HOW TO CALCULATE PV ARRAY SIZE FOR A BUILDING?

HOW TO CALCULATE PV ARRAY SIZE FOR A BUILDING?

PV array or Photovoltiac array is the heart of any solar plant. PV Array is a group of solar modules which are connected with each other to produce the electrical energy from the sunlight. The output of the PV array is DC which is converted into AC using invertors.

The Size of the PV Array for a particular solar plant is calculated by following steps:

 

1. DETERMINE THE AVERAGE DAILY CONSUMPTION

The first step for calculating the PV Array size is, calculating the average daily consumption. The average daily consumption is the measure of total power consumed by the all the loads of particular location by period of one day. The consumption is measured in kWh or Wh.

EXAMPLE: Lets take an example of residential building. Suppose the average daily consumption of a house in 2kWh or 2000Wh.

For more details, the load is given following:

Consumption

2. DIVIDE THE AVERAGE DAILY CONSUMPTION WITH  INVERTER EFFICIENCY

The second step to calculate PV Array size is to divide the average daily consumption with inverter efficiency. Inverter is a device which convert DC into AC. In the household, most of the loads are works on AC supply. That is the reason why inverters are used. They take DC power from batteries and convert it into AC supply. There are different types of inverters which have different different efficiencies. The efficiency of an inverter is written in its specsheet and on nameplate also.

EXAMPLE: Suppose the efficiency of an inverter is 90%.

Thus,

Average daily consumption/ Inverter efficiency

= 2000Wh/ 0.9

= 2222.22 Wh

3. ADD DAILY ENERGY CONSUMPTION FROM DC LOADS

The third step is to add the energy consumption from all the DC loads in Step 2. Most of the load in household is AC but sometimes there are loads in house which work on DC Supply. No doubt, the value of DC load in house is very less as compared to AC load, but we should consider all type of load for calculating the PV Array size.

EXAMPLE: Suppose the energy consumption from DC load is 120Wh

Thus,

Total daily energy consumption = 2222.22 + 120 = 2342.22Wh = 2.342kWh

4. MULTIPLY ESTIMATED EFFICIENCY OF A BATTERY AND PV ARRAY

Efficiency is the ratio of output over input. Battery and PV array have different efficiency. In this step, the average efficiency is calculated by multiplying the efficiency of battery and PV array.

EXAMPLE: Suppose the efficiency of battery is 85% and the efficiency of PV array is 75%.

Thus,

Average Efficiency = Battery Efficiency * PV Array Efficiency

Average Efficiency = 0.85 * 0.75

Average Efficiency = 0.6375 = 63.75%

5. MULTIPLY AVERAGE EFFICIENCY WITH TOTAL SOLAR RESOURCE FACTOR

The fifth step is to multiply average efficiency obtained in step 4 with TSRF( Total Solar Resource Factor). TSRF is a product of Shading Factor and Tilt & Orientation Factor. TSRF provides a more complete picture of how much solar energy will be available for the solar panels to convert into electricity. This is because it takes into account both the percentage of available solar energy at a site given shading and how much of that energy will reach the surface where solar panels will be mounted given its tilt and orientation (TOF).

EXAMPLE: Suppose the value of TSRF is 0.9

Thus,

= 0.6375 * 0.9

= 0.5737

6. DIVIDE THE TOTAL DAILY ENERGY CONSUMPTION VALUE WITH THE TOTAL EFFICIENCY VALUE

In sixth step, the total daily energy consumption value obtained in step 3 is divided by the value obtained in step 5.

EXAMPLE:

= 2.342kWh/ 0.5737

= 4.082kWh

7. DIVIDE ENERGY VALUE WITH PEAK SUN HOURS

In this step, the energy value obtained in step 6 is divided with the Peak Sun Hours. The term “Peak Sun Hours” refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours. Since the peak solar radiation is 1 kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation.

EXAMPLE: Suppose the value of peak sun hours for particular location is 4 Hours.

Thus,

= 4.082kWh/ 4 hours

= 1.020 kW

= 1020 Watts

So, The Size of a PV array needed in in this example is 1020 Watts.

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