Mixing solar panels

[El Gringo]

Well a while ago I got some household solar panels for a really good price, nice quality and all, should suit my 24v system OK.

$_20.PNG

However I want to make up a grid of panels to cover most of the roof of the bus.
I can do that with 100w panels approx 650-700mm wide, however these only come in 12v as far as I can find anyway.
These for instance - https://www.ebay.com.au/itm/100W-Polycr ... 1438.l2649

So my question is can i run say 8 of these 12v panels running in series and parallel to get a 24v output and combine them with the 24v 265w panels?
Any and all suggestions very welcome.

Thanx,
Bernie

[BruceS]

Bernie you need to go back to square 1 and work up.
1. Check out ALL the maximum voltages & watts that your solar controller will handle.
2. etc.

For instance my controller will handle max of 120volts. My panels are VOC of 37v so 3 X 37 = 111volts.
I have 2 strings of 3's.
250w @ 6 = 1500w
So maybe tell us (or Terry) make & model of controller or at least the limiting factors.

[El Gringo]

Thanx Bruce.
Don't have a controller capable of anywhere near the amps/watts as yet.
If I can mix and match the panels as I hope (or something similar) I should end up with about 2800 watts @ 24+ volts.
I have a dingo and I was intending to get the rest done by T1.
The idea is to get the solar on the roof, get the Lithium from Terry and get the bus to his place for the hookup.
I haven't spoken to the maestro about that yet as my time frame keeps moving, but I was hoping either late this year or early next.
Guess I should talk to him soon though...

Cheers,

[jon_d]

It must have the panel pattern in every parallel string.

eg

20 parallel 12 V panels
or 3 strings of 1 - 37V plus 1-12V and 1-24V (as an extreme example)

And the controller need to match the set up.


For the sake of a couple of hundred dollars difference, buy the right panels

[bagmaker]

dont cover the WHOLE roof, leave a 200-250 wide gap down the centre for maintenance, wiring and cleaning

[T1 Terry]

OK, the panels you put up first have a Vmp of 29.8v, not enough to fully charge a lead acid battery but enough to charge lithium batteries.
The next issue is using 12v panels in series to make 24v, if either panel gets shaded that pair of panels will not produce any charging current .... but, there is a way around the problem. If you link all the 12v panels together is parallel and join one group to the other group in series, cabling size becomes an issue but every panel in each string is able to work with any panel in the other string or some from each.
Another alternative is to connect each 12v positive together looped from panel to panel, then also connect each 12v panel to its mates negative cable to produce 24v from those 2 panels or any one of the 12v panels connected in parallel. Now, all the negatives at the 12v panel have their own length of 6mm auto cable run back to the junction box and each of the positive cables on the 24v side of the pair have their own length of 6mm auto cable run back to the junction block.
Same deal with each of the 24v panels, extend the 2 cables using 6mm auto cable until they reach the junction box.

How they are connected up in the junction box is a hold different story and I won't attempt to make this post any more confusing by adding that into it

T1 Terry

[El Gringo]

It must have the panel pattern in every parallel string.

eg

20 parallel 12 V panels
or 3 strings of 1 - 37V plus 1-12V and 1-24V (as an extreme example)

And the controller need to match the set up.


For the sake of a couple of hundred dollars difference, buy the right panels

Thanx Jon,
I really would prefer to get the right panels but I can't find 24v ones anywhere near the sizes I need.
Like most buses there are hatches and other obstacles that have to be worked around, plus I got the 6 x 265w panels slightly damaged frames but brand new for $50 each, so that is a huge saving.
It's just that I want to fill in the rest of the area with smaller panels and that doesn't seem possible at 24v.

Cheers,

[El Gringo]

dont cover the WHOLE roof, leave a 200-250 wide gap down the centre for maintenance, wiring and cleaning

Thanx for the tip.

Cheers,

[El Gringo]

OK, the panels you put up first have a Vmp of 29.8v, not enough to fully charge a lead acid battery but enough to charge lithium batteries.
The next issue is using 12v panels in series to make 24v, if either panel gets shaded that pair of panels will not produce any charging current .... but, there is a way around the problem. If you link all the 12v panels together is parallel and join one group to the other group in series, cabling size becomes an issue but every panel in each string is able to work with any panel in the other string or some from each.
Another alternative is to connect each 12v positive together looped from panel to panel, then also connect each 12v panel to its mates negative cable to produce 24v from those 2 panels or any one of the 12v panels connected in parallel. Now, all the negatives at the 12v panel have their own length of 6mm auto cable run back to the junction box and each of the positive cables on the 24v side of the pair have their own length of 6mm auto cable run back to the junction block.
Same deal with each of the 24v panels, extend the 2 cables using 6mm auto cable until they reach the junction box.

How they are connected up in the junction box is a hold different story and I won't attempt to make this post any more confusing by adding that into it

T1 Terry

Thanx T1,

Good to know the big panels will actually work.
I remember discussing the series/parallel connection with you before (when I was going to use all flexi panels) and I have the drawing on file as to how to do it, which I think I understand pretty well.

Can I join the 2 strings together at a junction on the roof, or would it be better to run both lines down to the controller?
Keep in mind I want you to do the hook up with your magic box...
I was thinking to take them down separately and have separate fuses and disconnects at/near the controller.
That way it would be easier for you to hook up and also give me some power in the event one set of panels failed for some reason.

Cheers,

[T1 Terry]

Thanx T1,

Good to know the big panels will actually work.
I remember discussing the series/parallel connection with you before (when I was going to use all flexi panels) and I have the drawing on file as to how to do it, which I think I understand pretty well.

Can I join the 2 strings together at a junction on the roof, or would it be better to run both lines down to the controller?
Keep in mind I want you to do the hook up with your magic box...
I was thinking to take them down separately and have separate fuses and disconnects at/near the controller.
That way it would be easier for you to hook up and also give me some power in the event one set of panels failed for some reason.

Cheers,

Probably better to just fit the panels and we will wire them when the bus arrives up here. Because the 24v panels will have an Mpv and open circuit voltage much lower than the 2 x 100w panels in series will have, blocking diodes will need to be added to avoid cooking the 24v panels. The panel strings will need to be set up in groups of 40 amps max so the No Ark circuit breaker can handle the load from each group. We could use the 63 amp capable models as the cable size to carry 40 amps with minimal drop @12v will carry twice that @ 24v, but then the solid state relays become an issue. Moving from 12v to 24v brings in so many more complications, they can all be over come of course but many more factors must be taken into account.

T1 Terry