Challenges with Solar on boats

[john61ct]

Originally Posted by mitiempo

When I met Justin a few months ago I specifically asked about the 200 vs 220 watts as both are published. He said it was 200 and that they sometimes make mistakes. Seems the larger number is correct.

Well to me, more significant is understanding that spec isn't critical to start with, as it will be a different number depending on the actual Voltage of a given panel's output.

customers should watch Voc carefully and then just make their own call on over-paneling (or not) based on the input vs output amps specs.

[newhaul]

Originally Posted by john61ct

Yes it is, but when you keep arguing about common terms like 24V nominal", and post grossly inaccurate "math" like this



for a panel that has clearly been stated to produce at most 9A

that makes the higher-level discussion more difficult.

I think on this particular topic we can agree our priorities are different, and you are of course free to spend twice as much per panel's controller than what I consider sufficient.

Actually I just prefer that my customers are well satisfied with their solar installs. Not comming and complaining why I didn't design the system to take every advantage that is available. ( becides the diference in price between the controller that will barely handle.the job vs the one that will do it comfortably and not over heat and fail is negligible compared to happy customers refering friends to me.)

[john61ct]

Aha, sorry didn't realize where you were coming from, that you were a vendor?

[foggysail]

Originally Posted by john61ct

No, that is the **input** current limit. And unlike VoC, can be "over dimensioned" as with the watts specs, to be match against actual power output expected, not the panel data sheet's theoretical rating.

Yes, that is the real-world **output** limit, nothing to do with matching panel specs for input.

Again, the 440w number in the Victron literature is correct per Justin, not 400.

And it is just a ballpark for guidance, the **result** of using the 15A number, times an estimated actual voltage of 29V for "24 nominal" panels. Not a hard limit to use matching panel specs for input.

Of course, if the customer (unlike me) wants to spend more on a bigger size SC to make sure that every incremental peak watt of panel output is captured, then s/he **can** keep the panel's theoretical max power purchased under these SC ratings.

But for the very little useful gain in actual charge getting to the battery, when the next step up in size more than doubles the SC cost, I don't consider that good value personally.

I don't know where you are getting 20 ampere input current and that would be ridiculous if so. The spec shows the 20 amperes to be the maximum short circuit current of the converter. Further, in order for the input current to be greater than the output, the converter would require a boost converter and further, without going through teh math, the panel voltage would be too close to the battery voltage for the converter.

As to the 400 watts, I suggest that you read the specifications where it clearly pertains to a 24v application. The maximum output has little to do with power, it is the output current that determines the power for different battery voltages

[newhaul]

Originally Posted by john61ct

Aha, sorry didn't realize where you were coming from, that you were a vendor?

Actually john im not a vendor I'm a service provider ( shipwright to be exact) I design and install systems. Others sell me the parts(vendors).

[john61ct]

Distinction without a difference, I just meant "in the business" as opposed to an end-user or hobbyist

[newhaul]

Ok no problem but yes I am a service provider just like it says under my name and above my avitar
.

[Quadrille in JB]

Here are the pics I was trying to upload yesterday of my Sunpower 360w/70v panel with Victron 100/30 controller

[john61ct]

Originally Posted by newhaul

just like it says under my name and above my avitar.

I don't have access to any of that via my interface.

[newhaul]

Originally Posted by john61ct

I don't have access to any of that via my interface.

Ok apologies

[john61ct]

No worries dude, no offence meant nor taken, all good stuff. . .

[CapnCrunch]

Originally Posted by Btimmerman49

With the help of Alex at SeaTek Marine in Marathon I installed a single Sunpower 360W/70V panel on my little 27' Watkin's dingy davits using a Victron 100/30 MPPT. This setup works great. The Victron has a bluetooth interface to my iPhone which provides real time output as well as a 30 day history. When powering an isotherm ref/freezer, a PUR Survivor 35 watermaker, Simrad autopilot, large Garmin chart plotter, a 2000w inverter, a fan and various other items on the boat it often outputs slightly in excess of 360 watts. My house bank is 4-105 amp AGMs with a single 85 amp AGM for starting. I charge all of these at once using several Guest battery selectors. This just shows that you can add a lot of comfort to a small boat with a single high quality solar panel, MPPT controller, and adequate battery bank.

The above is similar to what my rig will be running in terms of usage. I was thinking about using 3 of these panels - http://www.solarhome.org/recrec290tp2290wsolarpanelblackframe.aspx - in parallel with 3 controllers charging a 12v bank of 6-8 lead-acid batteries.
1. Am I thinking too large in terms of bank size?
2. Would these panels (at 38.8 Voc) overkill - in terms of voltage or total wattage?
3. Can you connect more than one panel to a controller without the panels being in series?

Unlike most folks, I'm not all that worried about looking like a solar farm, I just dont want to have to deal with more equipment than I actually HAVE to. However, mamma likes her creature comforts and, of course, we have to keep her happy.

[john61ct]

Originally Posted by CapnCrunch

The above is similar to what my rig will be running in terms of usage. I was thinking about using 3 of these panels - http://www.solarhome.org/recrec290tp...lackframe.aspx - in parallel with 3 controllers charging a 12v bank of 6-8 lead-acid batteries.
1. Am I thinking too large in terms of bank size?
2. Would these panels (at 38.8 Voc) overkill - in terms of voltage or total wattage?
3. Can you connect more than one panel to a controller without the panels being in series?

Unlike most folks, I'm not all that worried about looking like a solar farm, I just dont want to have to deal with more equipment than I actually HAVE to. However, mamma likes her creature comforts and, of course, we have to keep her happy. [emoji2]

So around 800w, I would use a 4-600AH bank, larger if lots of sunny weather, smaller if not.

Volts and watts per panel, more small vs fewer large is really a question of physical space, mounting issues.

Yes paralleled panels is very common, keeps Volts the same, but adds up the Amps. Just need to size the controllers to match as discussed above.

Ideal for partial shading issues is one controller per panel.

I reckon find the controller you want then (if space allows) buy the biggest panel that size SC will work with, taking into account your preference for over dimensioning as discussed above.

[mitiempo]

Originally Posted by john61ct

Per Justin, the 440w spec (not 400) is published with regard to nominal 24V panels, nothing to do with output, just the calculated result of multiplying 15A times an estimated real-life 29V panel output.

Obviously following that number would be too much wasted panel power for a 12V nominal bank, but doing that would be impossible anyway within the 75V hard Voc limit, combined with the 20A guidance, the two specs intended to be used for panel selection when the customer is "over dimensioning".

I disagree as does Justin, just confirmed. The panels wattage can be doubled if the battery bank is 24 volts with the same amperage output as for 12 volt bank.

Quote from Justin: "If the battery voltage is higher the power is also higher at the same charge current."

Besides it would make very little sense to over-panel by such a large amount.

[foggysail]

Originally Posted by mitiempo

I disagree as does Justin, just confirmed. The panels wattage can be doubled if the battery bank is 24 volts with the same amperage output as for 12 volt bank.

Quote from Justin: "If the battery voltage is higher the power is also higher at the same charge current."

Besides it would make very little sense to over-panel by such a large amount.

You will need to state that a few more times for it to sink in