The first step in stetting up a photovoltaic system is to determine what time of the year will have the largest loads (loads are defined here) and then to select a month that you will use to design the system. You will also need to gather solar insolation data (insolation defined) for the sizing calculations.
Determining Design Month
Insolation data is most often presented as an average daily value for each month. When sizing a system, it is important to use the correct month. If the load is constant throughout the year, the design month will be the month with the lowest insolation. The array should then be installed with a tilt angle that yields the highest value of insolation during that month. This ensures that the system is designed to meet the load and keep the battery fully charged in the worst month for the average year.
If your load is variable for each month you will need a sizing worksheet. (Contact Eco Depot USA and we will send a pdf.) The design current is the average daily load for the month divided by the monthly insolation. The month corresponding to the largest design current should be used as the design month.
Source: Solar Energy Internationl’s Photovoltaics Design and Installation Manual. Page 33. This is the book used to train the pro’s. Learn more at www.solarenergy.org.
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