Last week I wrote about what I consider the main goal of green electricity efforts, namely to stop burning coal. You can do that, to some extent, by removing demand from the grid in places where the grid is coal-heavy. Even in other places, removing demand from the grid will be fairly effective at reducing the production of greenhouse gases.
Update: Since this article a flood of cheap solar panels from China has been changing some of the economics discussed here. I have not altered the article but some of its conclusions deserve adjustment.
No matter what you do -- conserve, or put up solar or wind -- your goal is to take power off the grid. Many people however, consciously or unconsciously take a different goal -- they want to feel that they are doing the green thing. They want their electricity to be clean. This is actually a dangerous idea, I believe. Electrons are electrons. In terms of reducing emissions, you get the exact same result if you put a solar panel on your house than if you put it on your neighbour's house. You even get a better result if you put it on a house that's powered by a coal plant, so long as you also reap the benefit (in dollars) of the electricity it makes.
People don't like to accept this, but it's much better to put a wind turbine somewhere windy than on your own house. Much better to put a solar panel somewhere sunny than on your own house. And much better in all cases if the power you offset is generated by more by coal than at your house.
However, the real consequences are much deeper. The following numbers reveal it is generally a bad idea to put up solar panels at all, at least right now. That's because, as you will see below, solar panels are a terrible way to spend money and time to make greener electricity. Absolutely dreadful. Their only attribute is making you feel good because they are on your roof. But you should not feel good, because you could (in theory, and I believe with not much work in practice) have made the planet much greener by using the money you spent on the panels in other ways.
The true goal is to find the method that provides the most bang per buck in removing load from the dirty grid.
Keep reading to see the math and a spreadsheet with some very surprising numbers about what techniques do that the best.