Export Gridview Data to Excel

public void ExportGridToExcel(GridView grdGridView, string fileName)
{
Response.Clear();
Response.AddHeader("content-disposition", string.Format("attachment;filename={0}.xls", fileName));
Response.Charset = "";
Response.ContentType = "application/vnd.xls";
StringWriter stringWrite = new StringWriter();
HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
HtmlForm hForm = new HtmlForm();
grdGridView.Parent.Controls.Add(hForm);
hForm.Attributes["runat"] = "server";
hForm.Controls.Add(grdGridView);
hForm.RenderControl(htmlWrite);
Response.Write(stringWrite.ToString());
Response.End();

}

button ExcelExport function

protected void btnExcel_Click(object sender, ImageClickEventArgs e)
{
string filename = "ClaimsDataYearwiseReport_" + ddlFromYear.SelectedItem.Value + "_to_" + ddlToYear.SelectedItem.Value + "";
ExportGridToExcel(grdProspectDet, filename);
}