System advice

lightsky

Inverter: 1.5KVA 12v low frequency inverter(220v output)
Battery: 1* 220Ah, 12v (Tubular battery)
My total load: 300 watt

My expectations: i would like to have a full time offgrid operation with little generator or national grid use.

I'm currently considering buying 2* 400watt panels connected in parallel with an MPPT charge controller.

MichaelK

Ultimately, I seriously doubt that you'll have full-time off-grid operation utilizing only 300W.  Honestly, you really can't expect 300W to power much of anything besides a few lights and a small TV.

For full-time off-grid living, I'd start with at least a 24V system, four 220Ah batteries, and four of those 400W panels.  With this, you could power a refrigerator, lights, TV, an electric fan, and most of the other items we like for 20th century living.

If you ever want air-conditioning, then double everything you see in paragraph two.

Photowhit

lightsky said:

Inverter: 1.5KVA 12v low frequency inverter(220v output)

My total load: 300 watt

Could you define your load a bit better? We need to get a time element.

Do you have a 300 watt load 24/7, or is it a total 300 watt hours?
Do you know how much energy your inverter uses by it's self?

lightsky

Thanks for your comments.
My load:
2* 45 watt Rechargeable fans @ 3 hours per day
4* 3 watt LED bulb @ 3hours per day
1* 42 watt LED TV 32inches @ 4hours per day
1* 50 watt laptop @ 2hours per day
2* Mobile Phones 10watt @ 2hours per day
And hoping to add 67watt refrigerator after installing PVs to run 5 hours during the day. 
I am not sure of the inverter self consumption.

Photowhit

So a daily load of;
90x3= 270 watt hours
12x3=  36 watt hours
42x4=168 watt hours
50x2= 100 watt hours
20x2= 40 watt hours
------------------------------
So @614 watt hours divided by inverter efficiency I'll use 85% -- 615/.85=724 watt hours plus idle use of inverter likely around 20 watts x 24= 480 watts. It might have a sleep mode which would use very little, but roughly...

Now where do you live and can you setup your array for optimal solar production, or will you have some shading during the day or have to angle your panels with your roof line or other constraint?

lightsky

@Photowhit Southern Nigeria is my location, there is no shading.

Photowhit

lightsky said:

@Photowhit Southern Nigeria is my location, there is no shading.

The nearest weather data, I could find was from ACCRA/KOTOKA INTL, GHANA, using PVWatts link below. Not sure how similar your weather will be;

https://pvwatts.nrel.gov/

Looks like you're 6 degrees above the equator, so I ran the numbers for an array facing south angled at 15 degrees (better for natural water run off, You might want an even steeper angle to make cleaning them easier...

So roughly the number of hours of direct sunlight will correspond to the chart below;

Generally You would want a system able to to supply the 724 watt hours daily load plus the inverter use, another 300-600 watthours.
I'm going to use 1000 watt hours total. In general you would want to stay in the upper 20% of the battery storage for daily use and no more than 50% after a couple days of rainy/overcast weather. Looks like you have pretty good daylight through out the year. I'd say you would be safe with 1000 watt hours of storage to 20% of a flooded lead acid battery bank. so you would need roughly a 5,000 watthour battery bank.

You say you have a single 12 volt 220ah battery. So basics are Amps x Volts = Watts 12V x 220ah= 2640 watt hours of storage.

So I would suggest if you would like to go without running a generator you would want 2 of those batteries.

So you would want a solar array that would be able to bring the battery bank back from 50% discharge to near full in a day of sunny weather. So there are also losses when charging a Flooded Lead Acid (FLA) Battery. Figure 15-20% just in the voltage difference when charging. A 12 volt nominal battery, which is full at roughly 12.7 volts will charge at 14.5-14.8 volts. The current will be roughly even, but you need the higher voltage to get the current flowing...

Solar panels have a name plate rating. These ratings are based on Standard Test Conditions (STC). In the real world they will produce less. Some now come with Normal Operating Cell Temperature values (NOCT) They are generally about 75% of the name plate.

These means you can expect about 75 watts out of a 100 watt panel. This is what you can expect when the panels are warm/hot. You may approach Standard Test Conditions(STC), in very cold fall days with good direct sun, but it will be rare.

So an array to recharge half of a 5000 watthour battery bank with a 4 hour sunny day would be roughly.
2500 watthours/4 = 625 watts per hour. 
625 x 1.2 for the battery charging inefficiencies = 750 watts
750 watts needed vs NOCT to STC would bring me to about 1000 watts of solar array at their label rating.

Hopefully this will help you design your system.  If this was for daytime use, with little energy coming from the battery, a clinic or school, you might be able to get by with a smaller system since much of the energy will come largely off the array, without the battery charging losses. 

You will want a MPPT type charge controller to maintain the charging parameters for charging the battery bank.

lightsky

I am grateful @Photowhit great information to work with.