How to Charge Your Cellphone Using Wasted Heat 214
Ilya writes "Companies such as BMW are investing in Thermoelectric Generators to make their cars more efficient by replacing the alternator. Thermoelectric Generators convert wasted heat from the engine into electrical power. This green instructable shows how you can use the same technology right now at home to harvest expelled heat from home appliances to charge your cellphone and other gadgets. Also features a lego racer powered by the roaring flames of a tea candle."
BWM? (Score:2, Informative)
Sipping From a Firehose (Score:4, Informative)
Given that the average American consumes 13,500KWh per year [nationmaster.com], getting a couple of Watt-hours into your phone from wasted heat instead of the grid isn't going to make a damn bit of difference.
Re:Thermodynamics (Score:3, Informative)
It depends on the temperature difference between the heat source and the heat sink; the higher the difference, the more efficient the conversion.
P.S. Ever heard of google?
Re:Thermodynamics (Score:3, Informative)
How much energy can you actually reclaim from a given amount of heat? Is it a constant fraction, if so where does that number come from?
http://en.wikipedia.org/wiki/Carnot_cycle [wikipedia.org]
For each unit of heat energy, the maximum amount of work (useful energy extracted) is (1 - Tc/Th), where Tc and Th are the temperatures of the cold and hot side of the process.
"In this house, young lady... (Score:3, Informative)
That would be the second law, that would be broken if you could recover all the heat. The third law is a bit more obscure and basically means that the first two laws apply to everything.
The amount you can recover varies according to the efficiency of the device you use to recover it, and depends completely on the details of your setup. Obviously no device is 100% efficient (that's the second law again), so you will never be able to recover all of the lost heat. It is possible to get remarkably high efficiency in some setups.
Re:Wasted heat? (Score:3, Informative)
You already have to use a radiator to get rid of the heat so you might as well do something useful with it.
Re:Wish I could harvest the power from my farts... (Score:3, Informative)
I guess farts are funny anymore.
Re:Sipping From a Firehose (Score:4, Informative)
I worked at Toyota for a while we have been talking about this for at least a year. The technology has been around for a long time, but we usually call them thermocouples. It's exactly the same concept, except they need to be much larger, and have a much higher temperature differential to be useful. The main problem is the size and weight. The weight is significant when you're looking to reduce mass to improve fuel economy, and obviously it adds cost to the vehicle.
As for extracted heat reducing the efficiency of the engine, after heat leaves the cylinder head, unless it is used to do work (as in a turbocharger) it is waste.
Not news, not new technology! (Score:5, Informative)
Re:Sipping From a Firehose (Score:4, Informative)
Currently automotive engines use a radiator to get rid of excess heat (internal combustion engines generate quite a bit of unwanted heat) usually the combination of a fan, and the movement of the car through the air, serve to cool the radiator so that it can accept more heat from the engine. Without a radiator the car would quickly overheat, which can cause (among other issues) cracked heads and/or engine blocks.
The alternator currently makes the engine work slightly harder (using more fuel and generating even more heat) to create electricity. By replacing it with a device like this which does not require the work of an alternator, and using the abundant "waste" heat, a vehicle would be more fuel efficient, and as an added bonus, the cooling system would be more efficient.
The bigger question than whether the engine will be more efficient or not, is whether the extra efficiency gained outweighs the extra costs and complications, and whether the new system can generate enough electricity to power all the accessories and charge the battery, especially on short trips on cold days where it takes longer for the engine to warm up (and therefore start producing electricity) and where the load demanded to start the engine drains the battery further.
Re:Sipping From a Firehose (Score:5, Informative)
OK fine I will run the numbers for you:
One day a month is statistically significant at around 3%.
My cellphone battery is 3.V, 750mAh, or about 3Watt-hours capacity. Emptying/charging it every week of the year gives about 150Wh consumption then, compared to 13,500,000Wh an American uses a year, or about 0.001%. This is statistically insignificant.
Hopefully that makes things a bit clearer for you.
Re:Sipping From a Firehose (Score:3, Informative)