Response.Clear();
    Response.ContentType = "application/vnd.msexcel";
    Response.AddHeader("content-disposition", "attachment; filename=rapor.xls");
    Response.ContentEncoding = System.Text.Encoding.Default;
    System.IO.StringWriter stringWrite = new System.IO.StringWriter();
    System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
    panel1.RenderControl(htmlWrite);
    Response.Write(stringWrite.ToString());
    Response.End();