The Power tagging scheme went through quite a bit of thought in 2013. Unfortunately, living on only a couple of OSM mailing lists, I didn't get to see any of the discussion. While most of the suggestions are pretty reasonable (if occasionally requiring improbably levels of system knowledge likely only known to employees) one part confuses me: generator:source vs generator:method.
The Wind Farm Tagging Thing
Anyway, while adding a small wind farm near where I grew up, I noticed a rather neat convention for grouping turbines into a wind farm: using a relation, as in:
<relation id='4515485'> <member type='node' ref='3308390472' role='generator' /> <member type='node' ref='3308390473' role='generator' /> <member type='node' ref='3308390474' role='generator' /> <!-- … more member nodes, one for each turbine --> <tag k='name' v='Middleton Wind Farm' /> <tag k='site' v='wind_farm' /> <tag k='type' v='site' /> </relation>
(real link: Middleton Wind Farm)
This is a tidy way of grouping turbines, as many wind farms aren't clearly enclosed. You could have all sorts of roles for transmission lines, control rooms, visitor centres, …
I'm pleased to see that the tagging scheme seems to be informally named after Carland Cross wind farm. Carland Cross was the first wind farm I worked on. Here's a view over to Newquay, as it looked to me in the summer of 1993: