using (ExcelHelper helper = new ExcelHelper(TEMPLATE_FILE_NAME, GENERATED_FILE_NAME))
        {
            helper.Direction = ExcelHelper.DirectionType.TOP_TO_DOWN;
 
            helper.CurrentSheetName = "Sheet1";
 
            helper.CurrentPosition = new CellRef("C3");

            //the template xlsx should contains the named range "header"; use the command "insert"/"name".
            helper.InsertRange("header");

            //the template xlsx should contains the named range "sample1";
            //inside this range you should have cells with these values:
            //<name> , <value> and <comment>, which will be replaced by the values from the getSample()
            CellRangeTemplate sample1 = helper.CreateCellRangeTemplate("sample1", new List<string> {"name", "value", "comment"}); 
            
            helper.InsertRange(sample1, getSample());
            
            //you could use here other named ranges to insert new cells and call InsertRange as many times you want, 
            //it will be copied one after another;
            //even you can change direction or the current cell/sheet before you insert
            
            //tipically you put all your "template ranges" (the names) on the same sheet and then you just delete it
            helper.DeleteSheet("Sheet3");
        }        

       private IEnumerable<List<object>> getSample()
    {
        var random = new Random();
        
        for (int loop = 0; loop < 3000; loop++)
        {
            yield return new List<object> {"test", DateTime.Now.AddDays(random.NextDouble()*100 - 50), loop};
        }
        
    }

using (ExcelHelper helper = new ExcelHelper(TEMPLATE_FILE_NAME, GENERATED_FILE_NAME))
{
    helper.Direction = ExcelHelper.DirectionType.TOP_TO_DOWN;
    helper.CurrentSheetName = "Sheet1";
    helper.CurrentPosition = new CellRef("C3");

    //the template xlsx should contains the named range "header"; use the command "insert"/"name".
    helper.InsertRange("header");

    //the template xlsx should contains the named range "sample1";
    //inside this range you should have cells with these values:
    //<name> , <value> and <comment>, which will be replaced by the values from the getSample()
    CellRangeTemplate sample1 = helper.CreateCellRangeTemplate("sample1", new List<string> {"name", "value", "comment"}); 
    helper.InsertRange(sample1, getSample());
            
    //you could use here other named ranges to insert new cells and call InsertRange as many times you want, 
    //it will be copied one after another;
    //even you can change direction or the current cell/sheet before you insert
            
    //typically you put all your "template ranges" (the names) on the same sheet and then you just delete it
    helper.DeleteSheet("Sheet3");
}        

private IEnumerable<List<object>> getSample()
{
    var random = new Random();
        
    for (int loop = 0; loop < 3000; loop++)
    {
        yield return new List<object> {"test", DateTime.Now.AddDays(random.NextDouble()*100 - 50), loop};
    }
}

You can create nicely formatted Excel files using this library: http://officehelper.codeplex.com/documentation

You can create nicely formatted Excel files using this library: http://officehelper.codeplex.com/documentation
See below sample:

using (ExcelHelper helper = new ExcelHelper(TEMPLATE_FILE_NAME, GENERATED_FILE_NAME))
        {
            helper.Direction = ExcelHelper.DirectionType.TOP_TO_DOWN;

            helper.CurrentSheetName = "Sheet1";

            helper.CurrentPosition = new CellRef("C3");

            //the template xlsx should contains the named range "header"; use the command "insert"/"name".
            helper.InsertRange("header");

            //the template xlsx should contains the named range "sample1";
            //inside this range you should have cells with these values:
            //<name> , <value> and <comment>, which will be replaced by the values from the getSample()
            CellRangeTemplate sample1 = helper.CreateCellRangeTemplate("sample1", new List<string> {"name", "value", "comment"}); 
            
            helper.InsertRange(sample1, getSample());
            
            //you could use here other named ranges to insert new cells and call InsertRange as many times you want, 
            //it will be copied one after another;
            //even you can change direction or the current cell/sheet before you insert
            
            //tipically you put all your "template ranges" (the names) on the same sheet and then you just delete it
            helper.DeleteSheet("Sheet3");
        }        

where sample look like this:

       private IEnumerable<List<object>> getSample()
    {
        var random = new Random();
        
        for (int loop = 0; loop < 3000; loop++)
        {
            yield return new List<object> {"test", DateTime.Now.AddDays(random.NextDouble()*100 - 50), loop};
        }
        
    }