How Much Solar is Enough Solar?

[Saldar]

If you are running lower in the SOC range, which is very typical in the real world, of between 20% and 70%, you will have essentially no real difference in power recovery compared to lithium, with a moderate sized AGM bank (400ah).

Hi Booster,

Would you explain how this depends on having a 400ah AGM bank? What would be different with a 200ah AGM bank? Can a smaller bank not take advantage of the whole alternator output? Would it need it?

[booster]

Personally, I think it is pretty silly to chastise someone for their choices or opinions. You may not agree with them, but that certainly doesn't make them wrong, or yours right, as both could be just fine for the application.

Saying

This is why it makes no sense to me to invest in solar

is no different than saying that solar is always needed. Both are incorrect. Change it to read "solar makes no sense FOR me" and the meaning is totally changed.

We all may at times question the need for any given option for an application someone has, but hopefully it will be based on matching of the parts of the system to stated use and not on if we like doing it that way.

All this reminds me of the perpetual kitchen location where we are often told that a kitchen is on the "wrong side" of the van, simply because the person's opinion is they don't like it there.

So--solar probably unneeded in davydd's van, although he does always add in the output when stating how long he can stay off grid. Essentially all charging has the engine running.

And--for us, and probably some others, solar can keep us off grid indefinitely with good sun, even with some microwave use and compressor frig. Engine generator is backup, not primary, charge method.

And, others may drive every day, no compressor frig, low power use, and get along just fine without solar or an engine generator. Perfect for them, but not for everyone.

To turn it around, many of us have and want propane onboard for various reasons. Davydd's van does not have propane, so it wouldn't be what we want. That doesn't make his setup bad for him, but it would make it bad for us. Just different opinions, not right/wrong/stupid/ or smart either way.

[GeorgeRa]

Originally Posted by booster

...............
Saying is no different than saying that solar is always needed. Both are incorrect. Change it to read "solar makes no sense FOR me" and the meaning is totally changed........….

This was the sentence which prompted my reply, you hit the nail on the head. Perhaps I should give a benefit of the doubt to this sentence as just a simple misunderstanding.

We often focus on technical hows without taking for account what the primary objectives are and it spins into the tail wagging the dog discussion.

[WingedRyno]

Originally Posted by gerrym51

things seem to be getting 'testy' on this thread. Hey-testy could be testoterone-lol.

I don't have anywhere;s the amount of solar-or battery power you guys have.

What is is.

It;s a pissing contest lately-i'd lose that to.

It's always fun in any human gathering to watch personalities emerge. Human nature is not deterred by the internet. It's like chimps with keyboards

[booster]

Originally Posted by Saldar

Hi Booster,

Would you explain how this depends on having a 400ah AGM bank? What would be different with a 200ah AGM bank? Can a smaller bank not take advantage of the whole alternator output? Would it need it?

I chose 400ah as it is getting more common (usually 4X6v batteries gives 400-440ah approx.), and the max charge rate area of 20-70%, or 50 % of capacity ah, comes out to a nice even 200ah at the full charge rate or close to it. It would take somewhere around 1.3 hours at full (thermally cycling 165ah per hour ) to get that 50%. A200ah bank would just cut everything in half, so 100ah recovery in .65 hours.

Which would be best would be based on your particular power use. If you have a gas frig and low consumption, the 200ah bank would be plenty, unless you wanted high output inverter for microwave or such. These low use folks would probably be in the 25-40ah per day range. The 400ah would be better for those with compressor frigs, coffee makers, big inverters to run the microwave or coffe maker,etc. These would use more like 50-80ah per day, or even a bit more, in most cases.

As you can see, the time to charge the 50% of capacity with the 200ah bank is very short if yu have an engine generator, so it may very well be reasonable to say that just using the standard van alternator would be totally adequate, as it would probably put yu back to similar times as the 400ah with an engine generator, which at under 1.5 hours is not much of a drive for most of us.

[Saldar]

You've explained a lot--thanks! I do have 200 Ah of battery and just got the "pendant" for the progressive dynamics charger. When we hook to shore power after coming home, I've never seen the pendant report bulk (=PD "boost") mode. I guess we've recovered on our 2 hour or more drives home. However the pendant reports absorb mode for days (=PD "normal" mode), before changing to float ("storage").

[eric1514]

This is Zamp solar doing this install. I can't imagine harvesting any power from that panel seeing as how it will be in a permanent shadow cast by the roof rack.

