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Should I use 36v PV panels


Strettonman

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6 minutes ago, blackrose said:

 

My panels are about 43v open circuit and they're connected in series. Or have I misunderstood what you're saying?

 

I tried to read up on this last year when I was doing the install, but the information has since been pushed out of the back of my brain by more important recent information (which admittedly now includes the exact location of M+S food halls in Shropshire). 

If I recall correctly, it was the series connection method where one panel being in shade meant all the other panels would reduce to that lowest output? 

I think I wired my rear panels in parallel because of this. 

I have graced many places with a royal visit (since my coronation as His Holiness the Prinz [sic] Regent of Whitchurch), and in most of these places there seemed to be stray bush or two waving itself about in front of the sun, and so I felt parallel was the way to go.  

 

 

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4 minutes ago, David Mack said:

And for the avoidance of doubt, that is the case whether the panels are in series or in parallel.

Regardless of battery type, both the MPPT and the BMV712 should show the same current actually going into the battery. Its just that that number is likely to be larger if you have lithiums.

 

Thanks David. I did wonder if the greater resistance of lead acids to charging would mean that fewer of your English amps would actually be allowed to get into said lead acid battery, and so a lower number might be shown on the BMV712 display. 

I seldom trouble myself with attempts to understand electrical matters- it seems such a proletarian and unforgiving pursuit. But sometimes sheer curiosity does overcome me. 

 

 

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53 minutes ago, rusty69 said:

Ok. No, I don't think they shouldn't be connected in series, they are just a higher voltage, and present a greater risk. I will let @BEngo expand. appologies for butting in.

 

No problem you weren't butting in.  When I installed my 2 x 43v open voltage panels most people here said connect them in series? My MPPT is 150v/60a.

Edited by blackrose
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Just now, blackrose said:

 

No problem. But when I installed my 2 x 43v open voltage panels most people said connect them in series? 

 

 

Exactly what I have done too. There are pros and cons of each configuration depending on time of year and shading probability. I think I even had mine wired series-parallel for a while. The point is though, that the higher the voltage the more chance of getting a shock from them. I suspect that is what was being referred to with the Low voltage v extra low voltage. I personally have never found it to be much of a problem, but the more you string together in series, the higher the voltage becomes (limited in some respect by the controller they are attached to).

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2 hours ago, Tony1 said:

I agree with magnetman in that Victron are a great option, especially for novices. There's a phone app with a really clear and intuitive interface, that allows you to control the MPPT remotely, which is quite handy. 

 

 

I thought you could only control the MPPT remotely if you bought an additional Victron unit for 200 quid that transmitted the signal? You can't control it remotely using bluetooth unless you're on the boat or very close by 

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1 minute ago, rusty69 said:

 

 

Exactly what I have done too. There are pros and cons of each configuration depending on time of year and shading probability. I think I even had mine wired series-parallel for a while. The point is though, that the higher the voltage the more chance of getting a shock from them. I suspect that is what was being referred to with the Low voltage v extra low voltage. I personally have never found it to be much of a problem, but the more you string together in series, the higher the voltage becomes (limited in some respect by the controller they are attached to).

The ones on the house, 2 strings of 6, run out at >200volts. Its only dangerous if you keep playing with them.

 

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7 minutes ago, rusty69 said:

 

 

Exactly what I have done too. There are pros and cons of each configuration depending on time of year and shading probability. I think I even had mine wired series-parallel for a while. The point is though, that the higher the voltage the more chance of getting a shock from them. I suspect that is what was being referred to with the Low voltage v extra low voltage. I personally have never found it to be much of a problem, but the more you string together in series, the higher the voltage becomes (limited in some respect by the controller they are attached to).

 

Yes. That's why I insisted on installing a big properly rated PV isolator switch. Cost me 30 quid and it's a great big thing but at least I can easily switch the panels off before doing anything with the batteries. There's no way I'd rely on covering the panels or a breaker that's not rated for those voltages. Removing a fuse would an option but the easier it is to isolate the panels the more likely one is to routinely do it as a matter of course.

 

 

Edited by blackrose
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47 minutes ago, rusty69 said:

Better in what way? Apart from the 200V bit.

The only issue I have had with the Tracer/Epever units is the reluctance to wake up in the mornings sometimes.....

It hasnt made me change though.

As a fresh install, I would probably go with Outback or Victron, however, old trusty Tracer is 10 years old now and still happy to be here.

Only one unit I have installed on other boats  failed,after having lightning strike, owner asked about the warranty(5 years after install)

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3 minutes ago, matty40s said:

The only issue I have had with the Tracer/Epever units is the reluctance to wake up in the mornings sometimes.....

It hasnt made me change though.

As a fresh install, I would probably go with Outback or Victron, however, old trusty Tracer is 10 years old now and still happy to be here.

