[parametrek]

Not practical though. Every time someone has done the math for a fully scaled up system (assuming magic technology that doesn't exist) it always has the same answer: Unless the power transfer system is nearly 100% efficient, using it on a typical highway results in the the highway turning into a molten puddle in less than a day.

If you want to run the numbers yourself a Tesla uses 300 watt-hours per mile on the highway. California route 60 sees 337000 cars per day and is 70 miles long. And an amazing power transfer system might be 75% efficient.

[jimrandomh]

Using your numbers, that's

    337000 cars/day * 300Wh/mile/car * (1-.75) = 654W/m

That road has four lanes (two in each direction), so if every vehicle is electric and is using the charger, it needs to dump a daily average 164W/m. For comparison, solar irradiance is 1.3kW/m^2.

So, I don't see the problem?

[parametrek]

Your efficiency calculation is wrong. It isn't 25% of 300Wh, 300Wh is the output. The input is 400Wh, with 25% loss or 100Wh. Not 75Wh as you have. And you have a bunch of other mistakes too.

Along the length of the road, that is 21kWh. At 75% efficiency, that is 7kWh into the road surface per car. Roughly 2.4GWh of energy ($200k worth of electricity) per day lost as heat into the roadbed in total. Assuming 4 lanes and a 3.7m lane width, route 60 is 1.7 million square meters of asphalt and that is 1.4kWh per square meter. (8x more than your number.) Still comparable to solar irradiation though. Asphalt might get a little soft on a busy summer day when everyone is also running their AC but it wouldn't be a molten puddle. If the chargers are only embedded in a narrow strip down the middle of the lane, that section might get very soft.

So at 75% I guess it is practical. But 75% is going to be extremely hard. And the first place this should be installed is Route 1, because it would be a highway-sized snow-melter that also happens to power vehicles.

Now ask yourself why we don't have defrosted highways. Installing roadbed chargers is going to be even more difficult.

[Retric]

100% of the loss does not end up in the road surface mostly it's radiated into space.

As a sanity check at highway speeds it takes ~30HP to maintain speed or a loss of 10HP or 7.5kw over ~60m (distance from one front bumper to next) x ~4m approximate width of a lane = 30w/meter which is a non issue. Lower speeds need less power, but can have more cars.

Further, not every car needs 100% power as batteries are still a thing, this is just for the subset of long distance traffic. And if you limit things to say 75% of a cars power demand that's still 4x the range.

[_puk]

Your "narrow strip down the middle of the lane", makes me wonder why it has to be under the asphalt and not simply embedded similar to cats eyes.

I'm picturing future roads looking like massive Scalectrix tracks...

[jimrandomh]

You mixed up watts and watt-hours. 1.4kWh/m^2/day is 58.3W/m^2.

[parametrek]

Ooops, thanks!

[Klathmon]

I think it might still be useful even if it's not enough to "increase" the charge of the car. Prolonging the driving distance by 50%+ on some highways would still be really beneficial.

Taking the thought to the extreme, it could also be used as a kind of traffic shaping/control system. Have some roads "energised" at specific times to provide an incentive to go a longer way to alleviate chokes or traffic jams.

That gives many people an incentive to take a longer path (whereas current systems/methods for this are kind of driver-hostile as the drivers going the longer route don't get any direct benefit)

[mikepurvis]

The issue isn't the efficiency from the car's perspective—it's what happens to the other 25% of the energy that doesn't go into the car. Hence the molten puddle road comment.

[organsnyder]

All the more reason to only run it at certain times of the day. Enable it at night, when electricity is cheaper, heat generation is less of an issue, and there's less congestion.

[wernercd]

How many millions... billions... would it cost to line all the roads? and then all the lost electricity due to inefficiency? All to give cars a little extra distance?

And then... when Road v2.0 comes out and it all has to get replaced? v3.0? Then flying cars and no one uses roads?

[Someone]

On the plus side, _if_ this sees wide adoption, that Tesla would need less batteries, significantly decreasing its weight and with it its energy use.

Also, the article is a lot more optimistic about efficiency:

"The group used an off-the-shelf, general-purpose amplifier with a relatively low efficiency of about 10 percent. They say custom-made amplifiers can improve that efficiency to more than 90 percent."

[agumonkey]

cover it with thermoelectric modules !