GM To Test Utility-Controlled Solar Charging For Electric Cars

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GM OnStar and TimberRock's on-demand solar charging

GM OnStar and TimberRock's on-demand solar charging

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If there's one thing that most people agree on when it comes to electric cars, it's that powering them with electricity generated by renewable energy is generally the greenest thing to do.

Solar is a popular choice with those in warmer climates, but even that endless nuclear furnace we call the sun isn't perfect--because it isn't always shining down on our solar panels.

GM's OnStar service and energy company TimberRock are looking at minimizing these disruptions with managed power and energy storage via the electric grid.

The basic premise is that solar power and even power from the grid itself is never constant.

There are peaks and troughs in demand and supply. If there's a peak when supply is low then energy can be wasted; if there's a trough when demand is high then there's a shortage of power.

Solar is particularly susceptible to this. Consider when your solar panels are absorbing the most solar energy--during the day. And when do you charge your electric car? Probably at night, while you sleep. The energy isn't being produced when it's needed.

TimberRock's solar charging canopies get around this by storing energy in a large battery system for whenever it's needed, and carefully metering out the energy needs of its small fleet of Chevrolet Volts. It uses an OnStar system called "Demand Response" to enable TimberRock to start, stop and modulate such a system.

Aggregation software can then apply this energy in the most efficient way. If there's an excess of it on a particularly sunny day and charging the Volt isn't a priority, power can be sent back to the grid to cover for any shortfalls.

The car could then be charged when grid demand is lower--still with clean, green solar energy.

While it would require owners to be happy with external sources being able to pick when their vehicle charges (a system of financial benefits is being suggested for owners willing to participate), it could prove popular with green-minded buyers.

“Down the line, this could really incentivize solar charging for EV drivers” said Paul Pebbles, GM global manager of Smart Grid and EV Services.

“This opens the door for solutions like this to be brought to the public, which could increase the benefits of owning an electric vehicle."

Would you be willing to participate in Demand Response charging to make running an electric car even greener? Leave your thoughts in the comments section below.


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Comments (20)
  1. The energy storage portion of this seems like overthink. For now and the foreseeable future the grid itself is the "storage system". During the day "your" solar panels (they could be storage panels leased somewhere in the desert, or they could be panels on your roof) put energy into the grid, reducing the amount of hydrocarbons that would otherwise be burned to energize the grid, at night the car is charged. The night-timing of the charging cycle is "green" in the sense that it uses equipment (the generating station) that would otherwise be unused -- no new power stations are required -- and the total amount of hydrocarbons burned is reduced by however much energy was created by the solar panels. And there's no batteries to maintain.

  2. I agree with Roger completely. One should never plan to charge an EV during peak grid hours (hot afternoons in summer, or very cold mornings in winter). Having solar on the grid is really a separate issue. EV owners should find out from their utilities how much renewable windfarm energy the utility is purchasing, and charge the EV when windfarm production peaks. In Texas that is 1:00 am in the morning. Let solar stand on its own. The idea of using solar in conjuntion with batteries is just crazy. The grid itself is a huge virtual battery, without the maintenance and losses inherent in actual batteries.

  3. Currently it takes a long time to charge EVs. Forcefully delaying the charging through convoluted systems would not be conducive to wider EV acceptance.

    To paraphrase a saying, charging delayed is charging denied.

  4. Sounds like a solution to a problem that doesn't exist, at least in California. With a standard home solar system tied into the grid, you generate the most power at peak use (and peak rate) times, when the power company needs it. And you can get paid for it if you produce enough and have a net metering plan. It offsets potentially dirty power plant generation at times when that is most needed. Load on the grid at night is generally low; there is extra power in the grid already to use.

  5. are you guys staying in touch with solar roadways ?

  6. just checked - in case you are interested, they are starting the installation of their first (a small parking lot next week).

  7. I don't think I want to add "wear and tear" to my battery by feeding power back to the grid. If it is leasing, that is one thing. But if I expect to keep my battery for 15 years and 200k miles, then this can't be a good thing.

  8. The batteries possibly used to feed the grid in that weird GM/On*/TimberRock scheme above are from the charging station, not the vehicle.

    (A regular charging port only allows power in anyway. The only exception I know of is the DC quick-charge port of the Leaf or i-MiEV, but the hardware that could tap their battery for emergency V2H is apparently only available in Japan).

    What GM/On*/TimberRock are trying to achieve with such a convoluted setup is a mystery to me; the explanations above don't make sense.

    I see no reason not to push the production of the solar canopy onto the grid as it is produced, skipping the batteries.
    And while demand response is beneficial, this IMHO should be implemented in the charging station, not the vehicle.

