[amalia (OP)]

John has an interesting question for us:
How are we going to charge electric vehicles in roads where there's no private parking spaces? Street lamps have been suggested, but there are a lot less of those than there will eventually be electric cars. And how much power can the street lamp cables supply? Do the cables in the street have sufficient capacity, or do we need to dig up all the pavements in out towns to put new cables in and install charging sockets?
What do you think?

[chiralSPO]

Street lams would definitely not be a way to do this. (lamps take electrical energy and turn it into light, why not harness the electrical energy directly, and not involve inefficiencies of conversion to and from light.

If we want to power cars as they drive on the street, energy will need to be supplied either through direct electrical contact (like bumper cars or trolleys), or through wireless transmission using some sort of EM (probably more like cellphone chargers than lamps, but who knows what future technologies might use.)

Whatever technology is used will still require several orders of magnitude more power than street lights, so more cables will be needed.

[Bored chemist]

Street lams would definitely not be a way to do this. (lamps take electrical energy and turn it into light, why not harness the electrical energy directly, and not involve inefficiencies of conversion to and from light.

I don't think anyone was advocating that.
The plan is to put a socket in the bottom of the lamp post.

[chiralSPO]

Street lams would definitely not be a way to do this. (lamps take electrical energy and turn it into light, why not harness the electrical energy directly, and not involve inefficiencies of conversion to and from light.

I don't think anyone was advocating that.
The plan is to put a socket in the bottom of the lamp post.

ah. good.

[evan_au]

The wires supplying street lamps are probably single-phase. You wouldn't want to put the large load of charging electric cars onto a single phase.

But the single phase used for street lamps is drawn from the 3 phases that go down every street. So it would be slightly more effort to connect to 3 phases, rather than just 1 phase. But the balanced 3-Phase load is much more efficient for the distribution grid.

Part of the commercial challenges would be:
- Different cars use different physical plugs (but standards are appearing)
- Different cars use different charging voltages and currents (but some standards are appearing, which allows the car and charger to negotiate a mutually compatible charging rate)
- Knowing who to bill for the electricity, and how they are going to pay for it. I assume that the above standards will cover this too?
- Who will be paying to install the charging points?
- What is to stop someone hogging the charging point, even after their car is fully charged? It sounds like we need an app that prompts someone to move their car when it is fully charged and/or tells someone when a charging point has become available. Financial penalties for tying up a charging point unnecessarily sound like they will be needed.
- Your average street power supply is unlikely to have a "spare" quarter-Megawatt, as required for fast chargers on highways. But they could certainly support a daytime or overnight charge, as residential consumption is lower outside morning/evening peak hour.
- Setting up the commercial terms for buying the electricity will be challenging - some streets have cheap excess power from rooftop solar during the daytime, and many countries have cheap excess power overnight from inflexible coal & nuclear power stations. But you want to discourage charging during peak hours, or when the street wiring is running near capacity.

[alancalverd]

Time to look at some numbers.

The UK currently consumes twice as much energy as petrol and diesel than electricity. So if we are going to convert to all-electric transport, we need three times the present grid capacity, not just for generation but for distribution too. Let's assume that some good fairy invents and installs a non-fossil fuelled generating system that can produce 15 times as much power, continuously or with 5 days' storage, as our present renewables.

Increasing the long-haul grid capacity (400 kV overhead lines) by a factor of 3 is feasible, provided somebody pays for it. But most of the work is actually done by underground 11 kV pipes, which are pretty close to maximum capacity in all towns and cities. So we have to dig up all the main roads and install two more pipes, plus two more low-voltage transformer stations for every megawatt we currently use - 60,000 new transformers at about £200,000 each (I last installed a 0.5 MW  unit about 10 years ago - the price may have increased a bit since then).     

Now the average street lamp runs at about 230V, 0.4A. Charging a 75kWh car (small Tesla) at that rate would take over 800 hours, so we are going to have to beef up the street light wiring a bit. Say 8 hours for a full charge = 40A wiring (like a cooker). But the average stay at a parking meter is only 0.6 hours and there are roughly 3 meters per streetlamp so to bring cars up to half-charge in anything like a reasonable time from a kerbside supply we will have to run an 800 amp armoured underground cable to each lamp.  That's serious cable, folks.

Then we have to pay for the electricity, so every street parking space will have not merely an outlet but also a credit card meter.   

There are about 35,000,000 road vehicles in the UK. If the economy is not to grind to a complete halt we need about one recharging point for each vehicle  because even with my suggested kerbside recharging system, it takes 10 times as long to refuel an electric vehicle than the equivalent diesel, and it will only travel half as far on a "tankful".

