"Please Don't Buy an Electric Car" | Hacker News Reader

"Please Don't Buy an Electric Car"

danpalmer.me

7 pointsdanpalmer15 comments

You can't really have an international grid on the scale you describe, due to transmission losses. If you take a conductor, even though for short distances the material it has negligible resistance, it comes out to be a limiting factor for long lengths (thousands of kilometres).

If you look at Joule's first law, which says that the heat produced by a piece of wire is proportional to the square of the current times the electrical resistance of the wire (ie. I^2*R), you'll notice it doesn't say anything about voltage. This is why power transmission lines for long distances usually have high voltages (~100kV) or even higher ones(the transmission lines where I live are 735kV). Unfortunately, there is a limit as to how much voltage that can be put, due to other problems caused by the high voltage itself (coronal discharge, arcing, etc.).

This is why electricity (per kilowatt, retail) costs me one third of what it costs my friend in Los Angeles; it's not technically feasible to send our low cost electricity all the way to there while still turning a profit. Note that this completely changes if there is high temperature[1] superconductivity, but at this point, it's not exactly doable[2].

[1] High temperature, in this case, essentially means without liquid nitrogen and other relatively exotic cooling methods. Your living room would be considered high temperature, for example. [2] The current superconductor with the highest transition temperature is HgBa2Ca2Cu3O8, at 133K (-140C).

You are a little pessimistic:

http://en.wikipedia.org/wiki/Pacific_DC_Intertie

http://www.abb.com/cawp/seitp202/25b65cc026636ebfc1257574004...

(The first link describes the system that reduces energy costs in LA by carrying it in from the Columbia river system, the second one is from the company behind the technology and discusses their plan to send 6 Gigawatts over 2,000 km in China)

The economics are certainly less favorable as distance increases.

Not really. Current residential electric rate here is 0.0541$/kWh, compared to 0.232$/kWh in LA. I am sure they would enjoy having this cheap electricity, but they're too far from here.

Furthermore, to take his example of solar electricity from the Sahara to the UK, the line of sight distance between both is over 3000km[1], includes underwater segments and is more than 25% longer than the longest HVDC link(the Rio Madeira, at 2375km).

Can electricity be sent over long distances? Sure, but not intercontinentally, or even intracontinentally if you're looking at, say, New York to Los Angeles.

[1] http://www.wolframalpha.com/input/?i=distance+between+the+sa...

I take the existence of the interlink as evidence that it lowers prices (this seems like a reasonable definition of profit here). Maybe it only works due to the regulatory situation in California. It would take some more information to decide how much of the price difference is due to the interlink.

I don't particularly think intercontinental systems are in the near future, but I don't think "a little pessimistic" was outlandish. What if ABB can push their tech 50% further?

The cable I mentioned in the UK that is carrying up to 2.2GW is an HVDC cable. That will supposedly work.

Sure, HVDC obviously works over considerable distances. The problem jfim is talking about is that each additional length of cable increases the price of the delivered electricity (because a longer cable is less efficient). So given a particular method of generating power, a particular consumption market and a set of cable characteristics, there is a distance limit on viable projects.

There are also other costs, other than only transmission losses. If you're crossing multiple countries (which would be the case in such a long cable), there needs to be a clear path for the cable to take(ie. pay people to use their land to put a power line on), multiple legal jurisdictions, a higher rate of failure because of the increased cable length, more maintenance, etc.

From speaking with an EE friend of mine, he mentioned that for long distances, DC is more appropriate and most of my (limited) knowledge revolves around AC. So it might technically be feasible, even though it would be politically hard to do so.

I am not an expert in this. The speakers however are, and are the ones researching the new cables. The answer is that they need to be High-voltage DC. The high voltage to increase efficiency, and the DC in order to make them compatible around the world.

An interesting discussion.

I'm wondering about some of the reasoning, though. For example:

> On top of all this extra power being used, we have targets to meet on reducing emissions. That means shutting down coal fired power plants, reducing our gas usage, and moving to cleaner sources such as wind, solar, wave, geothermal, and dare I say it, nuclear. How are we going to meet demand?

Are we actually trying to reduce emissions here, or just meeting someone's target for shutting down coal-fired plants? It's my understanding that a typical coal-fired plant produces around 500 megawatts. That's 12 million kWh each day. You quote a figure of 8kWh to charge an electric car. If that 8kWh is needed every day, then your coal plant gives you the ability to keep 1.5 million cars charged. If that 8kWh is not needed every day, then you get even more cars for the deal.

Now, shut down that coal-fired plant and replace 1.5 million (or more!) electric cars with fuel-burning cars. Have you reduced overall emissions? I'm not sure; but I think it is likely you haven't.

> Maybe we should all go out and buy electric cars. We will experience brownouts, electricity prices will soar, and it will be difficult. But hopefully it will start some change.

Or perhaps some of us should buy electric cars. As the number of such cars grows, electricity prices start rising. and then two things happen: (1) demand for electric cars drops, and (2) pressure from the public makes it likely that power-generation capacity increases. And then prices drop, and more people buy electric cars .... So I don't really see the need for a gloom-and-doom forecast.

In any case, as I said, an interesting piece. Please do more of them.

