The Wall Street Journal’s recent Energy Journal Report asked “The Experts,” a group of industry and thought leaders, to discuss what renewable energy sources they thought would be most successful. Among the responses, there were quite a few different predictions, as well as a consensus on which renewable energy sources would prosper going forward. Solar

Robert Rapier: My Money Is on Solar PV Solar and wind power have both experienced explosive growth over the past decade, but both still account for a very small portion of the world's energy. Global wind power capacity grew from under 5 gigawatts (GW) in 1996 to nearly 240 GW by 2011—a nearly 50-fold increase. But that translated into only 2.8% of the electricity produced in the U.S. and 1.6% of the electricity produced in China.

Likewise, since 2010 solar photovoltaic (PV) capacity has been added in more than 100 countries, and the estimated global capacity at the end of 2011 was 70 GW—a tenfold increase over the previous five years. But this resulted in only 0.5% of the global electricity demand in 2011.

Solar heating—consisting of solar water heating, space heating for homes and industrial process heat—is often overlooked in discussions of renewable energy. However, global capacity of solar heating applications is far larger than that of solar PV. According to the REN21 Renewables Global Status Report, at the end of 2011 total global capacity of solar hot water and space heating was 232 gigawatts of thermal energy (GWth) (including a solar water heater on my own roof in Hawaii). So there are some very-fast-growing renewable energy options, and there are also some that are well-established. But if I had to put my money on one option that will likely command a much larger share of energy production in the future, it would be solar PV.

Michael Levi: Three Reasons Solar Will Succeed If I had to bet on one renewable source ultimately making a very large impact it would be solar. There are three big reasons to look to solar over other renewable energy supplies.

Solar can take advantage of improvements in materials, computing and nanotechnology in ways other technologies can't do nearly as effectively. Energy innovation is at its most powerful when it can leverage gains in other sectors. Solar also has a host of initial niches it can grow in, from rooftop generation in places like California, to off-grid and micro-grid energy in often-sunny developing countries that lack good infrastructure. Having moderate-sized markets to grow in is critical to scaling technology and bringing costs down. Solar is also a much better match for our energy demand than wind is. Solar power peaks when it's hot—exactly when people want to crank up their air conditioners. Wind power peaks in the middle of the night when people are using a lot less power.

Jeffrey Ball: Solar's Future Seems Bright Most predictions about the future of energy turn out to be wrong. Oh, well. Here's one: Solar power could prove a big, though probably not dominant, energy source over the next couple of decades.

Longer term, solar's future seems bright. The cost of producing polysilicon-based solar panels—today's dominant solar technology—has plummeted over the past two years. In a few spots around the globe—places with lots of sun and quite high electricity prices—solar today is starting to compete on price with conventional power (albeit when taking into account the tax breaks these energy sources get).

Natural Gas

Craig Pirrong: Nothing Beats Natural Gas All renewables are cursed with fundamental problems that make their future stand-alone (i.e. unsubsidized) viability as anything but a marginal energy source highly questionable.

With respect to electricity generation, the major renewables (wind and solar) are both intermittent and diffuse. These are obstacles inherent in the source of the energy that will be difficult to surmount. One illustration. Here in Texas, when it gets hot—and the demand for electricity spikes—the wind stops blowing. Given the fact that we need generation most when it is hot, this is a serious deficiency. Solar has greater potential, given the prospects for innovations that improve the efficiency of solar panels and reduce the cost of producing them. But even for solar, the vicissitudes of the sun (which vary by season and location) and the diffusive nature of solar power limit its potential.

What's more, the revolution in natural gas undermines the economics of these technologies.

Hydropower

Mazen Skaf: Hydropower's Dominance Will Continue Even as a relatively mature technology, hydro will continue to attract attention due to the advantages it offers: Lowest LCOE, grid stability, and potential for energy storage and complementarity with other renewables. Further, hydropower (including small hydro) provides options for building additional capacity at existing facilities or installing generation capacity at dam locations with no current generation at attractive marginal investment costs in the range of $500 to $800/kW.

