The difference is the inverter, and the device you're looking for is a grid tie.
Thanks. I was seeing inverters for around $300, but the inverter in this kit goes for $830. That still leaves $1000 between the two kits, though. I'll figure it out.
From my Amazon search, it looks like certain inverters can be grid tied, or is it that you need a second inverter? To be clear, I wouldn't want to feed power back into the grid, just use grid power as backup, and I would want something that would plug into an outlet rather than be hard-wired.
Is there a best place online to learn about all this? Most of my searches bring up vendor pages.
If you wanted to spend a bit more you could power the house with your system. And I think in MA you can get some good incentives for it too. Especially with how expensive your electricity is, solar could be a big savings.
http://www.gogreensolar.com/collections/solar-panel-kits
It would definitely be a big savings, but it might not be practical. We would have to get an easement from our condo neighbor who holds the roof rights. I'll have to look into Massachusetts laws to see if DIY is even possible. I would have to have a contractor pull permits, and I wouldn't be allowed to do the electrical work myself, for sure. These complications are why I'm thinking more along the lines of a smaller non-grid-tie system. I might just end up setting up a pure DC system for small stuff, a la
Bakari's Instructable, but I'm at least researching the options for AC. Thanks for your help.