How will the Chevrolet Volt be better than a Toyota Prius plug-in hybrid?

And interesting and good question. Part of the answer depends on how one views things, which I'll get to in a second. But first let's clear up a common misconseption.

All electricity generated is used effectively instantly. Electrons are not really "flowing" like water, in A/C they vibrate back an forth (AC=alternating current), and across the network the vibrations must balance and hence AC must be consumed as its generated. The generators can play a bit with frequency and voltage to get balance, but there is never excess electricity in the system. There is no excess generation, but there can be excess capacity. Generators can operate in what is called spinning stand-by, where they are consuming fuel but not actually generating at full capaicty or at al as the the steam is generated but not all is sent to the turbines. That that is a mostly small fraction of the overall grid but is needed incase a large load happend quickly or to cover a loss if a disaster happens and some plant goes offline. That is not considered excess, its considered an important "safety" component of the grid, and even with gas peakers there will be some level of spinning reserves because when people turn on their power they cannot have a few seconds while a turbine spins up. This is, however, a small amount of potential power at any given time

How then does it have excess capacity?
The power industry forecasts demand at multiple time scales, and is always predicting how much power they will need and adapting their supply to meet that forecast. Plants are not binary and many plants can do what is called load-following (or partial-load following), where then can increase/decrease production e.g. by how much coal they burn which impacts the steam generated which impacts the power generated.

And with better projections they can do a good job in planning and meeting those needs. But for many baseload plants, especially coal and nuclear, the speeds at which the can follow is only part of it. There is also a range of adjustments they can make before it causes problems. Plants can have a minimal power-output, and if they go below this it starts to impact reliability and hence costs as the preasures get out of alighment and parts slightly cool. They also have a emergency-minimal level, below which they litterlay have to shut it off, let it cool down an then restart. A nuke normally takes 8 days to restart, a coal plant 3-5, so they really don't want to go below that level.

Because of the minimum levels, when coal and wind are integrated its often in the plant owners interest to keep the baseload at or above minimm, even if they pay to shut wind off. They generate more carbon tht way, but the plant owner does not want to risk the plant. There is a nice study on this at
http://www.cleanlineenergy.com/sites/cleanline/media/resources/Wind-Induced-Coal-Plant-Cycling-Public.pdf

In many places, especially in coal-dominated states, the baseload at night is far in excess of demand, and if given the choice the power companies would rather use coal than wind. It is one of the reasons the bulk-power rate can actually go negative.. power companies paying others to take the power because they want to avoid shutting down plants.
Here an interesting chart of prices from an EIA article

This is from the northwest, but negative bulk pricess happen in multiple places.


Some have argued that charging during the day is greener because it depending on peaker plants, plants that only run during the day and which use natural gas and are cleaner. Charging at night, the margin increase might actually help as plants running at lower levels are less efficient. I'm not aware of a good study on which is really better. But the best choice in my view is buying wind, which is often curtailed at night because there is too much to use.

So unfortunately, I cannot agree that just using the grid at night is "green", and the cost incentives may keep it that way for a while. I believe that the added marginal cost of green power, especially using it at night, is well justified because it sends a clear message to the generators on what to use. If you let them choose for you then, based on cost, they toss in a few more lumps of coal.

On the other hand, EV's are not just about carbon. Its still using US produced power, keeping the money local. And charging at night will cost you less, making it financially better than gas in most places. So paying for green is best, charging at night lowers costs and often combining the two with a time-of-day-use plan and it amy cost less overall than just charging whenever you want.

 

Keep at it. You do a great job explaining the intracies of operating different type of plants on the grid. The details on the situations that tempt a utility to dump the renewable energy for carbon energy are especially interesting....and the measures taken to prevent that. What is not mentioned is that some utilities must be exploring modifying the carbon plants to be much more adaptable (much better dynamic load following) so that more money can be made. Someone has to be aware that money can be made with those type of updates.

 

The old coal plants are not good at all for load following, and can not be modified in a cost effective way. This is one reason areas with many of these fight so hard against renewable regulations and pollution standards. Similarly nuclear plants in this country can not load follow well.

The best load following is done by gas turbines and gas combined cycle plants. These are the majority of new power plants being built. At current natural gas prices though more simple turbines are being built which are about 1/3 less efficient than combined cycle but much cheaper to build.

Money is also being invested in battery and fuel cell buffering of the grid to time shift some of the power.

 

Well new super-critical and ultra-super-critical and fluidized coal plants can do pretty good load following. There is a super-critical plant in germany doing 7% ramp rates, which is better than many NG plants.

