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How to select a solar system / wind turbine

One of the most confusing issues in the mind of most people is “How do I select the right size of a solar system or a wind turbine?”  We often receive calls from people who need help and guidance on this matter.

In order to make it easier, we are outlining a simple guideline which will help you in calculating your requirements and to select the most optimum system for your application.

The first step is to determine the electrical load for your facility. Most of us are users and are never bothered about what is the load.  All we know is the utility company bill that we pay monthly. It indicates the “units” consumed (i.e. kilowatt-hours or KWh) and the total amount to be paid. But it does not really show the electrical load of your home, office, factory, farm, etc.

The ideal method for calculation of the load is to use an ampere meter to know the no. of amperes being consumed by each load item.  You can get your electrician to do this measurement. An electrician would normally have his own ampere meter to do this work.

However, in order to get a rough estimation of the total load, you can also list down each item that is using electricity in the facility as follows and come up with your estimated total power peak load:

Item

No. of watts for each

Quantity

Total no. of watts

Lights

10W

 

 

Lights

20W

 

 

Lights

40W

 

 

Lights

60W

 

 

Lights

80W

 

 

Lights

100W

 

 

Lights

Other

 

 

Fans

40W

 

 

Fans

60W

 

 

Fans

80W

 

 

Refrigerator

See note 1 below

 

 

Deep Freezer

See note 1 below

 

 

TV

See note 1 below

 

 

Computer

See note 1 below

 

 

Iron

See note 1 below

 

 

Washing Machine

See note 1 below

 

 

Clothes Dryer

See note 1 below

 

 

Microwave Oven

See note 1 below

 

 

Small Appliances

See note 2 below

 

 

Air conditioners

See note 3 below

 

 

Pumps

See note 4 below

 

 

Motors

See note 4 below

 

 

Industrial machines

See note 5 below

 

 

Notes:

1. You can check the no. of Watts (W) printed on a label that you can find on the back of or inside the appliance.

2. Small Appliances: You may take a rough total of all the small appliances in your use.  Most of these will consume very little power. You may even ignore the very small loads like mobile phone chargers, etc.

3. Air conditioners:  Most air conditioners are inefficient and consume more power as compared to the rating.  

    • Room air conditioners:  Although the old room air conditioners (wall units) are getting out of fashion now, many homes and offices still have these installed.  These do consume a lot more electricity as compared to the split units.  We suggest that you estimate approximately 2KW per “ton” of air conditioning in this case. So a 1.5 ton A/C will be approximately 3KW

    • Split units: Split unit air conditioners are a lot more electricity efficient.  The consumption varies from manufacturer to manufacturer.  However, as a rule of the thumb, you can estimate approximately 2KW per 1.5 tons A/C.

4. Pumps and motors:  Normally pumps and motors are rated in horsepower (HP). One horsepower = 0.746 Kilowatts.  Many of the pumps and motors will have the Watts or KW also mentioned.

5. Industrial machines:  Most industrial machines will be 3-phase.  You need to check the load of each machine.  This should be printed on the plate of the machine.

System Design (based on availability of the sun and wind, and overall efficiency)

The sun is available only during the daylight hours. The radiation from solar rays is not strong in the early morning hours or in the latter part of the evening. Thus, depending on the location and latitude, the number of hours of available peak sun during the day is only around 6-10 hours at most. In case, your application requires power for 24 hours, then the solar energy system must be sized accordingly where the usage is 3 times the quantum of the electricity produced. However, in most home and office applications, the usage during the day would match the no. of hours of electricity produced by the sun.

solarmap

One other critical factor that needs to be considered in the case of the sun is the number of dark days at a stretch. In case of a cloud cover, the sun is hidden and the solar cells would not produce electricity.  One needs to determine the maximum no. of dark days at a stretch to calculate the size of the solar panels and battery bank so that there is sufficient power stored for this dark period.

Other minor factors that would affect the solar energy system calculation are environmental dust factors, latitude, efficiency losses of other allied equipment, etc.

Wind normally blows every few hours in a windy area. Wind blows in the day and at night. It blows in the morning or afternoon or evening or in the dark hours. It is not dependent on the appearance of the sun. It keeps on varying in speeds throughout the day and night.

We have designed our systems for the batteries to be able to sustain even when there is no wind for between 8-24 hours depending on the load.

The wind turbine keeps on producing electricity at varying degrees as the wind keeps blowing.

For Solar Energy FAQs, click here

For Wind Energy FAQs, click here