Jump to content

Should I use 36v PV panels


Strettonman

Featured Posts

I’ve not done any research into PVs yet but I am keen to get them on the boat in the next 6 months and someone has just offered me a couple of 36v 250W PV panels. I’ll obviously get an MPPT controller but will I need something special and are these types of panels a good idea for the boat ?

 

ive not seen them yet and have no other info but I suspect they are home PV panels. 
 

any advice ? 
 

thanks. 

Link to comment
Share on other sites

Pretty standard to use 36v panels these days.

 

Just get a Victron MPPT controller. Others are available but Victron really are the best for non professional grade installs.

 

 

 

Edited by magnetman
Link to comment
Share on other sites

Fine if panels in parallel works for you.  Panels in series would take you out of ELV territory into  LV electricity, where the requirements are more stringent, but not impossible.

 

N

Link to comment
Share on other sites

26 minutes ago, Strettonman said:

That’s good to hear. Thanks all.  If they look in good nick and will fit my roof  I think I’ll go for them. Is £70 a pop about right for decent second hand panels ? 

That's 28p/W, cheapest new panels (from Bimble) are 41p/watt but much bigger (410W or 600W), so a decent price.

 

https://www.bimblesolar.com/panelcompare?sort=price_per_watt

 

It's worth comparing the output per m2 with new panels, depending how old they are you might find you can get more output from the same space with new ones (but only by paying more...).

Edited by IanD
Link to comment
Share on other sites

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'm not sure a 30 amp unit will be quite enough for 500 watts of panels, perhaps one of our experts could confirm on that.

If not, you might need a 50 amp unit, which are around £300, so if you are trying to get it all done on a budget, the 50 amp victron is not a very cheap option.

  

The Epever tracer 40 amp units are good quality and more affordable, but are a bit more tricky to configure, and I'm not a fan of the PC software at all.

But at £120 ish, they do look a lot more attractive on price. 

 

 

Link to comment
Share on other sites

1 hour ago, Strettonman said:

That’s good to hear. Thanks all.  If they look in good nick and will fit my roof  I think I’ll go for them. Is £70 a pop about right for decent second hand panels ? 

 

As suggested, stick with 36v in parallel. That will give you at best 14 amps (250/36 x 2). This will increase through the charge controller as it reduces the voltage down to what you want and increases the output current. 

 

 

Link to comment
Share on other sites

10 minutes 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'm not sure a 30 amp unit will be quite enough for 500 watts of panels, perhaps one of our experts could confirm on that.

If not, you might need a 50 amp unit, which are around £300, so if you are trying to get it all done on a budget, the 50 amp victron is not a very cheap option.

  

The Epever tracer 40 amp units are good quality and more affordable, but are a bit more tricky to configure, and I'm not a fan of the PC software at all.

But at £120 ish, they do look a lot more attractive on price. 

 

 

2 x 250W 36V panels in series will only be about 7A, a Victron SmartSolar 100/15 is about £140.

  • Horror 1
Link to comment
Share on other sites

19 minutes 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'm not sure a 30 amp unit will be quite enough for 500 watts of panels, perhaps one of our experts could confirm on that.

If not, you might need a 50 amp unit, which are around £300, so if you are trying to get it all done on a budget, the 50 amp victron is not a very cheap option.

  

The Epever tracer 40 amp units are good quality and more affordable, but are a bit more tricky to configure, and I'm not a fan of the PC software at all.

But at £120 ish, they do look a lot more attractive on price. 

 

 

Not an expert , but I have 500W into a 30 A controller x 2. It obviously isn't ideal, but very rarely even approaches the limit. My panels are flat mounted though.

 

I also have a Tracer mppt (actually badged as Outback). If buying again, I too would opt for the victron. Whilst the tracer is configurable by the MT50 meter, and can be connected to bluetooth, I don't rate its tracking ability very highly.

 

If money was no object though, I would go for a proper outback, midnite or Morningstar controller.

  • Greenie 1
Link to comment
Share on other sites

8 minutes ago, Strettonman said:

As I said, I’ve not done my research yet so what’s the pros and cons of wiring them in series or parallel ? 

 

In series, one panel goes, they both go. If the panels are old, check to make sure they're diode protected. Without them, shaded areas can have an adverse effect on all parts of the setup. 

 

 

Edited by Higgs
Link to comment
Share on other sites

19 minutes ago, IanD said:

2 x 250W 36V panels in series will only be about 7A, a Victron SmartSolar 100/15 is about £140.

???

 

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.

  • Haha 3
Link to comment
Share on other sites

20 minutes ago, rusty69 said:

Not an expert , but I have 500W into a 30 A controller x 2. It obviously isn't ideal, but very rarely even approaches the limit. My panels are flat mounted though.

 

I also have a Tracer mppt (actually badged as Outback). If buying again, I too would opt for the victron. Whilst the tracer is configurable by the MT50 meter, and can be connected to bluetooth, I don't rate its tracking ability very highly.

 

If money was no object though, I would go for a proper outback, midnite or Morningstar controller.

 

My boat came with four small panels totalling 660 watts, and a tracer 40 amp unit, so I just assumed you would need a 40 amp MPPT to manage 500 watts of panels.

But I do sometimes see a level of charging current that approaches the maximum rating, and certainly in the summer with the sun overhead and the sky clear.