Maybe not surprising, but with deregulation + renewables came some interesting changes and there have been lots of groups looking at old coal plants. With modern computer controls they have gotten the ramp speed of sub-ciritical (i.e. old low-pressure) coal plants improved by 300%, allowing 3% load following, which is approaching older NG plants, which were at 4%. And 3% per min, of a large capacity, is a lot of power for load following. Nice article on it at A New Era in Power Plant Control Performance :: COAL POWER magazine

Of course in the mean time, gas plants have gotten faster. The new GE fast-peaker can go from 0 to 510MW in 10 min, and adding 50MW per minute can make up for rapid changes or even total unexpected loss of a renewable source.

But it also turns out that load following is getting to be less of an issue as the the predictive systems are getting better so "load following" is more and more becoming prediction following. There are many, myself included, that feel the days of large "base-load" plants are numbered. They either adapt, or will be turned off. Nice summary of some of the issues and changes in this article: Why baseload power is doomed | SmartPlanet

 

So, by your response, you do not posess a certificate or signed aftadavit from your green power plant attesting that you, as a consumer are indeed receiving 100% of renewable energy from your provider.

DBCassidy

 

He explained it to you, and either you're trying to harass him, or (more likely) you simply don't understand.

You're arguing that, since other people in America use energy generation that pollutes, then he is guilty by association, and that's a specious argument.

 

I try not to ascribe to malice that which can be ascribed to incompetence, but you have shown a clear pattern of negative and aggressive behavior that I believe are intentional attempt to deride the volt and volt owners, e.g. Posting no-sighting reports on the volt sighting thread, suggesting reasons for GM behavior for which you have no supporting evidence.

I prefer to think of Prius owners as educated and well meaning folks, buy I guess there are exception. I'm happy to try to work with those that don't understand, and can be a patient teacher. But one cannot teach someone that is not willing to learn. And I'm not sure others learn when I answer your questions, so since the majority of your posts seem only designed to malign the volt, I'll no longer respond to your questions... not answering is not to say your comments/questions are correct or incorrect, just that you don't seem to be here to learn or exchange meaningful information so are not worth my time.

 

I knew about the new plants but not the old. Most coal is over 20 years old and can ramp less than 2%. New coal plants are very expensive and require a large utilization factor and many years of payback. Stronger environmental regulations in this country are a significant risk. At current fuel prices, natural gas combined cycle is less expensive. Natural gas prices are likely to rise in the long term, but these risks seem small especially in areas where a high percentage of power is coal.

The bigger deal about natural gas turbines and cc over coal is they can start and stop easily and quickly. They are less expensive and produce lower SO2, NOx, and ghg. If a large percentage of power goes renewable, then utilization factor goes down, which also favors gas over coal.

 

I would agree that new plants are likely to be gas.. but retrofitting old plants to make them more efficient and better suited to integration with renewables is still a good thing as it can lead companies with old plants to add renewables like wind, before they add any new big plants.

 

That is correct. Please mind my assumption.

The limit has to do with the continuous power supply given by the ICE, which is an obvious GM choice (design). If in charge sustain, there is no electronic to limit that, it is a simple energy balance.

You are getting there...Atkinson cycle allows the BSFC to be in a good area, and in the case of 1.5l Prius, less than 230g/kwh from 20kw to 35kw output. Volt cannot get lower to 230, and to get 240g/kwh only between 17-30kw. 240g/kwh is almost full range of operation for Prius.

In the city weight does count, although I've driven a loaded Prius and got much higher MPG than Volt EPA. What do you think is the reason for the obvious defeat in highway?

MGs, I bet they are AC 3-phase syncronous as the HSD. What else is "quite different"?

 

Nope, if it was because of the ICE, then it would only apply when the ICE is on.. it applies to Pure EV mode, which is the only time I've experienced it. The car would always have the opportunity to limit it to available power since 100 downhill is a lot easier than 100 uphill, it could allow one to exceed one way and not the other. If one does not go into mountain mode early enogh and quickly climbs 5000ft at 75mph, the CS battery buffer will reach a minimum limit and the car will say "propultion limited", and the car will go only as fast as the ICE can produce power, which is about 65mph.
Cars without limiters are always limited by they energy they can produce.

Because the Volt epicyclic design has the large Ev motor as the primary drive motor and the ICE as the secondary element, it does not need as large a sweet spot because it does not have to swing as far in RPMs to balance the two. The HSD has a much small EV motor and needs the range to be able to provide a range of power demands with the ICE.

Well I drive a volt and get better than EPA.. so anyone driving carefully can do better.
But the gearing makes a difference as well. In CS mode the ICE must run at speeds fast enough to generate eletricty effectively. But with the ICE connected into the system there is a limited range of RPM that can provide the power and speed, and they don't include low speeds, below about 40mph the car switches to serial hybrid mode. Thus with the volt's more limited sweet spot in the BSFC, combined with the gearing choices, the Volt will not be in "parallel hybrid" mode in most city driving. Rather it will be in serial hybrid mode, where the ICE produces electricity and the drive is pure electricity. Before you jump in and say that Atkinson would help solve that, note that the problem is the tradeoff of generator efficiency vs ICE efficiency. If you look at the generator efficiency and BSFC below, you'll see that a larger sweet spot would not rally sove it as it would quickly leave the generator efficiency region.