  9. I think this fear is highly unwarranted; you're far more likely to impact battery life through fast-charging than through V2G.
    Presumably, you can control the rate at which you send power back to the grid and for how long.

  10. There is no fast charging on the Volt and I am planning to keep my Volt for a long time unless I can find a pile of cash to buy a Tesla S.

  11. The picture was missing an updated home charging station that can reverse the charge from the car and power the house at night. I will use my solar during the day for my home and car and then reverse the charge from my car at night. The only car that can do that is the Tesla, since my house would use less than 15kw overnight I would still have much charge available during the day. This is available for less than $1000 from ecototal in August, if I understand correctly.
    Imagine having two cars with that storage and things get much simpler...

  12. ...except, as very correctly pointed out by Roger and Charles above, storing electricity during the day, when it's in demand and expensive, to use at night when it's cheaper, makes no sense.

    It'd be even crazier to use pricey batteries for this, let alone have them attached to a vehicle.

  13. @John: And, except that carmakers are highly leery of letting owners pull energy OUT of the batteries at will for uses other than powering the car. They have warranted their batteries--and designed them--for predicted usage based on driving, not on powering your house or any other non-vehicle use.

    I haven't checked, but I'd bet that modifying your electric car to let you pull electricity out of the batteries immediately voids your warranty.

    This is why GM is carefully "studying" this kind of application--not offering it willy-nilly on today's plug-in cars.

  14. A simple regulated charger might do the trick, where the grid communicates with the charger and asks it to slow down
    when the grid is in emergency. that's usually only for 2 hours a day, if chargers were to kick down to half rate for that period, it would do a lot to mitigate demand.

  15. Nissan appears to be out in front of this:

    What exactly is "predictable" about driving? Don't you "pull electricity out of the batteries" the minute you touch the pedal?
    Isn't that what batteries are for???
    Every EV makes use of regen braking, which is putting electricity back into the batteries - at much higher rates than typical household use.
    If a full charge on a Leaf will get you ~80 miles and you cover that distance in 1.5 hrs, then the battery was putting out ~15 kW for that time.
    That's well above the peak draw for the average house.

  16. Hmmm...

    1. 15KW DC isn't exactly the same as AC. But for the purpose here, let us say that is similar as in RMS. A 15KW AC with 120V is about 125 A or 63A on two phase of the supply (240V).

    A/C draws about 30 A on 240. Electric dryer draws another 25A or so on 240. Electric water heater draws over 60A on 240V. Electric burner draws at least 12A each on 120V. Electric oven draws about 30A on 240V.

    So, an average house in the summer with A/C on and baking a pie will easily match that 15KW energy draw and if you happen to dry your clothes, you are easily over that limit.

    Most the newer homes come with 200A 240V circuits...

    Lastly, there is a major difference between using the battery for my driving vs. helping my power company.

  17. @XL, Nissan's Leaf-to-home is meant to provide its owner with power during an outage, not supply the grid.

    Next, if that's any indication, the peak demand for my house and its 4 occupants over the last entire year was... 6kW.
    (this probably means that the the dryer never ran at night -- I have a couple kW of solar).

    That's obviously without trying to pay any attention as to what was used when (I have 200A service, no need to care). In an outage, sane people will surely keep their consumption much lower.

    So yes, 15kW backup power seems more than plenty for a typical home. You'd need a heck of a generator to do the same...

  18. @Just O,

    I fully agree that EVs are great "power backup" during outage. But we got to remember that when that happens, it is a choice between keeping your "mobility" or keep the lights on. And it all depends on how long the outage is. Some of the "storm" related outage can last days if not a week.

    Your 6KW is extremely low for peak power. Since you mentioned solar, then it isn't exactly fair since the peak power is "offset" by the solar generation. I also assume you have a lot of "gas appliances" that doesn't require much electricity to run. An electric water heater alone can draw 8KW to 10KW. With A/C, that is easily another 7-8KW on top. When the power is out, your grid tied solar system will shut off as well.

  19. "So yes, 15kW backup power seems more than plenty for a typical home. You'd need a heck of a generator to do the same... "

    I agree that it is good enough for "backup" power. A 7KW generator would cost about $600 and it is very loud and heavy. When you need power during outage, the generator is only run from time to time for it. It is NOT designed for a "full on" mode.

    The Nissan system is a great idea except for the cost.

    IMHO, I think Volt is an even better fit for it since it comes with an onboard efficient generator and a battery large enough for peak power demand.

    But I certainly don't want to use EV battery for any kind of "Load conditioning" for the grid.

  20. I only see 2 practical uses for this system and they are both in the future 1) when batteries become so robust they have minimal wear after the equivalent of 500,000 miles and/or 2) when the grid goes over 50% renewable and we need batteries for when the sun doesn’t shine or when the wind doesn’t blow.

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