It may seem an obvious question, I know. And I'd be the first to admit that having devices I can interrogate remotely appeals to my inner geek, as does making stuff that isn't supposed to talk to anything but a closed-source, badly-written Windows app or a proprietary web service bend to my will. I'll freely confess that I'm a gadget freak, and that generating our own hot water and electricity is just cool.
But this isn't just about being geeky: it's about knowing what's happening in your system. For example, since having the solar water heating, I'd bet that we've saved nearly as much through being aware of what hot water we have and how long it takes to heat, as we have by generating it ourselves.
Equally, since I got the clamp sensor installed and talking to the computer, all of us at the Mill House have been very aware of saving energy - if you know that (for example) your house with most of its 'always on' stuff (fridge, freezer, server, etc) ticks over at 380W, then if you see a reading of 700W you'll start to investigate what's causing it. At some point I will let Anne post a breakdown of last year's energy savings here, but for now I'd just note that our electricity usage dropped by around 30% over 2011, just through knowing what we were using. (And, I should add before Anne does, through finally shutting down two Linux servers with very old power supplies. Old power supplies become very energy inefficient (several hundred Watts worth), which is why our house server is now a 60W miniITX box from the good folks at LinITX.com along with a similarly rated HP Media Server as a fileserver.)
But of course, that's just the first step. Sure, you can install your solar PV and sit back and watch the Feed-In Tariff money roll in on sunny days. But shouldn't you be using all that green electricity? As an example, our dryer is now on a timer (and once I get it set up, it'll be on a computer controlled switch, in fact) that only lets it run at times when the PV is likely to be generating most if not all of the power. (And sure, yes, we could hang it out in the garden. But both of us work, so being in to remove it when it rains isn't so easy...!)
Given the tightness of everyone's budgets generally, let alone the current move towards being at the very least energy efficient, and ideally as green as possible, I personally think it's vital to know both where your energy is coming from, and what's using it, long before the bill turns up. And setting things up to do so doesn't cost that much.