Electrical Car Consept – Feasibility

[Oznog]

Oznog

I’m getting the feeling that the know-how exists on this site and other forums to come up with a workable solution but the willingness to venture in something like this is not qualified, maybe because of a lack of knowledge specifically regarding the availability of new and incorporated technologies.

Virus

Well, this is the type of motor the EV builders use:
**broken link removed**
That's a series-wound motor which is very easy to build a powerful controller for, but it cannot do regen braking. Technically separately excited can do regen but I think people just tend to go for the far more complex AC drive motors.

Unfortuantely simply adding a motor/generator to an existing gasoline vehicle will not make it a "hybrid" like a Prius. The engine probably won't be any more efficient and in fact any energy stored in the batts will suffer efficiency penalties that will only reduce mpg. Unfortunately there have been some guys circulating plans on the net for this and lots of other things that won't work.

As far as putting batts in the trunk, here's the relevant info:
An EV converion car requires around 0.3 to 0.5 kWh per mile, with the weight of the engine taken out.
Large cars which started out with poor mpg end up on the high end of that.

So adding a big deep cycle batt, 100AH, actually only has about half that useable (varies though) because 1) you will murder that batt fast if you run it down all the way repeatedly and 2) something called Peukert's Equation says with high amp loads only part of the batt's capacity is even usable.
So say you count that as 50 AH, 0.6kwh as usable. That gets you around 1-2 mi of range per batt. A car will need to have its suspension reinforced for many batts. Also the added weight in ADDITION to a car engine will reduce the car's overall mpg nad kwh/mi needs. Well one estimate I saw said each 50 lbs is 1%-2% penalty in mpg for general driving (more energy needed to get it moving, more rolling resistance in the tires) and that batt I mentioned weighs around 75 lbs at least.

 

[Nigel Goodwin]

The oil countries and companies have total control of prices.

At this time, oil is the cheapest, safest, and most portable energy source.

Before any real alternative can get established, they'll just decrease oil prices till those options are killed. Then when it's done, they raise the price!

Well you get cheap oil in the states, in the UK most of the price is tax, so that couldn't happen anyway.

But in any case, the oil companies wouldn't do that, most are spending a fortune trying to find alternative energy sources - so they will continue to make money by selling you the alternatives, and the oil will be used for plastics production, and will last longer.

 

[Hero999]

The cheapest option is to have a diesel car and brew your own biodiesel.

 

[Pommie]

I think the battery problem will be solved by a chemist. If a chemist came up with a way to convert CO2 and Hydrogen to a hydrocarbon that uses electricity (or heat) that was reasonably efficient, similar to how Haber made fertilizer from Nitrogen and Hydrogen, then it would be the best battery ever invented. After all, a battery is just a way to store energy, why not store it as a liquid and use the same tank/engine/gearbox etc.

If such a process was discovered/invented then nuclear power stations or even heliostat arrays could produce vast amounts of synthetic hexane in remote deserts and the fuel could be shipped just like it is now.

The use of ethanol is a similar process. It (allegedly) takes the same amount of energy to make ethanol as it will produce when burnt. As long as that energy is from the grid then it is no different to a battery. The problem with ethanol is it uses up valuable resourses (food).


Mike.

 

[Hero999]

I think the battery problem will be solved by a chemist. If a chemist came up with a way to convert CO2 and Hydrogen to a hydrocarbon that uses electricity (or heat) that was reasonably efficient,

I don't see who that could be of any benefit.

It will take more energy in burning fuel to generate the electricity or heat, to convert the CO2 and H2O to a hydrocarbon than what would be released when the hydrocarbon is burnt. With out doing any calculations, I would estimate that the whole process would probably be around 10% efficient and that's being optimistic.

 

[Pommie]

Before the Haber process was discovered the idea of producing fertilizer from Nitrogen and Hydrogen was unthinkable as it would require vast amounts of energy. Haber found the catalyst that made it energy efficient.

The interesting thing about such a process is that most power stations produce vast amounts of steam and carbon dioxide. The chemist that comes up with that catalyst will rival Bill Gates for wealth.

Mike.

 

[Hero999]

Before the Haber process was discovered the idea of producing fertilizer from Nitrogen and Hydrogen was unthinkable as it would require vast amounts of energy. Haber found the catalyst that made it energy efficient.

All the Harber process does is reduce the activation energy for the reaction, not the amount of energy required to convery hydrogen and nitrogen in to ammonia.

It takes a certain amount of energy to break all the bonds in the CO2 and H2O, some of this energy is released when they bond together as a hydrocarbon. You don't gain anything by converting H2O & C2O to methane and oxygen, it just takes energy and funnyly enough more energy than what would be released when you burn the methane to get CO2 and H2O.

We are talking about the first law of thermodynamics, energy cannot me made or destroyed, it can only be converted from one form to another.

I'm not meaning to be patronising but you seem to be unaware of bond enthalpy.
**broken link removed**

Try doing the reverse of the example in the link above, calculate how much energy you would require to convert CO2 and O2 to propane.

