[Moreforles]

Originally Posted by TX_Dj

It's do-able... but how much would you want to spend? If you buy a nice RV for 100k, and put 400k into the drive/battery/charger systems, who would you ever resell it to when you no longer need it?

Right now with fuel costs and the economy the way it is..... it's easy to find some very nice rv's for around 10k..... and some not so nice ones that need a little more work for a lot less

[Moreforles]

Originally Posted by This is Bill

The electric RV.

Instead of buying a $75,000 -$100,000 brand new RV, what if I bought a used one for $10,000 as a conversion project? The technology has changed very little on the inside so it can be a few years old as long as it is clean and in working order (fridge, sofa/bed, tv, generator, toilet/bath, carpets, etc.).

The long flat roof is ideal for solar panels. If my RV is sitting out doors all the time, then it makes sense to have solar panels. The extra weight and cost is a draw back at first, but the savings over time

Or just not mess with and have a regular motor home with it's factory warrenties and shell out $2000 for gas each trip. Plus all the maint cost.

I've read a lot of these posts and a I'm interested in how this concept can be improved. Good day.

* Most or all of what you describe can be found in a smaller package (Class B) Used for around 10K (or less, if you start out looking for one with blown motor..... but rest of RV, clean and in working order.. with bed, fridge, microwave, generator ect........ A nice Class B with a slide or two can be very comfortable, large enough roof for some solar panels (I thought I heard of a printable solar Ink some time back, that would be great on awnings and such..... supposedly generated more power than conventional panels as well)

I was thinking along those lines - small Class B ERV or at the very least conventional Class B with electric upgrade.... trailer towed behind with small electric vehicle or scooter or both along with some or all of batteries and or generator and or more solar panels.... (wind turbine would be a must too, so batteries could be charged quietly at night while I was sleeping, when power hook up wasn't available and I didn't want to or couldn't run generator....)

[samborambo]

This is a really interesting thread. One day maybe I might tackle something like an electric RV.

A 40 seater bus uses about 100hp at 60mph cruising so you're looking for an industrial induction motor of about the same continuous rating. Buses actually have a very low coefficient of (wind) drag from its long narrow shape which is a good thing. However, when you multiply that by the 10m2 frontal area and also factor the 9 ton weight and higher Rolling Resistance compared to a car, the energy required would be around 260kWh for 180mi range at 55mph. You were pretty much spot on with the energy per mile at 55mph of 1120Wh/mi.

A little ambitious? Well, you're converting a luxury motorhome. You're probably going to spend US$50k on refitting on top of the US$90k for batteries.

[OCRVGUY]

How about if you only needed enough batteries to run a compressor and the rest of the electrical devices in the Electrically propelled RV? Instead of batteries providing the power for the drive train, use a generator that runs off compressed air to power the electric drive system. It would be similar to a turbine generator but instead of jet fuel burning through it, compressed air would be forced through it.

The electric compressor i mentioned would run and fill at least three tanks that the generator would syphon it's air supply from. I say three so you have a reserve tank but two might be sufficient if space became an issue.

This solves some of the weight issue with the batteries as the tanks can be carbon fiber and the generator could be very lightweight also, depending on the materials needed and the size requirement to generate enough kwh's.

If you doubt the compressed air generator is feasible, then look at this link: http://www.mdi.lu/english/

This is a car company that make a compressed air engine for a passenger car. Surely I could even connect an ac motor to the drive shaft and get enough electricity off that motor. Be cooler with a compressed air turbine though

[Overlander23]

So, you're proposing using the electricity that is stored in batteries to run an air compressor, to run a turbine, to generate electricity for the motor?

Errr, why not just use the electricity in the batteries? Converting one form of energy to another always incurs a loss due to inefficiencies. Converting electricity, to air, to electricity is a phenomenal waste of energy. You'll never get more electricity out of the compressed air driven generator than you put in to create the compressed air... by a long shot.

Maybe I'm just confused here...

[OCRVGUY]

Actually, the power is stored in the air tanks. I know I didn't explain it well but let me try another way.

The original problem was to go 200 miles in a day. If you carry enough tanks on board to run the generator to allow you to travel the 200 miles, then you only need the compressor to refill the tanks at the end of the trip. The batteries are to use the on board electrical devices and the compressor is for refilling the tanks. You can recharge the batteries and refill the tanks when you plug in.

if you want to go further than two hundred miles, then run the compressor off the batteries to re-fill the tanks. Couple this with some quality solar panels and maybe even extend range even further.

