Wednesday, 19 November 2014

How to install solar panel at roof top and stay off the grid life chapter-2

How to select the type, Quality and quantity of Solar Panel for living a Grid free life. What are the total daily Wattage requirement for average household.




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How to select the best solar panel for home to enjoy grid free life, is the most popular question asked by the guys all around the world. To understand how to choose the solar panel array one should be familiar with certain electrical terminology which are ( if you simply know this basic thongs skip this paragraph):

  • Voltage
  • Amperage
  • wattage 

    Voltage: The potential difference between two points. Is measured in Volts (V) and has the symbol                   ‘V’.

    Current: The flow of electrons in a circuit. Is measured in Amps (A)and has the symbol ‘I’.

    Resistance: A material’s opposition to an electrical current. Is measured in Ohms (Ω) and has the                          symbol ‘R’.

    Power: The rate of doing work. Is measured in Watts and has thesymbol ‘P’.

    Energy: The capacity for work, the product of power and time. Has the symbol ‘E’. The basic unit of              energy is the Joule, but electrical energy is normally expressed in Watt hours (Wh) or kilo                    Watt hours (kWh). One kWh is 1000 Wh.

    The relationship between these units is:


                      P = VI
                      or V = P/I or I = P/V

                      V = IR
                      or I = V/R or V = I/R

                     P = I2R



    Power equals voltage multiplied by current. This can also be expressed in the other two forms shown.

    Voltage equals current multiplied by resistance. Again there are two other forms shown. This is known as ‘Ohm’s law’.

    Power equals current squared multiplied by resistance.

    Now we are prepared to start the above discussion that How to choose the optimum solar panel for home.

    How to choose an optimum solar panel for homes.


    We have to consider different points when choosing optimum solar panel array. These points are:


    How much wattage we need daily:

    The wattage of the solar panel we need is the most important thing because buying a grater value solar panel is just useless and is wastage of money, and buying smaller value solar panel then the result may be very disappointing. So we have to choose the optimum solar panel.

    There are three main stages for solar power system:

    • Power generation from solar panel array.
    • Energy storage into batteries.
    • Use of that power stored in the batteries.
    To get optimum wattage from solar panel one should size them means choose the specification to his requirement means how much power they are going to use.

    The batteries is just the storage container for solar energy we get in daylight and we can use that power when there are no light available from sun means night time. So the battery should be calculated to the requirement and must be chosen wisely. Battery is the medium which provide the continous power even there is fluctuation from solar pannel output meansbatteries acts as a filter of power from solar panel array.

    We will size the panel and batteries later according to power requirement.

    Space requirement:

    There are different sizes (in terms of length, width and thickness of solar panel available in the market. We can choose the best one from them according to our requirent and space we have.

    We can also add panels together to get the overall size we need. If a 120 Watt panel is large in area available then use smaller panels side by side like 60w 60w two panel in our example.

    Remenber that for the equivalent wattage a crystalline panel will be smaller than an amorphous one.


    How to calculate the actual daily power needed and power we get daily from solar panel array.

    A quick sunshine hours guide for India:

    A summer's day will give you the equivalent of 7:30 hours sunshine in the India.  A 10Watt panel will give 75Watt in that day.

    On a winter's day, you'll get the equivalent of 4 to 5 solid hour of sunshine and so a 10Watt panel will give 40 to 50Watt in that day.

    These are fairly conservative figures – some companies use up to 6 hours in summer. You can do the same calculations with the Amps.

    Some simple steps for sizing a 12V system:


    • Find the Wattage of your appliances.
    •  List all the electrical appliances you’ll use in a typical day, and find out how many Watts they  each consume. Usually this is on the appliance or in its handbook. If you can only find a figure  for Amps, simply multiply this by its voltage (for example 12v or 220v), to convert it to Watts.

    Calculate your daily total Watt-hour requirement.

     Estimate how many hours you would use each appliance for over a typical week, then divide by 7 for a daily rate.

    Multiply each appliance’s wattage by the hours you’ll use it for in a day. Then add all the totals together to get the final daily total Watt-hours you require.

    Next calculate your panel size. Simply divide the daily total Watt-hours you require by the hours of usable light you expect in an average day. This will give you your minimum panel wattage. In the India, allow 4 to 5 hour of light in winter, rising to 7:30 hours by mid-summer.

    Then your battery size… Multiply your daily Watt-hour requirement by 7 to create a weekly requirement, and divide this by 12 to convert back to Amp Hours, which batteries are rated in. Multiply by two to give the correct battery size.

    Now finally, our charge controller.

    Size your charge controller according to the Amps produced by your panel. Calculate the Amps produced by dividing the panel wattage by 16.5.


    A worked example. In one week you want to run a 65W television for 4 hours, and an 8W light for 5 hours. Your daily Watt-hour requirement for the TV is 65 x (4/7) = 37Wh; and for the light you require 8 x (5/7) = 6Wh. Your total daily requirement is thus 43W. You only intend to use the system in summer, so you need a panel that is 43/4 = 11W or more. Your battery size needs to be (43 x 7 x 2)/12 = 50Ah. And you need a charge controller suitable for a solar input of at least 11/16.5 = 0.7A



    List of Some general appliances used on every household with their rated wattage:

    • Ceiling fan= 100watt
    • Laptop=50watt average
    • Desktop=120 for cpu + 150 for crt monitor= 270watt
    • Iron=1000watt
    • Vaccume cleaner=500watt
    • cfl=20watt 
    • Laser printer=375watt
    • Refridgerator 28 liter=380watt
    • Stupid Tv= 100watt
    • Set top box=50watt
    • Satelite dish=50watt
    • Microwave oven cooker=3000watt
    • Bulb=100watt
    • Heater=1500watt
    • Desert cooler= 250watt
    •  and e.t.c

    Now lets take a snapshort how the power flow in solar panel array system.

    Power flow:


    The principles of operation of a typical stand-alone solar power system are shown in figure 6. Electricity is generated in the form of low voltage DC by the photovoltaicsolar moduleswhenever light falls on them.

    This power is routed through a controller, which feeds whatever power is necessary to any DC appliances such as lights and uses any surplus to charge a battery. When there is less power being generated than the appliances are using, power flows from the battery to the appliances. The controller monitors the battery state of charge and disconnects the appliances if the battery becomes very discharged.

    Any AC (mains) appliances are connected to the inverter. This is not connected to the controller but directly to the battery. It incorporates its own control mechanism to ensure that the battery is not over-discharged.

    In next post i am going to calculate the power requirement of average Indian household and size the SOLAR PANEL, BATTERIES AND SOLAR CHARGE CONTROLER.  

    Thank you for reading. For any query please ask that in comment section. 
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