If you give a name as
author = {van Trijp, Remi},
in the .bib file, Biber decomposes this name into three parts.
- family name:
Trijp
- given name:
Remi
- name prefix:
van
The output of names with 'prefix' part is controlled with the useprefix option.
- With
useperfix=false (the default) the 'prefix' is essentially treated like a first name. You get 'Trijp, Remi van' for family-given order and 'Remi van Trijp' for given-family. The name is alphabetised under 'T'. Naturally then, mr. R van Trijp is cited only as 'Trijp'.
- With
useprefix=true the prefix is essentially treated as part of the last name. You get 'van Trijp, Remi' for family-given order and (again) 'Remi van Trijp' for given-family. The name is alphabetised under 'V' and cited as 'van Trijp'.
If you write the name as
author = {van Trijp, Remi},
in your .bib file and add useprefix=true to biblatex's options you get what you want.
Why does author = {{van Trijp}, Remi} not work?
This is parsed as
- family name:
{van Trijp} (note the braces!)
- given name:
Remi
Since we don't get to see braces in the output, for most intents and purposes then, this gives the same results as author = {van Trijp, Remi}, with useprefix = true.
You found one of the differences, though, if a name is printed in a context where the start of a sentence is detected (as is the case with \bibsentence), only the name prefix is capitalised, all other name parts are left as they are. This means that the family name {van Trijp} is not capitalised and comes out as 'van Trijp' with a lowercase 'v'. You may ask why biblatex does not automatically capitalise the family name as well. I don't know why, but I guess it is safe to assume that normally the family name starts with a capital letter anyway, so it would be a wasted macro call. Automatic capitalisation is really hard and should only be employed when absolutely necessary.
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{vanTrijp2015a,
Author = {van Trijp, Remi},
Year = {2015}
}
\end{filecontents*}
\usepackage[backend=biber, natbib=true, useprefix=true,
citestyle=authoryear-comp]{biblatex}
\addbibresource{\jobname.bib}
\begin{document}
\Citet{vanTrijp2015a} vs \citet{vanTrijp2015a}
\printbibliography
\end{document}

vanTrijp2013ais wrong. You want the input ofvanTrijp2015aand (very) probably the optionuseprefix=true– moewe Mar 05 '18 at 16:30