Motor vs Generator

[kwired]

Perhaps windmills on the ocean. Of course, that wouldn't be the only source but I believe there is always some wind on the ocean

Wind turbines are placed where there is sufficient wind to make it worth the effort of installing them - especially when you get into the 1megawatt sizes. But there is always at least some occasions where it is calm enough to not be effective for this purpose.

A wind farm is under construction practically all around where I live right now. 80 some towers. This is perfect time of year for them to assemble the towers, as we typically have less wind at this time of year. They still have been days where it is too windy to operate the cranes though, but last couple weeks hasn't been much wind and they have gotten a lot more done then earlier this summer. A few times they have worked at night because that is when it was calmer.

I think the energy these produce is being sold to out of the area, reality is it gets dumped into local grid and interconnections is how energy gets to wherever it is sold to. This area has highest local usage at times when winds are at lowest average, and times when winds are at highest average is when local usage is typically lowest. We can't depend on these turbines to supply the demand in the summer months when our demand is high, other sources must be online and for steam driven generators the boiler must be up to pressure, when the wind dies or there will be a shortage of power. You don't get that pressure up in a short time.

 

[RumRunner]

That's how regenerative braking on electric cars works, innit?

Exactly, the same principle but this is outside the RotoVerter scheme mentioned above where we are using AC motor.
What's more “exciting” is: electric cars use DC motors--unlike applications in industry where we make AC from generators to run our AC motors.

The big advantage of DC motors over AC motors is their infinite speed control while maintaining required torque to accomplish the task.
If you use rheostat for example, to adjust speed by varying the stator voltage through the rheostat's resistance range, and you ran out of range, you can then turn to adjusting the field magnetism to further increase the speed. This scheme however will have an impact on the torque somewhat.

More speed less torque. Stronger field magnet equals low speed.

This is not what you're asking—I'm just citing this because this is related to regenerative braking.

When braking, the traction motor field remains connected—the armature is disconnected from the power source which in this case the battery bank. While the car is coasting to a stop, the armature is acting as generator because the field stays connected (excitation is still present).

During this braking process the armature (now acting as generators) are connected to an array of huge resistors so called brake grids.
This puts an enormous load on the circuit. This large load imposed by the array of resistors will cause the traction motors (now acting as generators) to slow the rotation.

Furthermore, by adjusting the field excitation along with reduced rotation of the generator the vehicle can be brought to a virtual stop.
Ideally down to 3-5 MPH.

 

[LarryFine]

Regenerative braking returns some of the energy to the batteries.

Dynamic braking merely converts energy to heat in the resistors.

 

[RumRunner]

Regenerative braking returns some of the energy to the batteries.

Dynamic braking merely converts energy to heat in the resistors.

Both are correct, however OP was asking about regenerative braking for cars.

Regenerative braking does have issue when applied to cars. Returning the energy to the batteries does work but not in every situation.

When the batteries are still fully charged , like you just pulled away from the charging station, it puts the surplus energy in what is called unabsorbable state. Meaning , a fully charged battery will not accept any more and all extra energy will just get wasted in the form of heat.

Routing it to the resistor bank will not hurt anything and even used for space heating and that also keeps the braking system's integrity intact..

 

[electrofelon]

You said hypothetically speaking.

Real world, where is such a source the primary method of generation? If wind stops blowing there is no generation period. You can't even rely on such system to be a majority of your generation, if wind stops blowing you aren't going to instantly transfer to more conventional sources without a delay in there. If that alternate source is from a steam driven turbine, that boiler has to be on line and up to pressure at the time of transfer or there will be a shortage of power.

It is interesting to look at Texas. At times wind is making 30-40% of the states power. Here is an interesting article:

http://www.slate.com/articles/busin...nd_power_was_so_plentiful_one_night_that.html

The wikipedia article is a good read too:

https://en.wikipedia.org/wiki/Wind_power_in_Texas

 

[kwired]

It is interesting to look at Texas. At times wind is making 30-40% of the states power. Here is an interesting article:

http://www.slate.com/articles/busin...nd_power_was_so_plentiful_one_night_that.html

The wikipedia article is a good read too:

https://en.wikipedia.org/wiki/Wind_power_in_Texas

That 40% was during a low demand period. 30-40% is about the most they should plan to depend on, get too much higher and the wind happens to slow down significantly during a high demand period and they may find themselves in a shortage of immediately available energy to put into the grid. A loss of input energy is easier to predict with other sources, outside of a sudden major breakdown of equipment, but good maintenance practices limits that, so such major breakdowns would have to come suddenly from mother nature for the most part, storms, earthquakes, etc.