One day in the not-too-distant future -- probably sooner than many expect -- some parts of the world will have power grids that are completely powered by renewables. Eventually, the entire world could be powered by renewables.

These are not green pie-in-the-sky fantasies, but the conclusions of recent research.

There is no doubt that renewable resources are positively vast. Solar alone could power the world: The solar energy that falls on the Earth every minute is more than the amount of fossil fuel the world uses every year. Wind alone could provide about 15 times the world's energy demand. The recoverable geothermal heat under the U.S. is about 140,000 times its annual energy consumption. Wave power alone could supply twice as much electricity as the world consumes.

Capturing that energy, and being able to use it to power everything, is the hard part.

Probably the most ambitious attempt to quantify that challenge to date has been done by Mark Jacobson and Mark Delucchi of Stanford University, who have published a series of papers over the past several years outlining how it could be done. In 2010, they published two papers (Part I and Part II) estimating how the world's energy demand for all purposes -- including electric power, transportation, heating and cooling -- could be met with renewables by 2030, and replace the existing energy generation mix by 2050:

3,800,000 5-MW wind turbines

49,000 300-MW concentrated solar plants

40,000 300-MW solar PV power plants

1.7 billion 3-kW rooftop PV systems

5,350 100-MW geothermal power plants

270 new 1300-MW hydroelectric power plants

720,000 0.75-MW wave devices

490,000 1-MW tidal turbines

Storage in grid-connected electric and hybrid-electric vehicles

Increased grid transmission capability

(A quick word on units: A kilowatt, or kW, is 1000 watts. A megawatt, or MW, is 1000 kW. A gigawatt, or GW, is 1000 MW.)

Surprisingly, Jacobson and Delucchi found that this power generation infrastructure would actually reduce world power demand by 30 percent, using only 0.41 percent more of the world's land for footprint and 0.59 percent more for spacing, at a similar cost to what we pay today. The main barriers to the transition, they concluded, "are primarily social and political, not technological or even economic."

So we know that, at least in theory, a global energy transition to renewables could be done.

Important questions still remain, however. Could the variable generation from renewables, including intermittent ones like wind and solar, meet fluctuating hourly demand within a single transmission region? And what would be the lowest cost mix of technologies that could achieve that?

A real-world model

A new paper from researchers at the University of Delaware attempts to answer these questions. They developed a model of how the PJM Interconnection (the RTO that coordinates the movement of wholesale electricity in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia), constituting one-fifth of U.S. electric power demand, could be met using only wind, solar, and storage.

The researchers ran a simulation program which evaluated 28 billion combinations of wind, solar and various storage technologies against four years (1999 to 2002) of historical grid load and weather data to determine the least costly solution that would meet the actual hourly demands on that grid. The total power capacity on the PMJ RTO during the simulation years was 72 GW.

The researchers estimated the total generation needed for each type of resource, and did not specify the number and size of generators. But based on the information in the paper and its summary in ScienceDaily, I find that one of the model's solutions could be met with roughly:

4.25 million 4-kW (residential) rooftop solar systems

13,600 5-MW offshore wind turbines

38,000 3-MW onshore wind turbines

No more than 72 hours' worth of distributed hydrogen storage

Some of these numbers may seem impractically large at first blush, but they're useful for imagining what the system might look like, and they're feasible. A real-world generation mix would involve fewer and larger generators, including offshore wind turbines twice as large, larger onshore turbines, and commercial rooftop solar systems up to 500 kW in size, like those installed on Ikea and Walmart buildings over the past two years.

Including utility-scale solar PV and solar thermal systems in the mix would sharply reduce the number of rooftop systems needed. Adding geothermal and marine energy generation into the mix -- a reasonable bet by 2030 -- could sharply reduce the number of wind turbines needed. Finally, eliminating 30 percent or more of the load through efficiency improvements, which is certainly possible, would further reduce the system size.

If tens of thousands of wind turbines still seems unrealistic, consider this: Everyone now seems convinced that the U.S. will drill another 12,000 (or if Continental's CEO Harold Hamm is to be believed, 39,000) tight oil wells over the next decade, at $10 to $13 million each, which will become marginally productive "stripper wells" after 10 years or less. Is it so hard to believe that we could put up 50,000 wind turbines (at $1.3 - $2.2 million/MW capacity, or around $5 - $10 million a pop for a 5 MW turbine) in 20 years, which will produce energy for 20 years or longer?

Surprising results

Several remarkable conclusions emerged from the Delaware study.

Consider this graph of the simulation:

Over four years, generation from fossil fuels would have been needed only five times in summer months, at only about one-third of the total system generation capacity. That fossil fuel capacity would be met by natural gas.

This renewably-powered grid could meet 99.9% of the demand hours in 2030, at a cost comparable to today's grid power, without subsidies.

