“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Saturday, February 18, 2017

Once again with Pavegen

Image credit: imagine business development
(Note: the zombie image applies both to my blog and to the subject of this post.)

Pavegen, a Company that I've looked at before (see here and here) is still around and, apparently, thriving. Pavegen designs, manufactures, and installs tile systems that generate electricity via footfalls as pedestrians walk over them. Despite my lack of posting, I've not lost interest in all aspects of energy and, in perusing the web, I happened upon their new site. They've developed a new tile design and quite a presentation. The link is to a 49 minute video!

I thought I'd keep an open mind and evaluate it, despite my expressed disdain in the previous posts. Getting started, I found a couple of troubling things. At the 19:15 timestamp in the video, CEO and Pavegen inventor Lawrence Kemball-Cook states that the new Pavegen tiles are "200 times as efficient." Later, at the 28:10 timestamp, CTO Craig Webster states that Pavegen is capturing "about 20 times more energy per footstep" than the previous version of the Pavegen tiles.
Image credit: Pavegen

Well! First, an order of magnitude discrepancy in the claims is hardly something to ignore. But let's use Webster's claim of 20 times, since he's the CTO. Kemball-Cook walks across the tiles to demonstrate the data gathering capabilities of the tiles and the screen shows steps and energy generated (see the graphic at right, click to enlarge). It shows that Kemball-Cook has generated 65 Joules in 14 steps, or about 4.6 Joules/step. As an aside, some quick and dirty calculations with appropriate estimates leads me to conclude that he's generating at something like 8 watts.

In my second Pavegen post (this current one is my third) I estimated that the previous generation of Pavegen tiles generated somewhere between 3.5 and 7.2 joules per footfall (the lower from my estimates, the higher from data generated by a Pavegen installation). I'm hard pressed to see an increase of 20 (let alone the ridiculous 200) times in efficiency of energy conversion. Kemball-Cook and Webster both tout the efficiency of the new triangular shape and its ability to capture energy over 100% of the area of the tiles vs. the previous square tiles but that is, in no way, sufficient to justify their claim.
Image credit: Pavegen

I assumed from previous information that the mode of energy conversion was piezoelectricity. but it's clear from the Pavegen video that this is not the case, at least in this incarnation. Rather, it appears that a footstep spins a small flywheel that operates as a generator. Each vertex intersection of the triangular tiles rests above such a generator. I will concede that it's a very clever design.

Kemball-Cook and his team have big plans for the Pavegen system. Jeff Martin, CEO and founder of Tribal Planet, apparently has formed a partnership with Pavegen and, through the use of smart phones, anticipates that malls, stores, stadiums, etc. could track the energy delivered through the footsteps of a customer and then provide discounts, loyalty awards, etc. to the customer. Or, one could "donate the energy" to some developing world person who needs it. The mechanism for such a transfer isn't described.

But, as I stated in the previous post, I take about 5,000 steps on an average day. If each step were captured, I'd generate (if I weigh the same and walk similarly to Kemball-Cook) 4.6*5,000= 23,000 joules, or 0.0064 kilowatt hours. In my city of Anaheim, CA, that would be worth a little under eight hundredths of a penny. And, to reiterate, that's not my trip to Target, that's my walking for an entire day. The cost of a Pavegen tile isn't stated, but Kemball-Cook does state that Pavegen's goal is to bring the price close to that of a standard tile through mass production.

There's no doubt that the tiles do generate electricity, probably at the rate of around 8 watts for each walking adult. And there's no doubt that that level of generation can be used for area lighting or similar. But the energy isn't free, it's energy added to that of walking without the tiles. Now, it may be the case that in the generally overweight United States (I can't say about England, the home of Pavegen), having people spend more energy to walk might be desirable.

In any event, at the outset of the video, Kemball-Cook mentions that lighting accounts for nearly 20% of all electricity generated world wide and, after saying that he didn't know that, doesn't say anything further about it. He leaves the impression that he'll show that Pavegen tiles can alleviate the need for mains power for that use. Umm... no.

In my office, there are about 32 people. Most don't walk around as much as I do but let's assume that they do. Most of my walking is at work, say 4000 steps over nine hours. This rate, at 4.6 joules/step, equates to 0.6 watts or so. If all 32 people in my office did the same, it would be 19.2 watts. That wouldn't light one of the four fluorescent tubes in my office, let alone the entire 12,800 square feet of the floor we occupy. It's true that LEDs would do better but there's no chance that 19 watts would come close. And that generation, in a work day, would be about 0.017 kilowatt hours, worth less than two cents.

Pavegen has a fascinating gimmick and a clever design, but it won't put a dent in electricity use. And the electricity comes, ultimately, from the sun. We eat the plants and animals, and fertilize them with products of sunshine from millions of years ago to give us the energy to 
pump the Pavegen tiles.

Update: There's significant discussion at the website of the ability of the tiles to generate data and wirelessly transmit it. This could be used to determine traffic patterns in stores, malls, museums, etc. and to locate "hotspots" for patron activity. I strongly suspect that, after the "gee whiz" factor of the trivial energy output wears off, such data will be the real value (or, as my close friend and associate, Dr. Boris Stein, would say, "the dry residue"). Were I an officer at Pavegen, I'd offer a cheaper option of the tiles without the generators to be sold for the data gathering capability.

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