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Old 22-09-2013, 18:19   #46
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Re: Lithium or Solar?

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Originally Posted by noelex 77 View Post
The lead acid charging voltages are higher and therefore closer to Vmp than lithium.

Maximum charge voltages on lithium are in the order of almost a whole volt lower than lead acid.

This gives much more gap between battery voltage and Vmp for lithium batteries leading to more potential gain from the voltage conversion inherent in MPPT.

Not recharging a severly depleted la battery ,. which is when you need Imp. LA voltages range below to above Li. thats his point.

dave
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Old 22-09-2013, 18:48   #47
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Re: Lithium or Solar?

Lithium or Solar? Go Solar. Solar will last and is now cheap as it gets. Batteries will get cheaper in the future.
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Old 22-09-2013, 18:56   #48
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Re: Lithium or Solar?

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Lithium or Solar? Go Solar. Solar will last and is now cheap as it gets. Batteries will get cheaper in the future.
+1 if you must choose, choose solar.
the best price right this moment is DM 158w solar panel, solar module 158w, 12V Solar Panel
they do not require MPPT neither.
i will buy mine when i get down south, shipping is nasty high. ($100 for two panels)
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Old 22-09-2013, 19:47   #49
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Re: Lithium or Solar?

I'm my own worst enemy, i've introduced an issue that will drag this thread off topic. is it possible to split the MPPPT v PWM for charging lithium batteries off to a seperate topic and drag the off topic posts over there with a link to it? Please? It is an interesting topic on it's own but not what this thread was about.

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Old 23-09-2013, 01:14   #50
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Re: Lithium or Solar?

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Not recharging a severly depleted la battery ,. which is when you need Imp. LA voltages range below to above Li. thats his point.

dave
We need to compare a normal charge cycle to determine the relative gains of MPPT, not the unusual case of a severely depleted LA battery.

Even with the abnormal case of a severely depleted lead acid battery it does not take long for the battery voltage under charge to rise above the maximiun safe charging level for lithium.
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Old 23-09-2013, 01:31   #51
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Re: Lithium or Solar?

It is 10AM local time here and my lead acid batteries have just hit 13.8v. They have gained 16AHrs out of a typical 130AHrs that the solar panels will put in today.

With a small taper at the end of the day that means that for 75%+ of the solar input they are going to have a voltage at, or above the maximum safe voltage for a lithium battery.

The higher the battery voltage the less the gain from MPPT.
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Old 23-09-2013, 05:06   #52
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Re: Lithium or Solar?

As it appears this topic is not going to be split off, I feel a number of points appear to be have missed in the basic understanding of how solar panel behave and how controllers charge batteries.
As a solar panel increases in temp the voltage that the max amps are produced reduces. Typical 18vdc @ 25 DegC and this reduces by 0.38% per deg C above 25 degs.
this is the cals from a gentleman on another forum regarding these thin film panels,
Vmp 18v, presumably at 25C
Max temp 80C, that's 55 degrees of derating
.38% / C derate, = 20.9% derate @ 80C
18v - 20.9% = 14.24v

Now, to charge a battery with a terminal voltage of 13.6v you will get zero current flow if you try to charge at 13.6v or less, there must be a voltage differential or delta to cause current to flow, like water down hill. By the time the cells reach 13.8v the current requirement has dropped to a low level so that 14.24v will create a 0.44v differential, enough for some current to flow, as the voltage drops more current will flow.

There is no way impedance matching will improve this current flow, if the supply voltage is reduced to increase the amps the current flow will reduce so that is counter productive, the controller must function in PWM mode to get any charging to occur. Low voltage battery charging MPPT controllers do not have a voltage boost function, this function is in the world of solar roof top back to grid converters, a whole different world and non of the logic involved with them crosses over to low voltage battery charging units, if a salesman tries to use the comparison line it is smoke and mirrors B/S, nothing more. You could rig up panel cooling though, then the expensive MPPT controller would work.

The only way an MPPT controller can be of any advantage in these conditions is to increase the supply voltage by linking the panels in series. This requires bypass and blocking diodes to be placed at each panel to stop the output of the other panels being feed into that panel if it gets shaded, it's not only to increase the output from a system in partial shade, it is to stop the shaded panel being turned into a heater element and burning it out, a common problem in series connect systems is inferior capacity/quality diodes are used. Each diode has a voltage drop of 0.7v, a Schottky diode around half that amount, but a loss is a loss no matter what you call it, if you don’t believe it’s there, touch one of the diodes while the panels are in full sun, the blister will remind you.
Next, the controller must now converter this higher voltage down to a voltage high enough to cause the batteries to charge, this creates heat in the unit as every conversion results in losses manifest as heat, no one has created the zero loss circuit yet as this requires ultra conductors and they are still a dream.
So, to get the MPPT controller to show some advantage losses must be added..... does this sound logical when a system already exists that doesn't suffer the losses and is cheaper to buy?

T1 Terry
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Old 23-09-2013, 05:40   #53
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Re: Lithium or Solar?

Typical solar cell temperatures are about 45C so the typical Vmp in practice is higher than the 14.24v you quote. However most of your points are valid which is why the gain from MPPT is only small.

However, the gain is greater for a battery with a lower charge voltage. Maximum lithium charge voltages are a hotly debated subject as you know, but settings are much lower than with lead acid.