The moral of the story is that chemicals only store energy, they don't create it.

 

[Pommie]

The moral of the story is that chemicals only store energy, they don't create it.

That was exactly my point, chemicals are the perfect battery.

Mike.

 

[Hero999]

That was exactly my point, chemicals are the perfect battery.

Chemicals are the perfect battery as the can store large amounts of energy, the problem is have to burn them to get heat energy which you then convert to mechanical work; this is horribly inefficient. The second law of thermodynamics means that it's very inefficient as it determines how much work can be extracted from a temperature differential.

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

You, need a primay energy source to convert the H2O and CO2 to a hydrocarbon like methane. Assuming the source of energy is a heat source The maximum efficiency is governed by the maaximum temperature the process will effectively work out and the temperature of the sourroundings.

You need a way of converting the chemical energy back to work and this again normally involves burning it. Yet again, the maximum efficiency is governed by the combustian temperature and the temperature of the surroundings.

It turns out that practical heat engines are very inefficient as current technology doesn't allow for the high temperatures required to make them efficient. Given that a typical coal fired power station is only 36% efficient and an automotive engine is only 25% efficient, the overall efficiency will be less than 9%, even if you ignore the losses involved in converting the CO2 and H2O to methane and back again. You're much better off using a hydrocarbon like oil or natural gas to fuel your car rather than a coal fiered power station.

This is the reason why there's so much interest in hydrogen fuel cells which allow us to convert them in to electricity more directly from hydrocarbons rather than burning them and using an inefficient heat engine to generate electricity.

 

[Virus]

Say, I like your way of thinking, at a power station you have excessive heat that is lost in the form of steam , you also have the potential in the high pressure steam that is also lost and the burnt ash.

What would the end product be (for example) if the waist at a power station could be reused in different ways, any idea’s.

Come to think of it what was the price of fuel when coal power stations where built (developed originally)? ? ?, one would think their would be a flood of research into recovering this loss of energy.

 

[Hero999]

The ash can be recycled in to building materials.

Waste heat can be used to heat surrounding buildings in district heating systems.

 

[Nigel Goodwin]

Come to think of it what was the price of fuel when coal power stations where built (developed originally)? ? ?, one would think their would be a flood of research into recovering this loss of energy.

There has been, and presumably still is, lots of such research - and coal fired power stations are amazingly efficient - the heat lost in the cooling towers is only a relatively tiny amount.

 

[Hero999]

That's not true, a typical coal fired power station is about 36% efficient, a supercritical plant is only 45%. The only way to make it more efficient is to use the waste heat for district heating.

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

 

[Nigel Goodwin]

That's not true, a typical coal fired power station is about 36% efficient, a supercritical plant is only 45%. The only way to make it more efficient is to use the waste heat for district heating.

But how much is wasted in the cooling towers!.

In my experience, you can't use the waste for district heating because the plants are usually miles from anywhere?.

 

[Hero999]

But how much is wasted in the cooling towers!.

A lot of energy is wasted in the cooling towers, often they use a river as a heat sink but the increased temperature can create problems with the oxygen being less soluble in the water which can kill fish.

 

[Nigel Goodwin]

A lot of energy is wasted in the cooling towers.

But only small in percentage terms for the running of the plant.

 

[Pommie]

Hero,

Maybe you can explain something that has confused me for a while concerning the Carnot engine.

Carnot seems to take the view that a body at 100ºC has 373*x energy available. A body at 50ºC has 323*x energy available, therefore the most energy we can recover is the difference between the two.

Taking the above bodies, I can recover 50/373 (Delta T/T hot = 13%) parts of the energy available. However, to put the system back to it's initial state I only have to add back the energy I have managed to extract. That is, heat the hot body from 50ºC to 100ºC.

This seems like a 100% efficient system to me. I think the view that the energy available has a datum at absolute zero is flawed.

Mike.

 

[Hero999]

Nigel,
No, if it's not used to run a district heating system then most of the energy from the coal is wasted. A supercritical plant will waste 55% of the energy in the coal. There's nothing that can be done about it, the laws of thermodynamics limit the amount of work that can be done given a certain temperature differential.

Carnot seems to take the view that a body at 100ºC has 373*x energy available. A body at 50ºC has 323*x energy available, therefore the most energy we can recover is the difference between the two.

What Carnot says is that the amount proportion of heat that can be converted to useful work depends on the temperature difference between the two bodies and their absolute temperature. The remaining heat energy goes in to heating up the cold sink and is wasted.

Taking the above bodies, I can recover 50/373 (Delta T/T hot = 13%) parts of the energy available. However, to put the system back to it's initial state I only have to add back the energy I have managed to extract. That is, heat the hot body from 50ºC to 100ºC.

No, if you put back the amount of energy you've managed to extract. you will not heat is back up to 100ºC.

Think of a hydroelectic power station, the maximum efficiency is deturmined by the the pressure difference of the water on one side of the turbine relitive to the other side of the turbine which is deturmined by height of the dam. Not all the potential energe in the water can be converted to mechanical energy because the water will keep moving after it's been through the turbine.

