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Ramp Creates Power As Cars Pass
Ant wrote to mention a BBC News report on a ramp that generates power via passing cars. From the article: "Dorset inventor Peter Hughes' Electro-Kinetic Road Ramp creates around 10kW of power each time a car drives over its metal plates. More than 200 local authorities had expressed an interest in ordering the £25,000 ramps to power their traffic lights and road signs, Mr Hughes said."
Yes, yes it is. The energy your car expends pushing on the road is turned into kinetic energy, which manifests as the car going forward. The losses are heat from friction (which you can't do anything about) and mechanical (sound and movement) energy transmitted to the road. You can minimize the mechanical losses by making your road as stiff and hard as possible. These things do the opposite -- make the road soft and squishy (by using plates that shift down when weight is applied). This causes the car to lose extra energy, some (not all) of which can be turned into electricity.
An automobile is a wonderful thing, and modern ones even give a smooth ride. The reason we get a smooth ride is this wonderful energy absorbing system called 'suspension', which absorbs about 95% of the energy of a road bump before it actually transfers to the vehicle occupants. The reverse is also true. The suspension has a few major components, the first being the sidewall of the tire. When you hit a bump, the tire deforms, and aborbs a significant portion of the impact energy. Typically, tires are designed so they can continue absorbing such bumps long enough that the tread wears out before the sidewall fails, but, if you spend a lot of time driving on real bumpy roads, you'll know, sidewalls fail long before the tread is worn. The second portion of the suspension is the shock absorber, and like a tire, it has a life expectancy. After absorbing some finite number of impact shocks, it ceases to function. It is quite possible to calculate a 'cost per bump' based on the replacement cost of tires and shock absorbers.
So, in the overall energy transfer equation here, we start with an internal combustion engine, that takes gasoline as an input, provides torque as an output, and is approximately 35% efficient. That torque is then transferred thru the drive train to provide propulsion, a process that typically runs 95% efficiency. Now, for a vehicle in motion hitting this bump, the vehicle suspension will absorb 95% of the impact, so the transfer of energy from the car to the bump is only about 5% efficient, with the vehicle suspension absorbing most of the impact. Tally up all the efficiencies along the way, 0.35 * 0.95 * 0.05 and you get 0.0166. So, to generate 1 kw of electricity from this device, you have to burn the equivalent of 60Kw of gasoline, and then let it flow thru the inefficient transfer mechanisms. To top it all off, you are purposely introducing extra bumps into the system, ie causing mechanical wear on the vehicles, which will in the long run have a measureable cost, probably substantially higher than the value of the electricity being generated.
If this is a 'step forward' for renewable energy, I'd sure like to know how that comes to being. To me, it looks like the most wasteful mechanism I've seen yet to convert gasoline into electricity. I cant remember EVER seeing any hair brained method of generating power thats LESS efficient than this one, with the exception maybe of the cartoon method of driving a windmill with an electric fan.
I can see one, and only one application where this is potentially 'viable', and thats to power traffic lights at locations that are so far out of the way, no grid power of any kind is available. I know of a few tunnels in the remote parts of northern british columbia where that would be the case, it would mean they dont have to keep the generators running on diesel 24x7 to light them up. Then again, from a pure pollution point of view, it's probably wiser to run an efficient generator 24x7 than to consider this kind of low efficiency energy transfer device.
Then again, if i was in the business of selling tires and shock absorbers, I'd probably consider the idea of offering a subsidy to towns looking to purchase this device. One of these at every traffic light in the jurasdiction would likely do wonders for my tire business, probably give full payback in a couple of years. Then when folks do come for replacements, upselling them to good quality steel belted tires that can withstand the extra abuse would be a trivial upsell, just point at all the artificial bumps in the road, and make sure they understand, normal tires just wont survive on these roads....
If it was designed well, the maintenance should be negligible. There might also be a benefit in that the lights would stay on in a power outage.
As far as electricity usage goes, I would guess that each bulb might be 200 Watts. Depending on the design of an intersection, there would probably be between 8 and 16 of these lights on constantly. According to http://www.ukpower.co.uk/running-costs-elec.asp the cost per month would be about £130/month, or a bit more than £1500/year. Assuming there is no interest (or increase in the price of electricity) it would take almost 16 years before these savings make up for the cost of the equipment. Many governments make investments on this time-scale anyway. Additionally, if it could be used to power more than one traffic light, it might only take 7 or 8 years to pay for itself.