I recently checked into solar buy vs lease (monthly and pre-pay). I end up going with buying. I ruled out monthly leasing early on, because it’s super expensive when you add it all up. It’s only good if you have no cash. If you do have cash, I would suggest one of the other two options. The reason I buy is because:
1) it’s mine, so after 20 years, I don’t have to give it back or buy it out (who knows what the price they set then). So, if the system actually stay functioning well past 25 years (since that’s when its warranty ends), then your average monthly cost would be lower.
2) flexibility. If you sell the house, you don’t have to worry about buying out the system. If you don’t have the money to buy out the system, you’d have to make sure the buyer would want to take over your lease and is qualified (credit wise) to take over the lease. I don’t think you can buy out the system early. IIRC, you have two times to buy it out, either at 7 years or 20 years. You have to pick that date ahead of time.
3) you’re locked into the current technology. Solar, like any other technology, I expect to improve over time and get cheaper. If this holds true, 10 years from now, I can sell my panel on craigslist and buy new, more efficient panel. Especially if my usage goes up. You can’t do this with leasing.

Now, the pro for leasing are:
1) no worry about maintenance (although I’ve talked to a couple honest sales guy and they said they haven’t had a service call ever).
2) no up front cost for monthly lease and lower than buy price (after all rebate) if you do prepay. Prepay was around $1-2k cheaper. However, you still have to buy out the system at a later date. So, the total cost would most likely be more expensive than buy.