Export line chart into excel using asp.net

private void ExportToExcel()
{
try
{
Response.Clear();
Response.Buffer = true;
Response.AddHeader("content-disposition", "attachment;filename=OverallReport.xls");
Response.Charset = "";
Response.ContentType = "application/vnd.ms-excel";
using (StringWriter sw = new StringWriter())
{
HtmlTextWriter hw = new HtmlTextWriter(sw);

//To Export all pages
dgvTrendChart.AllowPaging = false;
this.SearchOverallList();

dgvTrendChart.HeaderRow.BackColor = Color.White;
foreach (TableCell cell in dgvTrendChart.HeaderRow.Cells)
{
cell.BackColor = dgvTrendChart.HeaderStyle.BackColor;
}

for (int rowIndex = dgvTrendChart.Rows.Count - 2; rowIndex >= 0; rowIndex--)
{
GridViewRow row = dgvTrendChart.Rows[rowIndex];
GridViewRow previousRow = dgvTrendChart.Rows[rowIndex + 1];

for (int i = 0; i < row.Cells.Count; i++)
{
if (i != 3)
{
if (row.Cells[i].Text == previousRow.Cells[i].Text)
{
row.Cells[i].RowSpan = previousRow.Cells[i].RowSpan < 2 ? 2 :
previousRow.Cells[i].RowSpan + 1;
previousRow.Cells[i].Visible = false;
row.Cells[i].HorizontalAlign = HorizontalAlign.Center;
row.Cells[i].VerticalAlign = VerticalAlign.Top;
}
}
}
}
dgvTrendChart.RenderControl(hw);

//style to format numbers to string
string style = @"";
Response.Write(style);
Response.Output.Write(sw.ToString());
Response.Flush();
Response.End();
}
}
catch
{
//throw new Exception("");
}
}