off grid design

[Geopart]

hello, i trying to design an off grid pv system for a telecoms off grid bts with battery back up.I would like to know if my calculations are in order

My system voltage will be 48v and my total electrical load is 2.7kw, assuming the pv will supply for 10 hrs, it will mean a load of 27kwh.

battery capacity for a 24 hours backup
2.7kw x 24hrs =64.8kwh. PSH=5, Batt efficiency=0.85, and cycle discharge =0.5. therefore Ah rating =64.8k/(48x0.5x0.85)= 3,200Ah

solar panel data
250Wp, Vmp=31,Voc=37.9 Isc=8.76, Imp=8.07,

Therefore number of panels in series= 48/31= 2 approx
load current= 64.8Kwh/(48x0.8x5) =338A
Therefore number of pv panels in parallel = 338/8.76=39 panels
total panels = 39x2 =78
array size = 250x78=19.5Kwp

[Mike90250]

Whoa.
Ain't going to happen with existing tech, in any affordable manner. You gots to learn the maths first
> load current= 64.8Kwh/(48x0.8x5) =338A
or is it :
> for 10 hrs, it will mean a load of 27kwh.

and what is "array size = 250x78=19.5Kwp"

If you want us to do your homework, you have to use conventional terms.
You have left out the many solar charge controllers needed to convert the PV voltage to battery charging voltage.

> assuming the pv will supply for 10 hrs
Not on planet earth, won't happen. You might get 5 or 6 hours of production at the equator. Morning sun and evening sun go through too much atmospheric soup to be useful. Your prime solar hours are 9am - 3pm

[Geopart]

The total load to be supplied is 2.7Kw and the location is close to the equator with minimum peak solar hour of about 5.
I want to design a solar system with 48V dc system voltage and a battery backup for 24 hours, so my battery will supply 2.7kw x 24 hours =64.8kwh.

with a 50% depth of discharge and 85% efficiency, my battery amp hour rating will be 64.8Kwh/(48x0.85X0.5)= 3200Ah

solar panel data
250Wp, Vmp=31,Voc=37.9 Isc=8.76, Imp=8.07

number of panels in series= 48 v/ 37.9 = 2
current supplied by the battery banks = 64.8Kwh/(48x0.8x5) = 337.5A
current in one panel = 338/8.76= 39A,
Does this mean i would require 39 panels in parallel??
making a total of 2x39=78 panels

for the charge controller, considering a 25% safety factor, current rating will be 1.25x8.76x39= 427.05A

Thanks

[SunEagle]

The total load to be supplied is 2.7Kw and the location is close to the equator with minimum peak solar hour of about 5.
I want to design a solar system with 48V dc system voltage and a battery backup for 24 hours, so my battery will supply 2.7kw x 24 hours =64.8kwh.

with a 50% depth of discharge and 85% efficiency, my battery amp hour rating will be 64.8Kwh/(48x0.85X0.5)= 3200Ah

solar panel data
250Wp, Vmp=31,Voc=37.9 Isc=8.76, Imp=8.07

number of panels in series= 48 v/ 37.9 = 2
current supplied by the battery banks = 64.8Kwh/(48x0.8x5) = 337.5A
current in one panel = 338/8.76= 39A,
Does this mean i would require 39 panels in parallel??
making a total of 2x39=78 panels

for the charge controller, considering a 25% safety factor, current rating will be 1.25x8.76x39= 427.05A

Thanks

With a system that large you would be using MPPT Type charge controllers. A simple way to size that CC is to divide the total panel wattage by the battery system voltage.

So for a 3200Ah 48v battery system you will need around 320 amp of charging power or 320a x 48v = 15.4kw of panels.With 62 of those 250 watt panels you get 15.5kw total.

Working backward that 15.5kw system will yield ~ 323 amps (15.5kw / 48v = 323amps). That would require 4 x 80amp CC's. Which would require each to have 15 to 16 of those 250 watt panels wired to it. Depending on the max DC voltage input they would probably be set up as 4 sets of 4 wired in series / parallel.

All that can be done but I am worried about how you plan on creating that 3200Ah 48volt battery system. That is huge and would require both environmental permits and toxic waste approvals.