Sunday discussion - Would you go electric?

[Propellor]

So if we drive along merrily using all our motor can give, presumably 80kW, then a fully charged battery pack will last 18 minutes? Is that how it works?

Or is that just the rate at which the battery can deliver power and battery charge is worked out another way?

[xbr500f]

The battery could feed a more powerful motor. You are right, if you were to run the 80kw engine continuously at full power it would deplete the 24kWh battery quickly. That would have to be done in a test lab as I can't see how that would happen in real life.

Watch the very excellent Formula E racing for a better explanation.

So far all the questions have been about the engine and battery. I'm surprised that charging has hasn't been discussed in more depth.

[Propellor]

So far all the questions have been about the engine and battery. I'm surprised that charging has hasn't been discussed in more depth.

Charging at home.... A lot of cars are parked on the street. Most of the rest on a driveway. Hardly any in a garage. So how does one go on?

What type of motor are they, generally? AC or DC? Brushless? How is the speed varied? Do they need a gearbox? Is the motor cooled? How? 

[Propellor]

Got a bit side tracked reading about Galileo's wheel paradox. Which turns out to have been aristotles first anyway. Fascinating brain teaser.

[guest564]

When you calculate the battery capacity you have to consider that you can't fully discharge or charge the Lithium batteries because it drastically reduces their life. Generally they are charged to something like 80% of max. capacity and discharged to 20% min, I think Nissan run 75/25 so only 50% of capacity is available for use. The other problem is that the battery capacity is limited by the weakest cell so you may have even less capacity after a period of time.

[xbr500f]

I always charge my battery pack up to 100%. The majority of other EV owners do the same.
I'm over 24,000 miles in 20 months and so far there is no apparent reduction in capacity. With only 4 months to go until my lease finishes I doubt that I'll see any change.

The taxi firm in St Austell say that one of their cars hit 100,000 miles before it dropped 8%. That is after the car goes on a rapid charger 6/7 times a day.

[guest564]

I always charge my battery pack up to 100%. The majority of other EV owners do the same.

100% of available capacity - the electronics won't let you run a 100/0 charge/discharge cycle. Limiting the charge/discharge amount increases battery life from something like 300 cycles to 2500 cycles or more. If you're careful and never discharge the battery to the limit then it can last even longer.
A racing vehicle will use full capacity because battery life is less of an issue.

[xbr500f]

Thanks for the reply, that's useful information.

With the maximum number of battery recycled that could give me around 237,000 miles. Presumably the range would drop off towards the maximum number.

A couple of things to consider as well. The Leaf has an air cooled lump for a battery pack but others have a liquid cooled unit. On my longer trips the battery temperature had hit a maximum of 10 bars (out of 12). The last battery report from Nissan still looked great though. Storage of the car has been suggested as a potential problem area, so I don't leave it fully charged while away on holiday. Leaving the charger attached for long period also seems to discharge the 12v battery. The 12v needs the car powered and the inverse running to recharge it.

I've just been asked by one of the Nissan dealers to take the latest 30kWh Leaf for a 24 test drive. With 27kWh capacity (do I believe) that suit most of my journeys. Before I hand my own car back I have a major outlay where the windscreen wipers need to be replaced

[xbr500f]

So the question now is would you buy a new diesel / petrol car instead of an electric one.

To summarise the benefits of a EV :-
Running costs (fuel and servicing) are a lot cheaper
More efficient power train
Greater reliability
No need to warm up the engine before you give it some welly
Avoid trips to the petrol stations.

Downsides:-
Time taken to recharge on longer runs
Battery life concerns
Battery capacity on standard family cars (not Tesla)

There was an interesting article on reporting Scotland a few days ago. EV users on the islands are hooking up to the wind generators. They already have the wind turbines for their homes and farms, and can now charge up their EV's as well. Smart!

[Propellor]

How does the power/weight ratio compare?

With respect to the power train, what does this consist of?

I believe that the overall efficiency is good, taking into account the initial power generation. Although wind turbines are a funny thing. I tend to think of them as efficient even though their mechanical efficiency probably isn't so good. Maybe I'm thinking this because the energy source is not finite in the same way as reserves of oil or gas?

Cheers.

[iansoady]

 Although wind turbines are a funny thing. I tend to think of them as efficient even though their mechanical efficiency probably isn't so good. Maybe I'm thinking this because the energy source is not finite in the same way as reserves of oil or gas?

Cheers.

It's a bit tricky to compare. The best thermal power stations have thermal efficiency of less than 50% (the proportion of energy in the fuel which is converted to useable power). Alternators themselves are quite high efficiency in converting mechanical energy into electrical energy - up to 98% although I would expect this to be a bit lower for wind turbines as the generators are smaller than those in "conventional" power stations.

So given the wind is effectively free, wind turbines (and by the same argument wave, tide etc generators) are much more efficient.

[Propellor]

 Although wind turbines are a funny thing. I tend to think of them as efficient even though their mechanical efficiency probably isn't so good. Maybe I'm thinking this because the energy source is not finite in the same way as reserves of oil or gas?

Cheers.

So given the wind is effectively free, wind turbines (and by the same argument wave, tide etc generators) are much more efficient.
[/quote]

That's exactly what I'm thinking.

Although oil is "free" in that it's there for the taking. How long before governments tax the breeze....?

[blew]

Is it not strange that all the energy sources that are free receive huge subsidies? Wind turbines are paid far more for their small amount of electricity than power stations using coal.The proposed Swansea Barrage,using free tidal power,has stalled because the company that proposes to build it want FOUR times the going rate for the electricity it will produce.It's strange that electricity producers that use free power sources (wind,tides,whatever) receive far more money than those who pay for their fuel.

[iansoady]

I think you're ignoring the enormous subsidy that the Chinese will be getting for the Hinkley nuclear white elephant. It dwarfs any subsidies for proper renewable energy.

You say "small" amount of wind power - in fact, in the second quarter of 2015 at more than 25% renewables exceeded coal. http://www.theguardian.com/environment/2015/sep/24/renewable-energy-outstrips-coal-for-first-time-in-uk-electricity-mix

[xbr500f]

Very interesting comments about the use of renewable power. I didn't realise that the UK was using so much.

I found an interesting YouTube video (search national grid : fully charged). Although it was filmed a few years ago, when the use of renewables was in single percentage figures, the question was asked about demand for electric vehicles snd could the grid cope. The answer is yes.