How to wire up 6 solar panels and controller

[Sven...]

So after a long time contemplating it, I finally bought myself a proper solar charge controller - the Outback FM60. Specifications are here:

http://www.outbackpower.com/products/charge_controllers/flexmax/

 

For the leftover money, I got some solar panels - namely, 6 x 80W monocrystalline panels. Specifications are..:

Optimum voltage: 17.39V

Optimum current: 4.61A

Open-C voltage: 21.97V

Short-C current: 4.98A

Operating temp.: 47C

Temp.coefficient of VoC: -0.35%/C

Max series fuse rating: 12A

 

The panels will be fixed flat on the roof. The purpose of this installation is to supply most of my power needs in Summer, a little bit in Winter, and help charging the batteries all round. There are 6 x 110 Ah 12V domestic batteries. As a continuously cruising liveaboard with no access to mains power, I trust this kit will go some way towards keeping my batteries alive and topped up.

 

Now I am pondering how to wire everything up, and what type of cable to install...

 

The beauty of having 6 panels is that they can be wired in a number of ways:

 

- All panels in parallell (17V, 27A)

- Three strings of two panels (35V, 14A)

- Two strings of three panels (52V, 9A)

- All panels in series (104V, 4.6A)

 

As discussed in these forums, there are distinct benefits to connecting more panels in series:

 

- Higher voltages and lower amperes will mean less energy lost to heat in the cables, and/or cheaper cables.

- With higher voltages, charging will start earlier in the day and importantly, continue longer into the evening... which is very good for batteries.

 

But there are drawbacks as well – especially, it seems that shade can severely affect the output if the panels are connected in series. My lighting conditions will vary - I guess there is going to be a continuous mix of sun and shade all the time.

 

I am tempted to connect all the panels together in one long series, but have seen advice to step up only two or three times from the battery voltages...

 

Is there any risk at all that one long series could be too much for the controller? I certainly would not want to hurt that baby, but it seems it can handle up to 150V, and 6 x 22V makes only 132V... still leaving some margin (in case of cold and bright weather I guess).

 

Could it be an option to connect the panels differently in Summer and Winter? I suppose it is crucial to get the voltage as high as possible in Winter especially.

 

There is also the question of what cable to get? The panels will be around 10 meters from the controller, so voltage loss in the cables will be an issue. I would think 4mm cable is OK if I go for the highest voltage (104V, 4.6A), but am not sure about the next step down (52V, 9A). Perhaps it can be an idea to lay two sets of cables all the way...effectively, 8mm.

 

Since the controller can handle all the different wiring configurations, it will be tempting to try every option and measure the outcome over several sunny days.

 

Should I just plug the cables from the panels straight into the controller, or is an isolator and/or fuse recommended... especially if I will play around with the wiring?

 

As to connecting the controller to the batteries, there is another 2m distance so probably some thicker cable would be good there. I plan to bypass the main isolator.

 

Sven

[station tug]

I measured the out put on my panels yesterday I had a shadow from one of the guide ropes from the wind turbine...was a very thin line accross the panel...it was costing 25% of the output...

[Arthur Brown]

You need all the current that you can get so I'd wire al the panels in parallel to the controller then on to the battery.

[Chris Pink]

You need all the current that you can get so I'd wire al the panels in parallel to the controller then on to the battery.

 

The MPPT controller takes care of that.

 

The shading is a major issue. If you can deal with that then I would suggest 2 lots of 3, keeps cable losses to a minimum.

 

the advice "but have seen advice to step up only two or three times from the battery voltages:" does not apply to MPPT

[Justme]

 

the advice "but have seen advice to step up only two or three times from the battery voltages:" does not apply to MPPT

 

 

 

Actually it still does. Outback recommend that you only go up by one or two times the bank voltage so that the efficiency is at its max. However it will still be fine going much higher, the efficiency will still be over 90% (cant remember exact number but you will only drop by about 3% from its best). In fact I have 3 strings of 5 panels of a similar spec to those.

 

I do think that your 132v is far to close to the 145v shut down & the 150v release of magic smoke for comfort. In winter when its get down to -20c your array voltage will peak much higher (about 158v ish). I would go for two strings of 3 panels. Fit isolating diodes between each string & the controller so if one is shaded it wont affect the other string.