Not that it's a bad idea, but that retrofit residential stuff is such a pain in the ass (been there, done that (home automation and security installations)).
If you do pursue this, I would suggest you do what I figured out rather quickly: concentrate on only new construction and only custom homes. Forget the retrofit, and forget the tract-home developers where the builders just want to turn the units quickly and not get the homebuyers distracted with fancy add-ons.
Also, depending on what state you're in, certifications and regulations can be cumbersome also. And lastly (well, not last, I could go on about this for days...) if you haven't done this before, getting decent E&O and general liability insurance will be somewhere between expensive and impossible, many insurers don't want to insure someone with no experience running around a $400K jobsite with fancy power tools and equipment.
All the above being said, I would still say go for it under the right conditions. I personally find "hardware" startups 100 times more challenging and rewarding than web-app or general software startups. No offense to the software guys, it's just a whole different world when you are producing or working with physical goods.
If you do pursue it, contact me offline and I might be able to give you some advice and pointers about things, plus some other products you could carry/install that go along with the energy conservation theme.
It's definitely a burgeoning industry, but you really do need a decent amount of certification to be taken seriously. I used to work in clean energy and it is becoming somewhat of a crowded field, especially for residential solar. You'd be setting yourself up for some strong future business, but right now the costs of solar installation for homeowners is quite high, especially considering the federal tax credit for solar systems is about to expire. There might be some more incentives that will drive increased use under the next president, but there likely won't be much within the next half-year.
Not sure how things are where you live, but the geographic market I was working in saw mostly retrofits and very little integration with new construction. As the cost of producing solar panels continues to decrease, you'll be strengthening your position, but until that happens you likely won't be making very much money.
Another thing to consider is the proliferation of larger solar companies that operate on a franchise model and include service and maintenance into the cost of the system.
If you're very passionate about clean energy and have the time to dedicate over the next 5-10 years, I say go for it, otherwise you won't see very strong returns. Just my 2c...
Research the market size, the barriers to entry, the competition, how you might differentiate yourself, the threat of a disruptive technology making you obsolete, etc.
The solar panels currently in widespread use are:
* Expensive * Limited in Capacity * Fragile-ish
So if I were you, I'd be looking at third-gen solar and finding ways to bring that to people in ways your competition cannot.