If you’re paying any kind of attention at all to the presidential campaign or state politics or international politics, you most likely hear politicians talking about achieving “100 percent clean energy” within 20 to 30 years.
What you probably don’t hear is that, at the moment, having renewables may also mean having at least a little bit of fossil fuels.
If that sounds counterintuitive to you, you’re probably not alone. But think about it: sunlight and wind are not constant, and we like our electricity to be continuous. So, at night or when it’s calm, those solar panels and wind turbines can’t be used to generate electricity — we need something else to provide as much electricity as we use or might need. This is what grid operators and utilities call “balancing the grid.”
At the moment, generators or maybe even power plants often fill those gaps created by the inherent variability of renewables. Some utilities, however, are increasing their flexibility in providing power from different sources with batteries, which are becoming less expensive to produce and big enough to store electricity to fill the minutes or hours without wind and sun, according to Nathanael Greene, a renewable energy expert with the Natural Resources Defense Council, but are still not quite cost-effective enough. (There are also a few other storage options, like pumped hydroelectric storage, compressed air energy storage, among others.)
So utilities are turning more and more to natural-gas or oil-fired reciprocating engines to provide this flexible electricity. These internal combustion engines work like the ones in our cars, quickly providing relatively small amounts of power. In the last two decades, about three times as many of these engines have been added to the grid as were in the 50 years prior, and most of them are in states with large and growing renewable electricity capacity — like Texas, California and Kansas — according to a report from the Energy Information Administration.
The need for stable, reliable electricity to balance out renewables is often played down in conversations about the transition to clean energy, according to Mark P. Mills, a physicist, engineer and senior fellow at the Manhattan Institute, a free-market think tank, who recently wrote a report that calls ambitions for a transition to 100 percent renewable electricity as an exercise in “magical thinking.”
However, according to both Mr. Greene and Mr. Mills, these reciprocating engines may actually be an improvement, both in terms of efficiency and fossil fuel reduction. Typically, the way to balance the variability has been to keep a traditional coal or gas fired power plant running at part load so that there’s no interruption. These reciprocating engines, by contrast, can go from zero to full power in as little as two minutes. (Combined cycle turbines, another type of generator, can take much more time to start up, usually more than 30 minutes, so they are sometimes kept in “spinning reserve,” which means they’re using fuel but not producing electricity. In that way, they’re less efficient, but they’re bigger and can produce more electricity.)
Antelope Station, a 165 megawatt electricity producer in Texas, has 18 reciprocating engine generators to balance out wind variability, and can get to full operating capacity in 5 minutes. They can be run individually or together, depending on how much electricity is needed, and, according to their website, save a significant amount of water, which is important in parts of Texas. (Golden Spread Electric Co-Op, which owns Antelope Station, did not respond to an email requesting comment.)
What renewable-energy advocates like Mr. Greene are waiting for is a drop in the price of batteries to make them more cost-effective than natural gas, or increased flexibility in the grid market, like in the western grid’s Western Energy Imbalance Market, which, among other things, enables excess renewable electricity to move where it’s needed. To Mr. Greene, these solutions are imminent. To Mr. Mills, they’re unrealistic.
Either way, it’s worth remembering that without some investments in battery technology, grid flexibility, and innovative storage ideas, renewable electricity won’t be enough on its own, and may almost always be dependent on fossil fuels. SOURCE