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Old 07-08-2017, 15:15   #16
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Re: Solar design - 12 Volt or 24 Volt?

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The Outback MPPT controller only works when the input voltage is over 15 volts.
MPPT controllers do not boost voltage (with rare exceptions). Therefore the panel voltage has to above the battery voltage but there is no requirement for the panel voltage to above 15v with the Outback controller.

So called "12v" panels have a STC Vmp of around 17-18v which is fine for charging 12v batteries. There is no need to connect them in series with most controllers. The popular Victron units are a possible exception beceause of an unusually high start up voltage.
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Old 07-08-2017, 17:25   #17
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Re: Solar design - 12 Volt or 24 Volt?

The voltage actually needs to be much higher than what you guys are talking about for MPPT tech to deliver any advantage.

The lowest spec Victron handles 75V no problem, probably 28-50 would be ideal.

So just buy the panel to optimize for your controller.

If you want to stick with nominal 12V (18+V in reality) then you may as well get a PWM controller.
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Old 07-08-2017, 17:43   #18
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Re: Solar design - 12 Volt or 24 Volt?

I have a 48 volt system. One reason, the inverter I use puts out more watts at 48 volt. But the big reason was smaller wires throughout. Especially battery to inverter. It allowed me to have other banks in places further away from the inverter w/o very heavy cables. My goal was to go 2+ days w/o charging and the additional banks let me expand that.
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Old 07-08-2017, 22:50   #19
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Re: Solar design - 12 Volt or 24 Volt?

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The voltage actually needs to be much higher than what you guys are talking about for MPPT tech to deliver any advantage.

The lowest spec Victron handles 75V no problem, probably 28-50 would be ideal.

So just buy the panel to optimize for your controller.

If you want to stick with nominal 12V (18+V in reality) then you may as well get a PWM controller.
If you have higher voltage panels you must use an MPPT controller. With 12v panels you have the option, but the gains are just as valid.

The advantage of MPPT is not as great as the advertising material would suggest. It depends on a lot of factors, but around 10% is in the right ball park.
However, if you have limited space, as is the case with most boats, this extra output is helpful. There are often further gains because the high efficiency panels are more readily available in higher voltage panels. The high voltage panels need an MPPT controller.

In terms of the output per surface area High efficiency panels with an MPPT controller can do significantly better than low efficiency panels with a non MPPT controller.
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Old 07-08-2017, 23:13   #20
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Re: Solar design - 12 Volt or 24 Volt?

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If you have higher voltage panels you must use an MPPT controller. With 12v panels you have the option, but the gains are just as valid.

The advantage of MPPT is not as great as the advertising material would suggest. It depends on a lot of factors, but around 10% is in the right ball park.
Over 20% in this test by Mainesail:
MPPT vs. PWM Controllers Photo Gallery by Compass Marine How To at pbase.com
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Old 08-08-2017, 03:35   #21
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Re: Solar design - 12 Volt or 24 Volt?

There are good reasons why the solar panels are rated for 18V. These will go down to 15 or even 14 V as they get hot, so the idea is to get a voltage above the battery charge voltage in hot environments.

So the efficiency of a MPPT charge depends on the temperature of the panel. At low temps the panel will output the 18V and the MPPT can do its magic and gain 30% and up, at higher temps the panel will reduce its voltage and the MPPT will gain less down to 0 very high temps. So it depends on your conditions if a MPPT makes sense.

Actually increasing the voltage to get some charge at low lights is not the reason for the 18V. The panel will already generate a voltage above the battery voltage at light levels where the current is still neglectable.

So it makes no sense to serialize panels to improve charging at low lights.
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Old 08-08-2017, 05:19   #22
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Re: Solar design - 12 Volt or 24 Volt?

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I am curious what boat can support such a large solar array.

60' catamaran possibly?
It can be done; we have a club member (also a member here) with a 2800w array on his Defever 41; all depends on how you mount them; his replace the aft canvas enclosure.
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Old 08-08-2017, 09:12   #23
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Re: Solar design - 12 Volt or 24 Volt?

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Thanks for posing the link. It was discussed on the forum some time back. I read everything MaineSail publishes and would suggest anyone interested in maintaining their boat does the same. There is some great, practical, advice.

Like many of MaineSail's articles, it takes a scientific approach to answering boating questions . The results showed an MPPT regulator beat a none MPPT (sometimes called PWM) regulator by 20.8%. However, it it should be noted that this was charging lithium, not lead acid batteries. The lower charging voltage of lithium gives MPPT a greater performance boost (as MaineSail correctly notes). I seem to also remember the temperatures were quite low, but my memory may be wrong on this point.

There has been other published data. There was a comparison of MPPT (Victron 75/15) and non MPPT regulator (Sunsaver PWM) published in the Yachting magazine PBO in 2015. The results showed a 10.9% gain for MPPT.

My own tests were less formal, but after a couple of years with a very good quality PWM regulator (Plasmatronics) I changed to a MPPT controller (for another 5 years worth of getting nearly all our power via solar and MPPT). I noticed about a 7% improvement.

These differing results are to be expected. The exact improvement will depend on many factors. Perhaps the most important is temperature. In the warmer climate of the Med it is not surprising I noticed less change.

