Not only is the USPS a great proving ground, used postal vehicles tend to filter out to the public.

Between USPS and UPS, this could be huge.

Is it just me, or is there a trend underway towards ultracaps for storage rather than batteries?

Unfortunately, Boston is not very well positioned in the biodiesel market or supply infrastructure. But in the midwest, that could be of significant value, especially outside the bigger cities, were the slightly higher NOx should not make a difference.

It is true that since motor homes spend most of their time at cruise, they would not derive much direct benefit from the regenerative breaking. It is also true that aerodynamic cleanup would be very helpful.

One way in which a hybrid system could help motor homes improve efficiency, however, is by allowing for engine downsizing. If electric assist is available for the (relatively infrequent) times a motor home has to accelerate, then the combustion engine can be made radically smaller. And for any given vehicle cruising at an particular speed, a smaller engine is more efficient.

For instance, many new Winnebago Class A motorhomes come with ~350 hp engines. I'm guessing here, but I cannot imagine that cruising at 65 MPH requires anything more than 100 hp to overcome rolling resistance and aerodynamic drag, even for something that big. Downsize the engine to 120 hp, and you can cruise fine but would have a good deal of trouble accelerating briskly or climbing mountains at speed. Add an electric assist, and depending on how big you make the battery you can accelerate for short stretches at a good clip, and even climb some hills at speed before exhuasting your electricity supply. Considering what distances motor homes travel, and how much time they spend at cruise, and how much gas they consume, anything that helps cruising economy even moderately could save good money.

Remember, even though the Prius only gets about 45 MPG on highway cruise, that's better than many similarly sized (and similarly zippy) cars, like the Ford Focus (34 MPG hwy). The former has a 1.5L I4 engine tuned to produce 76 hp, while the latter has a 2.0L I4 engine tuned to produce 136 hp. Shrinking the engine and its power output that much is an important part of the savings. Scale that effect up to motorhome size, and real money is at stake.

The idea of long-distance electrification is interesting but very challenging. First of all, it would need to be done along with the truckers, because they would be a huge and natural market for such a thing. Beyond that, you would neet to work out the technical issues. Using ground level rails would probably be prohibitively dangerous and impractical. Using overhead wires is an equally mature technology and more natural solution. It would be expensive to string up such wires, but if you did it on the most important highway corridors, you might get enough customers. Most important is to get a large enough installed base of compatible vehicles. They would need to be serial hybrids with electric motors robust enough to sustain the vehicle at long-distance cruise. They would need to have enough on-board generating capacity to run them when they were on non-electrified roads. They would ideally to be able to switch modes while in motion, rather than having to stop and switch engines, like the dual mode diesel/electric trolleybuses we have here in Boston. There would also have to be a way to meter usage and bill the costs. But in the long term, the ability to substitute electricity for liquid fuels in road transport could be a major improvement. European railroads are already highly electrified, and it provides many important air quality, and now cost benefits to them.

While there are alot of motor homes, there are not nearly enough to worry about. There are more postal delivery vehicles and their use is ideal for a series hybrid.

Trash trucks, city cabs, local busses, local delivery services can all benifit greatly from hybrid or even all electric vehicles.

If they just rounded off some of the sharp corners and put another 10 degrees of rake in the winshield of that box they could accomplish the same fuel economy without all the expensive hechnology. Or hell they can just buy modern sprinter vans with 2.7 litre diesel instead of that oaf. Is anybody awake at USPS?

coal burner:

Where do you get a coefficient of drag of 0.45? I've been searching for the numbers for various trucks, RVs, vans and such and have a hard time finding them.

But assuming that you could get the number into the mid 0.3's, you could probably mount a 175 hp engine, or smaller, and get sustained cruise speeds of at least 75 mph. That's cutting the typical RV engine by half, in hp terms.

If a typical gas RV gets around 6 MPG (1), then over a (conservatively estimated) 150,000 mile service life (2) it will burn 25,000 gallons of gas. Increasing fuel economy by 20%, which an engine downsize enables, saves 5000 gallons over that service life. At a fairly conservative $2.33/gal, that's $11,650, meaning that a hybrid system will most likely pay for itself over the life of the vehicle, just by allowing you to downsize the engine and save modestly on cruising economy.

