No, you can't - you are not understanding the context. I'm talking about the massive amounts used in the entire power grid system, not you in your own home. In very small amounts you can with UPS systems and batteries that are for individual use or company use, and you can feed some of the extra back like you can with solar or wind generation. But for the massive amount of power that goes through the grid system there is no storage of power - the power companies cannot create a couple hundred megawatt hours of electricity off hours trying to utilize their unused capacity and store it for use during the day. A very large percentage of the power generating capacity is not used during the night and is really useless.

The pumping of water uphill that NYC and others use is close but it's not storing electricity, it's storing potential energy. It isn't turned back into electricity until the water runs back through the turbines.

 

I wonder if those buildings in NYC that freeze water at night also pump it to the top floor so as it melts...

Answer me this...

Water feezes at 32F and the resulting ice cannot be cooled below that temperature. Wouldn't be better to use brine or anti-freeze into which more engergy can be stored unit/volume?

 

I guess I can't answer that one exactly - but most of the systems I read about are ice-based, not brine or glycol based. Could it take and release more energy when its converted into different states (liquid to solid and vice-versa) than just keeping it in a liquid state? Haven't looked into the reasonings behind why they use ice most of the time.

I would think it's the same type of properties as freon in an air conditioning system. Indoors it pulls heat out of the system by the expansion of freon from a liquid to a gas and at the condenser unit outside it expends that heat out by compressing the gas back into a liquid.

http://en.wikipedia.org/wiki/Thermal_energy_storage

 

Ice storage systems store the energy of conversion from water to ice. The energy is released when water above the freezing point absorbs the energy of conversion, turning the ice back to water. The conversion temperature is adjusted with additives, like glycol.

 

wwest — Indeed you can cool water ice to below the freezing point of water. Your freezer does it all the time!

Stan

 

Cooling ice below 32 deg is not much of an advantage in energy storage (or, to be more precise, storage of lack of energy). It takes a huge amount of energy transfer to make the water change phase and turn into ice. The energy transfer in freezing or melting is enough to heat or cool the water/ice by about 80 deg C or 145 deg F.

Also, storing electrical energy by any means - batteries, pumped storage, etc - is very inefficient because of the losses in the two conversions required.

 

Are you sure?

In an orchard ice is often used as an insolator when the temp drops below 32F.

 

"..is very inefficient because of the losses in the two conversions required."

You mean like when cruising on teh hwy and the FEH/MMH ICE being used to charge the battery and then the battery charge being used to drive the wheels?

I coundn't agree more.

 

This is probably not the place for a physics lesson, but yes, due to the laws of thermodynamics any object will eventually equalize to the exact same temperature as its surroundings. If it is -10 degrees in the air, any water, ice, metal, plastics, oranges, whatever, will eventually reach -10 degrees also.

In an orange grove, for example, the fruit has sugar, and sugar lowers the freezing point to less than 32'F ( 0'C ). I don't know exactly, but let's say, 28'F. As long as the oranges are 29'F, they won't be harmed.

Pure water ( or tap water for practical purposes ) does freeze at 32'F.
As long as water is in the process of freezing, it will stay at 32'F.
If the surface of the orange has 90% ice and 10% water, the surface will stay 32'F. Once the entire surface freezes, ( all the liquid is now solid ) the ice will start to cool to ambient air temperature.

So the key to protecting fruit groves is to keep the sprinklers going all night. As long as there is some liquid water on the surface of the fruit, the ice under the surface will stay at 32'F. And there is about 4'F of "buffer" (28'F) before the fruit gets damaged.

This is based on the principle of heat of fusion.
ALSO... as water goes from liquid to solid, it actually GIVES OFF HEAT!
So making ice, actually makes heat from the oranges' point of view.

Ice giving off heat? Sound impossible? Then think of the reverse.
Do you have to put heat into ice (or an orange ) to melt it into water?
Then the reverse must be true. ( and it is true )
You get heat out of water when you change it to solid ice.

You actually get 335 Joules or 80 calories PER GRAM of water changed to ice. You only get 4.18 J or 1 calorie changing 33'F water to 32'F water.

You also only get about the same, 1 calorie per gram changing 31'F ice to 30'F ice. It is the change of state that is important, to both orange groves, and energy storage devices. Just like your air conditioner that constantly changes liquid to gas, and makes the air cool in your home, and then moves the gas outside, and makes it back into liquid, and dumps heat outdoors, in the process.

Changing water into ice on the surface of the orange, actually dumps heat into the orange!!!

 

BUT that does NOT make it bad! It is opportunistic in nature.

If you are on a cross desert hike, and there is only 1 water hole every 25 miles, you might have to drink when you are not thirsty, to be "more efficient" than your partner who only drinks when he is thirsty, and skips a watering hole here and there.
-John