Changing the in text citation for specific entries

I have been looking for an answer to my problem for quite a while now and was not able to find one that really meets my requirements.

I am using biblatex with citestyle alphabetic. For most cases this is absolutely fine. But now I would like to cite a study and would like a specific set of letters to appear in the text.

The biblatex source looks as follows:

@Report{Kost2018,
  author        = {Kost, Christoph and Shammugam, Shivenes},
  title         = {{Levelized Cost of Electricity Renewable Energy Technologies}},
  institution   = {Fraunhofer ISE},
  year          = {2018},
}

Now, with \autocite{Kost2018}, as expected, the citation comes out as [Kos+18].

What I would like instead is something like [ISE18] because the reader will more likely know this institute rather than the author. Also, if I cite several studies of that insistute, it is more clear to the reader.

I would be really greatfull if someone could help me on this.

You can use the biblatex key shorthand:

@Report{Kost2018,
  author        = {Kost, Christoph and Shammugam, Shivenes},
  shorthand     = {ISE18},
  title         = {{Levelized Cost of Electricity Renewable Energy Technologies}},
  institution   = {Fraunhofer ISE},
  year          = {2018}
}

Description from the biblatex documentation:

label
A designation to be used by the citation style as a substitute for the regular label if any data required to generate the regular label is missing. For example, when an author-year citation style is generating a citation for an entry which is missing the author or the year, it may fall back to label. See § 2.3.2 for details. Note that, in contrast to shorthand, label is only used as a fallback. See also shorthand.

shorthand
A special designation to be used by the citation style instead of the usual label. If defined, it overrides the default label. See also label.

Reference: How to specify bibliography alpha key without modifying the .bst file or using BibLaTeX