates above battery voltage providing boost in cold temperatures when
battery is low (<45*C) or high temperatures (>75*C) or in low irradiance

*** www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/
*** www.solarcraft.net/articles/comparing-pwm-and-mppt-charge-controllers

Aye.

[thataway]

Foggy:

[Foggy]

After mix-'n-matching, using various combos of panels for my space,
I agree the best choice for my plan is 2 semi-flexible 55W panels from same Mfg.
same everything else.

Still no answer, except Greg, on whether to connect 2 panels in parallel or keep
them separately wired each with their own controller. Irregardless of how they are
wired, each panel will be subjected to unequal radiance (shade variations, on
curved pilothouse). I am tempted to wire them separately and let them each do
their own thing the best they can without one good performer being dragged
down by the other in shade or less optimum angle to the sun.

If panel cooling is so critical, why does Go-Power allow their semi-flexible panels
to be mounted with adhesive directly to a metal RV top (no spacers or relief
underneath)?

I'm a fix and forget with panel mounting on the pilothouse and forgetting about
tracks or poles for moving them around for best sun angle, etc. This may appeal
to others but not my cup of tea. Too many other (appealing) things to do.

Thanks again, Bob.

Aye.

[thataway]

If you want the simplest answer--wire each 55 watt panel separately to the battery bus system with a PWM controller appropriate for that size panel.

If I put solar on my boat, I would put two 100 watt panels, with articulation mounts, bypass diodes in the panels, and both wired MPPT controller.

Over 90% of RV owners today, use MPPT and wire all of the panels thru the one controller. They buy panels with have bypass diodes, which will minimize the effect of shading when wired in parallel.

I have no ideas why Go-Power allow their semi-flexible panels
to be mounted with adhesive directly to a metal RV top. It is going to be a little less efficient. But I suspect that they want to sell more panels, and it is easier to install that way without putting holes in the roof so people buy them.

I have a single 200 watt rigid panel, on my RV, to 6 Golf cart batteries. I use an MPPT controller, sized so I could put 2 more panels 200 watt on the roof, if I wish. The problem is that we find often we are in shaded camp sites if we are boondocking off the grid.. So even if we had 600 watts of solar panels, it would not provide us enough power to run 22 cu foot household refrigerator. If we don't have solar power/grid power, or are on the road (where the 200 amp alternator does fine), we run the generator and 140 amp battery charger about 4 hours a day.

[jkidd]

[Marco Flamingo]

A few posts back the discussion was about solar controllers and where does the electricity go when the battery is full. Then I saw that somebody had a hot water heater on their boat. Is it a 12V hot water heater? I have a couple of 12V hot water heater elements (fits the standard opening) from past projects. That might be something Brats with hot water might want to think about. Don't let that solar power go to waste. Heat some water.

Mark