Response.Clear();
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.AddHeader("Content-Disposition", "attachment; filename=Test.xls");
        Response.ContentType = "application/vnd.ms-excel";
        System.IO.StringWriter stringWrite = new System.IO.StringWriter();
        HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
        TestControl.RenderControl(htmlWrite);//TestControl - контрол данные которого необходимо экспортировать, в данном случае div.id
        Response.Write(stringWrite.ToString());
        Response.End();