Our first year with lithium

[Neeves]

We have 3 MPPT controllers. We group panels with the same shading characteristics. On the starboard guardrail we have a pair of series wired panels ( to suit a 24v system) on a dedicated MPPT. The port side has a similar series wired set up with its own MPPT. The roving 4x50w flexible panels are wired as 24v and have their own MPPT. The 3 MPPT controllers get their voltage information from the victron smart shunt via Bluetooth so regardless of where they are located in the wiring, they know the actual battery voltage rather than what they see at their terminals.

Correct me if I am wrong.

Normally MPPT controllers use voltage, from the shunt (or wherever), to determine their operation of the panels for which they are wired. In your case this is the voltage of the entire system, not of a specific part. The actual voltage at the MPPT controller is ignored for control of the MPPT controller and hence the panels to which they are wired. All the MPPT controllers will react the same way whether the voltage is high or low for the panels for which (or to which) they are wired.

If the panels effectively use, my understanding, the average - why not have one controller?

If this is correct why the MPPT controllers and not a cheap and (maybe not) cheerful PWM controller?

Jonathan

 

[Sea Change]

Panels have different working voltages.
I was fortunate to find four 12v (nominal) panels that had the same working voltage. They are wired in parallel to one MPPT.
Another matched pair are in parallel to the second MPPT, at a different voltage.

Prices and specs change but at the time I was building my system, it wasn't really any cheaper to buy one big MPPT than two smaller ones. And when I accidentally cooked one a few months ago (don't disconnect the battery with the panels still connected ) it meant I still had half my system working.

 

[GHA]

Panels have different working voltages.

which also change constantly, the victron app trends shows the MPTT solar voltage hunting around to try to keep the power output as high as possible, one of mine right now is averaging just under 17v, the other above 18v. Busy little devices

 

[B27]

There's a balance between having more/better MPPT and just spending the money on more panels.
One extreme is to have max power tracking at cell level.
The other is just to lump everything together in parallel and load it down to a typical max power voltage which is commonly around 18V for small panels.

The simple approach is often pretty close in efficiency, and of course the aim of the game these days is to have enough panels that there's normally excess power over a charging cycle.

Last summer we were using a simple £10 controller, our fridge worked exactly the same as if we'd had the most expensive MPPT system imaginable.

Diminishing returns!

 

[geem]

There's a balance between having more/better MPPT and just spending the money on more panels.
One extreme is to have max power tracking at cell level.
The other is just to lump everything together in parallel and load it down to a typical max power voltage which is commonly around 18V for small panels.

The simple approach is often pretty close in efficiency, and of course the aim of the game these days is to have enough panels that there's normally excess power over a charging cycle.

Last summer we were using a simple £10 controller, our fridge worked exactly the same as if we'd had the most expensive MPPT system imaginable.

Diminishing returns!

There are other considerations. Redundancy. If we have a failure on one MPPT, we can run all our 720w of tilting solar mounted on the guardwires off one of our Victron 100/50 MPPTs. The second issue is different spec panels. Out roving flexibility panels need their own MPPT. Running panels with the same shading characteristics also improves output.
When you are running a fridge from a small array of panels/panel it's not the same as running your whole boat as we, and other do. A cheap PWM type regulator would waste quite a bit of power in. We can't mount any more solar so we like to maximise the output of what we have

 

[GHA]

Last summer we were using a simple £10 controller, our fridge worked exactly the same as if we'd had the most expensive MPPT system imaginable.

Diminishing returns!

Though compared to a victron system with mppt's talking to a smartshunt if you spent lots of time using your batteries/solar your cheap controller will kill them. Either through overcharging or if it has float it will undercharge them. Same end result, dead batteries well before they should be.
Every boat is different, probably most on here don't get their power system used much apart from some weekends & couple of weeks in the summer so not such a big deal, though float is.

 

[Laser310]

Those of you not buying the, very expensive, Victron batteries.., what are you using?

I won't be building them myself.

It seems that most of the Victron batteries do not have a built in BMS, where many of the other brands do.

Is it okay to use the built in BMS?

