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Can the grid handle all the new electric cars? April 8, 2008

Posted by OldGuy in Alternatives, energy conservation.
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I read an interesting post at HybridCarBlog.com. If we all suddenly went out and traded our gas guzzlin SUVs for all-electric cars, could the electrical grid handle the load? Or would plugging in at the end of our commute home cause such a drain on the system that brownouts at 6pm would become common?

I think he’s overstating the case. He’s assuming the electrical grid is already saturated, and has no spare capacity to absorb a new drain. He assumes everyone will plug in at the same time, and that office buildings will still be running full bore at that moment. And he assumes current electrical draws.

I think people will plug in to a trickle charger as they get home, which varies from 3:30 to 7pm. There will not be a spike, but a gentle increase, similar to turning on a few more light bulbs and TVs. It will happen as office buildings go dark and silent. My office is on motion detectors after 5pm, and if I work late and sit still too long, I’m suddenly in the dark until I stand up. And he assumes there will not be any improvements in conservation.

One conservation effort I’m working with increases power transformer efficiency. Radio amplifiers are notoriously inefficient – around 9%. The emerging technology in the labs today should push that to 30% in the next year, perhaps to 50% efficient by the end of the decade. If similar technology were applied to computers, the electrical demand would drop.

Even more important, increasing efficiencies should decrease the need for as much electrical power to run those new cars.

Which should help the electrical grid handle those new electric cars.

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Comments»

1. JeffS - April 24, 2008

This is a nice collection of posts. People have speculated about ways to cope with a grid challenging early evening PHEV/BEV charging load. The trick is practicality. It occurs to me that if a current limiting meter was required to recharge autos sometime before unregulated vehicles create a problem, the cost could be contained.

Here’s how it would work. Each substation would receive instantaneous capacity availability data from the grid. When it receives notice that an increment of capacity is available or if it senses a drop in its local load, it would transmit a distinctive pulse on the local power lines engineered to traverse the local interconnect with high reliability.

Current limiting meters having autos connected for recharging would react to each pulse by increasing their output by a very small increment. As the evening progresses, there will be a cascade of pulses ratcheting up the charging current on each of the autos until there is no further change in load – e.g. all the cars connected are charging at their maximum rate. At this point pulses would be sent continuously to catch up late connecting cars. Fluctuations from other loads would be handled in the conventional manner.

A system like this requires no separate communication channel, is single duplex, robust and will act effectively to limit load increases placed by autos to occur at a rate that the system can respond to without stress. Individual pulses can be obscured by transient phenomena but it should be impossible for a sufficient number to be dropped to keep a vehicle from being fully charged in the morning.

This would be practical if a low cost receiver was be engineered to receive the pulses reliably and increment the rate of charging accordingly. This may be a baby step compared to the grand digital grid solutions being promoted by wireless telcos, but I bet it’s a 90/10 shot at creating a scenario that is in range of other power management technology that’s coming on line now. Altair Nanotech makes high power-density lithium ion batteries. They delivered a 2Mw / 300kwh battery to the AES power company last December to use for power stabilization.

Power companies generate about 3% more power than is needed to react to instantaneous changes in load that gives them time to adjust generation. If they use a battery to react they save the fuel cost used to generate the mostly wasted “active reserve”. The payback for the battery is several months and it lasts for 20 years.

There’s no need for high precision, two way, broadband digital management to achieve high quality power management because a battery gets the fine structure power management done faster and better for a fraction of the cost.


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