Research out to optimize
uncertain energy future
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Utilities and grid operators traditionally deal with these what ifs by building in margin: reserves of power generation capacity. “You effectively pay money for a possibility,” Anitescu says. “Maybe that possibility occurs. Maybe it doesn’t.” Renewable resources introduce added possibilities, prompting engineers to build additional conventional power to increase margin. That adds costs and – because most of the extra plants burn gas or coal – pollutants that could offset the environmental benefits of wind or solar.
State of Illinois power grid network and price fields. Click image to enlarge and for more information.
Engineers typically determine margin in off-line studies carried out long before grid operators actually dispatch energy to meet demand. “That means (margin) is not set in light of all the available information you have at the time you have to make decisions,” he says, such as how much generation is available at a particular moment. Computation could take that information – about the state of the system, how much renewable power is expected to be available and other conditions – into account when making dispatch decisions. “Then maybe you have less margin. It will cost you less to operate the system.” The goal is to use more renewable energy with the same safety margin and reliability.
State of Illinois electricity price fields in a stochastic scenario. Click image to enlarge and for more information.
Getting there, however, is a huge challenge. First, regulations say grid operators must account for system state and generation capacity (based on demand, weather conditions and other factors) out to at least 24 hours ahead – and update dispatch decisions at least once an hour. “That multiplies your problem by 24, because you have to consider 24 specific time horizons at any time. If I make my decision today, I have to consider the impact it’s going to have all the way to the same time tomorrow.” The problem may only get more difficult. Grid operators and regulators have discussed extending the time horizon to as long as 72 hours and tightening update frequency to less than an hour – perhaps as little as every five minutes, Anitescu says.
Second, the calculations have to represent the entire power network: a giant graph of generators, transmission lines and other facilities, with each part a variable in the calculation. Just in Illinois, where Argonne is based, the grid has thousands of parts – but grids typically are controlled over much larger areas, like the entire Midwest.