Need some help with safety components

joker55 · July 2017

Hi, I'm in the process of buying a solar system (DIY) and could really use some advice.

I live in Africa (Malawi), and we have very little choice of components available. Ive tried my best to get the main parts together, which are:
6 x 300w 24v mono panels
4 x 200AH 12v AGM batteries
MPP Solar PIP 2424 MSD 2400w 24v Inverter and Dual MPPT Charger (40A each)

Ive had to settel for these components for lack of choice, and importing being a little too expensive out here.

What i need help with is 2 things:

Firtsly, the wiring of solar panels to inverter: I was thinking of doing 3 parallel 300w panels to each MPPT charger, so 900w @24v to each of the 2 MPPT 40A chargers. How would i wire this? What components would i need to join each 3 panels to each charger?

Secondly, I need suggestions on safety of wiring, so fuses/breakers/disconnects? Where in the system to put them and what size (Amps/Volts)? Wire sizes?

Basically need to buy the rest of the components apart from the main bits. I can purchase the wiring from here, but all fuses/breakers/disconnects I will need to order from the UK. Bearing in mind I am in Africa with very little law requirements regarding the safety of the system, so I would need the very minimal components in order to protect the system.

I would be extremely grateful for any help, also if you could link relevant products i can buy from an online uk retailer would be very helpful. I have a relative visiting us in about 10 days time and they could buy and bring it over for us, so a little constrained with time.

All help is much appreciated.

mcgivor · July 2017

The inverter charger appears to be a grid tied unit, is this correct, you posted in off grid, is why I ask....more later

mcgivor · July 2017

Or is this the one you have?
Please include the panel specifications on back of panels, VOC, IMP, VMP etcetera. Without details suggestions would be based on speculation. Also include the charge controller specifications, maximum input voltage and so forth.

http://vi.vipr.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=142068867332&t=1490082836000&tid=10&category=41980&seller=maximum_solar&excSoj=1&excTrk=1&lsite=0&ittenable=false&domain=ebay.com&descgauge=1&cspheader=1

joker55 · July 2017

Evening,

Thanks for the interest

The inverter is not grid tied no, it does not feed back to the grid, but what it does have is the option of having the grid as a backup tho, so can charge the batteries from grid should you wish, one of the reasons I chose it as that would be a benificial feature here in Africa.

So yes the system is not going to be entirely off-grid, but rather a backup system during blackouts which occur all too frequently.

Panel specs:
Max Power - 300w
Voc - 45.5V
Isc - 8.64A
Vmp - 36.9V
Imp - 8.14A

The link to the inverter is below (2nd one in the spec table):

http://www.ebay.co.uk/itm/Solar-inverter-3kva-2400W-24V-with-80A-mppt-solar-charger-60a-battery-charger-/321952098522

Again, thanks a bunch for any and all help, very much appreciated.

Estragon · July 2017

Wiring the panels will be connecting each string of three by connecting from positive on one panel to negative on the next, leaving you with one positive and one negative mc4 per string. Typically you would get an mc4 (8-10ga) cable for each string twice the length needed to reach a breaker box. The cable is the cut in half, leaving a male connector on one, and a female on the other. Note that if you go with the controller and panels listed, strings of 3 won't work as the controller only works up to 80v and may be damaged at over 100v.

The positive leads of each string are wired to a DC rated breaker in the box. Maximum size should be specified by the panel maker. 15a is typical. The negative leads go to a buss bar in the box or directly to controller.. Strictly speaking, you could skip these breakers and go directly to the controllers with just two strings, but they make handy disconnects. With more than two strings, they're required. Midnite "baby" boxes are useful for this.

The output breaker size from the controller should be specified in the manual. I would use the heaviest wire that fits in the controller. Likewise, breaker size for the inverter (if you end up with separarate unit) should be in the manual, and again I would use the heaviest cable that fits. These breakers are not optional.

For wring batteries I would use at least 2/0 or even 4/0

joker55 · July 2017

Thanks for your reply.

The max Voc for the charge controller is 100V with the MPPT range being 30-80V, hence why I wanted to put each 3 panels in paralell to keep at 24V (Voc45.5) and 900w. Three panels in paralell would mean 37.5Amps if i calculate correctly, so does that mean i need a 40Amp breaker?
Would I connect them positive to positive and negative to negative? Or do I need to connect the 3 panels through a combiner and fuse each panel? This is where it gets difficult for me and trying to figure out my fusing/breaker needs and combiner box and such.
The panels are Amerisolar mono panels, Made in China but giving the impression it is a US company. Again, its the best i could find here.

Had a look on ebay uk for midnite stuff.....found nothing unfortunately.

When u say charger breaker, u mean from panel to CC or CC>Batteries?
Inverter breaker is Battery>Inverter or Inverter>AC board?

Thanks for the help

Estragon · July 2017

Sorry, I misread it as strings of 3. With 3 strings of 2 panels each, Voc would be 91v. I assume you're in a warm climate (voltage gets higher in the cold), so you should stay under the 100v limit. It might still be a problem though in that if the voltage is >80v when the sun comes up, the controller won't charge. Mvp is okay, but that's only if the controller has the charging load. If you can find the lowest expected low temp for your area, and the temp coefficients for the panels, you could work out how much of a problem this might be.

With 3 strings in parallel, each should have a breaker in a combiner box, and a larger wire and breaker from combiner box to controller. You would wire panels 2 in series by connecting + to -, and the the parallel (+ to +) in the combiner box. You could do it the other way around (parallel at the panels) but it usually ends up costing more for larger wire to carry the low voltage/higher current. If the array will be really close to the controller, it might be okay.

joker55 · July 2017

The charger/inverter is a dual 40A MPPT and has dual input (40A each). So my plan is 3 panels in parallel on 1 input and 3 parallel on 2nd input

So Voc would still be of single panel. Thanks

Estragon · July 2017

That should work. You'll want to use a voltage drop calculator to figure out wire size needed for the distance involved at the combined current for each parallel inputs to the controller and size breakers accordingly.

Need some help with safety components

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