It’s going to be interesting as wind and solar gets consistently cheaper than even the marginal fuel cost of gas. i.e. even if you already own a gas plant, it would be cheaper to build a wind farm just to be able to reduce fuel use. We’re approaching a world where the primary energy drivers will be renewable, and fossil fuels will be competing with energy storage.
> ..fossil fuels will be competing with energy storage
Since fossil fuels are energy dense, it would be interesting if we come back full circle by producing hydrocarbon fuels for energy storage by recycling atmospheric carbon using cheap renewable electrical energy.
Edit to clarify, there are more energy dense substance than hydrocarbons (ex. Hydrogen), but hydrocarbons would have advantage of having ability of being useful in existing infra (IC engines, gas pumps, storage containers, etc.)
Unless you want to cover really significant amounts of land in solar panels wind farms, you shouldn't use synfuels unless absolutely necessary. Not only do you use half of the energy just making the fuel, all applications where you burn it have terrible efficiency compared to electric alternatives. ICEs have an efficiency of maybe 30%, heat pumps easily produce two or three Joules of heat for every joule of electricity.
We already devote really significant amounts of land to energy in the form of corn for ethanol, ~10% of total US cropland. Corn only captures 1% of incoming light vs ~20% for PV solar, so it would be a huge gain in land efficiency to replace corn ethanol with an energy equivalent amount of PV.
I think creating aviation fuels from renewables is the path towards carbon-neutral aviation as one example where this tech makes sense. Shipping might be another, but I’m less familiar there.
But it might (big might) be worthwhile for a transition period.
ICEs are my pet peeve, mechanical engineers keep coming up with all those ways of improving efficiency, and to be fair, in the last 30yrs they got it to be "good" but the actual % numbers are awful regardless.
Efficiencies might seem bad, but thermodynamics limits the efficiency of any heat engine (of which an ICE is one) according to the absolute temperature of the hot and cold side of an engine. This is called the "Carnot efficiency" and it's comparable to a no-friction mechanical system, or a no-resistance electrical circuit.
For an ICE, assuming combustion temperatures of 550K and assuming the radiator can cool the system to 50C, the Carnot efficiency is (1 - Tc/Th) = (1 - 333K/550K) = about 40%.
That's a hard theoretical limit that assumes all processes are reversible. Real engines have irreversible thermodynamic processes so the Carnot limit can never really be attained.
In other words, your complaint isn't with the engineers, it's with thermodynamics.
(note: ICE engines are modelled using the Otto cycle rather than the Carnot cycle, but that's a bit more complicated and leads to efficiencies that are even worse. The Carnot efficiency is an upper limit for all heat engines, including steam engines, Stirling engines, turbines, etc.)
550k is a low combustion temperature. “Modern military jet engines, like the Snecma M88, can see turbine temperatures of 2,900 °F (1,590°C).” https://en.m.wikipedia.org/wiki/Turbine_blade
Absolutely. But I read the comment as complaining about efficiencies of automobile engines, not modern military jet engines. The combustion temperature of gasoline is 553K.
I am aware of the Carnot efficiency, my issue with the engineers is that they can't make big gains anymore, exactly because of the Carnot limit.
Best way of making a gasoline car (not the engine - the car) efficient is taking the throttle of the engine out and attaching a hybrid/regenerative generator/motor to it.
But, for very long term storage efficiency is not that import. If you’re buying at an average of say 1c/kWh and selling at 20c/kWh in 6 months it’s mostly a question of what your storage costs per day as well as maximum output is.
I first worked that out in response to a claim that solar thermal plants were better than PV because they can store energy as molten salt and produce power at night. What sinks that claim is solar is cheap enough that you could heat your salt with electricity from solar panels and be ahead.
At the point there is no need to use salt. You can use a referable electrically driven gas turbine and get about 70-80% round trip efficiency.
Someone pointed me to a link where round trip efficiency was analyzed, with the claim that ammonia is better than hydrogen or methanol for energy storage. Apparently hydrogen compression takes a big hit, although I'm not clear if that's still the case if the hydrogen is burned in stationary turbines (that compressional energy could be recovered).
Ammonia's energy density by volume is nearly double that of liquid hydrogen — its primary competitor as a green alternative fuel and it is easier to ship and distribute. "You can store it, ship it, burn it, and convert it back into hydrogen and nitrogen,".
..he shows off one of the devices, about the size of a hockey puck and clad in stainless steel. Two plastic tubes on its backside feed it nitrogen gas and water, and a power cord supplies electricity. Through a third tube on its front, it silently exhales gaseous ammonia, all without the heat, pressure, and carbon emissions normally needed to make the chemical. "This is breathing nitrogen in and breathing ammonia out,".
Companies around the world already produce $60 billion worth of ammonia every year, primarily as fertilizer, and MacFarlane's gizmo may allow them to make it more efficiently and cleanly. But he has ambitions to do much more than help farmers. By converting renewable electricity into an energy-rich gas that can easily be cooled and squeezed into a liquid fuel, MacFarlane's fuel cell effectively bottles sunshine and wind, turning them into a commodity that can be shipped anywhere in the world and converted back into electricity or hydrogen gas to power fuel cell vehicles..
Cost increases linearly with capacity, which is undesirable at scale. You want sublinear scaling. For example, to store a year’s worth of US electrical generation using batteries would cost approximately 500 trillion dollars.
1) Huge number, but why would you need an entire year of energy in reserve
2) If there was a desire to build that many batteries, cost would surely decrease exponentially as new mines, factories, etc. open up and competition increases.
Gas plants more or less have to become "peaker" plants. They'll get paid more for the electricity but run for much fewer hours, plus a payment for being on standby. Effectively they'll be competing with storage, yes.
This will shift any new gas plants away from combined cycle toward simple cycle. Minimizing capital cost will be more important. Steam turbines may be on their way to the technology museum.