Only one unit I have installed on other boats  failed,after having lightning strike, owner asked about the warranty(5 years after install)

 

 

Me neither, but if I had the choice again, I would go Victron.

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50 minutes ago, rusty69 said:

Better in what way? Apart from the 200V bit.

You can watch what it's doing, especially as the batteries are expensive lifepo4s. It can be putting in 79 amps one second with its cooling fan working hard and then its down to a couple of amps then in float. It's a reassuringly expensive unit with a good warranty. When I went over to it my panels produced more energy in the same time than the tracers. 

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9 minutes ago, blackrose said:

 

Yes. That's why I insisted on installing a big properly rated PV isolator switch. Cost me 30 quid and it's a great big thing but at least I can easily switch the panels off before doing anything with the batteries. There's no way I'd rely on covering the panels or a breaker that's not rated for those voltages. Removing a fuse would an option but the easier it is to isolate the panels the more likely one is to routinely do it as a matter of course.

 

 

Nothing wrong with covering the panels if you haven't got an isolator. The high voltage side is at the panel side anyway, not the battery side, though its the current that will likely kill you.😂

Edited by rusty69
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34 minutes ago, blackrose said:

 

I thought you could only control the MPPT remotely if you bought an additional Victron unit for 200 quid that transmitted the signal? You can't control it remotely using bluetooth unless you're on the boat or very close by 

 

When I said remotely, I was thinking via bluetooth rather than via the internet.

The times when I might want to switch off the solar charging would be, for example, when I'm at the tiller on really sunny day and I can't easily go indoors- so I do find that the ability to switch it off from the tiller is a handy thing for a solo boater. 

 

It would be nice to monitor things from 100 miles away, but its not important or frequent enough to justify £200. 

If I leave the boat for a week or maybe two, my plan will be to leave it in a marina rather than on the towpath, and in a marina I can just leave the lithiums disconnected at around 40-60% SoC, so that no charging is actually needed. 

 

As an aside, one of my future ideas is to switch/redirect some solar charge into the lead acid starter battery (which also runs the bilge pump), so that if the boat was left unattended for a month the starter battery would stay well charged. 

 

 

 

 

 

 

Edited by Tony1
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2 hours ago, Tony1 said:

 

Thanks Nick, that makes sense, even with my customary dunce cap firmly in place- lower voltage means higher current. 

But lithiums charge more efficiently than lead acids, right? And lead acids have a much greater resistance to being charged as they get more full, right? 

So I have a theoretical question for yourself and our other experts (theoretical because I will never willingly use lead acids again)- how does this more efficient charging behaviour of lithiums show itself on monitors like the BMV-712, and also on the MPPT units?

 

I know that if my MPPT says 30 amps are being generated, my BMV712 will correspondingly say that my batteries are being charged at 30 amps (if I'm not using anything). 

But what happens with lead acids?

For example, as the lead acid battery gets more full, does the BMV712 indicate that (say) 15 amps are going into the batteries - which might reflect the true situation? 

A BMV712 will only tell you what is actually going in, right? 

And does the MPPT carry on saying 30 amps are being produced, even though the user is not going to see those 30 amps coming back out of the batteries? 

Or does the MPPT reflect the increasing resistance of the lead acid batteries, and show a reducing level of charging current? 

 

I think an even better question might be- why concern myself with the travails of lead acid troglodytes on a Thursday night?

Many of these people will be too busy sacrificing gerbils to read my educational posts.

 

 

The BMV and the MPPT both show actual charge current at the time. If there is no load from the boat's systems, these values will be the same (within the bounds of measurement error). The BMV will also show actual discharge current at night. That is the easy bit!

 

It gets more complicated when you consider the SoC indication of the BMV (forget the SoC indication of an MPPT, it is guesswork and bad guesswork at that!).

Firstly we need to consider what we mean by "efficiency". There are two types of "efficiency" relating to batteries, charge efficiency and energy efficiency. Charge efficiency relates to Ah out vs Ah in. Don't be confused by the word "charge", it doesn't specifically relate to charging the battery, it means the physical thing called charge, SI unit coloumbs, integral of current.

 

Whereas energy efficiency relates to watt-hours out vs watt-hours in. Not the same thing at all!

 

Consider a battery whose capacity is 100Ah. How much useful energy does that represent? No idea, unless we also consider the voltage.

One 100Ah cell at 3.2v doesn't have a lot of energy, whereas a 100Ah 96v battery has lots. Ah on its own is not a measure of energy, likewise current is not a measure of power. We also need to consider the voltage at which that charge or current is provided.

With that in mind, the charge efficiency of a Li battery is a bit better than an LA battery but not much. I find it is about 95%, which is surprisingly low until you consider that at the fractional C usage we have on boats, the BMS perhaps takes up some significant Ah and more so when it is balancing. My Trojans (LA) seemed to be about 93%. Not a lot of difference.

