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Comment by jackreichert | Hacker News Reader

This is also the missing piece to move over to a more renewable energy source. Coal is on demand. If there is a need for more, you can spin up more factories, and many site waiting just for this.

Most renewable energies are reliable, but over longer periods of time. With a way to store energy, and have it dormant in the grid waiting to be used, this creates the surplus needed so we can switch to solar and wind and be able to rely on output.

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Your point is correct, but the details are wrong: coal (and nuclear) provide so-called "baseload" power, while natgas and hydro provide "peak" power (this is why natgas plants are called peakers). Coal has a very long spin-up (and spin-down) time. If you've studied process control, the first-order time delay is on the order of hours to days. Natural gas and hydro have time constants of ca. minutes. Moreover to your point, batteries have very short time constants (but a plethora of of other problems).

So, for coal, is it just because of thermal inertia? The size of the whole thing? Do they need to load the coal in a specific way?

That's very likely due to size. Things like powerplants get more efficient as they get larger. (And as they get more complex by piling on more optimizing subsystems.)

Thermal inertia. Boilers have to be brought up to temp, and do not take well to throttling like a combined cycle natural gas plant.

For coal, I think it is because of the large turbines used. They have to be brought up to temperature gradually because they are very large precision made hunks of metal.

As has been mentioned, the boilers themselves do not heat up that quickly; however, you _also_ have to mix the pulverized coal with hot air and then pump it into the firebox for combustion.

If you're coming up from a cold start, you're going to need to pre-heat the air, probably with electricity and/or natural gas. With this in mind, it's not so much that they don't generate power right away, it's that they don't generate enough power to overcome the cost of their initial inputs.

From a power plant perspective, you aren't "started" until your output power is larger than your input power.

Plus for Brown Coal, you must run dryers powered by the waste heat. These take DAYS to get up to speed.

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