24v Dual solar panel connection

[rhinotwenty]

Hi, i have 2 banks of 24v batterys,(connected in parallel) to an isolation switch fed by 2 banks of solar panels.

Solar panel bank 1, has 2 x 80w monocrystalline panels,approx 4.5A maxoutput.

solar panel bank 2 has 2 x100w polycrystalline panels,approx 6A max output.

 

? if i connect both solar panel banks to a junction box, then run a feed from the junction box to a 20A mppt controller,will the mppt controller be sending approx 10.5A to the batteries via the isolation switch ?

 

Tia

[smileypete]

Hi and welcome to the forum

 

If both solar panel banks have the panels connected in series, and the panel output voltage Vmp is the same for the panels in either bank it should be fine.

 

Usually the label on the back states Vmp or a google search on the panels model number will turn it up.It's normally around 18V or 36V though not always!

 

The 20A MPPT should handle 360W of panels going into a 24V batt bank no problem, the MPPT will send up to around 14 amps. The MPPT cabling must be protected by an appropriate value fuse in the positive at the battery end though.

 

cheers, Pete.

~smpt~

[rhinotwenty]

Thanks Pete, each pair is in series(24v) for the polychrystaline pair the vmp is 17.3 per panel(voc 20.6v) x2. & the vmp on the mono pair is 18v per panel(voc 22.25). x2.

 

Would an mppt controller just see the combined voltages from both sets of panels,ie (34.6 +36=70.6) as 1input , which it would be as its only being fed by 1pr of cables from the junction box ?

 

I already have a 10A pwm controller,would i be better off just buying another pwm controller for the second solar bank,then connecting the feeds to the battery banks isolater switch?

 

By the way this is a great forum,& non of the usual yanks spouting nonsense.

Edited November 6, 2013 by rhinotwenty

[Boaty Jo]

By the way this is a great forum,& non of the usual yanks spouting nonsense.

 

Stick around kid

[smileypete]

Thanks Pete, each pair is in series(24v) for the polychrystaline pair the vmp is 17.3 per panel(voc 20.6v) x2. & the vmp on the mono pair is 18v per panel(voc 22.25). x2.

 

Would an mppt controller just see the combined voltages from both sets of panels,ie (34.6 +36=70.6) as 1input , which it would be as its only being fed by 1pr of cables from the junction box ?

 

I already have a 10A pwm controller,would i be better off just buying another pwm controller for the second solar bank,then connecting the feeds to the battery banks isolater switch?

 

By the way this is a great forum,& non of the usual yanks spouting nonsense.

 

The best way to connect would be the two 80W in series, and the two 100W in series, then connect the two series pairs together in parallel at the junction box, then two wires from the junction box to MPPT, something like:

 

 

 

 

If the panels have standard MC4 connectors then there are MC4 splitters that would allow parallel connection without needing a junction box, like:

 

 

http://www.ebay.co.uk/itm/Solar-Panel-MC4-T-Branch-Connectors-Cable-Splitter-Coupler-Combiner-USA-Ship-/251364785066

 

Having 2 mono panels and 2 poly panels in parallel might not be the perfect match if they have different voltage/current curves, should be OK.

 

MPPT will give better performance over a wide range of conditions, though in high temperatures with fairly full batts in your case there won't be much difference with PWM.

 

Maybe just buy a 20A MPPT and keep the 10A PWM, might be handy say as a backup or for keeping a start battery topped up.

 

The EP Solar/Tracer MPPTs seem to get good feedback around here, the 20A ones are quite cheap too if bought direct from Asia. Buy do avoid the el cheapo MPPTs because some of them aren't really MPPTs and are in fact cheap PWMs!

 

cheers, Pete.

~smpt~

Edited November 7, 2013 by smileypete