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  • Writer's pictureBrian Harbin

How to Calculate the Solar Power You Need

Anyone thinking of going solar will need to know the size of the solar power system they will require to power their home. The question relates not just to the amount of solar panels you will need but also the overall capacity of the system you choose.


In order to work out the average energy requirements of your home it is a good idea to look at your previous energy bills. Calculate the amount of energy you will require by multiplying the hourly energy requirement of your home by the peak sunlight hours in your local area and then divide that by the wattage of the panel of the solar power system you are looking at.


It is a good idea to use a relatively low wattage of 150 W and a high wattage of 370 W in order to set a range. Take into account the size of your roof and other factors such as the sunlight received by it.


How much energy do I currently use?


Check your electricity bill to see how much energy you are currently using in your home. This will usually be listed as something similar to “Kilowatt hours used” and then check the length of time the bill represents (normally 30 days). If kilowatt hours are not shown on your bill look for the beginning and end of meter readings and then take off the previous reading from your most recent bill.


Daily and hourly usage are required for calculations, so if a daily average is not shown on your bill, divide the annual or monthly average by either 365 or 30 days and then divide the resultant figure again by 24 to work out your average hourly usage. The answer will be in KW.


A smallish home in a temperate climate may use around 200 kWh every month while a bigger home in a warmer environment may use closer to 2000 kWh per month. The average home in the United States uses around 900 kWh every month, which works out as 30 kWh every day and 1.25 kWh per hour.


The average daily energy usage of your home is the average you should use to work out your solar power requirements, which will be the number of kilowatt hours a solar power system will need to be able to produce in order to cover the majority if not all of your home’s electricity needs.


One factor that it is important to take into consideration is that solar powers do not operate at full capacity during every hour of the day. The efficiency of a system can for example be temporarily reduced by weather conditions. Experts therefore advise that a cushion of around 25% should be added to the target daily average of your home’s energy usage in order to ensure your system will be generating all of the clean energy that you require.


It is important to know how much electricity you use and the hours of the day you tend to use it most when searching for an appropriate solar power system for your home.





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