The norm is to put your panels facing north, but the other way to do it is to install your strings East/West. If you have limited north facing roof I would suggest you look at the east/west option.
I have 2 strings facing north on one MPPT, and then 1 string east and 1 string west on another MPPT and to tell you the truth if I had to redo my setup I would do them all east/west. You have more power for longer duration in the day.
Here is a thread with more information about it. Solar panel direction East/West vs North
You can over spec your system on current (I suggest not more than 20% extra), but not on voltages. Although the Victron MPPTs will protect itself for over current AND over voltage, the overvoltage is not recommended. Overvoltage will shut down the MPPT (think no solar power), while overcurrent will just limit the production but you still get power.
Something else to remember is that the current limit from your MPPT is on the battery output which is not the same as the PV current.
The PV panel will run at 84V and produce the 10.85A or 911.4W. (84V x 10.85A)
Your MPPT will charge your batteries to 54V using 16.88A (911.4W / 54V)
For 4 strings this gives you 67A output
If you use the 150/60 that output will be clamped to 60A so you loose 7A.
But then remember this is all peak theory. In practice your panels are heated during the middle of the day, or that one small cloud decide to come hover over your panels for most of the day. For this reason I would rather add more panels that will give more current sooner that gets clamped at it’s peak.
That is true, but the Victron controllers also have a maximum current that it can handle on the PV side. If it needs to clamp the PV voltage down (for example, in an overvoltage situation), the full short circuit current from the modules runs through one of the FETs in the MPPT, and for the 150/60 that limits the maximum PV-side current to 50A.
That is one reason you usually want to push the voltage up, because that allows you to oversize a bit more comfortably. So a 3x3 array (usually running around 120V-130V during the day) would technically be the better option if you could be certain that you’d never get a super-cold morning.
Trina made a “smart” panel at one point – I wonder if they still do – that includes a clamp on the panel itself. For these panels, there is a maximum voltage that is not dependent on the temperature. On a cold morning the electronics on the panel itself clamps it to a safe voltage. With these on the roof, you could go 3-wide without worrying…
On my sketch you will see I am planning a east and west array but thought north is a good start and will give me the most benefit immediately. East and West will be in the future
Muldersdrift can get pretty cold and we regularly had -3 last winter so think I’m going to be cautious and rather not take my voltage too close to the Mppt max
That was my thought exactly. But what I saw afterword is that the East facing get sun about 1 hour before the north string, and the west still gets sun 1 hour after the north facing string. So house has power for 2 extra hours just from the east/west.
But you can’t go wrong either way.
I need to buy my battery and inverter cables and I see the manual states 70mm2 but that is serious overkill for the short distance I have to run. Technically 25mm2 can handle more than enough and 35mm2 will do it comfortably. I measured about 1,5m from furthest battery to busbar and about 0.5m from inverter to bus bar. I have double pole 125A breakers for battery cables and 125A fuse for positive to inverter. I am putting in 30x10mm busbar with 8mm threaded holes. Any comments please?
When I had a DC Ripple, the first thing everyone asked: What is the return length of the cable, and what is the mm2?
My thoughts are, why skimp on a couple of rands on 4m of cable when one can do it right one time and forget about the cable for the next decade or more?
I also use 125amp fuses on my 5kva, 1) as protection for the BMS AND 2) I don’t ever want more than 125amps pulled from the batteries, like in never.
Yes that is the table I am referring too. I also decided on the 125A for the same reason as you.
I get your point, but the 70mm to fit in the breaker is going to be a real squeeze, maybe I should not have got the breakers and should have fused the batteries instead.
Ran into same problem … so I got these fuse holders, problem sorted. Am fusing Pos and Neg. EDIT: Idea I have, must still do that, is to use the 3rd fuse for the MPPT …
Must also say that my batteries are on wheels, easier to work in the space, so the 70mm2 cable I got from Jaco is coming in very nicely for me, to move the batts out of the way.
Thanks for the reply, think Im just going to get the 70mm cable and if it doesn’t fit breaker go the same route with the fuse disconnector. I have two batteries so need to double up my cables to bus bar so need about 8m with bit to spare.
The idea of the super thick cable is to get a nice low voltage drop at full power (preferably under 1%). Regulations allow up to 3% (if I recall?), so that is the reason why most lookup tables will tell you 35 is fine even though the inverter-maker advises 70.
I run 50mm^2 on my 24V 3kVA, so I see no reason why that would not be sufficient for a 5kVA 48V unit. But if you can find 70, and there are no other technical reasons not to use it… use it!
I see some discussion about how well east and west facing panels perform. East and West facing panels will outperform North facing panels in summer but not in winter and around the equinox I doubt that E and W panels will out perform North facing panels.
It is all very well and good to speak of best performance but we don’t all have the choices. Sometimes we just have to make do with what we have. I have a huge development occurring next door that practically shades out my north facing roof in the winter. I therefore can’t benefit from a north facing array when I need it most, in the depths of winter.
So I managed to connect the batteries to my Octo, needed to make a cable up with pins 345 on battery input, going to ve.can 378 pins.
Between batteries is just a standard network cable and you need to change dip switches so it picks up two in parallel one master and one slave
Had to first figure out that you need to change the ve.can settings on the Octo to (can-bus BMS)
Only after that did it pick up the batteries and all settings are already set and all values come up ect
I don’t think EW ever outperforms N, but panels are much cheaper than batteries, so EW combinations are more efficient because you need less batteries. You’ll still need more panels overall.
So if you are putting 18 panels up, it might be better overall to put 6E, 6N and 6W than 18N because you will need more batteries with 18N to make it effective.
Personally for me 6N and 12W works quite well, but I don’t really have an E facing roof (it is EESE, my W roof is really WWNW).
Got my panels, Canadian solar 435w.
Decided to buy now as stock of solar items are either becoming scarce or very expensive. Put them on a shelf at work to rest before they get put to work in the next month or two.
Got my busbar connected to the inverter. 100x40 trunking fits in perfectly under the cover of the inverter.
Don’t have my fuse switches yet for my batteries so will have to wait. Tomorrow hopefully wiring inverter to db boards.
