khalidusman: Sizing breakers for my off grid system

BB.

From Khalidusman:
Hi everyone I need suggestions regarding dc/ac breakers size for my 3.2KW inverter, 24V dc (2*12 each having 230AH capacity), 8 solar panels connected in series (8*450w, Voc 48v, 8amp dc). Total current and voltage of pv is 8.5Adc/366Vdc during day time approximately. Total load of house appliances is almost 2.8Kw. Note: Battery to be used for 900-1000watt load back up only. Kindly recommend breakers size for pv input, battery input, Ac input and inverter output. Thanks in advance 

Welcome to the forum Khalidusman,

I have copied your "comment" from your "wall"... Nobody really watches the walls--You need to created a new discussion (thread) and everyone will see it and have a chance to respond.

I believe you are in Pakistan--So I do not know your electrical code and components vs what we use here in North America.

Looking at your high voltage Solar array--They are all in series (8x 450 Watt panels in series). And your charge controller can take upwards of ~500 or 600 volts Vpanel max input.

Need details about the Vmp/Voc/Imp/Isc (voltage maximum power, voltage open circuit, current maximum power, current short circuit) for the solar panels (and, in theory, the maximum series protection fuse from the panel specifications).

Can you give us a link to the hardware (inverter/charger/solar charger/etc.)?

Also--Regarding your loads--A 1,000 Watts for how many hours per day?

I suggest understanding your loads (Watt*Hours per day), size the battery bank to support those loads (typically 25% discharge for two day, to 50% state of charge --- Or ~4x daily load is nice).

And then there is sizing the array for your battery bank, loads, and hours of sun per day... Something like this:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Sargodha Pakistan
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 58° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.75	5.45	5.77	6.20	6.47	6.22
Jul	Aug	Sep	Oct	Nov	Dec
5.39	5.33	5.55	5.88	5.40	4.73

With circuit breakers and fuses... There are 3 major specifications. The maximum current (like 5,000 Amps dead shorting battery bank), Maximum voltage (around 30 volts for a 24 volt battery bank--Note that AC vs DC voltage ratings are usually different). And the trip current...

In North America, typically our breakers and fuses are designed to trip at 100% current (can be minutes or hours), and not trip at 80% load. For systems that have a long period of steady current (like 5 hours charging a battery bank), I suggest that you take the "working current" such as 50 amps from battery bank @ 24 volts:

• 50 amps * 1/0.80 (or x 1.25) = 62.6 --- Round up to next standard size (70 or 80 amps)

Remember that fuses/breakers are there to protect your wiring from catching fire--So, if you use an 80 amp fuse/breaker, the wiring should be rated for 80 amps too.

-Bill

Dave Angelini

I was hoping it was you Bill that was going offgrid.  I am still saving a 5 acre lot for you below

https://photos.app.goo.gl/5cb1FzLkAa22UGpB8

Most 24v battery banks that are wired correctly (2/0 or 4/0) use a 175 or 250 ADC breaker/disco/

BB.

Very kind of you Dave--My wife has always been a bit of a city girl... However if California gets even crazier (if that is possible), then may be out of state next.

But the reality is that taking care of in-laws, and our kids are here. Will probably just run the clock out.

-Bill

jtdiesel65

What are people using for breakers on the newer 600v controllers? SE has a 600v controller, but it doesn't appear that they make a breaker that is more than 125vdc for their XW panel. The biggest ones I've found from other manufacturers are 300vdc. I think you could conceivably be over 500v on a controller at times, but I can't find breakers that will handle that.

Dave Angelini

Schneider is the preferred maker of high voltage circuit breakers, fused and unfused. They sell them in the store here.
Most people who think about it a bit, would not want 600vdc inside the power distribution panel that has their 48vdc and 120/240. 
Not really a new controller either. It was developed before and field tested here in 2010.

jtdiesel65

OK, I'm confused. The XW manual with wiring diagrams has the pv breakers in the XW power distribution panel. I'm lookin g at:

https://www.solar-electric.com/lib/wind-sun/Conext-XW-Pro-Installation-Guide.pdf

and if I go here

https://www.solar-electric.com/residential/circuit-protection/circuit-breakers.html?manufacturer=56

All I see are 125vdc rated breakers. Are they somewhere else? Does SE not put the pv breakers in the xw panel anymore?

thx

Dave Angelini

The DC breakers from Schneider that one can buy for a PDP or mini PDP are rated at 160 vdc.
Schneider does not put anything in their panels except the 250 amp DC breaker. The installer installs the other breakers. As I wrote above about your question on 600vdc, it does not go in the PDP for obvious reasons, I would think. FRIDAY! 

BB.

Some mfgs will take two or more ganged (common trip) and wire them in series (2x 150 VDC in series = 300 VDC breaker "pack").

https://www.solar-electric.com/midnite-solar-300-volt-30-amp-dc-circuit-breaker-mnedc30-300.html

-Bill

jtdiesel65

I think my confusion is the wiring schematic for the PDP is for the mppt 60 and does not apply to their 600vdc controllers. The 600VDC controllers need an external high voltage  disconnect on the PV side.   Looks like also that SE doesn't spec out a breaker on the PV side, just a safety switch. Page 32+33 of

https://www.solar-electric.com/lib/wind-sun/Conext-MPPT-80-100-Install-Guide.pdf

The charge controller to battery breaker could reside in the PDP even with the 600vdc controllers since they are battery side which is 24v or 48v.

thanks

Dave Angelini

Here is a link to a disco that just about every grid inverter uses. Pretty common and available with fused strings for more than 2 strings.
Schneider training has used this Disco since the 600v controllers came out around 2010.

https://www.solar-electric.com/square-d-600-volt-30-amp-dc-array-disconnect.html

The failure modes and effects analysis with the Schneider 600v controllers have zero chance of getting 600 volts over to the low voltage DC side, if it is wired correctly.  It is in the design choices that were made back in the day.