Finnish City Inaugurates 1 MW/100 MWh Sand Battery

Good idea but why is it being measured in MW/MWh when it’s not an electrical battery? I know they can be converted but maybe it should be measured in actual thermal units like Btu?

Finland probably doesn't use US customary units like BTU (British Thermal Unit).

In fact even Britain doesn't often use such units - even gas boilers, heat pumps and some AC are specced in kW. You do see BTU (the /hr is often missing) sometimes on AC marketing. My theory is 18000 sounds big and impressive and 5.2kW sounds "meh". We definitely don't talk about "tons", and we buy gas in cubic metres or "units" (which is just kWh)

W and J are the SI units for power and energy. Those units make the most sense to use in Europe, regardless of the type of energy.

Wh is an abomination that has come about because professionals think consumer brains would expose if they ever saw the unit watt-seconds (J). No consumer had any preconceived notion of either Wh or J, so had we used J from the start, it wouldn't have been a problem...

(Yes, same with Ah vs C, though the battery pros also shot themselves in the foot by starting to use C (electrical charge) to mean "the capacity of this battery" when talking about charge rate, a.k.a. current.)

I dunno, 1kWh seems quite natural as a unit of building-scale energy usage when you know a kettle or space heater is about 3kW. We think about energy usage much more in terms of kW and hours than in watts and seconds. And even in small devices like an LED bulb, 5W is more obviously 0.005kW than, say, 2 hours is 7200 seconds.

And in this context it's much more obvious that it can notionally deliver energy at a peak rate of about 1% capacity per hour. If you said 1MW/360GJ, I don't think that would be nearly as clear.

Same for batteries, which started with car batteries/deep cycle batteries, rather than AA batteries, which usual don't even say, and phones. A battery that provides 1 amp (at 12V, but that's already given in a system) for 50 hours. Makes immediate practical sense, especially when equipment is often labelled in current draw and you can measure amps with an ammeter. 2.16MJ far less so.

Watts and watt-hours are generally used internationally for heating; the Btu is largely a historical oddity in most places outside the US.

Also it is a mess, as is traditional for US customary units:

> A Btu was originally defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit at a constant pressure of one atmospheric unit. There are several different definitions of the Btu that differ slightly.

(Best one is still the fluid oz, tho. A US customary fluid oz is about 29.6ml, a US food labelling fluid oz is exactly 30ml.)

Absolutely agree.

This still falls under the "but we're used to it" argument. That notion that it feels natural, I argue, is a result of you having seen both W and Wh in enough contexts that you start building intuition for them. Had we had W and J, you would have been able to build the same intuition.

> If you said 1MW/360GJ, I don't think that would be nearly as clear.

Wouldn't have been using the hour as the mental reference. As you say, it's impractical. We would have probably rounded the 86,400 seconds in a day to 100,000 and used that as the reference for comparisons. There's nothing noteworthy about the hour in this context.

> A battery that provides 1 amp (at 12V, but that's already given in a system) for 50 hours. Makes immediate practical sense, especially when equipment is often labelled in current draw and you can measure amps with an ammeter. 2.16MJ far less so.

I argued Ah could have used the SI base unit C, not that we'd use J. Whether you count As or Ah is still just a matter of building intuition.