Due to the high cost of storage with today's technologies, the researchers found that it was cheaper to build almost three times the generation capacity needed to meet demand than to build exactly the generation capacity needed with more backup. However, based on the enormous amount of research and development going into storage technologies worldwide, I am confident that significantly better and cheaper storage options will be available by 2030. Better storage would reduce the number of generators needed to meet the Delaware researchers' model, substantially reducing the cost of their solution.

Powering ahead

Briefly, let's review.

We know that the renewable resources are orders of magnitude larger than what we need to run the world.

We know that the grid can be almost completely powered by renewables, with a small amount of natural gas standby generation, using a reasonable and feasible number of collectors.

As I detailed in March , we know that renewables now provide up to 30 percent of the power on well-managed grids in Europe, and could do the same in the U.S. Indeed, the German experience has shown that renewables tend to push nuclear and fossil fuel capacity off the grid.

As I wrote in October , we know that a renewably-powered grid is actually more stable than a conventional fossil fuel-powered grid, and can accommodate an even larger percentage of intermittent renewable power. All it takes is good grid design and planning. Those who argue that the grid will always need 100 percent standby capacity from conventional fossil fuel plants because renewables are intermittent are simply wrong. It's like saying that because removing one leg of a three-legged milking stool will make it fall down, all chairs must have exactly three legs. Building the grid for distributed renewables is like building a chair with 50,000 legs -- it's inherently more stable than the centralized generation architecture of today.

We know that storage is advancing rapidly, and will enable very high penetration rates of renewables in the coming decades.

And we know that by 2030, renewably-generated grid power will be no more expensive than the grid power we have today, using very modest assumptions about the future cost of fossil fuels. In my expert opinion, nearly all of the comparative cost studies I've seen are far too conservative on that point. By 2030, the cost of fossil fuels will be far higher than historical trends suggest, making renewable power competitive with conventional power much earlier than anticipated.

In fact, recent studies show that unsubsidized solar generation could be cheaper than conventional grid power within a decade. Following current cost trends, solar is already competitive with regular grid power in sunny regions like the Southwest United States, at $0.12/kWh, and will be the cheapest way to generate power in Latin America, Africa, the Middle East, Australia, India, and much of Asia by 2018, as I wrote last November .

A new report from the Institute for Local Self-Reliance finds that 300 GW of unsubsidized solar power will be competitive with conventional grid power in the U.S. by 2022, meeting 9 percent of the nation's electricity demand. As the report's author John Farrell observes, the challenge is no longer how to build renewable power cheaply enough; it's how to prepare for it.

Even in the laggard U.S., despite the high-profile troubles of some manufacturing companies, solar is powering ahead. A new report from the Solar Energy Industries Association and GTM Research finds that third quarter solar installations jumped 44 percent over the previous year. The U.S. will install a record 3.2 GW of new solar capacity in 2012, bringing the national total of solar PV to nearly 6 GW. And that growth rate is expected to continue, with 7.8 GW of new capacity installed in 2016.

Meanwhile, the list of countries aiming to supply most or all of their grid power from renewables continues to grow. The most recent is Australia, which recently released a white paper outlining how the country could meet 40 percent of its power from renewables by 2035, and 85 percent by 2050.

To repeat Jacobson and Delucchi: The barriers to a totally renewably-powered world are social and political, not technological or economic. And those barriers are falling fast.

So get ready, grid operators. The energy transition juggernaut is coming. The only real question now is whether you'll be ready for it in time.

Photo: BrightSource's 377 MW Ivanpah solar project, the world's largest solar thermal plant, now under construction in California's Mojave Desert. Image from Brightsource.

Update, Dec. 13: After soliciting feedback on this article from the principal author of the University of Delaware paper, I should clarify a few things.

First, the simulation modeled the PJM grid load in 1999-2002, but with 2030 prices. They did not try to predict the grid composition or load in 2030. Partially, this was to simplify the calculations they needed to perform and stay within their computational constraints.

Second, the lowest-cost solution they found used grid-connected vehicles for storage, not the hydrogen solution I described in the article, although hydrogen was a close second (and the researchers may have overestimated its cost, so it might in fact be the cheapest of the storage technologies they used in the simulation). The generation and storage capacity for the grid-connected vehicle solution is shown in the following table.

That solution could be satisfied using:

4 million 4-kW (residential) rooftop solar systems

17,940 5-MW offshore wind turbines

41,333 3-MW onshore wind turbines

No more than 72 hours' worth of distributed vehicle storage

The authors also point out that at 90 percent penetration, there was no solar in the system. Only when the penetration of renewables was increased to 99.9 percent did the solar portion rise to around 30 GW, with the inland wind generation staying roughly the same.

The authors acknowledge that other technologies, like demand response, could lead to even cheaper systems, and could be incorporated into future simulations.

This post was originally published on Smartplanet.com