Posted by Taunto on February 18, 2007, 11:24 pm
I'm just trying to figure some efficient, cost effective ways to
"time-shift" energy usage, for charging at night when rates are cheap,
and discharging when not.
Seems like battery storage is to inefficient. Flywheels are expensive,
and liable to fly apart.
What about pumping air into a tank, and then running it backwards when
needed? Would need some sort of motor that runs on compressed air.
What are the inefficiencies of this route?
Posted by Eeyore on February 18, 2007, 11:30 pm
Taunto wrote:
> I'm just trying to figure some efficient, cost effective ways to
> "time-shift" energy usage, for charging at night when rates are cheap,
> and discharging when not.
> Seems like battery storage is to inefficient. Flywheels are expensive,
> and liable to fly apart.
> What about pumping air into a tank, and then running it backwards when
> needed? Would need some sort of motor that runs on compressed air.
> What are the inefficiencies of this route?
Fairly significant. Using compressed air is lossier than batteries.
Graham
Posted by Vaughn Simon on February 19, 2007, 8:42 am
> I'm just trying to figure some efficient, cost effective ways to "time-shift"
> energy usage, for charging at night when rates are cheap, and discharging when
> not.
> Seems like battery storage is to inefficient. Flywheels are expensive, and
> liable to fly apart.
> What about pumping air into a tank, and then running it backwards when needed?
> Would need some sort of motor that runs on compressed air.
Actually, that could be the easiest part. With a proper design, the
compressor could easily be the motor. By the way, you would need a very large
storage tank and/or very high pressures.
> What are the inefficiencies of this route?
Terrible. There are good reasons why compressed air energy storage is not
common.
Besides the usual things (friction, motor losses, generator losses) you
have a special kind of thermal loss. Simply put: When you compress air, it gets
hot, and you supply the energy to make that heat. Unless you recover that heat
somehow, it is energy lost to you forever. When you expand your air to generate
power, it suddenly gets cold. This reduces the expansion (and the power you
extract) and creates problems for your motor. It can end up encased in a big
block of ice!
Vaughn
Posted by HVAC Guy on February 19, 2007, 10:34 am
Taunto wrote:
> I'm just trying to figure some efficient, cost effective ways to
> "time-shift" energy usage, for charging at night when rates
> are cheap, and discharging when not.
That would only work assuming you are charged based on time-of-day
use. Not many people are.
What about having a situation where you would mechanically lift some
large mass using excess energy (solar, wind, low-cost utility power,
etc) and then use the stored kinetic energy when you need to convert
it back to electricity by running a generator as the mass is lowered.
Efficiency would depend on how much you could reduce friction I guess.
See these:
http://www.columbia.edu/~zk30/gravity.html
http://www.halfbakery.com/idea/energy_20storage_20gravity
Posted by d.s. on February 19, 2007, 10:49 am
> Taunto wrote:
> > I'm just trying to figure some efficient, cost effective ways to
> > "time-shift" energy usage, for charging at night when rates
> > are cheap, and discharging when not.
> That would only work assuming you are charged based on time-of-day
> use. Not many people are.
> What about having a situation where you would mechanically lift some
> large mass using excess energy (solar, wind, low-cost utility power,
> etc) and then use the stored kinetic energy when you need to convert
> it back to electricity by running a generator as the mass is lowered.
> Efficiency would depend on how much you could reduce friction I guess.
> See these:
> http://www.columbia.edu/~zk30/gravity.html
> http://www.halfbakery.com/idea/energy_20storage_20gravity
Some utilities are experimenting with RTP, real time pricing, for
consumers who sign up for it. Usually the consumer will save, but
some months they might pay more. Overall they save. This allows
consumers to adapt their lifestyle to avoid using electricity when
prices, to the utility, are highest. I'm just looking for ways to
help the consumer smooth over the bumps and still save.
Some utilities are already using underground caverns to store
compressed air during the evening, and reversing it during the day. I
was looking for something that a home could use.
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> "time-shift" energy usage, for charging at night when rates are cheap,
> and discharging when not.
> Seems like battery storage is to inefficient. Flywheels are expensive,
> and liable to fly apart.
> What about pumping air into a tank, and then running it backwards when
> needed? Would need some sort of motor that runs on compressed air.
> What are the inefficiencies of this route?