Let's imagine we could generate the required power from windmills. These cost about £2,000,000 per megawatt. We need about 500 GW installed capacity to keep the transport system going, so that's an investment of £1000 billion needed for generation, and roughly the same for long-haul distribution, plus the cost of replacing all the road vehicles (about £2000 billion). Let's set a target date of 2050. We need to spend £133,000,000,000 every year from tomorrow, assuming no need to replace any of the turbines or cars that wear out in the next 30 years. That's £6,650 per household every year, just down to street level, never mind the actual sockets and meters.

Evan's question of standardisation will disappear as soon as a government specifies the kerbside socket. It will then be up to every manufacturer to make his cars compatible. Ideally, of course, this will be an international standard, but as long as it doesn't match any existing product, it doesn't matter what it is or where it is first installed, so here's a chance for the UK to lead the world and set the standard. Our national economy will go down the toilet, but we'll be setting a fine example of doing the right thing for the wrong reason. I suggest we adopt the existing 440V 3-phase 63A industrial plug (which will minimise the wiring cost) and leave it to the car makers to install the appropriate converter for their particular batteries: after all, there is only one type of diesel fuel (maybe two types of gasoline) and it is up to the manufacturers to adapt their engines to use it.   

[Bored chemist]

The UK currently consumes twice as much energy as petrol and diesel than electricity. So if we are going to convert to all-electric transport, we need three times the present grid capacity

Unless, of course, electric cars are more efficient- and they are.

There will be an increased demand from electric cars.
But it's not the trebling you are talking about.

[alancalverd]

New electric cars are indeed about 80 - 90% efficient at converting input energy to motive energy.

So if our replacement fleet is "all new", we might just need to double the grid capacity. Problem is that batteries decline in recoverable capacity down to about 50% at replacement time, and over the next 30 years  your rustproof, non-tyre-consuming brakeless electric car is going to need at least two new batteries. If we can ignore the manufacturing cost of these (after all, they are made in China, where fossil fuel consumption and CO2 emissions don't count) we are looking at a mean conversion efficiency of about 75%, still admittedly better than diesel, until you factor in the grid transmission loss and the energy cost of installing and maintaining the grid capacity. And then you have to scrap all the existing vehicles and build new ones without using fossil fuel.....

There are plenty of 30-year-old buses and trucks on the road today, and quite a few 15-year-old cars, because the major moving parts, though more complicated than electrics, last a lot longer than batteries. The more closely you study the question, the less attractive an all-electric fleet looks.

My preference is to move towards a hydrogen economy (it's already happening in Orkney) or to use "free" electricity to synthesise liquid fuel and use as much of the existing technology and infrastructure as possible.

[Bored chemist]

So if our replacement fleet is "all new", we might just need to double the grid capacity.

I suspect that the grid already has twice the capacity of the grid.
Yes, that' s not a typo.
There is a limit to how much power we can distribute on average, and there's a limit to what it can distribute as a peak.

To deliver the peak needs during the day the grid has to handle a lot of power, but at night the demand drops a lot.
My guess is that, at least in some domestic markets, night time use is half the peak use.

In effect, we just have to charge batteries on "economy 7" electrical power.

[alancalverd]

One of the joys of electricity was turning night into day. If we are restricted to charging vehicles overnight, we have pretty well eliminated private transport for pleasure and restricted bus services to even less than they are now! It is very difficult to sell a product that is less convenient than what is currently on the market. Overnight economy charging may just be acceptable if you have a private drive and no social life, but it doesn't address the original question of charging where there is no domestic supply at street level.

Present grid distribution capacity doesn't greatly exceed present generation capacity - why should it? It isn't just a matter of heat loss in the wires, but switchgear, monitoring and transformer capacity. You have to make economic decisions when local demand increases: do we use 11 kV overhead, 11 kV underground, or high voltage overhead? The answer is not universal. HV overhead is cheapest per kW-mile but needs HV switchgear to connect to the existing feeders so the initial installation is a protracted business and needs major land purchase and wayleaves. 11 kV underground is the only urban option but disrupting traffic has an economic cost to everyone else. 11 kV overhead looks like a simple matter of bashing wooden posts into farmers' fields  but it is vulnerable to weather and vehicle impact - cheap to install, expensive to maintain.

It's all reminiscent of an old Irish story. "How can I get to Cork?" "If I was you sir, I wouldn't start from here." Electric road transport looks obvious and ideal close up, but if you stand back and look at it in a real world context, it probably isn't the best way forward.