 

That is charge efficiency, and that is used in the SoC calculation within the BMV. So if you have taken out 10A over 10 hours, you will need to put back 10A for about 10.5 hours to get back to the same SoC reading on the BMV.

 

But as I said, when you are considering anything to do with SoC and Ah, you are not looking at useful energy available because it doesn't take into account the voltage at which that charge (integral of current) is going to be supplied at.

 

When you look at the charge and discharge voltages of Li vs LA, you start to see the real difference. LA charges at 14v or more, maybe 14.6v in its latter stages. It discharges at perhaps 12.5v or maybe down to 12v. So we have maybe getting on for 2v difference between charge and discharge voltages. So straight away, even assuming 100% charge efficiency, the energy efficiency of LA is only about 85%, and worse at high rates of charge and discharge. Whereas as you know, with Li the voltage difference between charge and discharge is much less. Modest charging is done at less than 13.6v, discharging maybe around 13.2v so only 0.3v difference giving an energy efficiency (assuming 100% charge efficiency) of perhaps 97%.

Both those figures are worse in practice due to the charge efficiency being less than 100%, but even so the Li remains streets ahead of the LA.


And that of course is before you consider the efficiency advantage of charging Li from a genny or engine - much less time spent running the genny/engine with very little current going in.

 

And all that of course is why you love your lithiums more than is acceptable in decent respectable society.

 

Can't blame you though!

 

 

Edited by nicknorman
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33 minutes ago, rusty69 said:

Nothing wrong with covering the panels if you haven't got an isolator. The high voltage side is at the panel side anyway, not the battery side, though its the current that will likely kill you.😂

 

Nothing wrong until the covers get blown off. Yes the high voltage side in on the panel side assuming the controller is working properly! I'm not taking that chance however small.

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34 minutes ago, Tony1 said:

When I said remotely, I was thinking via bluetooth rather than via the internet.

 

 

So I don't really see any advantage of "remote monitoring" if you're only 10 yards away from the controller. I do like the display and charging breakdown that the Victron gives you, but on the other hand I'm not sure I'd want to pay all that money for a MPPT controller that doesn't have its own display where they expect you to use your phone. What happens if you lose your phone or if it's not working?

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15 minutes ago, nicknorman said:

 

....

And all that of course is why you love your lithiums more than is acceptable in decent respectable society.

 

 

What happens in the electrical cupboard, stays in the electrical cupboard

 

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3 minutes ago, blackrose said:

 

So I don't really see any advantage of "remote monitoring" if you're only 10 yards away from the controller. I do like the display and charging breakdown that the Victron gives you, but on the other hand I'm not sure I'd want to pay all that money for a MPPT controller that doesn't have its own display where they expect you to use your phone. What happens if you lose your phone or if it's not working?

I find the BMV712 bluetooth function quite useful. Yes you are right I could just move myself to be in front of the BMV712 display but then I am lazy and the display is only visible in the engine room, not visible in the saloon watching the telly with G&T, nor at the steering position. If I lose the phone I will get another one but in the mean time I can use the iPad which also has the App on it. So far I have not lost my phone since I got the BMV712 and even if I did, the ratio to having access to the bluetooth data vs not having access to it is going to be very large. If it was critical to have access to the data (I can't see that it would be) then one could have a cheap second hand smartphone in a drawer somewhere. I just replaced my iPhone 6S with a new model after 6 years, the trade in for the 6S was less than a tenner so I kept it.

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26 minutes ago, blackrose said:

 

So I don't really see any advantage of "remote monitoring" if you're only 10 yards away from the controller. I do like the display and charging breakdown that the Victron gives you, but on the other hand I'm not sure I'd want to pay all that money for a MPPT controller that doesn't have its own display where they expect you to use your phone. What happens if you lose your phone or if it's not working?

 

I'm certainly not saying any of the victron features are showstoppers, its kind of nice-to-have stuff, but I'm glad its there.

The display can be done on any device, so losing my phone isnt an issue in that respect.

Like Nick I keep two old phones handy that also have the app installed, so I can view the battery and MPPT status whilst stood at the tiller, or whilst using my main phone as an actual phone (not that I would ever be that retro, obvs). 

On some days in the summer I'll have 50 amps of solar coming plus an engine charge, and it may be that I'm looking to cycle down the lithiums to a lower SoC, which I try to do every week or so.  

So if I then remember that I need to reduce the SoC, I have the ability to stop the solar charging without leaving the tiller- not a huge deal of course, but a handy feature. 

One other side benefit - to society in general - is that I can keep an eye on the solar charging (and turn it on or off) without leaving my laptop or my beer. 

