Generally, I agree with Galen. Installing solar doesn't mean that you'll be saving lots of money. I live in Hawaii where the cost of grid electricity is mind boggling expensive, and even so, the cost of installing most solar installations (including tax incentives) doesn't equate to cash savings for years and years. There needs to be other reasons for installing solar other than quick cash savings.
Our homestead is completely off-grid. People mistakenly think we have free electricity. We installed a small system that cost $20,000 in hardware. (We install and maintain it ourselves.) Every six years or so we need to replace the battery bank ($800 to $1000). We need to buy and maintain a back up generator that gets replaced when we replace the battery bank. (Just because the gas engine runs doesn't mean that it's putting out the electrical rating we need. These things wear out.) That's around $800 to $1000 buy the new generator. I'm not sure what the gasoline, oil, and maintenance parts come to, nor the distilled water for the batteries. Our solar panels are 20 years old this year, so heaven knows how much longer it will be before we be thinking of replacements. Luckily our inverter, charge controller, and the rest of the equipment has never failed, but they could, thus requiring expensive replacements.
No, solar surely isn't free. It costs to install it and maintain it. And for newbees it's even more expensive because they make mistakes while learning. For example, we killed our first battery bank in 3 years simply because we didn't know what we were doing.
The reason we went off grid was strictly economics. The electric company wanted almost $30,000 to run power to our house. Going was DIY solar was an immediate savings for us. But for folks already on the grid, changing to solar may not be a savings for years, if ever. And if they go with a grid tied system with no battery back up, then they aren't any better off......except that they may feel better about "going green" (whatever they think that is).
Grid power gives the homeowner flexibility and reliability. Plus the ability to budget monthly expenses fairly accurately. Off grid means that you need to think about how much power you are using and when you might need to use more than normal. For example, I know that I need to run the generator when I use high energy consuming equipment, or want to do the laundry on a cloudy day. I know that my system can't maintain a heated spa, so I'd be crazy to buy one as a Christmas present for hubby. I need to be mindful about the running of my power, because I can't even consider running the water pump, washer, freezer, frig, microwave, and hair dryer all at the same time. Being on the grid, a homeowner wouldn't even have to think about that. Plus budgeting isn't easy. Cash layouts will come in big chunks, not little bits each month.
People going from grid to off grid (usually grid tied) need to look carefully. Saying that you save money is usually ignoring the upfront purchase cost, or end-of-lease expenses. Others reasons, like Galen's, might be a good reason going solar. One of our friends installed a grid tied system because he wanted his wife to be able to afford to stay in their home after he died. He is significantly older than she is. He has the money now to spend on going solar and knows that she will have a low monthly income after he passes. So installing solar gives him peace of mind.