March 21, 2014
Wind More Sustainable Than Solar Power
Brett Smith for redOrbit.com - Your Universe Online
The modern-day electrical grid is based on the notion of electricity on demand as generated by the burning of fossil fuels. Environmental and resource concerns have prompted a shift to renewable energy sources such as wind and solar power, but these energy sectors must grapple with the fact that the sun doesn’t always shine and the wind doesn’t always blow.
One solution is to store surplus wind or solar energy for later use and a new study from researchers at Stanford University has found that the wind energy sector can afford enough grid-scale storage to provide three days of uninterrupted power.
The study, which was published in the journal Energy & Environmental Science, also concluded that the solar industry can only afford about one day worth of energy storage.
"Whenever you build a new technology, you have to invest a large amount of energy up front," explained study author Michael Dale, a post-doctoral research associate at Stanford. "Studies show that wind turbines and solar photovoltaic installations now produce more energy than they consume. The question is, how much additional grid-scale storage can the wind and solar industries afford and still remain net energy providers to the electrical grid?"
"We looked at the additional burden that would be placed on the solar and wind industries by concurrently building out batteries and other storage technologies," Dale continued. "Our analysis shows that today's wind industry, even with a large amount of grid-scale storage, is energetically sustainable. We found that the solar industry can also achieve sustainable storage capacity by reducing the amount of energy that goes into making solar photovoltaics."
To reach their conclusion, the Stanford team looked at a range of storage systems for the grid, including batteries and geologic methods, such as pumped hydroelectric storage. The researchers found that wind power, in particular, lends itself to cost-effective energy storage.
"Wind technologies generate far more energy than they consume," Dale said. "Our study showed that wind actually produces enough surplus electricity to support up to 72 hours of either battery or geologic storage. This suggests that the industry could deploy enough storage to cope with three-day lulls in wind, common to many weather systems, and still provide net electricity to society."
For solar power, the researchers discovered that more work is required to make grid-scale power storage energetically sustainable. The study showed that some solar systems, such as single-crystal silicon cells, are expanding so quickly that they are net energy sinks – meaning they require more power than they deliver to the electrical grid. From a power standpoint, these types of industries "cannot support any level of storage," the researchers said.
"Our analysis showed that, from an energetic perspective, most photovoltaic technologies can only afford up to 24 hours of storage with an equal mix of battery and pumped hydropower," Dale said. "This suggests that solar photovoltaic systems could be deployed with enough storage to supply electricity at night, and the industry could still operate at a net energy surplus."
The key advantage wind power has over solar, the Stanford team said, is its relatively quick return on investment.
"Within a few months, a wind turbine generates enough electricity to pay back all of the energy it took to build it," said study author Sally Benson, a professor of energy resources engineering at Stanford. "But some photovoltaics have an energy payback time of almost two years. To sustainably support grid-scale storage will require continued reductions in the amount of fossil fuel used to manufacture photovoltaic cells."
"People often ask, is storage a good or bad solution for intermittent renewable energy?" Benson asked. "That question turns out to be way too simplistic. It's neither good nor bad. Although grid-scale storage of wind power might not be cost effective compared to buying power from the grid, it is energetically affordable, even with the wind industry growing at a double-digit pace.
"The solar industry needs to continue to reduce the amount of energy it needs to build photovoltaic modules before it can afford as much storage as wind can today,” she concluded.