Solar Setup Help!

dspizzle · May 2018

Hello, I was recommended here to get some feedback from a different forum.

I believe this setup will work well for me. My main question is wire sizing. Am I heading in the right direction?

Thank you,
Dustin

Image: https://us.v-cdn.net/6024911/uploads/editor/gn/r5sejmddlvnc.jpg

mcgivor · May 2018

Can more details of the inverter be supplied, having a shore power input would mean an inverter charger with an internal transfer switch, what wattage is the inverter and what is the component at the bottom feeding off the DC bus ? Inverter appears to be an Aims product, yes/no? Your 4 panels in series exceeds the voltage input of the controller, 16 AWG is too marginal a gauge from the panels to the controller. Having 3 strings of batteries requires careful arrangement of conductors to ballance charge /discharge, the use of a circuit breaker would be advantageous in leu of a fuse in both locations, to provide a means of disconnect. Just a few observations and questions and first post, welcome aboard.

littleharbor2 · May 2018

You're pushing the max Voc. Actually with a 12 volt system your voltage IS too high. You should wire your array 2s2p. Your voltage will be at a good level for the MPPT controller to do its thing and not run hot by stepping down the voltage so much. You still don't need fusing on the array to controller wiring. That being said, it is nice to have breakers between the array and controller as well as between the controller and battery bank. This allows you control in doing maintenance or troubleshooting of the system.

Image: https://us.v-cdn.net/6024911/uploads/editor/iz/k5pb0ovlxqqd.jpg

Estragon · May 2018

I'd use an MC4 cable (usually 10ga?) for the pv to controller, mainly because it's an easy way to make a weather resistant connection to the MC4 connectors at the ends of the series array. I'd put a breaker on the circuit, if only for a handy disconnect.

The fusing for controller and inverter should be as recommended by manufacturers. I'd use breakers though, as they make handy dissconnects, don't need spare fuses to reset, and aren't much different in cost considering holders and spare fuses.

With 3 parallel strings of batteries, you should fuse each string. If space allows, a better configuration would be a single or at most 2 strings of larger batteries.

As well as knowing loads on the ac and dc load centers, you may want to check on the maximum wire size that will physically fit on the dc terminals of the dc panel and inverter. For the Classic controller, 4ga is max (4ga finely stranded is really tight and needs to be trimmed a bit to fit).

Have you run the panel through Midnite's string sizing tool? It seems to me the 150 is limited to 162v max with 12v nominal bank voltage, and a cold morning might put you over. A classic 200 would give you more headroom there, or alternatively 2 strings of 2 panels in parallel configuration.

littleharbor2 · May 2018

Need to ad, If you go the breaker route you need DC rated breakers. The ones shown are Square D QO breakers. They are ok for a 12 volt system. There are Square D QOU breakers which will work for 12/24/48 volt systems. If in doubt just use Midnite Solar or Outback DC rated breakers. They are good up to 150 volts.

https://www.solar-electric.com/obdc-100.html

https://www.solar-electric.com/mnepv.html

mcgivor · May 2018

Another look at the image, the panels should be fused, being 24V nominal panels, they could be utilized in parallel, in which case a combiner with breakers for each panel would be preferable, operating at a voltage significantly higher than nominal with MPPT results in higher losses, approximately double nominal voltage is the best in most applications.

BB. · May 2018

What AC Watt rated inverter? Sine Wave?

More or less, with a 12 volt battery bank, a 1,200 to ~1,800 Watt AC inverter is the "workable" maximum size. Voltage drop with high current devices and 12 volt battery banks is a real pain. 4/0 cable is very large diameter and expensive. Difficult to terminate (bigger than holes in bus bars/binding screw assemblies). More or less, you want 0.5 volt or less voltage drop (short heavy cables) from your battery bank to the AC inverter.

For your 660 AH battery bank, for flooded cell lead acid batteries, you want a maximum of ~1.65 kWatt (1,650 Watt) rated AC inverter (and max typical solar array wattage--Basically 250 Watt AC inverter for every 100 AH of 12 volt battery bank)--Larger than that (and larger loads), is really more current/energy than the battery bank is capable of supplying.

Also, large inverters tend to take a fair amount of Watts just to "turn on". Possibly 20-40 Watts of "Tare Losses". If you are running the system 24x7 hours per day--That can be a lots of wasted energy. Possibly a second inverter to run small loads 24x7 (Laptop computer, LED lighting, cell phone charging, etc.). A 300 Watt MorningStar 12 VDC input Pure Sine Wave inverter takes 6 Watts Tare, and has a "standby mode" where it will check for >6 Watt loads every second, and turn on when an AC load is present.

-Bill

mike95490 · May 2018

Your panels Voc at dawn is 160Vdc - which will put the controller into hypervoltage mode, for some time, till the panels warm up and voltage drops below 150V.

Solar Setup Help!

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