Device wraps around hot surfaces, turns wasted heat to electricity

Could work well on things like exhaust pipes

But most cases, moving hot waste, the loss of heat is a side effect (the waste material just happens to be hot), and may in fact be an undesirable side-effect that squanders energy. Now, they don't need to squander that energy.

Easy example is a chimney - they're only trying to get rid of the exhaust gasses we don't want inside, and DGAF if it is cold or hot. In fact, heat exchangers are often installed to attempt to capture some of the lost heat and minimize losses.

Same for waste liquids going for treatment, or actual product exiting a hot process and going into a cold/ambient temp process -- they've got to dump the heat, far better to grab some energy on the way out.

Of course during the year there are times, when heating is not needed. Then it would make sense to use the heat otherwise.

A device like this is not useful in a system where you are actively pumping heat around.

Take an ordinary house. The default, low-energy state is the one it tends to if we don't mess with it. The inside and outside of the house come to about the same temperature as energy leaks in through the insulation and holes in it, though slowly.

Now we put in a heat pump. This changes the system. With a little energy input, we capture the energy in the inside of the house, and we move it to the outside. The energy state of the system changes, it begins to gain energy as we put some in to create the heat differential.

Then we attempt to capture this heat differential. We place a heat engine, which one of these devices is, across our temperature differential. Assuming total efficiency for both processes, which we do not in reality have, our heat engine undoes the heat differential and produces for us the exact amount of energy we ourselves put in to create that heat differential. The inside and outside now come to some resting state, possibly with a constant heat differential upheld by the pump and actively sabotaged by the engine. Theoretically, we get net 0 energy and dysfunctional air conditioning, but in practice, we get a net loss of energy to inefficiencies.

The same applies to the water analogy. Imagine two tanks of water connected by a porous wall. The state it reaches naturally is that both tanks are at the same level through water seepage, though it is slow. If we place in a pump, we get a pressure differential across the tanks: one tank becomes higher and another lower. Then we place a wheel across the differential to take advantage of that pressure. Energy is generated, and at the same time the height difference is lost. Again net 0, though in reality you will experience a lot of inefficiencies.

If the point is to do air conditioning, you cannot recapture energy from the heat. Just running the air conditioner at a lower power achieves the same result more efficiently. Similarly with the water pump, it will in reality be more efficient to just not pump as much water up, and you will reach the same result.

Do you have a way of utilising or storing electricity/heat? If so, either are more efficient than not doing so. For example, if it's cold where you live and the heating is usually running... just expelling the heat from your fridge into the house is efficient. If you are cooling, it's not. Electricity would be better... or at least piping the heat out.

I looked into the economics at one point. Would be great for a laundromat or hotel, not so much for the average single family home.

Perhaps only if you fill a large tub or a pool every day.

The disabled and frail do not.

Might be an urban legend.

I believe the result was that the value of power generated was so utterly dwarfed by the costs in copper, inverters, etc. - not to mention additional maintenance costs - that it was at least an order of magnitude outside of making sense.

Some of those economics certainly have changed over the last 15 years but many (I’m looking at you, copper) are rather fixed and won’t go down over time.

Also

> 1.4 TRex bites worth of force

I have never seen T Rex bites as a unit of measurement before and I love it.

In fact it's a perennial design winner in various design contests that are judged by designers and not engineers or scientists. It looks awesome when you design some cool little gadget that "harvests" enough energy to power a small town from a soccer ball or something. The fact that it doesn't work is not a disqualifier in those contests. It't totally what I'd enter at this point if I were going to enter such a contest, it's an obviously winning play.

But the floor that converts foot traffic to energy doesn't generate much energy, and is very unpleasant to walk on. The soccer ball that extracts energy from the kick means that it has extracted energy from the kick, so it doesn't go flying away like a soccer ball should but is more likely playing with a ball of damp laundry. Guess what kids don't want to play with? The "lift a rock to power a light" does work, but it provides a lot less light for a lot less time than people think, and the rock ends up being pretty heavy. (But it does have at least some legitimate use cases, just not as many as you might hope.) The bike that extracts energy from the biker is so insanely unmarketable that what's winning in the market right now is the exact opposite, the electric bikes that supplement the biker's power.

(Also I will add as honorable mention the "solar powered X" that is spec'ed with one or two orders of magnitude too few solar panels. Putting panels on the top of your electric car may even be theoretically worthwhile in the long run, but only as a small supplement to the car. The idea that you'll be toodling down the highway at 75mph on 10ish square feet of solar panels is risible. Multiply that by some large two-digit numbers.)

What's the total energy expended to produce those 80 kJ worth of orange juice, though? You need to power agricultural machines, food trucks, etc. etc.

Show me a wind-powered lithium battery factory and I'll change my mind.

That's no different to turning up your radiator.

It's the first law of thermodynamics, isn't it? I'm not a physicist.

Well... for every rule there is an exception I guess, there was a Mercedes demonstration vehicle that used a modified diesel engine without a coolant loop and insulated head to keep the heat in the engine. It never made it to production due to cost but the thing was ridiculously efficient.

besides, water in a ice engine need to be cooled down fast, at the rate these device extract temperature from the sources, you're going to have to need a huge surface area being extracted, or two set of radiators - one to control the circuit temperature, the other to cool the generators.

these device application are a lot narrower than one might expect.

I am only an armchair inventor. I once got as far as registering a company, and filing a business plan, but I noped out of it.

I just like to follow the science and noodle with the equations, hoping for something interesting.

The main problem for this application, I think, is maintaining a temperature gradient. So you add a heat sink to the cold side, but that only gets you so far. And then you have the extra cost and CO2 burden of manufacturing a heat sink (and aluminium is particularly dirty).

My plan was to look for places with a sustained temperature gradient. So, I sandwiched a peltier between the hot and cold pipes in my old house, to power some LEDs. As long as the house was occupied, there was always cold running water on one side, and hot tap water on the other.

So, if I was building, say, a power station, where cold water is being pumped in. I would arange the cold pipes close to the hot in one spot, insulate the outer surfaces, and stick a peltier generator in between. You can also use heat pipes (like on CPU fans) with coolant, to wrap the source hot/cold pipes, without needing a flexible peltier.