Exporting gridview to excel sheet

System.IO.StringWriter sw = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter htw = new System.Web.UI.HtmlTextWriter(sw);

        // Render grid view control.
        reportGrid.RenderControl(htw);

        // Write the rendered content to a file.
        string renderedGridView = sw.ToString();
        File.WriteAllText(Request.MapPath("~/Account/temp.xls"), renderedGridView);
        htw = new System.Web.UI.HtmlTextWriter(sw);