Whenever anyone talks about sustainability, there are three basic facts that need to be understood:
1 - Nothing you build will last forever.
2 - There's no such thing as something for nothing.
3 - Throughout history, industrial economies have changed from one resource to another, usually without so much as a headline in the newspaper.
Since number three is the fact that is most surprising to many, I will begin with it. 200 years ago, houses and buildings were constructed almost exclusively from wood and brick. In those days, efficient methods for making both were common, but steel took days to manufacture, and had to be made from already well processed pure iron. Both the fuel and time needs were tremendous to conduct two separate chemical processes each taking days. Further, the quantities made were whatever you could fit in a single crucible.
Bessemer discovered a fast process for making steel in 1855, so fast in fact that it only took 10-20 minutes. The result was the first steel buildings and ships. With Steel, the size of structures increased tremendously, and the skyscraper, along with its steel elevator, became not only a possibility but something neccesary to provide commercial space for the fast growing cities. It also allowed for the internal combustion engine, whose fine moving parts cannot be made effectively from other materials, and with it the car and the airplane.
The Bessemer process could remove many impurities from the original iron ore, and together with the Blast Furnace, silion and silicates, manganese and permanganates, carbon, and sulfur could all be effectively removed. The one thing it could not effectively remove, however, was phosphate, so for the process to work, low-phosphate ores had to be used.
Unfortunately the world began running out of low-phosphate ores in the 1950's, so what did the invisible hand "do"? It introduced two new processes. The first was the Basic Oxygen Process, which took slightly longer (30-40 minutes) but could remove phosphate from the molten steel and had tighter control over the chemistry, allowing new alloys such as Boron Steel to be produced for the first time, and Stainless Steel (also known as Chromium Steel) to be produced inexpensively, and the exact carbon content to be dictated to a hundredth of a percent. The cost is a little higher, but you get higher quality with it. The second was the Electric Arc Process, which for inexpensive steel needs would recycle scrap metal effectively. Between these two, quality improved, new resources were used, and the world did not end, while the Petronas Towers in Kuala Lumpur would set a record for the tallest building in the world a few decades later.
This is not the only example. When strikes and labor politics made the price of coal more expensive, Americans switched to heating with oil and natural gas. Before this, Europeans had switched from firewood to coal as the great forests of Europe were gradually axed away during the Middle Ages, but those castles, those great Cathedrals, and all the splendor of medieval art and music was made with fireplaces burning wood, and those were still around when the wood went away, and before then, it was far easier to go outside to axe a tree then to go underground and risk your neck mining for coal.
No power plant or road we build today is going to last 60 years, so why are we thinking in terms of 600? We should only consider what power sources will still be available 60 years from now when building that plant, and the free market has a device for that too, it's called a futures market. Investors buy up resources now to sell them later at a higher prices, creating a clean and smooth and flat distribution of resources when the market is sufficiently large and well informed, and they do try to be both for their own self-interest. And if people really will benefit from more expense now to avoid expense later (e.g. flourescents), they will buy them, but they probably don't, as they are already in debt and one dollar not repaid now will be a dollar repaid with interest later.
Lastly, and addressing number two, whenever something is used, something is lost, and that includes the materials to build solar panels, and the materials used to make the materials to make solar panels, as plastics and long complex molecules are almost always involved. There is always chemistry involved, and always wasteage, and the free market is a far better evaluator of what the true costs of that wastage is then some government bureaucrat whose never had a job outside of bureaucracy, or scientist specifically trained to only see from the perspective of his field. There is more to cost then electricity and fuel - even things like transportation, labor, land, and the space and finances lost from holding inventory are significant. The reality is that sustainability is not sustainable, as nothing is and we will see when the climate changes and the wind no longer blows where it did, or we run out of some chemical required in the manufacture of solar panels, or even great dust and ash from a supervolcano eruption block the sun. Everything must shift with its right and proper season, and this includes all sources of energy. Sustainability is a vain and impossible notion.