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Here,

Required backup time for batteries = 3 Hours

Load = 800 Watts

Inverters Rating =?

Required No of Solar Panel =?

No of batteries =?

**→ **As we know the Inverter should be greater then 25% the total load.Now we calculate the total watts required so we have to consider the losses also.

So, 800 x (25/100) = 200

Total load = 800+200 = **1000 Watts**

This is the rating of the Inverter

**→**The required backup time is 3 hours and if we install 12V, 100Ah batteries then the total watts-hour is

=12V * 100Ah

=1200Wh

Backup time for one battery

=1200Wh/800W

=1.5 hour

We required backup time is three hour. so, No. of batteries required=3/1.5=**2**

Our required batteries is 2 having ratings of 12V, 100Ah for 3 hour back-up. You must have to install both the batteries into **parallel connection.**

**If you have batteries and wants to find the backup time then use the below formula:**

Back-up Time = (Total watts-hour * No. of batteries) / Total Load

In our case, Back-up Time= (1200 Wh x 2 Batteries) / 800W = 3 hour

**why batteries are in parallel,not in series?**

If we connect batteries into series connection then current is same and voltage can be found by addition of all voltage into circuit or loop (Vn=V1+V2+V3+…..+Vx). So, if we connect the 2 batteries into the series then voltage will be 24V. Here, you can see the voltage are double but only voltage are double not the capacity of voltage.

Here, we connected two batteries into parallel so the total amp-hour will be 200Ah and voltage will be 12V. As we know that the charging current should be 1/10 of batteries amp-hour. So, Charging current = 200Ah * (1/10) = **20A** and P=VI=12*20=**240W**. This watts are required for solar panels to supply the our load.

Let’s Suppose you have 60W solar panel then,

No. of solar panels required = 240/60 =4

So, **4 solar panels are required having 60W, 12V and 5A ratings.**

Total power required (P) = VI = 12 * 30= 360W

The number of 60W solar panels are required is, 360/60W = 6. Therefore you have to connect **6** **solar panels are required having 60W, 12V and 5A ratings.**

This is circuit diagram of above example and calculation |

Here, the charging current for battery is 20A and 10A is required by direct DC load. So, we need to install charger controller having rating about 30A-32A.