[syhprum]

The use of Hydrogen to power electrical vehicles via fuel cells  is often advocated but does this not require high purity Hydrogen and possibly high purity Oxygen can this readily be obtained ?
One alternative would be to burn the hydrogen in a IC engine producing nitrous oxide as well as water and power conversion of less than 50%.

[alancalverd]

Making pure hydrogen and oxygen is a doddle if you have free electricity and lots of water. Hence the experiments in Kirkwall.

Purity isn't a problem. Wartime vehicles ran on producer gas  CO2: 5.8%; O2: 1.3%; CO: 19.8%; H2: 15.1%; CH4: 1.3%; N2: 56.7%; burned in ambient air, as did most of European industry until the 1960s. You only need pure gases if you are going to faff about with fuel cells and new electric cars. Much cheaper and vastly better for the environment to use the engine you already have, with whatever combustible stuff you can make from organic waste, atmospheric carbon, or water. 

That said, my mining engineer son is investing in copper and lithium, so don't let me discourage anyone from filling the planet with mine tailings and fossil fuels - it takes as much (mostly fossil) energy to make a new electric car as it will use in its life.

[Bored chemist]

If we are restricted to charging vehicles overnight,

How fortunate then, that nobody said we should.

It's all reminiscent of an old Irish story. "How can I get to Cork?" "If I was you sir, I wouldn't start from here."

Given a choice, I'd not start from here either.
But this is where we are. So we need to work out which way Cork is.
You seem to advocate travelling North to get there.

[alancalverd]

Economy 7 electricity was your idea. IIRC it's only available at night.

I'm starting my journey from where we are, with a huge investment in all sorts of highly practical and convenient machines that run on vaporised liquid fuel, and a worldwide system for distributing that fuel to an adequately tight specification. Additionally we have vast quantities of organic waste as general rubbish, sewage, inedible bits of agricultural products, and plastics. And the promise of unlimited free electricity  whenever the wind blows or the sun shines, but not when we want it. So the sensible thing to do is to devise means of using this opportunistic energy to convert waste into liquid fuel. The political and economic consequences of doing so would be enormously advantageous to the UK, turning this country from a net importer to a self-sufficient or even net exporter of a strategic essential.   

[Bored chemist]

Economy 7 electricity was your idea. IIRC it's only available at night.

The impossibility of charging vehicles on the normal tariff due to some "restriction" is your idea and... and not one of your best.

[alancalverd]

In effect, we just have to charge batteries on "economy 7" electrical power.

Ipsi dixit.

I don't see the recharging of electric vehicles as being in any way impossible - it's just physics. But if we want to retain present levels of convenience with all-electric transport the engineering will be extremely expensive, inconvenient, and require a great expenditure of fossil fuel, to achieve.  If the real objective is to reduce and eventually eliminate the use of fossil fuels, as we must do for short term political and economic reasons and long term sustainability, there are better ways to go.

[teragram]

The use of Hydrogen to power electrical vehicles via fuel cells  is often advocated but does this not require high purity Hydrogen and possibly high purity Oxygen can this readily be obtained ?One alternative would be to burn the hydrogen in a IC engine producing nitrous oxide as well as water and power conversion of less than 50%.

I think modern fuel cells take oxygen from the ambient air, but the hydrogen must be high purity.
The Clean Air Transport for Europe project, running fuel cell powered buses proved that the vehicles used overall in excess of 80% more energy than the baseline diesel vehicles.

The BMW "Hydrogen 7" ( an ICE powered car modified to run on hydrogen) required 220% more energy overall than the average European car.

[teragram]

. Additionally we have vast quantities of organic waste as general rubbish, sewage, inedible bits of agricultural products, and plastics. And the promise of unlimited free electricity  whenever the wind blows or the sun shines, but not when we want it. So the sensible thing to do is to devise means of using this opportunistic energy to convert waste into liquid fuel.

What would be the efficiencies involved in converting waste to liquid fuel? 

[Petrochemicals]

Its very unlikely that with driverless cars most people will own a car, why bother with the parking spaces, just imagine how much that land is worth ! I suppose they would just have charge ports put in like they do in city cenres at present.

Also we produce 20 percent of electricity from renewables and we use 4 times as much fossil fuels than electricity, so about 4 percent of our total energy use comes from renewables. Only ten years left to save earth, we can do it !

I do like the bumper car idea though!

[Bored chemist]

So, you don't understand the "in effect" bit.

In effect, we just have to charge batteries on "economy 7" electrical power.
Ipsi dixit.