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Automotive Technology
John Stenlake's Blog
- Do Electric Vehicles Need More Love (or do they dream of Electric Sheep)?
OK, apologies to Philip K Dick fans for the title... My 'need more love' comment refers to the fact that it is often said these days that EVs 'need connected services' in a way that conventional vehicles maybe don't. I thought it might be interesting to explore that hypothesis a little bit.
So to get started, I suppose the Dick reference (OK, that just got my blog blocked by any of you using family safe browsers) is more appropriate than it might first seem. While YOU might be busy dreaming of electric sheep (whatever floats your boat) it's more likely that your EV will be slightly busy charging itself, plugged securely into a nice high voltage supply in your garage. As an aside, it might arguably be more useful to be plugged into a lower voltage, higher amperage supply, but that's not the way the interconnect standards are written and from a safety and convenience point of view high current connections are sub-optimal, so the die is already cast there, I believe.
But there is a fundamental question to be answered there. Is it OK that everyone plugs in and trickle charges as soon as they get home, once EVs, EREVs (extended range electric vehicles) and PHEVs (plug in hybrid electric vehicles) start being sold in volume? If you think about that in US terms for a moment, which state is likely to have the highest penetration for the foreseeable future of these vehicles? Full marks for the answer 'California'. And which state of the union has some of the biggest power capacity and distribution challenges, especially in summer months? Right again.
So if nothing else, the means of being able to variably schedule charge cycles so the load can be deferred to non-peak periods and potentially spread across the population of vehicles is fairly important. This is actually not that hard to achieve, but it does require a service that provides a logical interconnection between utility companies and EVs. In an ideal world, all EV charge cycles would fit within a small number of hours to be easily schedulable in this spread model and still be available when their users need them in the morning.
Even though a simple charge scheduling service would help, the model breaks down pretty quickly. How is this enforced - what's to stop users turning 'renegade' for their own convenience and mobility security ('damn everyone else, I want to ensure I have a full battery at 6am')? What is my battery is sufficiently large, or my in-home charger infrastructure so simple (eg. just a straight 110v connection) that I need 12 or 13 hours to charge my battery? What if things become critical despite all our best predictions and the grid needs to disconnect some users to save itself?
Fairly quickly I believe we arrive at a scenario where unmitigated charging is unlikely to be very acceptable for very long. In other words, an EV with a simple adapter cord plugged directly into a standard mains voltage socket. There are two areas of rationale for this - one being the requirements of the power company to manage these charging events, the other being the convenience of the user, who will probably want more than 110v in most cases quite soon, and can probably be sold on the benefits of spreading the charge load over time, perhaps purely on the notion that taking 'surplus' generating capacity at non-peak times (or at least removing the need to throttle down generation where it can be done, which still carries expense) is good for the planet, as it removes stress from peak times and avoids the need for additional capacity through improved utilization.
If that kind of altruism isn't sufficient to carry the day - and it probably won't be (excuse my skepticism) then it's relatively easy to start incentivising users to behave in prescribed ways. For example, offering a home electricity rate discount for people that subscribe to mitigated charging vs. unmitigated - in some ways this is not dissimilar to the interruptable power supply tariff available in certain states for running air conditioning, or the overnight tariffs available in some countries originally for running storage heating as well as domestic appliances on a timer switch. The mitigation device - charging station in the garage - could easily police appropriate behaviour by reporting when the car was connected to it. Between the device, the vehicle, and the home meter, there are many levels of sophistication that could be applied to detect 'rogue' charging, even though I am sure there are many creative people who would try to find ways around those techniques.
Logically, though, we are probably on a roadmap towards a domestic electricity market. This already exists for grid participants and large corporate users - and technology certainly provides what we need to enable extension to consumers. How might this work? In the case of home overnight charging, to stick with that pattern for a while, it's likely that the rate you would pay:
- might vary from one night to the next depending on demand (which as we all know depends on multiple other factors - weather conditions, available capacity, extraordinary events that increase consumption eg. a superbowl, cup final, grand prix or perhaps these days the final of some televised 'talent' show)
- would vary depending on when you are asking for power (more expensive in early evening when people are cooking, less expensive in the small hours)
- would probably vary according to the rate at which you want to draw power from the grid (higher rates would attract a premium except in the case where the utility finds itself with a surplus to sell for some period of time - in some cases they might want to incent high charge at times of very low usage to clear the grid of chargers for the morning peak)
It's almost certainly the case that this application of market forces is the only way to incent the kind of behaviour and coordination between participants that is needed to optimize this ecosystem (to justify that statement further would require a sociopolitical discussion, so I won't). At this stage our simple service - which up to now just scheduled charging, monitored usage, and cut the connection to the grid in extremis - just got rather more complicated, although the principles remain the same.
Now the user reaches home and connects the car to the charger unit. At some stage - whether on a per event basis or more generically via the application of business rules and thresholds - the consumer makes some decisions and in some cases tradeoffs between what he or she is willing to pay and the desire to have a fully charged battery at some time. Certain strategies might carry more risk than others - in general, the more the charge window is deferred and the longer it takes the more likely that you will not have a full battery in the morning even if notionally you should. Equally high charge rates on a hot day may not be achieveable in practice due to battery pack overheating and the need to back off the charge rate commensurately. The consumer can interact with this information and this strategy on a number of devices - the vehicle screen, the charger unit itself, on a smartphone, on a PC, or on an intelligent TV screen (what we sometimes refer to as the '10 foot display' like Windows Media Center or Xbox).
Once you drive away from home, the same energy market serves your needs in enabling a diverse set of charging solutions. From slow/trickle charge points built into public and private car parking spaces, to 'charge while you wait' facilities built around natural gathering points such as branches of Starbucks or popular shopping destinations, to charge facilities added to existing filling station real estate - with a probable bias towards fast charge systems to the extent that the can be capacitized (bad pun there for geeks and EEs) - a range of solutions are likely to become available, all ideally enabled by the same marketplace systems, and findable / reservable by connected services as appropriate.
Reservable?, I hear you say... until all parking places are equipped with charge points, it's likely that smart car park operators will allow EVs to reserve the spaces that actually have this facility, rather than them being 'wasted' by a conventional vehicle. Additionally, it's highly likely that even when battery packs emerge that can handle fast charge, that public capacity to use this capability is likely to be severely limited. Even a relatively modest 1.6kWH battery pack (as fitted to the GM Volt, providing 40m plug in range from 70% of its capacity) would pull about 8000W to charge in 15 minutes. If you assume a 415v connection (about as high as you could practically go) that's 20 amps. Per vehicle. Getting that power from the grid in real time in a distributed model is a long way from being trivial. So to satisfy fast charge, local storage is likely to be required - the equivalent of today's underground fuel tanks, perhaps. That means limited capacity over time, which probably means if you want to guarantee getting that charge when you need it you might want some kind of reservation system (which would, I a