 

[geem]

Those of you not buying the, very expensive, Victron batteries.., what are you using?

I won't be building them myself.

It seems that most of the Victron batteries do not have a built in BMS, where many of the other brands do.

Is it okay to use the built in BMS?

Building them yourself sounds difficult but it really isn't. My wife can do it under supervision. It's really just making some end plates and 'compressing' the cells to allow you to fix the bank of cells down in your battery box. Wiring the little BMS wires is simply following the instructions that come with the bms.
It's more of an issue in my opinion,of every other aspect of how you design your charging system to suit the lifepo4 chemistry.

 

[lustyd]

but if you sit at anchor for weeks - hydro is obviously of no value

Depends where you sit. Chichester Harbour offers 4-5kt tides for 8 hours a day while at anchor and probably another 8 hours at 3kt so a suitably set up hydro unit would be quite effective. Not true of a lot of great anchorages, but in this case it's more consistent than solar. I doubt it's as effective as solar, so I'm certainly not arguing with your sentiment, just pointing out that it's not always no value.

 

[Trident]

As Geem said above - multiple MPPT allows for redundancy and for varying panel types. So my set up is 4X 40v 320w panels - in two banks of two (though all right next to each other on the roof) which are in series to give near 80v from each bank. This works great at the moment but I wanted to allow for higher sunlight in the Med and Tropics which means I may be better off with 4 in parallel. I wired so I could just swap plus around and do either and the max amps could run through one MPPT but I give the banks one each so that they work less hard and get less hot but if one breaks then I can put all the wires in to just one until a replacement is available

Then I had three panels of 23v on the next controller due to the different voltage . Finally I put two more panels on last week, also 23v but in series again so 46v and thus a 4th controller. Again if I lose one I could change the series or parallel config and run all the flexi panels through one controller (maybe 4 of the 5 if I wanted to series as I think 100V is the max but can't remember without looking it up)

I use Renogy stuff for all the solar and batteries - Renogy panels , their Rover Lithium MPPT controllers (flawless after 5 years daily use) and the Renogy Smart Lithium batteries because in testing they were considered second only to Battleborn but at half the price and use an extremely good BMS system that can handle 200a per battery. I can wholeheartedly recommend these batteries BUT make sure you get the Smart Lithium which connect the BMS with RJ45 connectors so that all work together as a single bank - they have Bluetooth versions as well now which DO NOT work as well - the battery part is the same but BMS is not quite the same and the BT is quirky so doesn't always do quite what it should .

 

[geem]

As Geem said above - multiple MPPT allows for redundancy and for varying panel types. So my set up is 4X 40v 320w panels - in two banks of two (though all right next to each other on the roof) which are in series to give near 80v from each bank. This works great at the moment but I wanted to allow for higher sunlight in the Med and Tropics which means I may be better off with 4 in parallel. I wired so I could just swap plus around and do either and the max amps could run through one MPPT but I give the banks one each so that they work less hard and get less hot but if one breaks then I can put all the wires in to just one until a replacement is available

Then I had three panels of 23v on the next controller due to the different voltage . Finally I put two more panels on last week, also 23v but in series again so 46v and thus a 4th controller. Again if I lose one I could change the series or parallel config and run all the flexi panels through one controller (maybe 4 of the 5 if I wanted to series as I think 100V is the max but can't remember without looking it up)

I use Renogy stuff for all the solar and batteries - Renogy panels , their Rover Lithium MPPT controllers (flawless after 5 years daily use) and the Renogy Smart Lithium batteries because in testing they were considered second only to Battleborn but at half the price and use an extremely good BMS system that can handle 200a per battery. I can wholeheartedly recommend these batteries BUT make sure you get the Smart Lithium which connect the BMS with RJ45 connectors so that all work together as a single bank - they have Bluetooth versions as well now which DO NOT work as well - the battery part is the same but BMS is not quite the same and the BT is quirky so doesn't always do quite what it should .

