Challenges with Solar on boats

[newhaul]

Originally Posted by CapnCrunch

I'm not getting this. The Victron 100/15 specs read "Maximum PV power, 12V 1a,b): 200W (MPPT range 15V to 100V)"

My 290w panel specs show "Voc = 38.8VDC/ Isc = 9.58 A. I thought the Victron model numbers represented Voc/Isc?

If panel wattage is the determining factor, it looks like I would have go to the 150/35 at a cost of $295 ea vs. $90 ea for the 75/15. And, since the 150/35 is rated for 650W, I would need two of them . The damned panels only cost $175 ea, so I would be spending more for the controllers than for the panels.

As for your question about start batteries, for me, it always came down to the "oh s**t" factor. If one of two batteries in parallel went bad, it drags the other down with it. Whereas, if a single batty goes bad, I can always jump off the other if I need to start the engine quickly.

The ratings on mppt controller s is max voc and amps. You have a36 volt panel putting out a max of 9.58 amps . To charge a 12 volt house bank you are reducing the voltage by a factor of 3which will increse the amps out by a factor of 3 which would give you an approximate amp to the batteries of 28.75. So yes you wod need a controller rated for 30 amps output.

[john61ct]

With Victron, you need to be careful to not exceed the voltage, so for the 100/15 unit, stay under 100V total panel Voc. Looking at just that factor you could safely put two 38.8V panels in series.

However there is quite a safety factor built into the second max Amps rating, which is **charging** amps; by exceeding that 15A you will "waste" some power output in (rare) peak conditions, but output a higher total power in average conditions, IMO a good value tradeoff.

However, the ideal for protection against shading losses is one SC per panel. For that purpose 75/15 would be fine, and IMO cheap at under $100 delivered.

Panels are getting cheaper and cheaper (until anti-dumping tariffs come into play), so with more efficient and sophisticated controllers, more and more valid scenarios can result in the SC component costing more than the panels.

Total system cost compared to just a few years, solar's a crazy bargain.

[john61ct]

Originally Posted by mitiempo

For a start the Victron 75/15 is rated for a maximum of 200 watts. At this maximum the output will reach just under 14 amps in ideal conditions.

Actually it's 220W at "nominal 12V" usually 17+V

But his panels are nominal 24V (actual 32V) where the max rating is 440W.

It really is the Voc (first number in model) that is critical for sizing, especially in cold climates.

The lsc short circuit amps maximum rating for both the 75/15 and 100/15 models is 20A.

[newhaul]

Originally Posted by john61ct

With Victron, you need to be careful to not exceed the voltage, so for the 100/15 unit, stay under 100V total panel Voc. Looking at just that factor you could safely put two 38.8V panels in series.

However there is quite a safety factor built into the second max Amps rating, which is **charging** amps; by exceeding that 15A you will "waste" some power output in (rare) peak conditions, but output a higher total power in average conditions, IMO a good value tradeoff.

However, the ideal for protection against shading losses is one SC per panel. For that purpose 75/15 would be fine, and IMO cheap at under $100 delivered.

Panels are getting cheaper and cheaper (until anti-dumping tariffs come into play), so with more efficient and sophisticated controllers, more and more valid scenarios can result in the SC component costing more than the panels.

Total system cost compared to just a few years, solar's a crazy bargain.

So you think loosing up to a possible 13ah per hour is an acceptable loss. That is almost half of the panels potential.

[newhaul]

Originally Posted by john61ct

Actually it's 220W at "nominal 12V" usually 17+V

But his panels are nominal 24V (actual 32V) where the max rating is 440W.

It really is the Voc (first number in model) that is critical for sizing, especially in cold climates.

The lsc short circuit amps maximum rating for both the 75/15 and 100/15 models is 20A.

John from the numbers the op stated one would assume that the panels are 36v nominal not 24v.

[john61ct]

Show your calc please?

Most panels actually produce even close to their STC rated output for a tiny fraction of the day and year, especially in warm weather.

If it costs a lot of money to get just a few extra AH per year, no I don't think it's worth it.

The anti-shading benefit of getting an excellent-value controller like the 75/15 into a 1:1 ratio with the panels will more than make up for it in a sailing context.

[newhaul]

Originally Posted by john61ct

Show your calc please?

Most panels actually produce even close to their STC rated output for a tiny fraction of the day and year, especially in warm weather.

If it costs a lot of money to get just a few extra AH per year, no I don't think it's worth it.

The anti-shading benefit of getting an excellent-value controller like the 75/15 into a 1:1 ratio with the panels will more than make up for it in a sailing context.

John reread post 196 please. And its not a few ah per year . It could be as much as 30 or more ah per day . Per panel.
So yes I do feel it would be.worth the extra cost.

