Greenhouse - automatic door opening

Hi all,

I'm a 'non' gardener, but I like the results there of so ...

The lean-to greenhouse has no opening windows - no not an easy option to 
put some in (without a full re-build - not my design etc. etc.) so can I 
use on of those window openers to open the door or does anyone have any 
other ideas?

I'd thought about a PV-cell (or several) and a few 12V computer case fans 
but ...

TIA

Nick