The comprehensive site for designing PV/Solar Electric Systems

Step 4 - Select the PV Panels to be used for the system

The First Key Component you need to design and select are the PV Panels. You need to Select PV Panels that will generate enough power to keep the loads you have defined in the previous steps. There are essentially 3 different types of PV Panels, Crystalline Silicon, Amorphous Silicon and other Thin Film technology PV Panels. Crystalline Silicon panels are the oldest, most reliable and highest efficiency PV panels in the market today. The one drawback of crystalline panels is that their properties are affected the most by temperature and their Power producing capacity decreases with increase in panel temperature. As a rule of thumb the PV Panel temperate is generally 25-40 degrees Centigrade above ambient temperature. Amorphous silicon and other thin-film technology panels are less efficient but have better temperature sensitivity and either do not loose power production capacity or sometimes improve their efficiency under higher temperatures. Refer to the section on PV Panels for a detailed discussion on their types and properties. Availability and pricing of PV Panels can be found at my partners PV Modules section.

In addition to supporting the loads, you must compensate for losses in the system as you design the PV array. You must take into account the losses in the battery (Battery Efficiency), loss of PV Panel efficiency due to higher temperatures if you are using crystalline panels, Losses to due to Dirt and Dust on the panels, Controller and Wiring losses and have a factor of safety for changes in meteorological conditions.

A Key component of the PV Panel design is the location of Installation of the system. This determines the "Solar Hours" of the location and is needed for calculating the PV Panels required for your system. Refer to Step-0 for detailed information on the solar hours and the reference sites where you can find the "Solar Hours" for your location.

The following calculations need to be done to select the number of PV Panels for your array:

Amp Hours required by the batteries =    ______KWH/Day_______
  Design DC side Voltage
Losses to be taken into account=     Battery Efficiency x ( 1-losses due to temperature) x(1-losses due to dirt and dust)x(1-controller and wiring loss)
PV array Amp Hour Capacity =    Amp Hours required by the batteries
  Losses to be taken into account x Safety Factor
PV array Amps required =    PV Array Amp Hour Capacity
  Solar Hours at location
Now, go ahead and select a PV Panel module from one of the commercially available modules. The module literature has specifications like the Open Circuit Voltage and current and Peak Power voltage and current.

The number of modules in parallel needed =    PV Array Amps Required
  Peak Power Current in Amps
The number of modules in series needed =    Design DC side Voltage
  Nominal PV Module Voltage

The Peak Power voltage is always greater than the nominal PV module voltage and this is required to charge the battery bank which will be at the nominal or design DC side voltage.

The total number of PV Modules required for your array is = The number of modules in series x The number of modules in parallel

The design section of this site has automated the calculations above and comes with a drop down list of all available commercial PV Modules to help calculate the number of modules required for your system. In addition to calculating the number of modules for your array you will also have an estimate of the price, the warranty on the modules and other characteristics of the PV Array.

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