I still think my ball park figure of 10% is not a bad starting point for those trying to decide if the costs and complexity of an MPPT regulator are justified. However, I should have qualified this number by pointing out this assumes a lead acid bank. I would once again stress that the actual average gain may be higher or lower than this and also stress that this is for a quality MPPT controller. Cheap MPPT controllers can be poor.

As long as you don't believe the commonly quoted advertising line of a 30% gain or the opposing view, as suggested in this thread, that there is zero gain for "12v panels" then you are more informed than most.
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Old 08-08-2017, 20:58   #24
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Re: Solar design - 12 Volt or 24 Volt?

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I still think my ball park figure of 10% is not a bad starting point for those trying to decide if the costs and complexity of an MPPT regulator are justified. However, I should have qualified this number by pointing out this assumes a lead acid bank. I would once again stress that the actual average gain may be higher or lower than this and also stress that this is for a quality MPPT controller. Cheap MPPT controllers can be poor.
Definitely every locale and system is different.

Here's my point of view when purchasing though. PWM controllers rarely have the adjustment found on good quality MPPT controllers. And good quality MPPT is nowhere near as expensive as it used to be. By good quality I mean from major manufacturers like Victron, Morningstar, etc. And a 75/15 Victron is not expensive.

I sell solar panels from one supplier in fairly large numbers. They only have PWM controllers to supply me. I sell maybe one PWM controller for every 20 to 30 MPPT controllers. The most often sold system is two 100 watt panels - either hard or semi-flexible with a controller. This is virtually always the Victron 75/15. The other supplier has a 30 amp PWM controller at the same retail as the Victron 75/15. The PWM has an lcd display but no adjustments can be made. Those planning to add more panels later choose the Victron 100/30, not the less expensive PWM rated at 30 amps.

I think that many manufacturers are putting more effort into MPPT than they were a few years ago. It reminds me of inverters. 15 years ago you could buy a very good quality modified sine wave inverter - Trace or Heart for example. Now modified sine wave is for the most part hard to find in a quality unit. Seems every manufacturer is putting all their effort into pure sine wave inverters now.
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Old 09-08-2017, 09:51   #25
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Re: Solar design - 12 Volt or 24 Volt?

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Panels come in a huge variety of shapes and sizes. Can you please link to the detailed specs of the panels you're talking about?

At this point in initial design I understand the 39" width as most common with 65" consumer and 77" commercial lengths as below.

Click image for larger version

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I'm open on particular panel model or wattage if you have any suggestions.
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Old 09-08-2017, 10:07   #26
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Re: Solar design - 12 Volt or 24 Volt?

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I am curious what boat can support such a large solar array.



60' catamaran possibly?

You know there is another thread busting on the YouTubers (queue the drone shot and the backbeat) but i find because they are actually out cruising I learn a lot from them. Not so much from their sound track but by carefully watching their gear setups.

I am fitting as much solar as possible. Maybe even more than possible with risk acceptance for a little panel damage. This led the design to (so far) -

Add a lifeline solar panel mount as part of the solution (thanks SV Sophisticated Lady)

Add a fixed, tubing lifeline setup (thanks SV Delos)

Then engineer together the lifeline mount and the fixed tubing so the panels can swing up and out at anchor.

Can that work?
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Old 09-08-2017, 11:56   #27
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Re: Solar design - 12 Volt or 24 Volt?

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Cheap MPPT controllers can be poor.
Lots of cheap controllers are fraudulently marketed as MPPT when they are no such thing.
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Old 09-08-2017, 12:46   #28
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Re: Solar design - 12 Volt or 24 Volt?

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Originally Posted by SecondBase View Post
You know there is another thread busting on the YouTubers (queue the drone shot and the backbeat) but i find because they are actually out cruising I learn a lot from them. Not so much from their sound track but by carefully watching their gear setups.

I am fitting as much solar as possible. Maybe even more than possible with risk acceptance for a little panel damage. This led the design to (so far) -

Add a lifeline solar panel mount as part of the solution (thanks SV Sophisticated Lady)

Add a fixed, tubing lifeline setup (thanks SV Delos)

Then engineer together the lifeline mount and the fixed tubing so the panels can swing up and out at anchor.

Can that work?
So what boat do you have?
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Old 10-08-2017, 08:51   #29
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Re: Solar design - 12 Volt or 24 Volt?

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True also for all other mainstream SCs, including PWM.

There are no quality "12V" panels with that low a voltage. Most are over 18V. That's what "nominal 12V" means.

The cheap little trickle ones that connect to a starter batt with no controller don't count.


That is why thisis false

Yes, but best is one controller per panel
--------------------------------------------------
If the above comments are correct, maybe someone can explain the fact that in the morning and the afternoon, not during midday, my voltage is around 40 Volts. I have three 130 Watt panels in series. If each panel would at least produce 15 Volt, than I should have a minimum of 45 Volt input. The wiring is in good condition with good connections.
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Old 10-08-2017, 11:02   #30
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Re: Solar design - 12 Volt or 24 Volt?

My point was in response to those thinking "nominal 12V" panels were actually rated close to 12V.

The STC Voc rating is just a theoretical maximum.

Actual voltage produced depends on many factors, including location latitude, panel angle, temperature of the PV cell, how clean, no shading etc.

Once your system is working, voltage variations should not be such a concern.

Power output in watts is the most important, and of course will be much higher - maybe even close to the panel ratings - at peak times than morning and late in the day.
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