Efficiency is very important when your energy is costly. But other attributes like reliability, safety, environmental benignity, "fit" in the overall energy system, and aesthetics start to take precedence over energy efficiency at some point.
The way things are trending with PV, efficiency may recede in importance in a couple of decades. Currently electricity costs tens of dollars per MWh. With developments in manufacturing and install protocols, and tech emerging from the lab, and using DC directly from PV panels, that cost may fall to $0.1 per MWh. Using that to manufacture your ammonia means you won't worry so much about pure efficiency
I still prefer methane over ammonia. Much less toxic when things go wrong.
Electrical motors are about as reliable and safe as it gets.
I agree energy will eventually get very cheap and plentiful, which would enable more frivolous uses of excess energy. But still, that won't happen any time soon and the value proposition of paying several times more for energy is very limited. And while there is a shortage of green energy, using it for the creation of fuels seems like it is costly and wasteful.
>Electrical motors are about as reliable and safe as it gets.
Electricity isn't free. If you're already wasting sufficient amounts of the requisite elements as waste products of some other thing you're already doing then finding a way to bond those elements and then burn the resultant compound for rotary power may be more economically efficient.
> If you're already wasting sufficient amounts of the requisite elements as waste products of some other thing you're already doing then finding a way to bond those elements and then burn the resultant compound for rotary power may be more economically efficient.
Your sentence is a bit vague, but "some other thing you're already doing" sounds like petroleum refining, which is precisely what we need to do less for use as a fuel. Also, ammonia created from petroleum isn't being wasted today. It's used for making fertilizer, and the whole process has a high cost in CO2 emissions.
When the time comes that we have so much carbon-free energy that we can afford to use the excess to generate ammonia, we ought to use it to displace petroleum based ammonia for fertilizer. There may be a few niches (ocean shipping) that require a liquid fuel like ammonia, but it makes little sense to use it for ground transportation. If a liquid fuel is required, things like sustainable biodiesel make more sense.
The way things are trending with PV, efficiency may recede in importance in a couple of decades. Currently electricity costs tens of dollars per MWh. With developments in manufacturing and install protocols, and tech emerging from the lab, and using DC directly from PV panels, that cost may fall to $0.1 per MWh. Using that to manufacture your ammonia means you won't worry so much about pure efficiency
I still prefer methane over ammonia. Much less toxic when things go wrong.