Current CO2 concentration in the atmosphere

Driving on LEDs

I think it’s absolutely crucial as we deal with energy and environmental issues that we recognize the interactions between pieces of systems, and between subsystems within our entire biosphere. Climate change, energy consumption, politics, economics, psychology, non-greenhouse gas pollution — it’s quite a big ball of stuff we’re trying to get our arms around and control, or at least keep from blowing up.

With this mindset, I found yet another of those “city X is saving Big Money by replacing old tech street lights with LED units” articles particularly interesting. We’ve all seen those article, thanks to the quickly rising uptake in LED street lighting. The article (blog post, actually) I stumbled across was, World’s Largest LED Streetlight Retrofit Completed In Los Angeles, which quotes a Forbes piece thusly:

Los Angeles is certainly not alone in making the switch to LED street lighting. I’ve reported at this blog, for instance, about the many other California cities, big and small, that have done the same. In March of this year, the City of Las Vegas finished outfitting 42,000 street lights with LED fixtures. One month later, the City of Austin, Texas, announced plans to install 35,000 LED street lights. And, in December of last year, CPS Energy said it would install 20,000 LED street lights in San Antonio.

But, owing to its size and influence, Los Angeles, with its partners, the Clinton Climate Initiative (CCI) and the C40 Cities Climate Leadership Group (C40), have done much to jump-start the market. Navigant (formerly Pike) Research recently predicted that shipments of LED street lights will increase from fewer than 3 million in 2012 to more than 17 million in 2020.

So, how much juice are we talking about, and what could all that suddenly available generating capacity be used for? Perhaps overnight recharging of PEVs (plug-in electric vehicles)?

Assume that each LED street light saves 88 watts over the old unit.[1]

Assume that each street light is on for 12 hours per day, on average.

That yields a savings of 1,056 watt hours per street light per night, or 1.056 kWh per fixture per night.

My Leaf S gets 4.8 miles/kWh, and I most certainly don’t drive with a light foot. Plus I’m not stingy with running air conditioning in the summer, thanks to my allergies.

Therefore, the lighting conversion frees up enough electricity to drive 5.0688 miles per fixture per night.

For Austin, that’s 177,408 miles per day, and for San Antonio it’s 101,376 miles per day.

For Los Angeles, and their 140,000 light conversion[2], that’s 709,632 miles per day.

If the projection of 17 million LED street light fixtures sold in 2020 comes true, that’s over 86 million PEV miles fueled per day from the savings. And that’s from fixtures sold in just that year, not a cumulative figure.

Now, this is the point where someone inevitably feels obligated to raise his hand and yammer on about how how the reduction in CO2 emissions per mile driven for an electric vs. gasoline vehicle is highly dependent on how the electricity is generated. And my response to all the Captain Obvious wannabes out there is:

1. Of course. Who ever said otherwise? If you find someone who does make such a ridiculous claim, my advice is to stop listening to him or her immediately.

2. Our electricity supply will get dramatically cleaner in the coming years, for the simplest possible reason: It has to. In the US in 2011, our electricity generation accounted for 41% of our CO2 emissions.[3] We can’t get close to the level of emissions cuts needed in the coming years and decades without dramatically overhauling how we push electrons down wires. And the situation is even worse in some other countries (like China and India) where their electricity generation is very coal intensive. Put another way, claiming that electric vehicles aren’t as clean as we’d like (even if they’re still cleaner than gasoline vehicles) and they won’t get cleaner is a prediction that we’ll fail to avoid very damaging, possibly catastrophic, levels of climate change impacts. That’s not a future I’m willing to sign up for.

The bottom line on all this is very simple: We’re engaged in a worldwide exercise in economics — the allocation of scarce resources — which means it is critical that we not get lost in details. The individual colored tiles on the wall might be pretty, and small clusters of them might create interesting patterns, but it’s only by taking several steps back and looking at the whole, wall-size mosaic that we can see how things fit together and, therefore, what we should be doing.


[1] I’m using the 42 watts vs. 130 watts figures from the article, LED streetlights move from pilot projects to widespread use

[2] See the Forbes article mentioned above, Los Angeles Saves Millions With LED Street Light Deployment

[3] See table ES-3 in the US EPA publication, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011.

3 comments to Driving on LEDs

  • Nice way of laying it out. Thanks.

    I, for years, have phrased it slightly differently:

    Petroleum fuels, inevitably, are getting dirtier over time per unit of energy content. Whethe deep water, fracked shale oil, tar sands, Venezuelan crude, the oil supply is getting dirtier with each passing year and will — unless (until) there is a renewable fuel breakthrough or some magnificent technological breakthrough — continue to get dirtier.

    Electricity, however, has the potential — the likelihood — to get cleaner per unit over time. Whether more efficient burning of fossil fuels, increased nuclear power, or (most importantly) the introduction/expansion of renewable electricity, our kilowatt hours will get cleaner inexorably over time. (We can (should) accelerate this process, but it is the natural business/technological trend even without serious climate policy driving it.)

    Thus, if one invests in a fossil-based fuel system (traditional ICE), it will pollute more tomorrow than today. If one invests in electricity based mobility, it will almost certainly be polluting less tomorrow than today.

    As a society, which works better for tomorrow?

  • Lou, I too have been happy to see the growing prevalence of LED’s. I love your closing paragraph, with the imagery of the mosaic, and how we need to stand back far enough to see how all the tiles fit together. Beautiful, and accurate.

  • Don

    Unfortunately though even though you are driving on a cleaner soure of energy, you are still driving dirt. Driving in its current form is not green nor sustainable.

    Take a 1000kg car with a person of 100kg. Mass efficiency is 9%. Fuel efficiency will vary but for an electric car we can say that the power station circa 50% efficient, transmission losses are around 7% and the car itself is 75% efficient. Power efficiency is 32%. Overall efficiency is around 3% before considerations of infrastructure.

    Even if we were to assume a 100% efficient power source (note renewables are not) then we would have a limit on power efficiency of approx 68%. This still leaves us at a measly overall efficiency of 7%. That mass term is hideously expensive.

    The best scenario I can come up with is an electric bicycle. Guessing a mass of 20kg, the mass efficiency can be gotten quite high and thus the limit then becomes the power efficiency. Not only that but around 50% of the effort will be put in by the user thus giving other benefits and reducing energy use further.

    No doubt the bike is not the easier option. But then again we do not do things because they are easy nor should we take the easy option of let someone else do it (i.e. decarbonizes the grid) as we have no influence on how quickly this can be accomplished. However this is exactly the sentiment that most people do propose at least in the UK. A report was done on thousands of people reducing their energy use in the UK. My comment on the report via the Guardian website is below. It is this reason why I am extremely pessimistic that a renewable transformation or reduction in energy usage is highly unlikely.

    “Yet when asked about driving less (transport is 41% of our energy use) and using less air flights, deep resistance was met (P15). Person responsibility in giving up leisure flights was resisted but business flights were the ones to be reduced. So even though the report says that 81% of respondents want to reduce their energy use, it is clear that very few actually will. This is a key point but is glossed over by the positive 81% figure. “

    Transforming the UK Energy System | UK Energy Research Centre