Without sounding like a braggart, I have to say that the response to the article has been remarkable. It has been one of the most e-mailed articles on WSJ.com. And I have been getting dozens of emails and lots of phone calls – nearly all of them positive. (One negative call came from a long-time solar power booster here in Austin who insisted my math was wrong.)

The response to the article, while flattering, leads me to two additional points: People are eager for information that helps them understand the problems of scale in any energy transition; and second, when it comes to future energy sources, we are going to need them all.

In the Journal article, I didn’t do anything fancy, just basic arithmetic. I looked at the latest data from the U.S. Energy Information Administration , which shows that total solar and wind output for 2008 will likely be about 45,493,000 megawatt-hours. That sounds significant until you consider this number: 4,118,198,000 megawatt-hours. That’s the total amount of electricity generated during the rolling 12-month period that ended last November. Thus, solar and wind are providing about 1.1% of US electricity needs.

I converted the energy produced by U.S. wind and solar installations into oil equivalents. The standard conversion of electricity into oil terms is straightforward: 1 barrel of oil contains the energy equivalent of 1.64 megawatt-hours of electricity. Thus, 45,493,000 megawatt-hours divided by 1.64 megawatt-hours per barrel of oil = 27.7 million barrels of oil equivalent from solar and wind for all of 2008. Divide that number by 365 days and you find that solar and wind are providing the equivalent of 76,000 barrels of oil per day. That sounds significant until you realize that America’s total primary energy use is about 47.4 million barrels of oil equivalent per day .

Put another way, that 76,000 barrels of oil equivalent per day is approximately equal to the raw energy production from an average-size coal mine. Last month, I visited the Cardinal underground coal mine in western Kentucky which produces about 15,350 tons of bituminous coal per day. Each pound of coal contains 12,500 Btus. Thus, on an average day, the Cardinal mine produces the raw energy equivalent of about 66,000 barrels of oil.

So how does America’s primary energy usage of 47.4 million barrels of oil equivalent per day, stack up? Well, oil has the biggest share, with about 19 million barrels per day. Natural gas is the second biggest contributor, supplying the equivalent of 11.9 million barrels of oil while coal provides with the equivalent of 11.5 million barrels of oil per day. The balance comes from nuclear power (about 3.8 million barrels per day), and hydropower (about 1.1 million barrels), with smaller contributions coming from wind, solar, geothermal, corn ethanol, wood waste, and other sources.

Looking back, I think the reaction to the Journal article comes from the fact that it gives readers a common, easily understandable unit of energy measure – in this case, barrels of oil equivalent per day -- that allows them to make an apples-to-apples comparison of different energy sources. And by doing so, the article exposes much of the nonsensical rhetoric coming out of Washington.

My second point: The reality is that when it comes to our future energy needs, we are going to need them all: hydrocarbons, nuclear, renewables, geothermal, etc. Or rather, we need almost all. Given a choice, I will leave corn ethanol off that list. The plain truth is that the world’s voracious hunger – about 223 million barrels of oil equivalent per day of primary energy – is simply too large for it to be satisfied any time soon with “green” power.

No matter how quickly solar power and wind power are able to grow in the next few years, we are not going to leave hydrocarbons behind any time soon. We can not, will not, simply substitute wind and solar for oil and coal any time over the next few decades. Trillions of dollars have been invested in the hydrocarbon infrastructure. We are not going to forsake all of that investment -- particularly now, with the global economy is a protracted slump -- in order to have a wholesale adoption of other sources of primary energy, regardless of their political appeal.

I’ll end here by quoting one of my favorite energy writers, Vaclav Smil. In November, he wrote an excellent article for The American about energy transitions, “There is one thing all energy transitions have in common: they are prolonged affairs that take decades to accomplish,” he wrote, “and the greater the scale of prevailing uses and conversions the longer the substitutions will take.”

Alas, neither Nancy Pelosi nor Barack Obama are being truthful with the American public about just how prolonged our energy transition will be.