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http://energybulletin.net/stories/2011-06-06/can-renewable-energy-outshine-fossil-fuels

Can renewable energy outshine fossil fuels?

I'm not popular with environmentalists when I tell them that renewables can only provide a small fraction of the energy that fossil fuels do in powering industrial civilization. In fact, I was recently called a liar at the screening of an anti-nuke film for suggesting so.

Many greenies imagine that someday we'll power our plasma TVs and computers with electricity from wind turbines and solar panels, drive electric cars to corporate jobs and fly biofuel-powered jets to European vacations. In short, they believe that our lives will be essentially unchanged when we switch from a dirty, fossil-fuel regime to renewable energy sources such as wind and solar.

To some environmentalists, what gets in the way of the renewable revolution is federal policy that favors greedy corporations. I've even been accused of secretly working for these corporations to spread disinformation about the promise of renewables.

But the question remains - can we live a high-energy lifestyle that doesn't pollute the atmosphere with climate- changing gases or depend upon finite fossil fuels? Can we keep our iPods and Blu-rays without destroying the planet?

Renewable enthusiasts claim that enough sunlight falls on the earth in one hour (or minute, depending on whom you talk to) to meet world energy demand for one year. And that if we covered just a small fraction of the planet's surface with solar panels we could produce all the energy we need - and more. To examine these claims of renewable energy's essential equivalence with fossil fuels, let's start with some basic principles:

1) Nearly everything is solar energy

The sun is the ultimate source of most of the energy we use, but we have to capture that solar energy in ways we can use it. Nature has its own "solar collectors" in the form of biomass (plants, trees), which have evolved over millennia to efficiently capture sunlight, and which we then burn, releasing carbon dioxide and energy. But the U.S. uses more energy each year than the amount the country produces annually through photosynthesis, the process by which solar energy is captured by U.S. forests, food crops, lawns, etc.

Fossil fuels are prehistoric biomass stores of plants and animals that have been concentrated over millions of years from intense geological heat and pressure into an extremely dense form of energy. Where solar panels can daily collect current solar energy, we daily burn oil from millions of years of solar energy - quite a difference.

2) It takes energy to get energy

To extract energy, process it into a form we can use and transport it to where it's needed requires large amounts of additional energy. Oil and gas wells must be drilled and pumped and the fuel transported and refined. Coal must be mined by stripping away land, digging tunnels or blowing up mountaintops. The materials used in solar photovoltaic panels must be mined and the panels manufactured. Corn for ethanol must be fertilized and mechanically-harvested. But also required is the energy to build the machines and facilities used throughout - drills, refineries, coal cars, tractors, etc.

A measure of how much energy is required for different sources is called "Energy Returned on Energy Invested" and is measured as a ratio, which is expected to sharply decline for diminishing, harder-to-extract fossil fuels. According to the report, "Searching for a Miracle" by Richard Heinberg, oil currently has a 19:1 ratio (19 units of energy produced from an expenditure of 1 unit), when it used to be closer to 100:1. Coal has a ratio of 50:1; natural gas is 10:1; wind is about 18:1; solar photovoltaics range from 3.75:1 to 10:1 and geothermal is from 2:1 to 13:1. Ethanol may take more energy to make than it yields at 0.5:1. Liquid fuel alternatives are especially low in their energy yield, making petroleum - which accounts for 95 percent of global transportation fuel - perhaps the hardest to replace.

3) Siting, intermittency, and storage

Renewable energy sources face other challenges as well. Many of the best sites for hydroelectric dams and wind turbines have already been taken so that with each successive installation the energy returned on energy invested drops. And sometimes the best sites are in remote areas far away from populations, so more energy has to be used for transportation and transmission.

Perhaps the most significant problem for renewables is their intermittency - solar panels only work when the sun is shining and wind turbines when the wind is blowing above a certain speed. So renewables can only be used as "peaking fuels" while the 24-hour, seven-day-a-week base load power that keeps hospitals, schools and police stations running comes largely from fossil fuels. Storage is a terribly complicated question, involving expensive batteries, themselves produced from finite minerals.
Today, wind and solar energy combined account for just a fraction of a percent (about 0.3 percent) of total U.S. energy use after nearly two decades of rapid growth. Hydroelectric stands at just over two percent while combustible renewables (which still contribute CO2) are nearly 10 percent.

It's clear that fossil fuels are required in copious quantities to develop and maintain the infrastructure for a renewable energy regime. In fact, that is the best possible use for these fast-diminishing, finite fuels. Then, renewables can ease the demise of the fossil fuel age, which fueled the most energy-intensive civilization on the planet.

Possibly in a century or two, renewables may be the world's primary energy source. It would be a de-globalized, less industrialized, more localized world where we would continue to rely on photosynthesis, thrive on low-tech, decentralized energy sources (micro-hydro, solar thermal, small-scale biodiesel) and use other energy as available. And we may only consume a quarter or less of the energy we use today.
Perhaps that's why people call me a liar. It's easier not to think about that.