Identifying patented inventions in a certain technical field can be very challenging if title words are relied on. An alternative approach is to use the International Patent Classification (IPC) printed on the patent specifications.
UN agency WIPO has now created an IPC Green Inventory to help when the interest is in green technologies. Clicking on the + signs open up subdivisions. Clicking on a class in the left hand column of the table then provides details of subdivisions within that class.
Hence it can be used simply to identify the right classifications to use in databases such as Espacenet. Alternatively, it can be used to find patent applications published in the PCT or "World" patent system, which is favoured by nearly all major, and many medium-sized, companies, as found on the Patentscope® database. A PCT does not give the applicant a granted patent, but does simplify and cheapen the process for getting patents granted for an invention across many countries. WIPO administers the PCT scheme.
Clicking on the class in the right hand column opens a table which tells you which are the leading companies publishing through the PCT route. Summaries of the applications appear below. An example is "Charging batteries", H02J 7/35, where the PCT specifications are listed here.
It is a pity that main drawings are not included, but the database is nevertheless a useful resource for anyone looking for information on green technology. These sites are all free, of course.