Your second point is essentially what was being said. We probably don't want everyone to buy an electric car right now, but we need enough that it forces the changes to be made.

As for the car charging, I'm not exactly sure on the figures for a typical coal-fired power station, but the UK has capacity for about 3 million electric cars right now, although that would be pushing it, bringing us right up to the maximum power generation we can handle. And remember, that's falling at the moment as a few plants are being turned off.

I don't do a lot of long form writing like this, and I feel I could improve quite a bit, so if you have any comments about how I could improve this piece, please let me know. Thanks.

You could make mention of the efficiency of load balancing on the grid since electric vehicles are almost exclusively charged at night during off-peak usage.

Also, the entire essay is predicated on that first scary stat of people using between 5-20kwh of electricity per day and the average car requiring 8kwh to charge. It would be useful to note how many days that 8kwh charge are good for, how many people does each car serve, etc. I.E. if that's a weekly charge with 2 people per car, the incremental electricity usage would be 8khw / 2 people / 5 days -- pretty much noise at that point.

I don't have the references for the first statistic, but I trust that the speakers know what they are talking about with it. And it seems a reasonable statistic. Even if it's off by 20% or something though, the issue still remains. I think you may be right in pointing out that some cars won't need charging that much each day, but remember that the spare capacity in our grid is very small, and 40% of energy (not electricity, just in general) usage goes on transport. We can't just move that 40% to electricity.

* Consider that a few days ago there was a discussion of what Denmark's going to do with the excess electrical energy their offshore wind farms are generating [1]. They're dumping some of it off as heat into district water heating; it could be charging electric cars.

* As noted above, electric car charging generally would happen at night, so its 8 KWH of energy draw would not happen at the same time as most of the other home's average draw of 20 KWH. KWH is energy, whilst KW and GW are power (energy over time). Distribution and service are built first to a power (KW / GW), not energy (KWH / GWH) demand specification. One must integrate varying power over time to get the resultant energy involved. So the comparisons of KWH to KW seems to me like trying to compare areas (energy) to distances (power); there's a dimension missing on one side of the two quantities, so they can't be directly compared.

* I don't think California is all that special in that it draws the least of its statewide power during the night [2]. Looking at today's demand graph [2], 11 PM to 7 AM appears to be below the average for the rest of the day; that's 8 hours to charge those 8 KWH, which means a 1 KW power draw (that's less than 5 Amps at England's 230 mains voltage).

* 1KW seems to me a not-unreasonable additional night time power demand once everyone's in bed -- though the licensed electrician who inspects your electrical service before you commit to an electric car and the requisite charger should be consulted first. 1 KW will charge that 8 KWH requirement in 8 hours (ignoring conversion inefficiencies for discussion). If the car charger varied its draw subtractively against the whole-home's power draw, then charging could start slow but when one gets home then ram up (increase power demand) as lights, TVs, and other home loads were turned off, keeping home demand constant (though of course using more energy than without the car, so you'd of course pay for that extra energy). If smart meters reported their total-home draw at six second intevals to the consumer, then the consumer's car charger could self-regulate its draw. None of the smart meter reporting I've researched informally report anything better than on 15 minute intervals to the consumer when they do so at all. You could get a home energy monitor installed to get that information yourself (cited in [1]).

* Even at the largest scale, of utility scale generation, night time charging evens out the load rater than adds to peak demand -- as long as charging starts after hours. If so, this becomes an opportunity, not a problem for the electric utility. They can make more money selling more power per day because with electric cars, now there increased demand at night that wasn't there before.

---

[1] https://news.ycombinator.com/item?id=5547979

[2] http://www.caiso.com/outlook/SystemStatus.html

* Here [1] is a position-paper proposing an HVDC pan-European "supergrid" of up to 4KM distance, including undersea HVDC, overlaying and working with the existing, less capable AC grids. No magic, no HT superconductors, just recent evolution of existing HVDC technology which will enable a "meshed" HVDC grid (not just isolated HVDC point-to-point links). It elementally observes that while high cable capacitance limits undersea cable AC transmission distance, it doesn't for HVDC; DC doesn't get through capacitance once charged, whilst "reactive" (capacitive and inductive) effects limit how much power can be extracted at the other end of a "long" transmission link (sorry, no reference right now on that). Avoiding reactive transmission losses is one of the reasons AC power distribution is optimal for moderate grid and distribution scale at its low frequencies of 60 Hz or 50 Hz. HV avoids ohmic losses, while low frequency reduces reactive losses up to the limits of some estimable built-out scale. Going to DC allows scaling out to longer distances than AC, even as ohmic losses are minimized by using HV (ohmic losses are elementally the same, whether AC or DC).

* Here [2] is a quick summary of recent improvements in HVDC transmission and high power "VSC" inverter techniques, citing [1], summarizing: "...there is now no doubt as to the feasibility of HVDC networks ferrying renewable energy resources from wherever they are in surplus to wherever they are needed."

[1] http://mainstream-downloads.opendebate.co.uk/downloads/WG2_R...

[2] http://spectrum.ieee.org/energywise/energy/the-smarter-grid/...

Reply on news.ycombinator.com