MGs in the Volt are permanent magnet motors.

The following diagram, from this MT article, highlights the differences in how the epicyclic gear is setup for the Volt and the Prius.


So the Volt has its traction motor at the sun, the ice on the ring and the wheels attached to the planet carrier.
So the Prius has the engine on the carrier, one MG at the sun and one between the ring and the wheels.

The Prius design limits the top speed without ICE because with the planet carrier fixed (ICE off), the gear ratio for MG1/MG2 is fixed and at higher speeds center gear has to spin too fast. So at some speeds the prius lets the ICE cycle (sometimes off) just to stay in range. Changes in MG1/MG2 could address that somewhat, but there is no variation in gear ration if the ICE is off. With the ICE on, there is a continuously variable range of gearing that can be used.

The Volt design has its traction motor at the sun, so has the major power where it can be used at any speed, but with the ICE on the external ring gear, where it is on the smaller side of the gearing fulcrum, there is a more limited range of
gearing to use the ICE direct power.

 

Where the ICE and MGs tie into the PSD are different.

The engine. GM has admitted they went with an off the shelf engine in order to save development time and money. An engine when installed in a non-hybrid has a turbo. Design is about compromise. Since the car is expected to be in EV mode most of the time, going with a less efficient ICE to control costs is a fair compromise. Just like the Prius PHV using a smaller battery and more ICE use is fair compromise for Toyota's design goals.

There are plenty of cars on the road that have their speed governed below what the platform is actually capable of. It's for safety, legality, and liability reasons. The Prius is one of them. AFAIK, there hasn't been a reason released for the Volt's limit.

 

Why are you bringing up the past? Please, refain from that tactic. Many other posters have asked you to do the same, but you are insistant on going that route. Now, back on topic, from your response above, I am going to take that as a "no" regarding posession of certicate of 100% renewable energy (validity) from your supplier(s).

In regards to my original question, a simple yes or no would have suffice to the above, not a long winded dissertaton which you have provided.

Also you appear to be anti-oil as well as having issues with carbon footprints - so be it.

If you do not wish to answer my questions, that is your choice. However when a claim is made on using "100% renewable energy", it will and should be challenged.

DBCassidy

 

Point well takened!

DBCassidy

 

There is a "Like" button you can use when you appreciate a post. Then you don't need to waste your time and other's with posts like the one quoted.

 

Here is another way the volt might be better. For Volt owners in TX.. they can get "free" charging at night (Of course the PiP can too, just get fewer miles for free)

Save With Free Nights Plan | TXU Energy


Well its not really free, its really signing up for a daytime cost of

12¢ per kwh (for the 12month plan, and lower rates for the ​

18 or 24month signup period.). So for a fixed rate during the day they give you unlimited free power between 10pm and 6am. (the 12c is a bit high for texas but if you can shift a lot of power to evening you can make out). ​

Guess, all the free wind power at night as them trying to find a way to make even a few cents, and get some peak shaving out if it at the same time. ​

​

Austin.. is this actualy this a good deal or just a gimmick? ​

​

 

I've read recently that the vehicle performance goal as per US-PNGV, for design purposes, a mid-size car should be capable of a 85mph maximum speed, along with other requirements, such as 6,5% maximum grade at 55mph.
On your post, driving beyond buffer would result in a limit of 65mph...IMPOV it seems that 65mph needs only something under 20kw output to overcome drag/friction/roll. To drive the Prius 3gen at 100km/h (62mph), Quattroruote italian magazine has measured 13kw required power, as an example.
I believe there is a typing error in your post...

 

The 65mph limit I was discussing was for driving up a mountain grade, not on level ground.
On level ground, CS mode can maintain at least 85mph (from my experience) for extended periods of time.
The Volt's CS_mode can supply upto 55kw, and as I recall the requirement for the volt from Areo loading is 58.5 kw @ 100 mph so that may not be sustainable, but I have no where to test it.

 

Started thinking about what you posed.. do you have reference. I don't believe that at 62mph the Prius needs only 13kW.. that would be much more efficient than a roadster, which I don't believe it is. It would mean a PiP should be closer to 130-140MPGe if sustained 62mph was only 13kWr.
(The roadster is 119MPGe)

I sent searching and found measurements for the the roadster:

which appears to give about 17kw at 62mph

I could find no speed vs kw measurement charts for the Prius or the Volt, so curious if you have the data from the prius.

 

What gen is the Prius tested? And about the roadster Tesla, does it mean it has less drag?