A March 13 Margaret Ryan report on AolEnergy says, "Integrating more renewables into the US grid will be costly and have unintended consequences, including potential for increased carbon emissions, that policymakers need to plan for, warns a new Massachusetts Institute of Technology Energy Initiative study."
The study's message for policymakers and regulators is that intermittent sources will cost more for total operations, and they have to decide who is going to pay for it – a message that is "not popular," conceded MIT Professor John Deutch.
Problematic for Generators
The US in 2011 received about 42% of its electricity from coal, 25% from natural gas, 19% from nuclear, 8% from hydro and less than 5% from renewables, but more than half the states are pursuing policies requiring more renewables use.
Read more about state policies leading renewable energy uptake on AOL Energy here.
Researchers found that, even now, increasing amounts of intermittent renewables are forcing grid operators to order cycling of fossil fuel thermal plants in order to keep the grid balanced. While natural gas combustion turbines can start and stop fairly quickly, coal and nuclear plants were designed to run flat out, with start up and shut down taking comparably longer.
For nuclear, load-following – raising and lowering power to compensate for renewables whose output varies over time, like wind and solar – stresses equipment and raises safety issues, said MIT Professor Howard Herzog. Moniz added that nuclear operating costs are so relatively low that decreasing nuclear output makes no economic sense.
Natural Gas the Clear Choice - For Now
For coal, Herzog said, load-following increases thermal and chemical stresses on plant components, decreases efficiency of fuel use with a concomitant increase in carbon emissions per megawatt-hour, decreases efficiency of pollution controls, and increases costs overall.
"In the absence of affordable storage," said Moniz, "natural gas remains the key backup for intermittent resources."
Right now, natural gas is also inexpensive. But, Moniz noted, with tens of gigawatts of older coal plants that can't meet new environmental rules expected to shut in the next few years, it's not at all clear natural gas prices will remain at their current lows over the long term.