Multiple Sources

Iván Martén: Expect a Healthy Mix of Renewables Several renewable-energy sources are technologically mature. Several already are making a significant contribution to energy generation, such as hydropower in Brazil, biomass in Finland, onshore wind in Denmark, solar photovoltaic in Germany or geothermal energy in Indonesia. Apart from hydropower, this strong footprint so far has largely been accomplished through strong regulatory support. Future growth of renewable energy will increasingly be driven by cost competitiveness with fossil-fuel based generation: The cost of renewables will continue to decline while the cost of fossil fuels is expected to increase further. Today, solar and wind have already reached this point in several countries that have abundant resources and high cost of electricity.

Moreover, an increasing share of fluctuating solar and wind energy will drive higher demand for flexible and dispatchable "green energy" sources. If electricity storage becomes cheap, as expected, that could be a true game changer.

In general, adoption of a diversified mix of different renewable energy sources including storage will benefit power quality and overall security of supply.

Jerry Taylor: The Best Prediction: Who Knows? Which renewable has the best chance of breaking through? No one really knows because no one can reliably predict which of the many ambitious R&D projects—if any—has the best chance of success. And no one can confidently predict what will happen to conventional energy prices…the other important factor in this equation. Confident predictions have been offered in the past but, as Vaclav Smil demonstrates in his excellent book "Energy at the Crossroads" (MIT Press, 2005), those predictions have been, without exception, not worth the paper they've been printed on.

All we can say for certain is that the government has no better crystal ball than the private sector so the former should not be second-guessing investments made by the latter.

Mark Thurber: Look Out for Wild Cards The most intriguing renewable energy technologies are those that have the most room to improve. Continued incremental improvement in wind and solar PV technologies should keep adding up over time, but the fact remains that these technologies have been around for a long time and are comparatively mature. More surprises may come from wild cards with which there is less experience. Perhaps concentrating solar power can make significant strides as we learn from the first large installations. Maybe the same subsurface expertise that has made unconventional oil and gas economic can lead to breakthroughs in enhanced geothermal systems, in which a hydraulic-fracturing-like process is used to create channels in rock through which fluid is pumped to absorb the heat at greater depths.

Kate Gordon: It Depends Where You Are This is one situation where the right answer really is "All of the above." Energy issues are inherently regional: Different parts of the country have different natural resources and energy needs. We see that in the oil-and-gas sector, with big new discoveries in North Dakota and California, but no major resources in the upper Midwest and Pacific Northwest, for example. Same goes for renewables: Some parts of the U.S. are windier than others, some are sunnier, some have better access to hydroelectricity or geothermal resources…. You get the point.

Ariel Cohen: Energy Is Not a Matter of Religious Faith Renewable energy is not going to come from one source, but from a number of technologies, including solar and wind, which for now appear to be the leaders in renewable electricity generation.

Different U.S. states and different regions of the world will have different energy mixes, including among the renewables. However, it is important to remember that for now these technologies are not competitive, BTU to BTU, with fossil fuels, if the government phases out the current tax credits.

Todd Myers: Whatever the Market Decides Let's imagine we are in the year 2025 and tidal power accounts for 10% of electric generation. That would be a dramatic increase. By that time, however, giving homeowners more control over their energy using the Smart Grid could reduce demand by a similar amount. If a penny saved is a penny earned, why would we focus more on "renewable" tidal power than technologies yielding the same carbon emissions reduction and energy savings?

Given a choice between algae-based biofuel or expanding high-speed Internet access to encourage telecommuting and reduced fuel use, which should we choose? Does it matter that one is a "renewable" energy source and the other isn't?
This is the beauty of the free market. As long as there are costs to energy use and the impacts of energy use, the free market treats all approaches equally, without politics, as long as they effectively save resources. Given a choice between solving our energy and environmental demands by narrowing our focus to a few choices or expanding our vision to include any approach that conserves energy, we will be more successful by embracing all potential options.

Based on the responses of all of the experts, the consensus is that while solar will be widely successful, a mixture of all of the renewable energy options seems to be the most successful. Interestingly, there won’t be one dominant source of renewable energy as much as there will be dominant sources for different regions based on the environment and the resources available.

To read all of the expert’s responses, head over to the Wall Street Journal.

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