I wish "who pays for the system" and "where the system is installed" are decoupled, via a market that lets investors finance the system and the installation and own the resulting energy, and house owners or other sites that merely provide a place to install the panels in return for $x worth of free energy every month. If you're a house owner, you'll bid on the X, or different energy companies could make you offers, and you'd pick one that you like. If you're an investor, you'd presumably choose the site that gives you the greatest ROI — the most sunlight, the highest grid prices, and the least rent to be paid to the house owner (x above).
This addresses your point about upgrading. You can install the newer system on another roof, without incurring cost of removing the older system, and generate power (and therefore income) from both panels at once. As long as the older system is generating more power than its annual maintenance cost, it doesn't make economic sense to dismantle it.
Decoupling also means that if you decide to invest in solar energy, you can have it installed in whichever part of the world (or at least your country) gives the greatest ROI: the most sunlight, and the highest electricity tariffs. Maybe you live in a rented house or an apartment where you can't install solar panels. Giving a higher return will encourage more people to invest in solar.
Other advantages of decoupling will be the ability to invest the amount you want, whether $1000 or $100K, rather than the price of one solar system, the ability to make additional investments if you have more money later on, and the ability to liquidate an investment any time you need the money, or in a financial emergency. People will also be able to dip their toes into this market with a small investment, and see how it performs, before making a larger investment.
What you're describing is what every solar company does right now. SolarCity doesn't sell you panels, they sell you 2 products. The first is electricity from panels they own on your roof. The other is a lease of panels they own on your roof that you get electricity from.
In essence SolarCity and everyone else bids for your roof and business through their pricing. (which currently undercuts utilities).
And SolarCity in return is creating solar bond products essentially, where the market can invest their capital in these roofs that SC is producing energy on, with the monthly bills as interest.
But it doesn't solve the issue the person you replied to highlighted, which is that it may or may not be financially advisable to 'hold out', and buy solar when the price has come down. After all, even if you don't buy and own the panels, the lease is still a 20 year contract. And there's no way SolarCity or any company would reduce those to short-term contracts because there are fixed costs that can't be recuperated in the short-term, meaning you need long-term contracts to get an ROI. (sending technicians to replace installations every few years wouldn't make financial sense).
So the end result right now is that yes, you could in a way (by investing in solar companies or their financial products) invest in other people's roofs, despite not dismantling panels on your roof, in say 5 years from now when new installations are financially better performing than your roof panels. But it doesn't magically make your investment in your own roof (or anyone's roof, 5 years ago, for that matter) disappear. The money is still locked up in that roof (whether you paid for it, or locked up money by signing a 20 year contract), and so merely decoupling everything doesn't solve that issue, and in many ways we're already decoupling to a large extent with the securitisation of roof installations.
I see. Thanks for educating me on how SolarCity, and solar companies in general, work. Your post makes a lost of sense, and it seems that we agree on many things.
As for money locked up in solar panels, that's no different from traditional investments. If a factory is built, a better factory may be built a few years down the line, rendering the first one an inefficient use of capital. That's an unsolvable problem (unless you have a crystal ball), and it doesn't deter people from making investments. What makes solar different?
This addresses your point about upgrading. You can install the newer system on another roof, without incurring cost of removing the older system, and generate power (and therefore income) from both panels at once. As long as the older system is generating more power than its annual maintenance cost, it doesn't make economic sense to dismantle it.
Decoupling also means that if you decide to invest in solar energy, you can have it installed in whichever part of the world (or at least your country) gives the greatest ROI: the most sunlight, and the highest electricity tariffs. Maybe you live in a rented house or an apartment where you can't install solar panels. Giving a higher return will encourage more people to invest in solar.
Other advantages of decoupling will be the ability to invest the amount you want, whether $1000 or $100K, rather than the price of one solar system, the ability to make additional investments if you have more money later on, and the ability to liquidate an investment any time you need the money, or in a financial emergency. People will also be able to dip their toes into this market with a small investment, and see how it performs, before making a larger investment.