I did a 14001 based study for a local group as part of my MSc, and 9001 training when I worked for Xerox many years ago, who were into that in a very big way.
I would say that if you follow MCS procedures slavishly then you are already part way there. The main benefits are two-fold - the process of bonding staff get from all working to the same standards and the subsequent change in mind-set. For 9001 this means 'getting it right first time' which itself should lead to cost savings. 14001 might give you some insights into how to run your company better but I would expect the gains to be minimal for a PV installer (as opposed to a large manufacturer, for example) as there will be fixed costs in becoming accredited and only variable savings against the lower overheads for small companies.
But of course it all depends on where you are starting from.
For a small company just start by writing an Environmental (or Quality) Policy (google for some examples) and see what ideas are generated.