Lights out in Dörentrup, but it’s too complicated

In Dörentrup, Germany, you can literally call up the streetlights.  It saves energy, but at what cost?

On 30 July, Time posted an article about the town of Dörentrup, Germany, where the local council recently voted to turn off streetlights at night to save energy and carbon emissions.  This naturally caused a fuss.  What’s the point of streetlights that are off when you need them?

Town resident Dieter Grote and his wife, working with the local utility company, came up with a solution.  You can now use your cell phone to send a special ID code to the utility, and the streetlights with that ID (grouped by stretch of road) will come on for a certain length of time.

The energy saved by turning off the lights at night saves the town (population, around 9,000) about 12 tons of carbon emissions per year.  That’s not bad.  And other towns around the world are asking Dörentrup for help to set up their own similar systems.

While it’s fine and good to try to lower consumption – especially when no one needs the service – I think their solution is too complicated.  First of all, there is a carbon footprint associated with the machinery and electronics needed to keep this new service running; I don’t get the sense that anyone has compared this footprint with the alleged savings.

Next, this system ties the utility infrastructure directly to the phone system quite deeply, in a rather centralized way.  You call the magic phone number, which no doubt accesses a facility in one of the utility’s plants, but by way of your phone provider.  The centralized system then has to understand the ID code, which can be dialled in or spoken (requiring voice recognition software).  The IDs are stickered onto every streetlight.  The system then has to direct the pertinent streetlights to turn on, keep track of the time, and then direct them to turn off.

If something goes wrong at the system’s home base, the streetlights won’t come on, even though they otherwise could.  If your phone’s battery dies, or you lose signal strength, you can’t control the lights, even though they would respond otherwise.  If you don’t have a phone, or your hands are otherwise occupied carrying groceries or whatever, you might not be able to use the phone – again, you can’t get the streetlights to work.  If you can’t read the ID sticker on the streetlight (because the streetlights are off), then you might enter the wrong ID or be unable to figure out the ID at all.  Vandals could change the ID stickers.

These are all failure modes that don’t need to exist.  There are probably others that I haven’t thought of.

I would suggest something simpler.

Residents would carry some kind of semi-active sensor, like a battery-assisted RFID tag, or the GPS locator already in many cell phones.  A small unit would be attached to every streetlight, that can detect the presence of a nearby RFID tag or GPS locator.  The unit then turns on the streetlight, and keeps it on till the signal moves out of range.  This can be rigged to ensure that two or three streetlights are on for each person.

Assuming these kinds of sensors have the required range (and I think they do), I think this is a better solution because:

  • no hands are required to activate the system;
  • no hardware/software needed at the central utility facilities;
  • power for the streetlight unit can be drawn from the streetlight itself;
  • the RFID battery can last ‘way longer than a cell phone battery;
  • no need to remember phone numbers or look up streetlight IDs;
  • this kind of distributed/decentralized system is more robust and resilient than centralized alternatives; and
  • fewer streetlights would be on, and for shorter periods.

In other words, I think my suggestion is more effective, without giving up efficiency.  It compartmentalizes the whole on-demand streetlight system so that failures anywhere are less likely to affect related systems.

Seems like a no-brainer to me.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s