[icec0o1]

compressed air doesn't have that good of an energy density. You'd need HUGE tanks to propel an RV 200 miles, pretty much the tanks would the the size of the RV. Further, compressing air is not very efficient of a process. I would venture a guess that, for the very high compression required (1000psi) the efficiency would be in the 50%.

So we're burning gas or coal with about 80% efficiency to get electricity that you'd use to compress air and lose 50% more of that energy. Further, air drive trains aren't the most efficient so say 80% and you get to something like 30% of the energy stored in natural gas/coal is used for propulsion. You might as well buy a 35mpg ICE which will do 25-30% efficiency in burning fossil fuels.

The reason batteries are the standart storage medium is because they are 95%+ efficient in storing and releasing energy. Moreover, electric motors can also be in the 90%+ efficiency and there are far less moving parts.

Three words for air. Don't go there.

[ga2500ev]

Originally Posted by Overlander23

So, you're proposing using the electricity that is stored in batteries to run an air compressor, to run a turbine, to generate electricity for the motor?

That is the proposal.

Errr, why not just use the electricity in the batteries? Converting one form of energy to another always incurs a loss due to inefficiencies. Converting electricity, to air, to electricity is a phenomenal waste of energy. You'll never get more electricity out of the compressed air driven generator than you put in to create the compressed air... by a long shot.

Maybe I'm just confused here...

No confusion. OCRVGUY was trying to get around issue of having either tons or a mint's worth of batteries in the vehicle. The problem is that the energy density of compressed air makes it just as impractical.

A more realistic possibility is liquid nitrogen. It has the same profile as compressed air, but the phase change to liquid and back can store much more energy than compressed air. Also storage does not require pressurized tanks.

The energy density is still bad. As outlined here:

http://en.wikipedia.org/wiki/Liquid_...iquid_nitrogen

Energy density of liquid nitrogen

Any process that relies on a phase-change of a substance will have much lower energy densities than processes involving a chemical reaction in a substance, which in turn have lower energy densities than nuclear reactions. Liquid nitrogen as an energy store has a low energy density. Liquid hydrocarbon fuels by comparison have a high energy density. A high energy density makes the logistics of transport and storage more convenient. Convenience is an important factor in consumer acceptance. The convenient storage of petroleum fuels combined with its low cost has led to an unrivaled success. In addition, a petroleum fuel is a primary energy source, not just an energy storage and transport medium.
The energy density — derived from nitrogen's isobaric heat of vaporization and specific heat in gaseous state — that can be realised from liquid nitrogen at atmospheric pressure and zero degrees Celsius ambient temperature is about 97 watt-hours per kilogram (W-hr/kg). This compares with about 3,000 W-hr/kg for a gasoline combustion engine running at 28% thermal efficiency, 30 times the density of liquid nitrogen used at the Carnot efficiency [2].
For an isothermal expansion engine to have a range comparable to an internal combustion engine, an 350-litre (92 US gal) insulated onboard storage vessel is required

The bottom line is that a 100 gallon non pressurized tank would be more doable than 50 highly compressed air canisters.


As for the efficiency, it's less of an issue than normal. The OP pointed out that they get "free" access to a 120V 50A outlet for their slip when they pay the $25 to park the RV for the night in the RV park. So essentially they can pull 6 kWh worth of power for however many hours they are there.


So it remains an issue of carrying that energy in a portable fashion. While batteries are efficient, there is a large weight/cost burden to be paid to carry them. Though the liquid nitrogen route is much less efficient it does offer the possibility of generating the range required without weighing a ton or costing a mint.


The other hidden advantage to liquid nitrogen is that in a lot of places you can buy it off the shelf very very cheaply. A log of airgas companies have liquid nitrogen as a byproduct of liquid oxygen generation. In some places it would be possible to fill that 100 gallon LN2 tank for as little as $20.


So it offers quite a bit of flexibility. You can get LN2 from outside sources. You can use your own distiller to produce it yourself just add electricity.


Finally the energy density listed is only to 0 degrees Celcius. Warming the LN2 to normal air temp will release even more energy.


The best bet would be to have a hybrid with as much batter capacity that can be afforded to carry/pay, with a LN2/generator system to charge the batteries.


Just some thoughts. LN2 actually has some measure of hope
whereas compressed air simply won't cut it.

ga2500ev

[icec0o1]

Personally I wouldn't want to be anywhere near a vehicle with a 100 gallon liquid nitrogen if it gets into an accident, especially in a non-pressurized, strenghtened container.


Although, thinking about it, if you collide with an ICE, it could spill over the engine or gas tank and put out any fires. Either that or explode. You wouldn't need the jaws of life either as all the metal that it comes incontact with would become brittle enough to kick down Just hope none of it gets on you. .