Can renewable energy make a dent in fossil fuels?

That's how many rooftops you'd have to cover with solar panels to displace a cubic mile of oil (CMO), a measure of energy consumption, according to Ripudaman Malhotra, who oversees research on fossil fuels at SRI International. The electricity captured in those hypothetical solar panels in a year (2.1 kilowatts each) would roughly equal the energy in a CMO. The world consumes a little over 1 CMO of oil a year right now and about 3 CMOs of energy from all sources.

Put another way, we'd need to equip 250,000 roofs a day with solar panels for the next 50 years to have enough photovoltaic infrastructure to provide the world with a CMO's worth of solar-generated electricity for a year. We're nowhere close to that pace.

The great obstacle to get around with OTEC implementation for wide and practically useful levels is cost. It is expensive and is at and is not cost effective to mass produce at this time. This type of energy is very clean and would not add pollutants to the air. We are not as technologically advanced in this area and therefore, we do not have the technology to work with the plant and produce it on a large scale basis. At this time, it could actually in fact damage the environment so much more research needs to be done.

But don't blame the solar industry. You'd also have to erect a 900-megawatt nuclear power plant every week for 50 years to get enough plants (2,500) to produce the same energy in a year to equal a CMO. Wind power? You need 3 million for a CMO, or 1,200 a week planted in the ground over the next 50 years. Demand for power also continues to escalate with economic development in the emerging world.

"In 30 years we will need six CMOs, so where are we going to get that?" Malhotra said. "I'm trying to communicate the scale of the problem."

The CMO is a figure you might begin to hear more as utilities and governments map out their renewable energy strategies. SRI's Hew Crane came up with the term as a way to normalize all the different measurements (kilowatt-hours, BTUs, million barrels of oil equivalents, cubic feet of gas, etc.) in the energy business.

It's also a big enough measure to suit the global energy market without saddling everyone with a train of zeros. Many of these stats and a far lengthier discussion of the issue will be found in a book coming from Oxford University Press by Crane, Malhotra, and Ed Kinderman called A Cubic Meter of Oil.

And judging by some of the stats Malhotra gave me, the book will alarm policy makers, environmentalists, and pretty much anyone else interested in weaning ourselves from fossil fuels. (To be honest, one of the truly great things about this job is getting the bejeezus scared out of you on a regular basis. One day, China is plunging into a water crisis. The next day, doctors report seeing malaria spreading to new regions because of climate change.)

One of the more compelling aspects of Malhotra's research is how it highlights the amount of energy, particularly in the form of fossil fuels, that the world consumes. Oil provided about one-third of worldwide energy (1.06 CMO) in 2006 followed by coal (0.81) and natural gas (0.61). Together, the three fossil fuels accounted for 2.48 CMOs of the 3 CMOs consumed that year.

The figures drop quickly after that. The fourth largest source of energy is biomass, mostly in the form of burning wood. Biomass, however, only provide 0.19 CMOs, while hydroelectric and nuclear provided, respectively, 0.17 and .015 CMOs.

Wind and solar accounted for less than 0.005 CMOs.