Li-ion Battery Banks

[CatNewBee]

Originally Posted by noelex 77

My guess would be with lithium batteries and 36 cell “12v” panels, the average gain in power would be about 20.8% .

Good evidence (theoretical or experimental) of a different outcome than MaineSail’s result would be valuable, but it seems to me to be in the right ball park.

The gains from MPPT technology are not enormous particularly for lead acid batteries, but even with this type of battery the 5-15% average gain with “12v” panels should not be dismissed so lightly, especially on yachts where there is often a limitation on the space available to fit solar panels.

Don't get me wrong, MPPT controllers are great, if you have the money, go for them! To get most out of the invest, use also high voltage panels, not the 36 cell 12V, then you will have a decend output even in cloudy conditions. This is the upper side of the coin, but pricey.

If you are low on budget, chose 12V panels with 36 cells, buy one more panel insted of spending the money on a MPPT, a PWM will do the job too with this panels quite with the same output and your extra panel will outperform your 5...10% gain from the MPPT for the same budget.

[noelex 77]

Originally Posted by CatNewBee

To get most out of the invest, use also high voltage panels, not the 36 cell 12V, then you will have a decend output even in cloudy conditions

High efficiency solar panels are often worth the extra money on a boat. These types of panels will extract more power from the limited area that is frequently the constraining factor when installing solar.

The high efficiency panels also sometimes have cells that are a little better at extracting power under low light conditions.

Virtually all the high efficiency panels are also high voltage panels (Solbian is one exception), so if you want high efficiency panels virtually the only choice is high voltage panels. High voltage panels can only be used with MPPT controllers.

High voltage on its own is not an advantage. High voltage panels are exactly the same as connecting a number of smaller 36 cell 12v panels in series. While there is some dispute, it is generally agreed that to connect these panels in parallel creating a larger low voltage panel would be better.

An example helps. If we take three 100w “12v” 36 cell panels and if we connect them in series electrically, we create a single 300w high voltage (36v) panel. If we connect them in parallel electrically we create a single 300w 12v panel. Most people would suggest the latter option is better. However, we can also buy a 300w high voltage high efficiency panel. This will be smaller than three 100w “12v” low effeciency panels and other than being more expensive, it is the best choice on a boat. Its advantage is not the high voltage, but the high efficiency.


Traditionally the only readily available option has been to connect cells together in blocks of 36 or “12v”. Parallel connection has generally been found to be superior. So when connecting together two blocks of 36 cells it is better to create (electrically) a larger panel keeping the lower 12v voltage rather than connecting the cells in series and creating (electrically) a single higher voltage 24v panel. It has been suggested that something in between, for example, groups of approximately 50 cells in series might actually be the best option. The theory does have some appeal and it would be nice to see some research in this area.

[CatNewBee]

Originally Posted by noelex 77

High efficiency solar panels are often worth the extra money on a boat. These types of panels will extract more power from the limited area that is frequently the constraining factor when installing solar.

The high efficiency panels also sometimes have cells that are a little better at extracting power under low light conditions.

Virtually all the high efficiency panels are also high voltage panels (Solbian is one exception), so if you want high efficiency panels virtually the only choice is high voltage panels. High voltage panels can only be used with MPPT controllers.

High voltage on its own is not an advantage. High voltage panels are exactly the same as connecting a number of smaller 36 cell 12v panels in series. While there is some dispute, it is generally agreed that to connect these panels in parallel creating a larger low voltage panel would be better.

An example helps. If we take three 100w “12v” 36 cell panels and if we connect them in series electrically, we create a single 300w high voltage (36v) panel. If we connect them in parallel electrically we create a single 300w 12v panel. Most people would suggest the latter option is better. However, we can also buy a 300w high voltage high efficiency panel. This will be smaller than three 100w “12v” low effeciency panels and other than being more expensive, it is the best choice on a boat. Its advantage is not the high voltage, but the high efficiency.


