SI Unit Volt Ampere (VA) printed wrongly with space

You can define your own units by \DeclareSIUnit. In your case I suggest:

\documentclass{article}
\usepackage{siunitx}
\DeclareSIUnit \voltampere { VA } %apparent power 
\DeclareSIUnit \var { var } %volt-ampere reactive - idle power 
\begin{document}
    \SI{10}{\voltampere}
\end{document}

I changed the document class from minimal to article. The drawbacks of the document class are described here: Why should the minimal class be avoided?