const
  ExcelApp = 'Excel.Application';

var
  Excel: OleVariant;

........



function TReportForm.CheckExcelInstall: boolean;
var
  ClassID: TCLSID;
begin
  Result := CLSIDFromProgID(PWideChar(WideString(ExcelApp)), ClassID) = S_OK;
end;

function TReportForm.RunExcel(DisableAlerts: boolean=true; Visible: boolean=false): boolean;
begin
  try
    if CheckExcelInstall then
      begin
        Excel := CreateOleObject(ExcelApp);
        Excel.Application.EnableEvents := DisableAlerts;
        //Excel.Visible := Visible;
        Result := true;
      end
    else
      begin
        MessageBox(0,'Excel íå óñòàíîâëåí','Îøèáêà',MB_OK+MB_ICONERROR);
        Result:=false;
      end;
  except
    Result := false;
  end;
end;

procedure TMainForm.Button1Click(Sender: TObject);
var
  WorkBook, Sheet: OleVariant;
begin
  RunExcel(True, True);
  WorkBook := Excel.Workbooks.Add;
  .......
  //Заполняю отчет
  ....... 
  Excel.Visible := Visible;
end;