Traditionally the only readily available option has been to connect cells together in blocks of 36 or “12v”. Parallel connection has generally been found to be superior. So when connecting together two blocks of 36 cells it is better to create (electrically) a larger panel keeping the lower 12v voltage rather than connecting the cells in series and creating (electrically) a single higher voltage 24v panel. It has been suggested that something in between, for example, groups of approximately 50 cells in series might actually be the best option. The theory does have some appeal and it would be nice to see some research in this area.

My panels are 330W panels with 96 cells, 1.05m x 1.55m in size, 62V Voc / 54V Vmp and Isc 6.xA.

Main advantage of high voltage / high efficiency panels is they are relatively small for the output, outpul low amps and high voltage, so you can use smaller cabling and connect them in parallel.

I have 5 of them, max current is then 30A, you can use a 35mm2 wire to the controller, that then outputs 100A to the battery. By using higher voltages and lower current the voltage drop along the wire is much less, what makes the whole thing more efficient.

[john61ct]

Larger high voltage panels - if you have room for them - are often cheaper per watt output and of a better build quality than the mass-market 12V panels.

MPPT controllers are no longer much more expensive than high quality PWM, and usually have more features that justify the higher price even without the greater efficiency.

The limiting factor on most boats is not spending an extra $100 on the system. Especially for a group paying for LFP batts (!)

It is how many square inches of flat panel mounting area you have available.

Getting the maximum charge output per that area is rarely a waste of money.

[Delfin]

Originally Posted by Stumble

I make no claim to expertise and haven't used them. But even the 'drop in' batteries will need a new battery charger from the same manufacturer as the batteries, a new alternator, and if you are running solar a new mppt. Basically every thing that puts power into the batteries need to either be reconfigured or exchanged with something that is acceptable for lifepo

And if you get it wrong in any way the entire bank can be fried and require replacement with just a moments inattention.

Compounded is the issue that even a lot of battery chargers with a lifepo charging profile are wrong, and the factory setting are dangerous.


I may be out of date on this, and new stuff I see always hitting the market. But as I understand it, it simply isn't ready for DIY systems unless you have a very strong background in battery technology, or are willing to spend the time to learn.

That hasn't been my experience. Same alternator, same charger, same regulator. However, managing them is certainly different and I am following pretty much the same regime as Seman and as recommended by CMS - charge until full, then turn off the charging system. Not complicated, and on a cruising boat the idea that you can't monitor voltage and acceptance rate of a battery bank suggests that you also probably can't avoid running up onto the beach, since both require situational awareness.

But I agree with you that the factory "LiFePO4" profiles on regulators or chargers should be viewed with deep suspicion. Pick a target voltage - it can be anywhere from 3.4V to 3.6V, and charge until full, then disconnect from charging. The difference between the 3.4 and 3.6 is just the time it takes for the batteries to fully charge. You can, as CMS notes, fry LiFePO4 at 3.4V if you keep putting that voltage to the batteries after they are not going to accept anymore current so just generate heat with additional charging, so what is critical is watching the acceptance rate. I use a Link 2000 and when the CAR drops to around .05C, I disconnect the batteries from the charging source.

[CatNewBee]

Originally Posted by Delfin

That hasn't been my experience. Same alternator, same charger, same regulator. However, managing them is certainly different and I am following pretty much the same regime as Seman and as recommended by CMS - charge until full, then turn off the charging system. Not complicated, and on a cruising boat the idea that you can't monitor voltage and acceptance rate of a battery bank suggests that you also probably can't avoid running up onto the beach, since both require situational awareness.

But I agree with you that the factory "LiFePO4" profiles on regulators or chargers should be viewed with deep suspicion. Pick a target voltage - it can be anywhere from 3.4V to 3.6V, and charge until full, then disconnect from charging. The difference between the 3.4 and 3.6 is just the time it takes for the batteries to fully charge. You can, as CMS notes, fry LiFePO4 at 3.4V if you keep putting that voltage to the batteries after they are not going to accept anymore current so just generate heat with additional charging, so what is critical is watching the acceptance rate. I use a Link 2000 and when the CAR drops to around .05C, I disconnect the batteries from the charging source.

if they do not get CURRENT, they wont produce heat and also wont FRY. No current, no heat. Its as simple as that.