There are many ways to go green, though as I have identified, the vast bulk of the problem is in just a few areas -- personal transportation, electrical generation, building design/heating/cooling and agriculture.

While those who focus on CO2 work from the fact that both Natural Gas and Coal, which produce 70% of the USA's electricity, emit CO2, coal is a much bigger villain.

• Coal is 50% of the US electricity supply, gas is only 20%.
• Coal produces all sorts of nasty pollution in addition to CO2, including sulfur products for acid rain, radioactive elements and worst of all, fine particulates, which are major killers of the elderly.
• Coal mining is highly destructive, and lives are regularly lost.
• Coal power plants are not as efficient as gas ones. This is both due to the simplicity of gas plants, and the fact that many coal plants are older. The worst coal plants are almost twice as inefficient, and emit more than twice the greenhouse gasses, as gas plants. Some modern coal plants are a bit better, but the gap is still large.
• Coal plants are slower to turn off and on than gas plants. They are better than nuclear plants.
• There are lists of more at other web sites.

The problem is that coal is cheaper. Particularly once you have the coal plant. I've seen estimates all over the map but many suggest that the fuel cost of coal electricity is in the range of just 2-3 cents per kwh, and 1-2 cents more for gas fired. Hydro doesn't really have a fuel cost, and while nuclear does, it's a much harder cost to measure.

That cheaper price has given us a 50% coal electric infrastructure. With hydro, the amount of water that is going to flow through your plant is fixed by the weather. You want to use all of it (ideally at peak times) and keep your reservoirs at the same level each year. Nuclear is hard to start and stop, so you use it for base load. It's expensive to build, but you want to use the plants you have to their capacity.

So my understanding is that if demand on the grid goes down (say, because somebody puts solar panels on their roof or conserves energy) the first reaction of the power companies is to burn less natural gas, because it's a bit more expensive, and the easiest thing to cut back on. However, the power grids (there are 3 main ones in the USA and various sub-grids) are not superconductors, so due to line losses, it is cheaper to reduce output on the plants closest to the reduced demand. So the situation varies a lot.

All the power sources have their downsides. Nuclear's are well known and controversial. Hyrdo is clean but destroys river systems and habitats. Gas emits CO2 but is clean as far as fossil fuels go. (Leaks of it also emit methane.) Oil is barely used. Coal's only upside is its price, and the existing base of coal plants and mines.

So while it is good to look at reducing all energy production that has problems, right now if you want to do something green, it's a fair, if broad statement to say that the best way to do it is to stop the burning of coal.

What that means for people who don't run power companies is that reducing electrical demand in a sub-grid that is heavy with coal (such as Chicago or West Virginia) is a fair bit better than doing it in a coal-light sub-grid like California. And doing it in a place like China would be even better.

There is an irony here. Californians tend, on average, to be more eco-conscious than others. This is the birthplace of the Sierra Club after all. And because it is natural for people to focus on where they live, you see lots of effort to conserve energy or use alternative energy in California. But the same efforts would get 65% more bang for the buck if they took place in the midwest or southwest. This calculator claims to report the CO2 cost of electrical production in each zip code. It uses numbers from the North American Electric Reliability Council (NERC) for different sub-grids:

This conclusion will be disturbing for some. If you're considering putting a solar panel on your roof in California, you would do 65% better at reducing pollution if you put the panel up on a roof in Arizona. (Actually a little better as Arizona has better sun.) If you are considering putting a solar panel up in Vermont, you would do almost 3 times better to put it in the southwest, since not only is their power twice as dirty, but they get a lot more sun.

What you would not get is the personal satisfaction of seeing panels on your roof and feeling that you personally are green. But there really is no such thing as solar electrons. Electricity is just electricity. There's a big grid (and not being grid tied is really non-green) and the most you can do is improve how green the grid is. It doesn't make a difference if you put the solar panels up on your house or a house across town. And it makes a positive difference if you put it up where it will have the best effect. It just doesn't feel as good.

Now, can you go put panels on another roof? Not at present. But it certainly could be made to happen. In fact, oddly, the tax breaks are better for corporations who put up panels then they are for individuals, though this may change with new laws. Leaving out rebates and credits, a business could be set up to offer people in high-sun, high-coal areas subsidized solar power on their houses. The money they would have paid their power company could go instead to pay your power company as you continue to buy energy from your cleaner grid, having reduced demand in their dirtier grid. This works best when the power prices are similar -- with PG&E's "tiered" pricing in California this may not pan out.

It would also be possible to set up green power companies that put up green power plants in coal-heavy areas. They sell their power there, and the income would flow to investors on greener grids to pay for their grid power.

However, in a future blog post you're going to learn something even more surprising, if you've been a booster of solar. It's that it is a poor idea to put up solar panels at all, even in the coal-heavy, sunny southwest. In fact, it's one of the worst ways you could use your money to green the planet. Stay tuned.