The same is true for our heat engine, work is done by the heat flowing from a hot region to a cold region, it can't all be converted to work because the cold region wouldn't be warmed up and the flow of heat would stop.

Here's an example, we have an ideal heat engine an a litre of boiling water 100ºC on the hot side and room temperature 20ºC on the cold side.

[latex]efficiency = 1-\frac{T_c}{T_h}=1-\frac{293.15}{373.15}=21.44%[/latex]

The heat energy required to heat the water to room temperature is.
[latex]Q = 4.2 \times 80 \times 4.2 \times 1000 = 336000J[/latex]
Given that it takes 4.2J to rais the temperature of 1ml by 1ºK.

The amount of useful work we can perform with our litre of boiling water is 0.2144*336000 = 72.04kJ.

 

[Pommie]

Your using the equation/theory I'm questioning as proof!!

OK, I take a liter of oil at 20ºC and heat it to 100ºC. I then use a Carnot engine to retrieve the available energy. If it's only 24% efficient, where does the lost energy go? Heat? Sound? Movement? If I then use 120ºC and 200ºC, why can I extract more? The energy added is the same (assuming non boiling liquid and an ambient of 120ºC). Where do the losses go in this case?

I'm not being flippant, I do believe that Carnot was referencing to absolute zero, and objects at room temperature hold vast amount of energy and this is why we can only recover a small amount. In reality, if we can recover the energy we have added we are vastly improving on Carnots efficiency equation.

To take your dam example, the dam should be much more efficient at 5000m to 4000m than from 1000 to 0 meters. This is exactly the same flawed thinking. Sea level is not the relevant datum, the lower level is. You only have to pump the water up 1000M to get back to status quo.

Mike.

 

[Hero999]

Your using the equation/theory I'm questioning as proof!!

OK, I take a liter of oil at 20ºC and heat it to 100ºC. I then use a Carnot engine to retrieve the available energy. If it's only 24% efficient, where does the lost energy go? Heat? Sound? Movement?

That doesn't make any sense if we don't know the ambient temperature.

Alright, assuming from your 24% it's about 20ºC, the lost energy goes in to heating up the room.

If I then use 120ºC and 200ºC, why can I extract more? The energy added is the same (assuming non boiling liquid and an ambient of 120ºC).

What's the ambient temperature?

If it's 20ºC then you'll be able to extract a larger proportion of the energy.

If it's 120ºC, then no, the engine will be less efficient.

Where do the losses go in this case?

As always heating up the cold sink.

I'm not being flippant, I do believe that Carnot was referencing to absolute zero, and objects at room temperature hold vast amount of energy and this is why we can only recover a small amount. In reality, if we can recover the energy we have added we are vastly improving on Carnot's efficiency equation.

Alright, here's another way you can look at it, I'm not going to do any calculations on it but you can turn the whole thing on it's head. At the moment we've only being discussing heat engines, we haven't discussed the heat pump. Heat pumps move heat from cold regions to hot regions and as they're reducing the entropy they require energy. If we used a perfect Carnot heat pump to move heat from our room in to the water we could boil the water using only 74.04kJ.

How does this work?

Where does the rest of the energy come from?

The room!

Before we ran 336kJ of energy through our heat pump and extracted 74.04kJ as useful work, the rest of the energy was transferred to the room. We may have raised the room temperature by a couple of mK but it's not enough to make any difference as far as we're concerned.

Now we're doing 74.04kJ work to heat the water back up again. The extra energy has come from the room, we may have lowered the room temperature by a couple of mK but it's not enough to make any difference as far as we're concerned.

Heat pumps are used in real life to heat houses and office blocks, normally the air conditioning is just run in reverse so the outside is cooled down more and the inside is warmed up more. A heat pump might only use 2kW of electrical energy but deliver 6kW of heat energy to the room, the 4kW of extra energy comes from cooling down the outside more.

In real life both heat pumps and engines are less efficient than their Carnot counterparts which is why you can't get 100% efficiency in general.

To take your dam example, the dam should be much more efficient at 5000m to 4000m than from 1000 to 0 meters. This is exactly the same flawed thinking. Sea level is not the relevant datum, the lower level is. You only have to pump the water up 1000M to get back to status quo.

Mike.

You seem to have got a couple of things confused, the hotter the cold sink the less efficient it is.

To be picky sea level isn't really the datum, it's the ambient pressure at sea level.

In truth, I don't know how well my analogy compares to the heat engine/pump.

If it did compare well, if you put low pressure region in a perfect vacuum it would become 100% efficient. Come to think of it that makes sense, in practice you couldn't have a vacuum since there would always be molecules filling it from the high pressure region.

The same goes for our heat engine, if we put the cold sink at 0ºK our Carnot engine could run at 100% efficiency but in reality you can't get to 0ºK because heat from the warmer region will raise the temperature above 0ºK.

Another thing, please don't confuse work with energy, energy is all around us (in the form of heat) but we can't do anything with it. Energy gradients are the only thing that can do work and entropy (the inability to do work) always increases as the energy gradiants in a system even out.