Modifying the format of a bibliographic entry for a link in `biblatex`

Bascially, biblatex-ieee assumes that @online entries have a date or year entry. If not, you get empty parentheses. See also Remove parentheses for empty year field biblatex ieee style, where Joseph Wright (the developer of biblatex-ieee) comments that date/year is required in IEEE style. My answer there shows a patch to avoid the empty parentheses in case of a missing year.

In all bibliography styles that I am aware of, however, it would not be enough to just give the URL and access date of an online source. One should almost always give at least author, title and publication year of a source.

For this specific entry you could either give {wind-turbine-models.com} as the author or Lucas Bauer and Silvio Matysik. According to the site the entry was first added to the database in 2013 and last updated in 2015.

documentclass{book}
usepackage[x11names]{xcolor}
usepackage[style=ieee,refsection=chapter]{biblatex}
usepackage{hyperref}

hypersetup{citecolor=DodgerBlue3, urlcolor=Blue1, colorlinks=true}

usepackage{xpatch}
xpatchbibdriver{online}
  {printtext[parens]{usebibmacro{date}}}
  {iffieldundef{year}
    {}
    {printtext[parens]{usebibmacro{date}}}}
  {}
  {typeout{There was an error patching biblatex-ieee
            (specifically, ieee.bbx's @online driver)}}


begin{filecontents*}{jobname.bib}
@online{GEV_MP_R_specifications,
  author  = {{wind-turbine-models.com}},
  date    = {2015-08-28},
  title   = {Vergnet {GEV MP R 275/32}},
  url     = {https://en.wind-turbine-models.com/turbines/436-vergnet-gev-mp-r-275-32},
  urldate = {2020-06-13}
}
@online{GEV_MP_R_specifications:onlyurl,
  url     = {https://en.wind-turbine-models.com/turbines/436-vergnet-gev-mp-r-275-32},
  urldate = {2020-06-13}
}
end{filecontents*}
addbibresource{jobname.bib}

begin{document}
cite{GEV_MP_R_specifications,GEV_MP_R_specifications:onlyurl}

printbibliography
end{document}