WRONG
Please send us an electronic version of the Purchaser’s technical expertise dated 29 November 2014.

RIGHT
Please send us an electronic version of the Purchaser’s technical opinion dated 29 November 2014. 

Do NOT translate ekspertyza as expertise.

These words are false friends and have completely different meanings.

Expertise means “skill or knowledge in a particular area or required by a particular job or profession, which is acquired by study or practice”.

Expertise is an uncountable noun which describes a concept. Synonyms for it are ability, competence, skill, proficiency, professionalism.

Here are some examples of how to use it:

Some jobs require a high level of technical or theoretical expertise.
The firm’s many years of experience ensure that its expertise in this field is second to none.
Temporary employees provide expertise and skills in response to changing needs.
By awarding you this prize we wish to recognise your hard work and remarkable technical expertise.

Ekspertyza is a countable noun and describes a type of document.

Ekspertyza should be translated as “opinion, expert opinion, evaluation, assessment, examination, analysis” depending on the context.