Designing a Hybrid or Off-Grid PV System

Before Start first thing you need to know is that how much load you will run on the PV system. A load is

any piece of electrical equipment people want to use in their homes and offices. When sizing a battery-

based system, you need to establish exactly what loads you want to run .This information serves as the

basis for all of your other calculations throughout the design process.

To calculating the loads of each item use the following formula:

Energy (in watt-hours) = (Watts Hours per day Days per week) 7 days per week

After calculating the watt-hour of an individual device next add all those watt-hours together to

calculate the total watt-hour which will run on the PV system.

For Example

Now after determining the total load you want to run on PV system the next thing you need to

determine is the size of battery you require for storing the power.

Batteries store the electrical energy generated by the modules during sunny periods, and deliver it

whenever the modules cannot supply power.

Normally, batteries are discharged during the night or cloudy weather. But if the load exceeds the array

output during the day, the batteries can supplement the energy supplied by the modules.

The interval which includes one

Ideally, the batteries are recharged to 100% capacity during the charging phase of each cycle. The

batteries must not be completely discharged during each cycle. No single component in a photovoltaic

system is more affected by the size and usage of the load than storage batteries.

To calculate the battery bank you require use the following procedure below

Determine the average daily AC watt-hours (or kilowatt-hours) consumption level. (this is

explained above)

Divide the watt-hours value from Step 1 by the 0.9 which is estimated inverter efficiency

Multiply the energy value from Step 2 by the desired days of autonomy which is around 2 days

for off grid system while for hybrid system 1 day is enough

Divide the value calculated in Step 3 by the temperature compensation value provided by the

battery manufacturer which around 0.9 for most battery manufacturers.

Divide the value from Step 4 by the allowable depth of discharge which is 0.5 for normal battery

and 0.8 for deep cycle battery

Divide the value from Step 5 by your desired nominal voltage for the battery bank mostly either

12 volt or 24 volt

Total Amp Hour of battery = Total Watt Hours (0.9 x depth of discharge x nominal

voltage of batteries)

The answer you get from the above procedure is the total Ampere Hour of Battery Backup you

require.

Now next thing is to calculate how much solar panels you require for that use the following formula:

Total Watts of Panels required = (Total Watt Hours Total Sunlight Hours Available)

x 1.3

To calculate the size of charge controller you require divide the total watts of your Solar Panels with

the amount voltage they are producing.

Size of Charge Controller (Amp Hours) = Total Watts of Panels x VOC (Open Circuit

Voltage)

You can check for open circuit voltage either by looking at specification of the solar panel or by

calculating it through a volt meter

As for Inverter or UPS neither uses a UPS/Inverter which is below your total load in Watts nor buy a

UPS which is above your total load in Watts.