There are times when those 660 watts of panels are putting out 45 or more amps (charging at around 13.8v to 14v).

But that said, I wonder if those seemingly high figures are partly down to me having lithium batteries, which seem to soak up all the charge on offer with very little resistance?

 

I see the same thing on my second set of panels, which are around 750 watts. There are plenty of times in the summer when they are putting out a charge over 45 amps, which I didnt expect to see in uk conditions- but maybe its partly the batteries that are influencing the amount of current that is going into them?

 

 

 

Edited by Tony1
Link to comment
Share on other sites

6 minutes 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.

 

I also have the dunce hat ready if needed. After winning it so many times I got to keep it

 

  • Haha 2
Link to comment
Share on other sites

3 minutes ago, Tony1 said:

 

My boat came with four small panels totalling 660 watts, and a tracer 40 amp unit, so I just assumed you would need a 40 amp MPPT to manage 500 watts of panels.

But I do sometimes see a level of charging current that approaches the maximum rating, and certainly in the summer with the sun overhead and the sky clear.

There are times when those 660 watts of panels are putting out 45 or more amps (charging at around 13.8v to 14v).

But that said, I wonder if those seemingly high figures are partly down to me having lithium batteries, which seem to soak up all the charge on offer with very little resistance?

 

I see the same thing on my second set of panels, which are around 750 watts. There are plenty of times in the summer when they are putting out a charge over 45 amps, which I didnt expect to see in uk conditions- but maybe its partly the batteries that are influencing the amount of current that is going into them?

 


I think you can expect a bit more current into lithiums during mid-charge because the charge voltage on the Li is likely to be around 13.5v whereas for LA it would more likely be 14.4v. Power being voltage times current, for a given amount of power if the voltage is a bit lower, the current will be a bit higher. Not massively so, but a bit. Which is ultimately a consequence of Li’s much better power efficiency compared to LA.

  • Greenie 1
Link to comment
Share on other sites

33 minutes ago, nicknorman said:


I think you can expect a bit more current into lithiums during mid-charge because the charge voltage on the Li is likely to be around 13.5v whereas for LA it would more likely be 14.4v. Power being voltage times current, for a given amount of power if the voltage is a bit lower, the current will be a bit higher. Not massively so, but a bit. Which is ultimately a consequence of Li’s much better power efficiency compared to LA.

 

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.

 

 

 

Edited by Tony1
Link to comment
Share on other sites

4 hours ago, BEngo said:

Fine if panels in parallel works for you.  Panels in series would take you out of ELV territory into  LV electricity, where the requirements are more stringent, but not impossible.

 

N

 

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

Link to comment
Share on other sites

4 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?

If connected in series, add the voltage of each panel together to get the total.

The total voltage should be shown on your MT50

Link to comment
Share on other sites

1 hour ago, Tony1 said:

 

I'm not sure a 30 amp unit will be quite enough for 500 watts of panels, perhaps one of our experts could confirm on that.

 

 

Controller output obviously has to somewhat match the panels otherwise one is just wasting money on either high output panels with low output controller or high output controller with low output panels. However, what I learned during my installation was that it's the controller voltage specification that's critical.

 

If you go over the current rating of a MPPT controller with too many panels it will just clip the current at the controller's maximum output, but if you exceed the voltage of the controller it will fry the MPPT circuitry. Apparently the Victron electrics are encased in black epoxy and if you damage them the can't be repaired and you end up with an expensive doorstop.

9 minutes ago, rusty69 said:

If connected in series, add the voltage of each panel together to get the total.

The total voltage should be shown on your MT50

 

Yes i know. I was responding to BEngo who said that over 36v shouldn't be connected in series.

Edited by blackrose
  • Greenie 1
Link to comment
Share on other sites

2 minutes ago, blackrose said:

 

 

Yes i know. I was responding to BEngo who said that over 36v shouldn't be connected in series.

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.

Link to comment
Share on other sites

1 hour ago, rusty69 said:

Not an expert , but I have 500W into a 30 A controller x 2. It obviously isn't ideal, but very rarely even approaches the limit. My panels are flat mounted though.

 

I also have a Tracer mppt (actually badged as Outback). If buying again, I too would opt for the victron. Whilst the tracer is configurable by the MT50 meter, and can be connected to bluetooth, I don't rate its tracking ability very highly.

 

If money was no object though, I would go for a proper outback, midnite or Morningstar controller.

Yes I had a a couple of tracers and then went to a midnite they are a lot better. Shush dont tell tell anyone but my controller can take up to 200 volts! And I have 5kw of solar 

Link to comment
Share on other sites

1 minute ago, peterboat said:

Yes I had a a couple of tracers and then went to a midnite they are a lot better. Shush dont tell tell anyone but my controller can take up to 200 volts! And I have 5kw of solar 

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

Link to comment
Share on other sites

1 hour ago, nicknorman said:

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.

 

So ... is 35A for 30 minutes going to be 70 Amps per hour or 17.5 amps per hour?

 

(I'll get my coat! :giggles:)

Link to comment
Share on other sites

1 hour ago, nicknorman said:

500w going into a 12v battery is going to be around 35A.

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

48 minutes ago, Tony1 said:

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?

Regardless of battery type, both the MPPT and the BMV712 should show the same current actually going into the battery (assuming you aren't running any 12V appliances). Its just that that number is likely to be larger if you have lithiums.

Edited by David Mack
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.