Amber Lin at The Bulletin of the Atomic Scientists describes the two-headed character of natural gas plants needed to implement “natural gas as a bridge fuel”, and sketches the stark reality proponents of that argument are embracing if they are serious about using natural gas, whether for electricity or heating, to reduce greenhouse gas emissions.
The basic fact is that in order to serve as a proper “bridge”, natural gas infrastructure would need to be decommissioned by 2050, including ceasing flows of the gas through the elaborate pipelines which criss-cross the United States. That’s because emission limits for CO2 dictated by Nature cannot be met otherwise, with 450 ppm CO2, just 40 ppm higher than where we are now, corresponding to the widely accepted +2°C warming limit. And, as that is unlikely, if we want to limit warming to +3°C 650 ppm is the overall limit, and +3°C brings us into a highly uncertain, dangerous, and eventually ice-free world. In particular, we might lose control of a portion of the warming process, since large natural stores of CO2 are quite likely to be breached and begin leaking at those temperatures.
The Presidential commission on the matter also sketched the key problem with using a “bridge fuel” mechanism to reach targets like this, namely, “A slow start leads to a crash finish”, meaning that to hit these targets, the abandonment of fossil fuels and their infrastructure must be pursued much more quickly than if we start early. I daresay, none of the proposals for new natural gas generation have incorporated operating lifetimes which abruptly end in 2050, or depreciation schedules which reflect that. In fact, the new Massachusetts Salem Harbor gas-powered electricity generator has a lifetime up through 2080.
Amber Lin tells how there are really two incompatible kinds of natural gas plants for electricity generation:
When constructing a new natural gas power plant, there are two options: a combined cycle or an open cycle. A combined-cycle power plant produces electricity with relatively high efficiency and low carbon emissions: When the gas burns, it heats and compresses air to spin a turbine and power a generator. A heat recovery system captures waste heat, which is routed to a nearby steam turbine to generate even more power. Combined-cycle plants have low operating costs, but because high capital costs must be offset, these plants are built to produce baseload power—available 24 hours a day. Open-cycle gas turbine plants lack the steam cycle, so their thermal efficiency is much lower, and their carbon emissions per unit of electricity generated are slightly higher. Their running costs are much higher than a combined-cycle plant, but they have a much lower start-up cost, so they are often built as “peakers,” plants that run only to support other power infrastructure during hours of high demand or when solar or wind isn’t available.
Considering the two choices in the larger context of natural gas as a “transition fuel,” a dilemma appears: To build the bridge, combined-cycle is what is needed—a consistent, efficient, power source that can effectively replace coal. But for a combined-cycle natural gas plant to be economically feasible, it would typically need 15 to 20 years to make up for start-up costs, and even longer to become profitable. This means that a combined-cycle plant built in 2016 would break even no sooner than 2031, and would have to run for several more decades to be a worthwhile investment. Levi’s 2030 limit for peak emissions, and roughly 2050 limit for zero emissions, translate to major fossil fuel reductions after 2030. Owners and backers, however, will not want to shut down gas plants that are just beginning to generate a profit. Thus, building combined-cycle plants in 2016 without an explicit understanding of their necessarily temporary nature—and with no financial incentives for early closures in the future—defeats the purpose of natural gas as a “transition fuel.”
Why not focus on open-cycle plants instead? While “peakers” make sense as backups for future renewable energy sources, they don’t make sense right now. In the current infrastructure, they can only run for a couple hundred hours a year before they cost more than they can earn; this is not nearly enough to displace coal. Closed-cycle plants can help build the bridge but cannot close it, and open-cycle plants can help close the bridge but cannot build it. Neither type of plant is both economically feasible in the long run, and powerful enough to meet today’s demand while cutting emissions in time to mitigate climate change. However, when natural gas is branded as a “transition fuel” in politics and in popular media, this crucial detail is rarely mentioned.
(Emphasis added by blog author.)
So natural gas plants are the Zaphod Beeblebrox of electricity generation, as they are duplicitous and their purpose is to distract from the true goals of natural gas infrastructure expansion, to prolong the day when fossil fuel assets are stranded because of government action to mitigate climate change, or, as increasingly plausible, it is taxed for its Carbon.
Luckily Arthur’s Betelgeusean friend, Ford Prefect, a roving researcher for that illustrious interstellar travel almanac The Hitchhikers Guide to the Galaxy, was more of an optimist. Ford saw silver linings where Arthur saw only clouds and so between them they made one prudent space traveller, unless their travels led them to the planet Junipella where the clouds actually did have silver linings. Arthur would have doubtless steered the ship straight into the nearest cloud of gloom and Ford would have almost certainly attempted to steal the silver, which would have resulted in the catastrophic combustion of the natural gas inside the lining. The explosion would have been pretty, but as a heroic ending it would lack a certain something, i.e. a hero in one piece.