protected void Page_Load(object sender, EventArgs e)
    {
dbcon = new DbConnection();
            sqlcon = new SqlConnection();
            sqlcon = dbcon.databaseconnection();
            sqlcon.Open();
            ds = new DataSet();
            sqladap = new SqlDataAdapter(str_Query, sqlcon);
            sqladap.Fill(ds, "TableName");
     }

 protected void Button1_Click(object sender, EventArgs e)
    {
        Response.ContentType = "application/vnd.ms-excel";
        Response.Charset = "";
        this.EnableViewState = false;
        System.IO.StringWriter stringWriter = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter htmlWriter = new System.Web.UI.HtmlTextWriter(stringWriter);
        DataGrid1.RenderControl(htmlWriter);
        Response.Write(stringWriter.ToString());
        Response.End();
    }