[BBQ]

Originally Posted by eric1514

This is Zamp solar doing this install. I can't imagine harvesting any power from that panel seeing as how it will be in a permanent shadow cast by the roof rack.

I agree. Any shadow, no matter how small, will seriously impact the panel performance.




Personally, I would not use flex panel unless there are no other options.

They cost more, and do not perform as well.
When glued to the roof, they tend to overheat and reduces output.
They do not last as long.
I would rather have a rigid panel that gives the RV roof an additional layer of heat insulation.

[Davydd]

My flex panels are not glued to the roof. Sprinters and evidently Promaster vans have ribs that prevent this. Mine are mounted to about a 1/8" thick ABS board that spans the 1-1/2 deep ribs so air circulates underneath. The roof also had an arc so the flexible panels are mounted to reflect that arc and edged in aluminum channels that attach to the gutters. Very low profile. You have to look close to see the edges.

[BBQ]

Originally Posted by Davydd

My flex panels are not glued to the roof. Sprinters and evidently Promaster vans have ribs that prevent this. Mine are mounted to about a 1/8" thick ABS board that spans the 1-1/2 deep ribs so air circulates underneath. The roof also had an arc so the flexible panels are mounted to reflect that arc and edged in aluminum channels that attach to the gutters. Very low profile. You have to look close to see the edges.

+1


That sounds stealthy.

[GeorgeRa]

Originally Posted by Davydd

My flex panels are not glued to the roof. Sprinters and evidently Promaster vans have ribs that prevent this. Mine are mounted to about a 1/8" thick ABS board that spans the 1-1/2 deep ribs so air circulates underneath. The roof also had an arc so the flexible panels are mounted to reflect that arc and edged in aluminum channels that attach to the gutters. Very low profile. You have to look close to see the edges.

If I understand your PVs mounting correctly the roof ribs are 3/8" high, not 1-1/2, so air flow could be limited on a stationary van.

[Davydd]

Sprinter roof ribs are higher than Promasters and they are spaced wider.

[GeorgeRa]

This is Sprinter's roof drawing from my solar panels installation on 2013 / 144 WB.

[booster]

I think the depth is getting mixed up with the width dimension. 3/8 deep and 1 1/2 wide makes more sense.

[mojoman]

My solar panels recommended a minimum of 11/2" clearance for cooling. They will act as shade and help keep you van cooler if there is some clearance under them. I went with 11/2" not including the ribs. They put out rated watts at high noon in the desert under very hot conditions.
Use the same recommendation as you would for sizing lead batteries, if you want 200 watts install 400 watts.

[GeorgeRa]

Originally Posted by mojoman

My solar panels recommended a minimum of 11/2" clearance for cooling. They will act as shade and help keep you van cooler if there is some clearance under them. I went with 11/2" not including the ribs. They put out rated watts at high noon in the desert under very hot conditions.
Use the same recommendation as you would for sizing lead batteries, if you want 200 watts install 400 watts.

Indeed, for solar panels the space underneath to allow convective cooling is important for efficiency. I have 1.5” gap to the PV panel frame and almost 2.5” to the bottom of the solar cells at the apex of the roof, larger gaps toward sides.

Solar panels with sufficient air gap acting as van's shade is not always an appreciated side benefit.

[GeorgeRa]

Originally Posted by booster

I think the depth is getting mixed up with the width dimension. 3/8 deep and 1 1/2 wide makes more sense.

You are correct, the width is indeed about 1.5". This is the roof picture from the 2008 Sprinter van.

[gerrym51]

Originally Posted by Davydd

My flex panels are not glued to the roof. Sprinters and evidently Promaster vans have ribs that prevent this. Mine are mounted to about a 1/8" thick ABS board that spans the 1-1/2 deep ribs so air circulates underneath. The roof also had an arc so the flexible panels are mounted to reflect that arc and edged in aluminum channels that attach to the gutters. Very low profile. You have to look close to see the edges.

David- are you getting that new ARV lithium battery upgrade?

[gerrym51]

my solar panels keep my house battery charged up in winter. Of course i have agm that requires constant topping off

[Davydd]

The point is the assumption flex panels are glued down on a Sprinter is a false statement as well as I am guessing the comment of 1-1/2" minimum is just as bogus rule of thumb without any reasoning other than assumed. The panels are lifted off the roof and air passes underneath. This is an actual photo of my panels and it is greater than 3/8". An air gap is an air gap. I'll take my stealth look close to the roof over any hiked up air dragging clunky look any day.