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Comment by danpalmer | Hacker News Reader

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.

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* 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.

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[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/...

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.

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