Even my gel lead acid batteries are at voltages for most of the peak sun hours that would make a lithium advocate run for the off switch. Flooded lead acid battery charging voltages would make you feint
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Old 23-09-2013, 06:30   #54
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Terry is right about mppt to a point. If the Vmp ends up close to the Li charge point ( basically by luck ) then assuming the battery requires Imp , the panel is at the max power point and an mppt controller adds nothing.

However once the Vmp moves from that point then mppt provides a benefit , which first must overcome the mppt losses it after that provides a real gain over pwm.

The mppt point does move with illumination levels as well , though not hugely but enough on the context of Li charge voltage. Here mppt is also an advantage especially on a boat where shading and poor incident angle is common


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Old 23-09-2013, 06:31   #55
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Re: Lithium or Solar?

I guess it depends where you live or use the panels to relate "typical" panel temps while being used. Most reputable panel manufacturers use an NOCT (Normal Cell Operating Temperature) of 48.5 deg to 54 deg, the testing station in the Aust outback has average temps of well over 80 degC and they have air gaps behind the panels as they are mounted on racking. The thin film panels mentioned in this thread have no air gap under them so no heat dissipation, a sheet of aluminium left lying on the cabin roof in the hot sun all day, 80 degC won't be far off the mark.

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Old 23-09-2013, 07:20   #56
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Re: Lithium or Solar?

Terry once again you arguing for only a small gain with all batteries from MPPT. It will be a very small gain or even a loss in very high ambient temperatures with little panel cooling airflow. I agree completely.

However, you are ignoring the fundamental question of differences between lithium and lead acid.

You have stated on several occasions that owners of lithium batteries have less to gain from MPPT regulators than owners of lead acid batteries.

I don't agree with this. I think the opposite is true.
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Old 23-09-2013, 11:46   #57
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Re: Lithium or Solar?

As an "ultra-low-power" cruising sailor, both as far as use and generation capabilities I would love to switch to Li cells for one reason only... While lead acid cells are unhappy with not being brought up to full charge, Li cells would seem to be content with whatever you happen to have available to feed them today.

Only charging sources I have available are 160W of solar, and a 60W light coil on the kicker. Have a "suitcase" type genset for power tools and last ditch battery chargiing. A week offshore in inclement weather makes it tough to get a 160Ah bank up to full charge. Know I am slowly killing my batteries, but until you all quit arguing, and start using Li cells in quantities large enough to get the mfg prices down, I am stuck with lead acid.

When I finally kill my lead acids through inadequate charging, the initial cost of an equivalent Li bank will probably still beyond the weight of the grouch-bag. Best news so far has been the broad introduction of LED fixtures for nav and interior lights.

Open to any suggestions as far as keeping a low input system topped up, short of more PV panels (no room). Next project is dedicated low noise dc generator.
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Old 23-09-2013, 13:41   #58
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Re: Lithium or Solar?

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yes but the point Scoobert makes is perfectly valid, you can get decent performance at a good bang for your buck out of LA and thats the truth. That doesnt invalidate those that want to "go" lithium, but one must be careful not to engage in "wishful" decision making.

dave
Dave,
Scoobert insists that as part of a switch to lithium being too expensive is that the HE must buy a new charger and regulator,
There is an assumption and insistence that the OP must also do this.
Any shore charger that has an AGM preset or adjustable will do, as will almost any ordinary alternator.
This insistence is misplaced and not factual in my opinion.
There are optimum options for Lithium of course, but most reasonably modern, already fitted charging systems should get one started shouldn't they?
The "bang for buck" of LA is not the subject of the OPs question re a FAST charging requirement, so what is its value here?
It the terms of the OPs question, it is irrelevant.
I get good value out of my 6xTrojans as they are used where the advantages of Lithium are not needed, horses for courses.
Cheers,
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Old 23-09-2013, 14:40   #59
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Re: Lithium or Solar?

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+1 if you must choose, choose solar.
the best price right this moment is DM 158w solar panel, solar module 158w, 12V Solar Panel
they do not require MPPT neither.
i will buy mine when i get down south, shipping is nasty high. ($100 for two panels)

There are much better deals around. A good price for solar is around $0.95 per watt, so about $150 for a 158W panel. I am buying 280W panels at about $260

ET Solar ET-P672280 280 Watt Poly Solar Panel .
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Old 24-09-2013, 06:21   #60
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Re: Lithium or Solar?

Thank you for all the posts! I turned my back for 2 days and theres 50 odd.

OK I apologise because I am new to all this, I don't know what type of alternator I have and my boat is on the other side of the world.

* Does anyone know what the standard Beneteau Cyclades alternator is 2007?
* Can this alternator handle Lithium recharging?
* What #Roughly# would I use ah wise per day with pumps, lights, music, auto pilot and fridge?

Once someone can say (extremely roughly) what I would be using in ah per day then can we use this hypothetical number to discuss if it would be cheaper or better (in Montenegro) to have Lithium batteries installed or Flexi solar on the canopy? If Lithium is $2200 for 400ah installed (I saw a guy from Tasmania use this figure) and it will be fully charged in the hour I use my engine anyway that would seem to be the best no?

DOES ANYONE KNOW A REPUTABLE INSTALL PLACE IN OR NEAR MONTENEGRO WHERE I CAN GET THIS WORK LOOKED INTO?

Thanks again.

Hvala is thankyou in Montenegro, names Riley. Haha sorry for more confusion.
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