This has the enormous benefit of allowing me to type out witty posts in internet forums, AND maintain my unhealthily intimate relationship with my batteries.  

 

Screenshot_20221124-215209.jpg

Edited by Tony1
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38 minutes ago, blackrose said:

 

Nothing wrong until the covers get blown off. Yes the high voltage side in on the panel side assuming the controller is working properly! I'm not taking that chance however small.

I flick the MCBs  off or the big DC rotary switches before playing with the electrics 

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14 hours ago, nicknorman said:

???

 

500w at 72v may only be about 7A but so what? An MPPT is rated for its output current, not input current. 500w going into a 12v battery is going to be around 35A. Not like you to make such a fundamental error. Consider yourself to be a very naughty boy. Stand in the corner for 30 minutes.

 

oops 🙂

 

Fundamental error there. My only excuse is that I'm so used to thinking about a 48V battery bank I neglected to notice that the OP presumably has a 12V one... 😞

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One thing to note with the Victron Smartsolar MPPT controllers is that you can set the max charge current with the bluetooth control application (android and presumably apple).

 

I did do this on one of my Victron controllers as it is only a 30 amp controller but the input is 650w which once down to the 15v charging voltage (LTO batteries) would be quite a lot more than 30 amps on a good summer day.

 

If you are happy to not take all of the potentially available power in summer but like to have a bit of a chance of getting something in winter then a cheaper controller is a valid option. I don't know if others do this. They probably do. Victron Smartsolar do have this function.

 

.

 

 

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1 hour ago, magnetman said:

One thing to note with the Victron Smartsolar MPPT controllers is that you can set the max charge current with the bluetooth control application (android and presumably apple).

 

I did do this on one of my Victron controllers as it is only a 30 amp controller but the input is 650w which once down to the 15v charging voltage (LTO batteries) would be quite a lot more than 30 amps on a good summer day.

 

If you are happy to not take all of the potentially available power in summer but like to have a bit of a chance of getting something in winter then a cheaper controller is a valid option. I don't know if others do this. They probably do. Victron Smartsolar do have this function.

 

 

 

I don't really understand why you'd need to limit the charge current of any MPPT controller? As I said previously, if the current specification of the controller (in your case 30A) is exceeded, the MPPT will simply clip the charge current coming out of the controller. It's the voltage specification of the MPPT that's the critical value not to be exceeded to avoid damaging it.

 

So what's your MPPT controller spec 30A/???V

Edited by blackrose
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6 hours ago, blackrose said:

 

I don't really understand why you'd need to limit the charge current of any MPPT controller? As I said previously, if the current specification of the controller (in your case 30A) is exceeded, the MPPT will simply clip the charge current coming out of the controller. It's the voltage specification of the MPPT that's the critical value not to be exceeded to avoid damaging it.

 

So what's your MPPT controller spec 30A/???V

 

This may or may not be appropriate. I charge my electric lithium bike battery from the load output of the charge controller and feed it through a gadget that can increase the voltage to 42v. The current needs to be set and is set in line with what the mains adaptor for the bike is set to - 2A. On a battery with a low charge state, the battery would probably accept more than 2A, but it might not be healthy to allow that. 

 

As it is a dull time of the year, the charge controller couldn't meet the 2A demand, so the output of the voltage booster gadget was set to 1A, in order to maintain a voltage output. Solars are not at their best at this time of year. At this time of year, the amps are just not available in large amounts. 

 

Between now and Dec 21st, we will lose another 35 minutes of light. 

 

In the summertime, the problem will be how to use the amps available. Once your batteries are charged, the amps available will not be utilised unless there are other things that can make use of the potential of the solar panels. 

 

 

Edited by Higgs
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1 hour ago, Higgs said:

In the summertime, the problem will be how to use the amps available. Once your batteries are charged, the amps available will not be utilised unless there are other things that can make use of the potential of the solar panels. 

 

 

Why is it a problem? Surely it's no more of a problem than if you were on shore power with your battery charger switched on 24/7. The batteries will only take what they can take and the MPPT will manage the panels.

 

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12 minutes ago, blackrose said:

 

Why is it a problem? Surely it's no more of a problem than if you were on shore power with your battery charger switched on 24/7. The batteries will only take what they can take and the MPPT will manage the panels.

 

 

Well, restricting the current output has never been something I bother about, with the lead acid batteries I have. Maybe I should alter my settings, because I have noticed it going into float when I'd like it to keep putting in the amps. And it does have those amps to give. If I swap from one set of batteries to another set, not previously on charge, I can see that the charge controller (panel array) does have those amps spare. They increase, as the fresh set of batteries demand. 

 

But I am at the moment trying to determine if I have a couple of weakening leisure batteries. 

 

 

Edited by Higgs
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