I received an email the other day asking about possibilities for range extenders in EVs, and I thought the response might be useful for others too..
I am interested in the possibilities of extending the rage of EVs. What is the practicality of imbedding solar panels into the bonet, roof and boot of electric car. I read recently of a WA chap who successfully converted a Suzuki Mighty Boy. By placing solar panel on the tiny roof of that thing, he has been able to extend his range. Also, you have your very own mini power station opperating for you while you are parked. Another suggestion is placing wind turbines on EV cars. Surely they would produce more electrity than any possible drag. What are your thoughts on the practicalities of these two suggestions.
This WA chap you mention is actually a friend of mine, Rod Dilkes (see evpower.com.au). In fact his Mighty Boy was the first EV I ever saw here in WA! (Though back then he didn't have the solar panels on it.)
Regarding range extenders in general, my personal opinion is that you're better off having stationary power generation (such as solar panels or wind turbines fitted to the roof of your house), and using that power to recharge your EV. In fact, ideally you grid connect your solar/wind system so they can feed power out to the grid during the day, then you use off peak power at night to charge your EV.
There's a good reason for this - the largest load on our mains power grid is during the day due to industry, while at night a lot of power is actually wasted because it is not economical to downregulate power stations. So grid connect solar systems are a great way to alleviate the power demand on the grid during the day, preventing the need for more fossil fuel power stations, and recharging EVs using the spare power at night.
Neither solar nor wind are particularly "potent" sources of energy, and the amount you could typically carry on a car does not add a significant amount of range to the vehicle. For some figures, typically you could fit about 200W of solar panels onto a car. Solar panels generally provide the equivalent of 5 hours at their rated power per day, i.e about 1kWh for a 200W panel per day, which is about 5km of extra range in a small vehicle. 5km may sound somewhat useful, but 1kWh worth of extra batteries weighs and costs less than a 200W solar panel!
Also unless you're very careful with your installation, the increase in aerodynamic drag will quickly negate any extra range they can provide. One exception may be vehicles like utes and vans, which often have a large, flat surface area which could accept maybe half a kilowatt of panels without negatively effecting the vehicle's aerodynamics.
Wind turbines are an interesting case, the only vehicle I've come across which does this is Peter Perkins' electric van (http://www.solarvan.co.uk/wind.htm). Wind turbines are never 100% efficient so in fact while the vehicle is moving you necessarily lose more power in drag than you can generate in electricity! On the other hand, if you have a wind turbine you can fold out while the vehicle is parked, it's possible to generate some power.
The biggest catch with wind turbines is that they only work well in a small percentage of the world where wind is regular and speed is consistent. In 90% of the places you'd leave your car you won't get much power from it.
It sounds hypocritical coming from someone promoting *zero* emission vehicles, but in my opinion the best range extender is having a small gas turbine generator to recharge your batteries. Gas turbines are very compact, reasonably efficient at their nominal speed, and gas has relatively low carbon content (short chain hydrocarbons). I envisage a device about the size of a briefcase which you could drop into your car's boot when needed to recharge the battery pack on the fly. This sort of system is also known as a "series hybrid", and is the principle used in the much-hyped Chevrolet Volt concept car (http://www.chevrolet.com/electriccar/)
Thalass
10:32pm, Thu, 27 Dec 2007
I've been looking into this sort of thing for my own project, and in the course of my reading I came across something called a Stirling Engine. It's a rather simple heat engine, that while it doesn't have alot of grunt (so you can't use it to directly drive a vehicle) it is very efficient (so you could use it to drive a generator at a constant speed ). They are also relatively simple to build at home, and by their nature are not fuel-specific. As long as one end is hot, and the other is cold (relatively speaking) the engine will function. This could be a constant flame from petrol, kero (my fuel of choice, since I can swipe it from work for free ), wood, anything really. Or it could be focussed sunlight, or geothermal heat... anything.
