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Comment by chefkd | Hacker News Reader

Any papers or books (or thoughts) on why humans developed IC engines before solar powered engines? At first glance solar power seems more accessible than digging for petroleum / natural resources + the sun held an important place in various early religions as well

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>why humans developed IC engines before solar powered engines?

IC engines are relatively cheap compared to other ways of transporting people and things, and society lacked a compelling motive to question the IC engine or to try to replace it till a scientific consensus formed (after computer modelling of the climate had become sufficiently cheap) that greenhouse gases were deeply involved in most climate changes and human-caused emissions were bringing discernible global warming -- in the 1990s.

Many engines, especially early on, can accept any external heat source as power. The most currently popular version of this is a Stirling engine, where you can find many toy engines of this type, like the wide bodies ones you can put on top of a hot drink.

Internal combustion was not actually popular for quite some time in early engines, I assume because it has more advanced requirements for fuel and ignition control, so if solar were a convenient enough power source it would have been used.

Yes, you can use the sun to heat up some water or some other fluid and in an abstract theoretical sense you can use the heat in the fluid to produce mechanical energy, but any engine small enough to go into a car or truck capable of providing enough energy to reliably overcoming rolling resistance or to make the car go up a hill is going to need a much denser power source than that.

Well yeah, as I mentioned if it were convenient to use solar for engines people would have done so. My whole point is that we had the technology and didn't do it because it's fundamentally not viable, not because of semiconductor technology.

Edit: oh, it looks like your radically edited both of your comments

Mirrors used to be difficult and expensive. There's no practical way (pre-semiconductor-era) to make thermodynamic engines on sunlight without a method to concentrate it, to achieve high temperatures.

At any rate, the areal power density is really low and wouldn't have been a good engineering choice, generally, even if it were available. (Agricultural pack animals were solar-powered machines all along. But, it takes no human work to build or maintain the fields of grass that they graze off).

There's an essay and a large HN thread about a related idea—why ancient Romans did not develop (combustion-powered) steam engines, what technological barriers prevented that,

https://news.ycombinator.com/item?id=32607187 (Why no Roman industrial revolution? (acoup.blog)", 519 comments)

Iron-age solar engines may have been impossible twice-over: impossible because of the lack of mirrors, and impossible again because of a lack of metallurgy for building high-pressure steam vessels.

Solar is weak. <1kW/m2. A small gasoline engine provides ~100kW of mechanical energy. That mismatch is what requires some magical conversion and storage to connect. Also, the semi-conductor used in photovoltaic solar cells required quantum theory to invent. The IC was “inventable” based on thermodynamics cycles etc. known in the late nineteenth century

The first big investments in petroleum were for lighting via relatively clean-burning kerosene. Petroleum as a fuel came later, when they had a lot kerosene byproduct lying around. There's a obvious problem with solar as a lighting solution: you also need good batteries.

> There's a obvious problem with solar as a lighting solution: you also need good batteries.

Or networks of mirrors.

My thinking gets stuck on the observation that before petrol, literacy after dusk was powered by the wax of bees and the blubber of whales.

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