Google Chrome's ad blocking is unfortunately not as good as Firefox's, so occasionally I see ads on the web. I generally ignore them, but I do click on the occasional one either because it's interesting or because I don't like it (since my clicks cost them money!). On The Straight Dope today I came across "Home Made Energy: Renewable Energy For The Rest Of Us". This company sells a guide which purports to tell you how to run your house purely off wind and solar power for less than $200. I'm skeptical.
First of all, electricity costs something like twenty cents a kilowatt-hour, and they're talking about saving some hundreds of dollars a month. So let's say $100 a month - that's 500 kWh a month, or about 700 W. More credible sources cite about $10/watt for solar power, or $7000 for such a system. So is this guide really nonsense? Not necessarily.
Solar cells are expensive to make - think of making microchips the size of a solar panel. Not quite fair - they don't need the density of components, but they do need the extremely pure silicon and the high-vacuum manufacturing - but a sign that there's a good reason they aren't cheap. A solar system also needs some electronics for converting electricity to a useful voltage, and some way to deal with the fact that the amount of solar power varies in a way that has little to do with the demand for solar power.
I think a reasonable guide of this sort might be able to point readers at where to scavenge used or discarded parts for all of the above. The power electronics are definitely something a clever amateur could build out of scavenged parts (at some risk to their life!), but I think it would take incredible luck to obtain solar cells that worked and were that cheap. It's also possible that a guidebook could explain how to take advantages of government programs to encourage renewable energy, perhaps obtaining discounts or tax credits on the hardware.
The biggest way governments or energy companies could encourage renewable energy of this sort is to eliminate the need for energy storage. Since most of the people who'd be considering this sort of project already have a connection to the electricity grid, if the utility company is willing, you could simply sell them electricity whenever you make more than you need, and buy electricity when you need more than you buy.
Ideally, as a homeowner, you'd get paid the same price for the electricity you sell as you pay for the electricity you buy. Unfortunately, this is often not the case. There are good reasons electric companies would pay less for electricity they get from homeowners than they charge homeowners; for one thing, all those wires to distribute the electricity aren't free. More subtly, it's really difficult to store electricity on the scale that utility companies deal with, so they have to work quite hard to make sure that the amount of electricity fed into the grid in any given second exactly matches the electricity drawn out of it in that second. Having countless small generators outside their control is going to make that job much more difficult.
That said, persuading companies to act in a way that costs them money but benefits all people is a natural role of government. Paper mills have waste treatment systems not out of the goodness of their nonexistent hearts but because the government charges them massive fines or shuts them down if their effluent is too toxic. So if the government were to force (or fund) companies to pay consumers the same price for electricity they generate as they charge for electricity they use, suddenly a lot more small-scale power generation projects would become cost-effective.
Incidentally, another approach for storing solar power for when you need it is to let it charge your solar car (or plug-in hybrid). This has even been proposed as a scheme to help load-levelling in the power grid.
Anyway, the upshot of all this is that I think that yes, it is occasionally possible to scrounge together a cheap renewable energy system. But I suspect that the claimed $200 is only possible with in the best possible case - scavenged parts, government subsidies, living in a sunny desert, having a cooperative utility company, and incredible luck.