Here at Gizmag we cover a seemingly endless stream of renewable energy technologies designed to wean us off our reliance on fossil fuels and improve the health of the planet. As important as such developments are, for these technologies to have an impact they must of course be implemented – and on a large scale. What has been sorely lacking is a plan to accomplish such a Herculean feat. Now researchers from the University of California-Davis and Stanford University have published a study that details one scenario to completely convert the world to clean, renewable energy sources – and they say it could be done in 20 to 40 years using technology available today at costs comparable to fossil fuel-based energy.

Electricity the key

The two part paper coauthored by
Stanford researcher Mark Z. Jacobson and Mark Delucchi, of
UC-Davis, evaluates not only the technology required, but also the costs and material requirements for converting the planet to renewable energy sources. Their plan would see the world running predominantly on electricity, with 90 percent of this sourced from
wind and
solar. The remainder would be made up from
hydroelectric sources, which would provide around four percent each, while
wave and
tidal power would contribute the remaining two percent.

For our transport energy needs, cars, trucks, motorbikes, ships and trains would be powered by electricity and hydrogen fuel cells, while aircraft would be fueled by liquid hydrogen. Commercial processes would also be powered by electricity and hydrogen, which would be produced using electricity. Meanwhile, our homes would eschew natural gas and coal in favor of electric heaters, while water would be preheated by the sun.

20 to 40 years

"We wanted to quantify what is necessary in order to replace all the current energy infrastructure – for all purposes – with a really clean and sustainable energy infrastructure within 20 to 40 years," said Jacobson.

To that end, the plan would see all new energy generation coming from wind, water and solar by 2030, and all pre-existing energy production converted by 2050. The researchers say that the millions of lives saved by the reduction in air pollution and a 30 percent reduction in world energy demand – thanks to the conversion of combustion processes to the more efficient electrical and hydrogen fuel cell processes – would help keep the cost of such a conversion down.

"When you actually account for all the costs to society – including medical costs – of the current fuel structure, the costs of our plan are relatively similar to what we have today," Jacobson said.

Addressing variability of solar and wind

To overcome that variability of wind and solar and ensure there is a reliable base load of energy Jacobson says wind, water and solar energy sources could be combined as a single commodity as they are generally complimentary. Solar peaks during the day, while wind generally peaks at night, and hydroelectric could be used used to fill the gaps.

The plan also envisages the connection of geographically diverse regions using long-distance transmission to overcome energy shortfalls in a given area. If the wind or solar energy generation conditions are poor in a particular area on a given day, connecting widely dispersed sites would allow electricity to be provided from a few hundred miles away where the sun is shining or the wind blowing.

"With a system that is 100 percent wind, water and solar, you can't use normal methods for matching supply and demand. You have to have what people call a supergrid, with long-distance transmission and really good management," said Delucci.

Additionally, off-peak electricity could be used to produce hydrogen for the industrial and transportation sectors and, as it is today, pricing could be used to control peak demands.

Material considerations

While the large-scale construction of wind and solar power plants would require large amounts of materials, the researchers found that even rare materials, such as platinum and the rare earth metals, are available in sufficient amounts for their plan to be realized. They say recycling could also be used to extend the supply further.

"For solar cells there are different materials, but there are so many choices that if one becomes short, you can switch," Jacobson said. "Major materials for wind energy are concrete and steel and there is no shortage of those."

Crunching the numbers

The researchers also calculated how many wind turbines, solar plants, rooftop photovoltaic cells, geothermal, hydroelectric, tidal and wave-energy installations would be required to provide 100 percent of the world’s energy needs. They found that 0.4 percent of the world’s land would be needed – mostly dedicated to solar – and that the spacing between installations – mostly wind turbine spacing – would add another 0.6 percent, much of which could be used for other purposes.

"Most of the land between wind turbines is available for other uses, such as pasture or farming," Jacobson said. "The actual footprint required by wind turbines to power half the world's energy is less than the area of Manhattan."

Long way to go

Already 70 percent of the hydroelectric sources needed to realize the plan are already in place, but only about one percent of the wind turbines required and an even lesser percentage of solar power. But the researchers say their plan is doable.

"This really involves a large scale transformation. It would require an effort comparable to the Apollo moon project or constructing the interstate highway system," Jacobson says. “But it is possible, without even having to go to new technologies. We really need to just decide collectively that this is the direction we want to head as a society."

Th researchers two part paper appears in the journal Energy Policy.