TECHNOLOGY:Solar tags from Sirit

The solar electric cell measures 56mm (2.2") by 14mm (0.55") and generates 3 microamps at 5V in light of 200 lux. It is mounted on the case of the tag, obviously to catch the sun through the windshield to which it is attached in the normal way.

The tag, which does not yet have a brandname, is a solar-assisted toll tag that still basically relies on the same finite-life lithium batteries, normally used in toll transponders. The solar cell will generally in the daytime provide most of the juice needed for the transponder in its quiescent mode, and it will supply a portion of the power needed in active mode.

Michael Briand chief exec at Sirit says the engineers calculate it should approximately double the life of the battery. The regular transponders, brandname Identity Title-21, last five to eight years and TCA is already having to replace transponders issued from 1994 onward because of dead batteries. The solar-assisted tag, Sirit says, should have a service life of 10 to 16 years.

The price premium will be 10 to 15% over the approx $27 for the regular California tag. Sirit is also offering to refurbish tags with dead batteries, installing a new battery or remanufacturing them into solar-assisted tags.

Why not go all-solar with a rechargeable battery such as the metal hydride batteries used in mobile phones?

Donald J. Bergeron, at Sirit says they looked at that, but for now there is no suitable rechargeable of the right size, capacity and price: “Our system memory is volatile, so additional circuitry and a small backup battery would have been necessary. Also, the charging requirements for rechargeable batteries are quite high, requiring a much larger solar cell covering possibly all of the back cover.”

But, they say, they’ll reconsider a full solar-rechargeable transponder if the technology becomes available at the right price.

A press release (7/25/00) from Sirit gives credit to TCA, its largest customer, for prompting it to develop the solar-assisted tag: “the TCA has consistently demonstrated both their ongoing commitment to technological leadership in the tolling industry and its commitment to the environment.” The press release is headed “Sirit delivers first environmentally sensitive transponder.”

Lisa Telles at TCA says the idea for the solar-tag came from one of their board members during a board discussion of a staff proposal for a large new tag order. Some of the new tags were needed to replace tags whose batteries were gone. Someone said: “Why don’t they make a solar-cell tag?” The staff put the question to Sirit, which agreed it was feasible. The development of the solar tags was a clause in a purchase contract with Sirit mid-99.

If the tags work out TCA could decide to offer the solar-tags as an optional alternative to the regular battery-only tags. Or it could go all-solar at some point. No decision on that has yet been made.

Alternatives

Other north American manufacturers. Mark IV and Amtech/TransCore seem likely to follow Sirit’s lead if other toll agencies are interested. There are alternative solutions to the dying battery issue: (1) to hardwire the transponder to the vehicle’s 12V electrical system, which is being done with Japanese electronic tolling, and which will probably be done when transponders are built into vehicles in the factory as original equipment (2) to abandon onboard power supply entirely and use the energy of the incoming signal in a pure backscatter tag, as implemented in the first generation of read-only tags, and now in the limited write-back sticker-tags recently introduced by Amtech/Transcore (3) to integrate electronic tolling with a mobile phone system or even with the kind of integrated location and communication systems GM has pioneered under the brandname Onstar. (Contact Michael Briand, Sirit 800 498 8760 www.siritcorp.com, Lisa Telles TCA 949 754 3411)