Don't mess with the engineers when physics is on the line

This is an open letter to Brandon Schollenberger, also sent by e-mail.

I received a pointer to your essay.  No, lying is not OK.  Neither is spouting off in utter ignorance.

TL;DR  You're not right.  You're not even wrong.  You wrote a mish-mash of conceptual nonsense that is cringeworthy to every student who scraped out a passing grade in AP Physics, and quite a few who never made it that far.  I'd say take it down NOW, but... it's already too late for you; someone archived it 2 days ago.  The web never forgets.

At its core, you do not understand the difference between energy and power.  Gallons of gasoline are a measure of energy.  Horsepower are a measure of power.  You can burn 5 gallons of gasoline making 5 horsepower for 20 hours, or making 100 horsepower for 1 hour.  It's vastly different amounts of power, but the same amount of energy.

On to specifics.  You wrote:

To understand what the lie is, you need to know the purpose of a pumped-storage hydroelectric (PHS) power station. Like any power station, a PHS station produces electricity for consumers. It does so by converting the kinetic energy of flowing water into electricity. However, it has an additional purpose as indicated by the phrase "pumped storage."

Perhaps if you had looked up the Wikipedia article about pumped hydro storage sites, you would find that there are precisely 9 of them in the USA with a total nameplate capacity of 13,612 megawatts.  (This will go up by a few hundred MW as Ludington is upgraded with more advanced and efficient pump-turbines.)  This is not what they can store (equivalent to gallons of gasoline); it's their maximum instantaneous output (equivalent to engine horsepower).  Average US grid demand is on the order of 450,000 MW.  All the PHS plants in the USA, running flat-out, can serve roughly 1.5% of average US grid consumption.

Obviously, there's a lot more than 13,612 MW of total hydro capacity on the US grid (Jacobson lists 87,480 MW).  Just as obviously, the vast majority of it is NOT pumped hydro.  The only energy they can store is the energy delivered by the rainfall feeding into their reservoirs.  This is limited by many factors, including minimum river flows for ecological reasons.  One thing they can't do is reach down and pull water back out of their outflowing rivers to store energy again.

When more electricity is generated in the electrical grid than is necessary, it needs to be disposed off somehow. It can be burnt off, but a better solution is to find a way to store that electricity until it is needed. In a PHS, electricity is stored by using the extra electricity to pump water into a reservoir at a higher elevation. Later, that water can be released to produce electricity. It is basically a battery you can charge when you have extra power and discharge when you need more power.

You can't generate more power than the grid needs, not for a significant time or fraction.  The reasons why involve BSEE-level mathematics which you obviously don't have, but the point is that there are NO significant stores of energy in the grid proper except for the sheer mechanical inertia of its large synchronous rotating machines (both generators and motors).  If you pump in power over consumption, those machines speed up past their rated speeds; a power deficit causes an underspeed.  Too much of a deviation trips generating plants off the grid and causes a blackout.  Generation must match load to a very high degree instantanously, and even more closely over time.

PHS systems can function as both generators and loads, but... 1.5% of average grid consumption.  That's a handy ±1.5%, but it's still only 1.5%.

If a power station produces 100 GW every hour, no more, no less, would we say it is impossible for it to output 1,000 GW in a single hour? I would hope not. If the station's electricity wasn't needed for 10 hours, it might store up 1,000 GW.

Aside from impoundment-fed hydro stations (both pumped and otherwise), the only stores of energy in powerplants on the grid are:

1. Coal stockpiles at coal-fired plants.
2. Oil tanks at oil-fired and dual-fueled steam and gas-turbine plants.
3. Uranium in the cores of nuclear power plants (by far the largest of all).

Nothing else stores significant energy.  A steam-turbine powerplant can cycle several million pounds of steam per hour from boiler to turbine to condenser and back to boiler.  There's nowhere in the plant to store millions or even thousands of pounds of steam, and the turbine can only accept it so fast.  The alternator which converts the turbine's output to electricity has its own instantaneous and sustained power limits, as do the transformers which put it out to the grid and the wires themselves.  It doesn't matter HOW many gallons-equivalent of gasoline you've got, you can only USE it as fast as the horsepower of your engine.

I will stop rubbing your face in your embarassment here.  I hope you have learned a lesson.  ¶ 11/07/2017 08:33:00 PM 11 comments