how to wire up solar panels

[emlclcy]

I've got 3 24v panels all wired in parallel going to a pwm charger. the plan is to increase this to 4 panels, change to a mppt charger and wire them in series / parallel configuration.

If the charge controller can handle the voltage would stringing them all in series be better than 2 pairs connected in series?

cheers

carl

[nicknorman]

I've got 3 24v panels all wired in parallel going to a pwm charger. the plan is to increase this to 4 panels, change to a mppt charger and wire them in series / parallel configuration.

If the charge controller can handle the voltage would stringing them all in series be better than 2 pairs connected in series?

cheers

carl

I don't think there would be much in it, but my gut instinct would be to go for 2 pairs of 2. If you do go for all-series be sure to take into account the Voc at low temperature since the Voc is often quoted at say 25C, but it increases as temperature decreases.

[Pete & Helen]

I've got 3 24v panels all wired in parallel going to a pwm charger. the plan is to increase this to 4 panels, change to a mppt charger and wire them in series / parallel configuration.

If the charge controller can handle the voltage would stringing them all in series be better than 2 pairs connected in series?

cheers

carl

 

Main reasons for being in series is that the current and therefore the voltage drop in the cables from the panels to the controller will be less, and any shading of individual panels will have less effect on the overall efficiency.

 

If you are going to exceed the controllers rated voltage then parallel / series combination is a good compromise

[Graham.m]

I've got 3 24v panels all wired in parallel going to a pwm charger. the plan is to increase this to 4 panels, change to a mppt charger and wire them in series / parallel configuration.

If the charge controller can handle the voltage would stringing them all in series be better than 2 pairs connected in series?

cheers

carl

 

Are your battery banks 12 or 24Vs

[MarkHez]

 

and any shading of individual panels will have less effect on the overall efficiency.

 

 

Shading of individual panels wired in series has MORE effect on the overall efficiency

[Jess--]

 

Shading of individual panels wired in series has MORE effect on the overall efficiency

the effect of shading individual panels will vary depending on whether the panels have bypass diodes fitted

[Loafer]

the effect of shading individual panels will vary depending on whether the panels have bypass diodes fitted

 

I did some trials on this matter some years ago, on my sea yacht with 2 x 21V panels and an 'Outback' MPPT controller. I wired a switch box that swapped them from series to parallel and back instantly, and was able to see which was best any time I chose.

 

There was no doubt then that parallel was marginally better than series. However, that was only 2 x 130W panels.

 

2p

[sjc]

If you go for a 2x2 configuration you should really ensure the bypass diodes are rated for the max current ( in this case 2 panels, rather than just one as for a series setup ).

[nicknorman]

If you go for a 2x2 configuration you should really ensure the bypass diodes are rated for the max current ( in this case 2 panels, rather than just one as for a series setup ).

Just trying to work out the logic for that. How can current from panels in one string pass through the bypass diodes of panels in another string?

[sjc]

If you imagine an "H", it depends whether or not you connect the horizontal.

[nicknorman]

If you imagine an "H", it depends whether or not you connect the horizontal.

Ah I see. Is it normal to connect across the H? And if so, why?

Edited December 10, 2015 by nicknorman

[sjc]

I have no idea if the H connection is usual, but it does happen. I guess it reduces your losses if only one panel is in shade ?

[Graham.m]

I've got 3 24v panels all wired in parallel going to a pwm charger. the plan is to increase this to 4 panels, change to a mppt charger and wire them in series / parallel configuration.

If the charge controller can handle the voltage would stringing them all in series be better than 2 pairs connected in series?

cheers

carl

 

 

Don't forget to fuse the cable from the panels to the controller and from the controller to the batteries. The fuse size depends on the current and the cable size. Also it would be a good idea to have a means of isolating the controller from the panels and the batteries, a suitable size switch would do.

[WotEver]

Also it would be a good idea to have a means of isolating the controller from the panels and the batteries, a suitable size switch would do.

Note that having the controller connected to the panels and not connected to the batteries is a very good way of killing many controllers.

 

The instructions on most controllers stress that the battery connection MUST be made prior to connecting the panels.

 

Tony

[Graham.m]

Note that having the controller connected to the panels and not connected to the batteries is a very good way of killing many controllers.

 

The instructions on most controllers stress that the battery connection MUST be made prior to connecting the panels.

 

Tony

 

Bearing in mind that some controllers are able to handle inputs up to a 150V DC might be an idea to be able to isolate it if it needs working on etc.

[Loafer]

150V DC is a dodgy force indeed. One mistake there, and you might not be able to let go of the bit that gave you the shock. At least with AC, you can disengage from the offending source, if you're quick enough to pull your hand away as the voltage descends towards zero, during one of its 'Hurts'!

 

OK, I admit to being silly again. Nurse...

[jenevers]

Don't forget to fuse the cable from the panels to the controller and from the controller to the batteries. The fuse size depends on the current and the cable size. Also it would be a good idea to have a means of isolating the controller from the panels and the batteries, a suitable size switch would do.

These look like a good idea as they combine switch and circuit breaker in one housing, which means fewer connections, compared to separate fuse and switch.

http://www.bimblesolar.com/extras/dc-circuit-brakers/40a-dc-breaker

Edited December 11, 2015 by jenevers

[Graham.m]

These look like a good idea as they combine switch and circuit breaker in one housing, which means fewer connections, compared to separate fuse and switch.

http://www.bimblesolar.com/extras/dc-circuit-brakers/40a-dc-breaker

 

I think the principle is a good idea and these if mounted in a protected panel or box would be fine. My concern is if mounted somewhere they could be brushed against that the kill button could easily be accidentally be activated and it not be notice that the breaker was off.

[emlclcy]

 

Are your battery banks 12 or 24Vs

24v

[WotEver]

 

Bearing in mind that some controllers are able to handle inputs up to a 150V DC might be an idea to be able to isolate it if it needs working on etc.

So by all means have a simple disconnect for the panels. But make the battery disconnect a more difficult procedure.

[Graham.m]

So by all means have a simple disconnect for the panels. But make the battery disconnect a more difficult procedure.

 

I would always believe this sort of control/switch/breaker should be in a protected position and not open to being brushed against etc. They have to be mounted such that the operation is a deliberate act.

24v

 

With 24V batteries I would suggest that the voltage into the controller needs to be above or equal to 30V.

 

What is the maximum input the controller will accept?

[emlclcy]

 

I would always believe this sort of control/switch/breaker should be in a protected position and not open to being brushed against etc. They have to be mounted such that the operation is a deliberate act.

 

 

With 24V batteries I would suggest that the voltage into the controller needs to be above or equal to 30V.

 

What is the maximum input the controller will accept?

Interesting question I don't know. It's a pwm system at the moment. I will investigate. ...

[emlclcy]

Interesting question I don't know. It's a pwm system at the moment. I will investigate. ...

it is rated to 125v, the system voltage is 24, the minimum being 18v. So I wired my 3 24v panels in series (they have a VoC of 38v) and the display on the charger said 80-90v but it didn't make any difference to the charge current but I was very overcast when I tried this

[WotEver]

I'd suggest you don't keep those 3 panels in series. VoC can easily be exceeded on a cool bright day and could quite possibly exceed 125V.

[Graham.m]

I'd suggest you don't keep those 3 panels in series. VoC can easily be exceeded on a cool bright day and could quite possibly exceed 125V.

 

Puzzled I don't see how you get to a panel output of 125V with a VOC of 38V and three panels. I make it 114V and that should not worry the controll panel.

 

@emlclcy When and if you get the fourth panel I would suggest twos in parralell and then put the two pair in series.