A neat trick that could give us the power needed to charge any number of electric cars is simple – switch all streetlights from sodium vapor lamps to LED streetlights. LED streetlights are far more power efficient than other lamps, plus reduce light pollution giving us the possibility to see the stars again. The primary goal of switching to LED streetlights is saving money (and greenhouse gasses) by consuming less electricity for the same benefit of well-lit streets. But the electricity reduction produces another benefit – the current electrical streetlight circuits would suddenly have spare capacity, that could be used for electric car charging.
It’s a compelling theory. Enough that at the Golden Gate Electric Vehicle Association (GGEVA) meeting yesterday, Sharon Hoff (a City of San Francisco employee who’s worked for years in developing electric vehicle charging infrastructure) floated this idea as a possible solution for those of us who own electric vehicles, but live in apartment complexes where we’re not allowed to charge our cars.
I live in that situation myself, and had been thinking of this exact scenario – if only my city would switch to LED streetlights and install charging stations on the light poles, I could charge my car on the street outside the apartment complex.
To recap the advantages of LED light bulbs over incandescent light bulbs
- They use a fraction of the electricity (the 60 watt equivalent bulb in front of me consumes only 9.5 watts)
- They last far longer (50,000 hours or more, versus 1000 hours for incandescent – the bulb in front of me is expected to last 23 years with 3 hrs/day use)
- They’re dimmable (Compact fluorescent’s aren’t)
LED streetlamps have a couple additional advantages
- The light pattern is far more directional, resulting in less light pollution
- The longer lifespan means less maintenance overhead because lighting units have longer lifespan before requiring replacement
So while the purchase price of LED lights is higher, the cost savings add up and they quickly pay for themselves.
The hope I had is that the electricity savings per light pole would be enough to be adequate to charge one electric car. The charging rate could be low — overnight parking of 12 hours at even a lowly 1.2 kiloWatt level 1 charging rate adds up to 45-50 miles of range gained. In practice many electric car owners successfully use level 1 (1.2 kiloWatt) charging at home without problem. But, of course, faster is better and if 6 kiloWatts were available through a light pole all the better.
Turns out that maybe there isn’t that much electricity per light pole.
For a somewhat typical LED streetlight, consider the General Electric Evolve Roadway Scalable unit. It’s part of a family of commercial LED lighting products which make it clear future cities will be far more energy efficient while still being well-lit. These units are direct replacements for typical sodium vapor streetlights. According to the data sheet electricity consumption is between 43 Watts and 269 Watts depending on the size of the given unit. They run off single phase AC electricity at between 120 volts and 277 volts. They’re expected to last 11 years, given a 50,000 hour service life at 12 hours per day of usage.
The GE website has several case studies of cities who have replaced their high pressure sodium vapor street lights with LED street lights. The measured energy savings were 50-55 percent. If the savings is 55%, then a 43 Watt LED unit replaced a 96 Watt sodium vapor unit, and the 269 Watt LED replaced a 598 Watt sodium vapor light.
Which, unfortunately, tells us that each light pole doesn’t have enough spare electricity capacity to be worth charging an electric car. Namely:
|LED Consumption||Sodium Vapor||Energy Savings (new energy capacity)|
|43 Watts||96 Watts||53 Watts|
|269 Watts||598 Watts||329 Watts|
This is calculating the left-over electricity capacity, per light pole, by switching from Sodium Vapor to LED street lights. To be certain of not overloading the street-light circuits, we can’t have the LED street light pole with electric vehicle charging consume more total power than the light pole did with sodium vapor lights.
Therefore the sodium vapor lights electricity consumption is the energy budget at each street light, and we see from the chart that the energy reduction by switching to LED lights is between 53 Watts to 329 Watts over sodium vapor lights.
This makes the charging rate too low to be of use in charging an electric car. If 1.2 kiloWatts is “level 1”, what would we call a 53 Watt charge rate? Level 0.05?
But that doesn’t make the idea impossible. Some parking lots have clustered lighting units. Four of the highest power streetlights add up to 1.2 kiloWatts, which starts to get into the ballpark.
Another consideration is the actual electricity supply at each street light. What if each street light is fused with capacity to run level 1 charging anyway? The discussion so far was about energy savings by switching to LED street lights. While the savings are significant, by itself this doesn’t seem enough to power electric car charging. But maybe cities generally gave spare electricity capacity to the street lights anyway, and there’s already enough electricity to run lower rate charging (level 1).
Finally, the stickler question will be collecting fees to be paid by the electric car driver for the electricity. Cities are looking to LED street lights to save on costs. They won’t appreciate increasing their costs because the electric car drivers want to plug into street light circuits to charge their car. Maybe there could be a coin operated charging station just like the parking meters cities already install?
An expensive route to take is making a deal with ChargePoint or GreenLots or other charging network to develop suitable charging stations, and manage a charging network and payments settlement system. What Sharon Hoff (San Francisco) suggested is the possibility of a sub-metering system that enabled directly charging back the consumed electricity to the car owners home electricity service.
The key point we have to remember is that, in our modern world, electricity is everywhere. It’s just a matter of developing models where entities like cities or shopping centers or workplaces can conveniently install lots of charging outlets to handle the large numbers of electric cars we’ll have on the road in a few years time.
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