How to Export datatable or datagridview contents to Excel without Interop

In a web forms application, I am populating a datagridview using datatable.
I need help to export this data from datagridview (or datatable) without using Excel interop method. 
Can someone please help with this. Thanks.
SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM myTable", sqlConn); DataTable datatable = new DataTable(); adapter.Fill(datatable); datagridview1.Datasource = datatable;