The Tigo Solar Sizing Tool is designed to help you determine the number of modules per string and how many strings the Tigo EI Inverter (US) will need to operate correctly. String sizing is a necessary part of any traditional solar PV system design and is an easy exercise to master.
The tool is divided into three sections:
- PV module data
- System data
- System output
Let’s begin with PV module data entry. First, you must have the module datasheet, usually found on the manufacturer’s website. For this example, we will use a standard 395 Watt PV module.
Locate the Electrical and Temperature Characteristic sections on the datasheet. These sections contain the data we need for the first part of the tool.
Copy and paste the applicable data into the sizing tool Module Data section (use the STC column ratings). Once you have done this, disregard the Module Datasheet as it is not required for the rest of this process.
Next, in the Location Temperature section of the tool, click on the Temp Lookup hyperlink.
This link takes you to the Florida Solar Energy Center (FSEC) Solar Reference Map webpage. We will use this tool to find the temperature data required by this section of the Tigo sizing tool.
The NEC (National Electric Code) does allow the use of the ASHRAE data used in the Solar Reference Map tool since record high and record low values result in a more restrictive design.
Use your cursor to find your city and select the nearest red flag. A window will pop up containing two temperature values.
Enter the Extreme Min value from the FSCE site into the Solar Sizing Tool Lowest temperature field.
Enter the 2% High Temp value into the Solar Sizing Tool Highest temperature field.
Next, we must enter system information.
Two pieces of system data must be entered: system location and the system size.
System Location has two selections- rooftop or ground mount. The array location is important since airflow affects PV array performance (cell temperature). A rooftop system will have restricted airflow under the array, while a ground mount will not.
Lastly, enter the system size by entering either the total number of modules or the system size in kW.
Now, let’s take a look at the results and recommendations!
Directly below the System Size entries is the String Lengths table. This table shows the minimum and maximum allowable modules per string. However, we must continue down the page to see the recommendations.
The largest section of the tool is the string sizing results tables. These tables show the recommended number of modules per string and the number of strings for the Tigo 3.8, 7.6, and 11.4kW inverters. The tool may or may not recommend a stringing combination for every inverter. If the array size exceeds the 200% array oversizing the Tigo inverters can accommodate, that inverter will show blank data fields.
In this example, the number of modules does exceed the rating of a single 7.6kW and 11.4 kW Tigo Inverter. Consequently, the tool indicates the design will require two inverters. The corresponding tables show the stringing for both inverters.
Notice the stringing is the same for both sets of inverters- 3 strings of 10 modules for inverter #1, and one string of 10 and one string of 11 modules for inverter #2.
The DC/AC ratio fields reflect the DC size of the array divided by the AC output of the inverter. A ratio larger than 100% indicates the PV array is larger than the inverter. Conversely, a ratio smaller than 100% indicates the array is undersized relative to the inverter.
Arguments can be made for either case, but generally speaking, when the Tigo inverter is used with the Tigo Battery, it is better to oversize the array. That excess PV is used to charge the batteries.
And that’s it! If you have any questions, please contact Tigo Support.