Tag Archives: electric cars

Powering electric vehicles in the city

Simple stuff today just to stop my brain seizing up, nothing terribly new.

Grid lock is usually a term often used to describe interlocking traffic jams. But think about a canal lock, used to separate different levels of canal. A grid lock could be used to manage the different levels of stored and kinetic energy within a transport grid, keeping it local as far as possible to avoid transmission losses, and transferring it between different parts of the grid when necessary.

Formula 1 racing cars have energy recovery systems that convert kinetic energy to stored electrical energy during braking – Kinetic Energy Recovery System (KERS). In principle, energy could be shared between members of a race team by transmitting it from one car to another instead of simply storing it on board. For a city-wide system, that makes even more sense. There will always be some vehicles coasting, some braking, some accelerating and some stopped. Storing the energy on board is fine, but requires large capacitor banks or batteries, and that adds very significant cost. If an electrical grid allowed the energy to be moved around between vehicles, each vehicle would only need much smaller storage so costs would fall.

I am very much in favor of powering electric vehicles by using inductive pads on the road surface to transmit energy via coils on the car underside as the vehicles pass over them.  Again, this means that vehicles can manage with small batteries or capacitor banks. Since these are otherwise a large part of the cost, it makes electric transport much more cost-effective. The coils on the road surface could be quite thin, making them unattractive to metal thieves, and perhaps ultimately could be made of graphene once that is cheap to produce.

Moving energy among the many coils only needs conventional electrical grid technology. Peer to peer electrical generation business models are developing too to sell energy between households without the energy companies taking the lion’s share. Electricity can even be packetised by writing an address and header with details of the sender account and the quantity of energy in the following packet. Since overall energy use will fluctuate somewhat, the infrastructure also needs some storage to hold local energy surpluses and feed them back into accelerating vehicles as required, and if demand is too low, to store energy in local batteries. If even that isn’t sufficient capacity, then the grid might open grid locks to overflow larger surpluses onto other regions of the city or onto the main grid. Usually however, there would be an inflow of energy from the main grid to power all the vehicles, so transmission in the reverse direction would be only occasional.

Such a system keeps most energy local, reducing transmission losses and simplifying signalling, whilst allowing local energy producers to be included and enabling storage for renewable energy. As one traffic stream slows, another can recycle that same energy to accelerate. It reduces the environmental demands of running a transport system, so has both cost and environmental benefits.




Isn’t graphene fun?

I’ve just been checking up on progress on supercapacitors to see if they are up to the job of replacing car batteries yet. It looks like they will be soon. Supercapacitors have lower energy density than lithium batteries, but can be charged extremely quickly.

My favoured technique is to build mats into the road surface every 50 metres (i.e. same as streetlights), and to charge the supercapacitor bank using induction as the car passes over them. That means that even a small energy capacity would be adequate. It wouldn’t have to power the car for 100 miles or more like a battery, but only for the first and last few kilometres of a journey where there are no mats. Otherwise, range wouldn’t be limited as it would charge all the time on the trip.

However, a few minutes ago I had another little spark of enlightenment. Why not also use the pads for propulsion too, using a linear induction motor?  (I like those)

If the pad gives an impulse to the car as well as a capacitor recharge, then the capacitor won’t need to be as big. And if the impulse is gentle enough, passengers won’t feel a jolt every time they drive over one.

Another little insight, hardly worthy of the name, is that with trains of self driving pods, the pods could be so close together on most journeys that they effectively have a continuous circuit from one end of the train to the other. That means that public transport pods that are only used locally and on certain routes might be able to get by with tiny capacitor banks.