Bifacial solar

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I polan to install four LG NeON 2 bifacial 400 watt panels on my boat this Summer. They should work great over a white roof.
 
Same here. I am still debating to have 4 or 6 panels. I could fit 6, but a bit tight. With this folding solution, it should not be a problem. If I have to stick with 4, it would be nice to have the new 500W+ BiFacial panels. I just can’t find any source, which sells it.
 
What charge controllers are you planning to use and how many?
 
LeoKa said:
What charge controllers are you planning to use and how many?
Click to expand...


I was hoping to use two, one for the two inner panels and one for the two outer panels that will slide under the inner panels while not anchored. Have not picked a brand and model yet, but I know they will need to be pretty big (like 50 to 60 amps) for the panels I wish to use. Victron SmartSolar MPPT 100/50, is one I may consider.



Something to consider is the charge rate that your batteries can handle. A big array needs a big battery bank. 6 500 watt panels will produce nearly 250 amps at 12V (there is efficiency lost in the DC to DC conversion). If you can't use that much to charge the batteries you have, there's no point having that much solar.

 
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I have 840 AH total in two banks. 8 Trojans.

Since the panels are big, have you considered individual controllers for each? Perhaps, 30A controllers per panel?
 
my understanding is that with Trojan FLAs you should not exceed a charge current of 13% of the AH rating and with Trojan AGMs, 20% of the AH rating. So if you have FLAs you are limited to 109.2 amps of charging current and with AGMs, you are good for 168 amps. That said having more capacity than that in your panels is desirable because you can still potentially get max charge current on cloudy days or off-peak sun times, but you need to be careful if you have too much MPPT output.
 
Bingo!
I’d like to have extra available. Either, because the PNW has plenty of cloudy days, or, I might add more batteries in the future. My goal is to be able to run my fridge and a chest freezer from the panels. It would be nice to have enough juice to manage my 30g water heater/110V, but that would certainly require 6 large panels.
So, my plan is to start with 4 panels, the largest I can get, and see how things work out. If the foldable solution (plus different angles) allows me to accommodate 6 large panels in the future, I might just get there.
 
LeoKa said:
Since the panels are big, have you considered individual controllers for each? Perhaps, 30A controllers per panel?
Click to expand...


The reason to use one controller for two panels is to get the voltage up by putting the panels in series. This helps efficiency when the panels are really hot.
 
Mischief Managed said:
The reason to use one controller for two panels is to get the voltage up by putting the panels in series. This helps efficiency when the panels are really hot.
Click to expand...



Is it a concern to you, to see the panels get hot?
PNW summer is very short and rarely hot.

How do you in vision your sliding panels? Do you have a structure in place, or plan for it? How will you do it?
 
Mischief Managed said:
you have FLAs you are limited to 109.2 amps of charging current and with need to be careful if you have too much MPPT output.
Click to expand...



How about having a controller, which can be set to a certain limit on the output? I think they exist.
 
LeoKa said:
Is it a concern to you, to see the panels get hot?
PNW summer is very short and rarely hot.

How do you in vision your sliding panels? Do you have a structure in place, or plan for it? How will you do it?
Click to expand...


I'm hoping to get enough juice to run air conditioning on really hot and sunny days, so efficiency improvements on days like that are a concern for sure.


I plan to have 4 panels in this sort of configuration: |||| on my aft deck roof. I will make a welded aluminum structure that holds the two inner panels in a fixed position on top of the whole assembly. The two outer panels will be mounted to telescopic aluminum rails equipped with HDPE sliders (to reduce friction) and they will slide out to port and starboard from under the inner panels when deployed. The entire 4 panel assembly will be mounted on another set of telescopic aluminum rails with HDPE sliders, and all four panels will slide aft about about 4 feet when deployed to avoid shading on the panels from my radar arch and to provide shade from the panels for my cockpit. The bottom set of fixed rails will be mounted firmly to the aft deck roof. When I am underway or in windy conditions, I will tuck the outer panels under the inner panels and slide all the panels forward where they will be least vulnerable and most solidly mounted. That said, the assembly will be very robust even when fully deployed. I won't be cutting corners when buying aluminum.


I am trying to figure out if it's possible to use MPPT controllers as DC to DC power supplies between battery banks. If this is possible, it would be an economical way to add LFP capacity to an existing lead acid battery bank. If it works, you could charge the LFP bank with the solar panels and use the LFPs to charge the lead acid batteries you already own through an MPPT. For example, your 840 AH bank is good for a usable 420 AH. Replacing that with LFPs would cost around 4 to 5 grand, you'd likely need a new inverter and battery charger to charge them from shore power, you can't have them in the engine room, and you still only have 420 AH available. However, if you used LFPs to charge the lead acid batteries through DC to DC conversion, you still have your 420 AH lead acid bank so that investment is not wasted, the LFPs can be placed outside the engine room, and your AH capacity increases by whatever size LFPs you buy. Additionally since you would be using DC to DC conversion, you are not limited to 12 volts on the LFPs. If you use higher voltage batteries, the MPPT controllers for the panels can be smaller and cheaper due to the current decreasing proportionally with the voltage increasing. A 24 volt battery bank would require half the current of a 12 volt battery bank, assuming the battery capacity (in watt/hours) is the same. LFPs are ideal for solar power storage too, since they can take practically all the amps you can throw at them when charging and do not have an absorption or float charge phase. Hope this makes sense...
 
What you are describing seems like a serious undertaking to build the sliding framing. I suspect, you have the tools and place to build something like this. It would be nice to see this in progress.

LFP means lithium batteries?

I do not know the answer to your question on DC to DC direct charging from LFP to lead acid, but I agree that it would give more flexibility for expansion, when the budget permits.
Perhaps, some of the experts will chime in.
 
LeoKa said:
What you are describing seems like a serious undertaking to build the sliding framing. I suspect, you have the tools and place to build something like this. It would be nice to see this in progress.

LFP means lithium batteries?

I do not know the answer to your question on DC to DC direct charging from LFP to lead acid, but I agree that it would give more flexibility for expansion, when the budget permits.
Perhaps, some of the experts will chime in.
Click to expand...


I do have a lot of tools and can fabricate aluminum and plastic stuff pretty easiliy. I will post photos for sure.


LFP is short for lithium iron phosphate. Those are the safe kind of lithium batteries.
 
Did you find out anything about your idea on DC to DC conversion to flooded batteries?
 
It's interesting to see these bifacial panels taking another run at the market. These first came out 10-15 years ago, and were pioneered by Sharp, if I recall correctly. But they never got market traction. I suspect it's because you could get the same additional power more cheaply by just adding more conventional panels. Trackers suffered the same challenge. And this was before panel pricing dropped from $5/w to sub 1$/w. I doubt that helped either.


But in a space constrained application like a boat, they might be a good fit.


As I recall, to get the effect of back lighting, you need to get the panels up off the surface below them. Is that practical on your boat? I think I'd want to check that carefully to see just how much of the back side power I might actually get?
 
Mischief, you wouldn't have drawings of you rack concept, would you? I need to come up with something for our boat too, and am always looking for clever ideas.
 
twistedtree said:
As I recall, to get the effect of back lighting, you need to get the panels up off the surface below them. Is that practical on your boat? I think I'd want to check that carefully to see just how much of the back side power I might actually get?
Click to expand...

That is correct. Not only off the surface, but 20-30 degrees angle, can help. This is why the supporting mounting/framing will make a big difference. Some guys are very creative and good with fabrication.
 
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