[john61ct]

Originally Posted by newhaul

John reread post 196 please.

None of those are real numbers. The actual output to a 12V bank from that panel, from even the most efficient controller, in real life is very very rarely going to come close to 15A, much less ever exceed it.

Given how much the larger controllers cost, it would be silly to optimize for rare peaks.

Better to get higher average output overall, spending a lot less money.

IMO.

[john61ct]

Originally Posted by newhaul

John from the numbers the op stated one would assume that the panels are 36v nominal not 24v.

No such thing AFAIK. But if there were, then the 12V max rating would be even less relevant, reinforcing my point.

In fact nominal "24V" panels need to actually be at least 36V, just like 16V is too low for nominal 12V.

These MPPT SCs are designed to accommodate "oddball" grid-tie voltages, so in fact the whole "nominal" nomenclature is getting to be obsolete.

[newhaul]

Originally Posted by john61ct

No such thing AFAIK. But if there were, then the 12V max rating would be even less relevant, reinforcing my point.

In fact nominal "24V" panels need to actually be at least 36V, just like 16V is too low for nominal 12V.

These MPPT SCs are designed to accommodate "oddball" grid-tie voltages, so in fact the whole "nominal" nomenclature is getting to be obsolete.

EcoSolargy ECO285S156P-72 - 285 Watt 36 Volt Solar Panel

[barnakiel]

Originally Posted by mitiempo

For a start the Victron 75/15 is rated for a maximum of 200 watts. At this maximum the output will reach just under 14 amps in ideal conditions. (...)

The regulator (at max 15A) is not very likely to limit us. It is a small unit for smaller installations.

I think the more likely challenge is absorption rate at battery closing on to full.

BTW How do you interpret this statement from Victron: "PV voltage must exceed Vbat +5V for the controller to start"?

Do they mean every morning or just the first start (out of the box).

Because it takes quite some time in the morning for my panels to get to say 17 Volt (wrong assumption?). And I am not willing to wire 24/12 for the sake of getting the Volts higher and the regulator happy.

Thanks in advance of your opinion.

Cheers,
barnakiel

[john61ct]

Originally Posted by newhaul

EcoSolargy ECO285S156P-72 - 285 Watt 36 Volt Solar Panel

LOL, right in the spec sheet "Nominal 24 V DC"

The word nominal means "that's what we call it but it's not really that"

[john61ct]

Originally Posted by barnakiel

I think the more likely challenge is absorption rate at battery closing on to full.

At that point a little 50W panel is enough, it's the TIME per day that is the limiting factor with solar.

Critical is SC programmability to make sure it stays at Absorb voltage right up to the bank being full (amps dropping to just a few).

Originally Posted by barnakiel

BTW How do you interpret this statement from Victron: "PV voltage must exceed Vbat +5V for the controller to start"?

Do they mean every morning or just the first start (out of the box).

Because it takes quite some time in the morning for my panels to get to say 17 Volt (wrong assumption?). And I am not willing to wire 24/12 for the sake of getting the Volts higher and the regulator happy.

First start every morning. That is why nominal 12V panels are often 18-22V to start with.

Low cost PWM are often the same, there just isn't any effective power available until volts climb well above the charging point.

Very efficient cells like SunPower help, but only a bit.

By "regulator" are you talking about the solar controller or something else?

[newhaul]

New 5000W 5kw 36V Solar Panels Home Power Generator Free Shipped By Sea | eBay

These panels are 36 volt
Here is the page with the specs.

http://vi.raptor.ebaydesc.com/ws/eBa...35&cspheader=1

[foggysail]

Originally Posted by CapnCrunch

I'm not getting this. The Victron 100/15 specs read "Maximum PV power, 12V 1a,b): 200W (MPPT range 15V to 100V)"

My 290w panel specs show "Voc = 38.8VDC/ Isc = 9.58 A. I thought the Victron model numbers represented Voc/Isc?

If panel wattage is the determining factor, it looks like I would have go to the 150/35 at a cost of $295 ea vs. $90 ea for the 75/15. And, since the 150/35 is rated for 650W, I would need two of them . The damned panels only cost $175 ea, so I would be spending more for the controllers than for the panels.

As for your question about start batteries, for me, it always came down to the "oh s**t" factor. If one of two batteries in parallel went bad, it drags the other down with it. Whereas, if a single batty goes bad, I can always jump off the other if I need to start the engine quickly.

You will not harm the controller but you will be limited to its maximum rated output current whether your batteries are 12 or 24v. It will not provide greater than 15 amperes. Now if your battery bank was 24v instead of 12, then your panel's full output power will get converted. Maximum power under this condition from the specifications is 440 watts but again, with a maximum controller output current of only 15 amperes.