If you assume a longer service life, greater increase in cruising mileage due to engine downsize (the Prius bests the Foucs by ~33% in EPA hwy numbers), or significant benefits on the smaller number of stop-and-go miles, the numbers get better.

It does not seem as dramatic as going from 20 to 50 MPG in city traffic, but starting from very low economy and very high utilization rates, a relatively modest increase in percentage terms compounds itself into a considerable margin in real terms.

The point of this extends beyond RVs. Any vehicle which mounts a combustion engine larger than what is needed for its sustained cruising speed could benefit. Larger combustion engines produce the power needed for brisk acceleration, but once you're done accelerating, they're just dead loss. When the stakes are high enough, it pays to look for alternative means of acceleration to save on the cruising.

Again, the real question is in the long-haul bus and truck market, to get closer to the original thrust of the article.

(1) http://www.rv-coach.com/current_category.82/FAQ.44/faqs_detail.html
(2) http://www.cruiseamerica.com/rv_sales/sales_faq.asp

"Very little of the Prius' highway ecinomy is related to it being an hybrid."

You can look at this from two perspectives. When cruising on the highway, the electric part does not work, so you could say that it does not contribute to highway efficiency. But on the other hand, the relatively small ICE and Atkinson-cycle are big contributors to the low consumption. Both these are only possible in a hybrid.

As someone else on this web site explained, you can only use the Atkinson cycle AND adhere to emission standards in a hybrid vehicle. So a non-hybrid Prius could not have an Atkinson-cycle engine. (I could not verify this, but is sounded plausible, so I'll take his/her word for it)

As for the low Cw: the volkswagen passat has a Cw of 0.27 only slightly higher than the 0.26 of the Prius. So it's not that much better than 'ordinary cars'.

Engineer-Poet's post may explain why a hybrid approach is of limited utility in diesels. But many RVs are actually gasoline powered. Even the big ones. Check out the Winnebago website for that point. Plus, many pickup trucks and medium size passenger vans are also gasoline powered. Even for users who spend most of their time cruising, enabling a downsize can make the hybrid worth it.

Worried about hills? There is a pretty simple solution, which long-haul truckers regularly employ. Slow down. A vehicle that can hit straight-and-level max cruise at 85 mph (and cruise efficiently at 65) without drawing on the electrics will have enough spare power at 50 mph to climb most hills without turning to electric power, if it is not too heavy. That's because cruise power requirements are tied to size and frontal area of a vehicle, while climb power requirements are tied to weight. That's why most highways in very hilly regions have an extra right lane for the ascents; it's for trucks to climb slowly without being rear-ended by cars which can climb faster.

"At this time, our primary source of electricity is coal or some from of hydrocarbon (natural gas, diesel, etc.) and it is best not to bring into a discussion what America "will" use one day. Keep with the facts of today and the next 10 years in your thinking - that much we can hang onto with some level of confidence for discussion's sake."

Really not true. Wind is 40% of newly installed U.S. electrical generation in 2006, and 45% of planned installations (announced, permitted, etc) in 2007.

Furthermore, PHEV's are ideally matched with wind: they provide the storage that wind needs, so that it is VERY realistic to assume that PHEV's would be powered by wind. In fact, the storage provided by PHEV's would reduce intermittency for the grid as a whole (even accounting for the intermittency introduced by the additional wind needed to power the PHEV's), enabling more wind than would be needed for the PHEV's, so that PHEV's could be considered carbon negative.

As wind generation does not use a heat engine cycle, the rest of this analysis does not apply.

If this analysis did apply, however, it would over-estimate the losses of an electrical cycle vs a gas ICE. First, even NIMH batteries have a 30% loss, not a 51% loss as assumed here (1-.7 x .7). Second the Li-ion batteries being tested for the next generation of hybrids (esp 2008 Prius) have much lower losses (I've seen claims of only 1%, though that seems hard to believe). Third, ICE efficiency is on the order of 20%, half of the roughly 40% suggested by this analysis for electrical engines, and a third of the efficiency they would likely get.

I agree with you about government not getting too involved. However, I think the feds will get way too involved, thinking that they need to spare people pain.