How do your Renogy flexible panels perform compared to your framed panels? I find my Renogy flexible panels perform considerably worse than my framed panels watt for watt. In the last month , the 200w of Renogy panels have peaked at 127w maximum output where as 360w of framed panels have peaked at 421w maximum output. They have peaked above their rated 360w on 16 days out of 30 days. Both sets of panels are angled to the sun and both are unshaded

 

[lustyd]

My 200W of Renogy flexible ETFE panels regularly go to 208W on a clear day so perhaps something wrong with yours given your better location.

 

[Sea Change]

Those of you not buying the, very expensive, Victron batteries.., what are you using?

I won't be building them myself.

It seems that most of the Victron batteries do not have a built in BMS, where many of the other brands do.

Is it okay to use the built in BMS?

There are plenty of ready built batteries out there- Fogstar seem to be popular.. Make sure it's got Bluetooth and that the BMS has a decent spec. You want to be able to adjust the parameters and see what's going on. On some poor quality batteries the BMS might have been low charging/discharging rates.

Assembling your own is really not rocket science. No soldering etc. Basic woodwork to build the end plates, a spanner to tighten up the bus bars, and some way of charging the cells to balance them. I bought a £30 adjustable power supply which is useful for other things too. If you use a BMS with active balancing you don't even need to do the top balance.

One big advantage of building your own is that they're much more compact than ready built. You will also save a significant amount of money, and get to specify quality components.

 

[Laser310]

One big advantage of building your own is that they're much more compact than ready built. You will also save a significant amount of money, and get to specify quality components.

I think it's not worth the risk of having trouble with insurers.

one insurer told me that a do it yourself installation would not be covered - even with off the shelf batteries. they wanted the installation done by a marine electrician with some sort of certification - i forget what it was.

So, I am interested in learning what batteries are popular with those who are not building them.

 

[Sea Change]

I think it's not worth the risk of having trouble with insurers.

one insurer told me that a do it yourself installation would not be covered - even with off the shelf batteries. they wanted the installation done by a marine electrician with some sort of certification - i forget what it was.

So, I am interested in learning what batteries are popular with those who are not building them.

In which case I would just contact a marine electrician and ask them to specify the batteries they like to use.

 

[Laser310]

In which case I would just contact a marine electrician and ask them to specify the batteries they like to use.

well, i am afraid they will just say "Victron", which are 3 X the cost of others.

I'm trying to have other ideas.

Are Renogy batteries used much in boats?

 

[steve yates]

I'm curious, if designing and installing a complete rewire of a boat, is there anything that would be done differently if the system was going to be powered by lithium instead of agm batteries?
ie, can I redo my electrics and then decide at the end if I want to go lithium or not for the power?
I was intending to keep it simple, two new 120ahr agms and an engine battery. But I must admit it's tempting if buying batteries from new to just go Lithium from the start.

 

[geem]

I'm curious, if designing and installing a complete rewire of a boat, is there anything that would be done differently if the system was going to be powered by lithium instead of agm batteries?
ie, can I redo my electrics and then decide at the end if I want to go lithium or not for the power?
I was intending to keep it simple, two new 120ahr agms and an engine battery. But I must admit it's tempting if buying batteries from new to just go Lithium from the start.

The obvious thing is to build your boat as a 24v system. It makes lots of sense with lithium as BMS are rated in amps. When you double the voltage to 24v, you half the amps so you BMS effectively handles twice the power. Your cables sizes to everything become much smaller for the same volt drop. As a consequence, the cost of rewiring the boat is much reduced

 

[geem]

I'm curious, if designing and installing a complete rewire of a boat, is there anything that would be done differently if the system was going to be powered by lithium instead of agm batteries?
ie, can I redo my electrics and then decide at the end if I want to go lithium or not for the power?
I was intending to keep it simple, two new 120ahr agms and an engine battery. But I must admit it's tempting if buying batteries from new to just go Lithium from the start.

The obvious thing is to build your boat as a 24v system. It makes lots of sense with lithium as BMS are rated in amps. When you double the voltage to 24v, you half the amps so you BMS effectively handles twice the power. Your cables sizes to everything become much smaller for the same volt drop. As a consequence, the cost of rewiring the boat is much reduced

 

[steve yates]

Its only a 30 foot boat, the devices cable sizes are only 1.5mm mainly anyway.