There are several types of stirling engine with different configurations - nasa is working on a linear-type one for use in spacecraft (using linear alternators to produce the electricity, like those torches you shake to charge), which I find very interesting - but they are a bit beyond an amature in a shed in the backyard.
Ultimately I would have one mounted in a trailer, which would hook up to the car for long trips and charge it on the go. I'd also build one or two of them at home to charge the car during the day. I personally prefer them (or the idea of them) to solar panels because I can build them myself, and maintain them myself - wheras solar panels are dead once they're damaged.
Of course it may not be possible for me to do this at all! But I know the concept works, as there is at least one company in the US building large arrays of solar heated stirling generators, which look like sattelite dishes with the generator at the focal point.
zidia
4:46pm, Thu, 10 Jul 2008
I am looking at converting a hilux ute to carry a substantial Qty of lithium. I was wandering about having a petrol generator in the tray to charge the batteries ( this goes against what I want in terms of green power, but I have grid connect solar being installed soon to relieve some of the guilt). I have 2 options as I see it, own an EV and an ICE, use the EV 90% and the Ice 10% or I put a petrol generator in the EV and have everything in one car.
I think that as long as the generator can handle the job and is substantially more efficient and less poluting than the ICE its a realistic solution to get people into EV's now until the technology improves.
My Q is has anyone done this all ready, what would a generator capable of extending the range to the equivilant of an ICE (or more)cost and weigh? Is there a generator on the market now suitable?
I have a lot of research to do on this topic I know, i'll check out generators and there output, how long it would take to charge the 46 3.2V 160A lithiums, how much fuel burnt, whats the difference between charge and discharge ratio while the cars running, how many K's its likely to extend the range.
So before I spent all my free time researching I thought I would see if there are some figures all ready done by some EV enthusiasts.
Andrew
Jens
1:17pm, Sun, 13 Jul 2008
Hi
My favourite for a range extender is a bio-diesel powered "pusher". A pusher is essentially an ICE engine, driver-train and suspension that looks like a trailer. Typically, pushers are the sawn off front of a front-wheel-drive car. It's useful to have a donor car for the pusher that is automatic and with cruise control, which simplifies the controls between the EV in front and the pusher behind. Basically the EV is for shorter range (whatever the effective range of your EV is). The pusher is to extend your range. Say you commute and shop around your city, but want to be able to go on a longer trip to another city. For the long trip you couple the pusher to the tow ball coupling and connect up the control / instrumentation circuits between the EV and pusher. It looks like the EV is towing the pusher, but in fact the pusher engine is running on bio-diesel and providing the impulse for you to drive at highway speed.
If you hit a hill that the horsepower of the pusher is going to struggle with, just slip your EV back into gear and give it a bit of electric assist. If you have regenerative braking you can regain part of the power used on the downslope. You can even use the pusher to recharge the EV in a similar manner (if you have regen). It makes more sense to me than attempting to recharge your batterypack while driving. If I would try and recharge through my on-board charger then I would be able to apply only 3 kW from a generator (13 A at 240 VAC). However, on long trips I pull over 200 A at 144VDC from my batteries. No on-board charger can keep ahead of that current draw. If you direct couple a petrol driven generator to a DC generator (or rectified alternator current), then you have a whole world of wiring and componentry ahead of you trying to harmonise the charging in the context of driving conditions.
On balance, I think the EV pusher idea is the most effective solution to being able to drive longer distances using a range extender. If you use bio-diesel as fuel you are relatively carbon neutral. If you are re-using a diesel car there will be much better pollution control fitted than your average portable generator. When you don't need the extra range and speed capability, then you put the pusher into storage. The side benefit is that you can make your EV conversion without the compromises or expense that grasping for extra range would impose on you.
). They are also relatively simple to build at home, and by their nature are not fuel-specific. As long as one end is hot, and the other is cold (relatively speaking) the engine will function. This could be a constant flame from petrol, kero (my fuel of choice, since I can swipe it from work for free 
), wood, anything really. Or it could be focussed sunlight, or geothermal heat... anything.
