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Re:uBeam's insider story by ex employee? by minimaxir on Wednesday May 11, 2016 @02:57AM (#11673123)
Keep in mind that you still need to obey the laws of thermodynamics. Those are rules startups can't ever break.

The writeup I linked has a good argument against the feasibility of wireless power for a TV:

> A typical large, flat-screen TV (eg. [42]) will draw about 60 watts. Since a TV is usually mounted in one place, some of the limitations get easier, but not all - if the TV is two feet (60 cm) from the wall, and the receiver is 40% efficient, that's still about 80% losses. To transmit 300 watts at 0.3 W/cm^2, one has to have a 1,000 cm^2 transmitter, a bit over a foot on each side (31.6 cm). One could make the transmitter smaller (100 cm^2, or 4 inches/10 cm across) by increasing the intensity to 165 dB, a level that causes burns "almost instantly" (from Question #7), but that seems unwise. Since most power outlets are near the floor, and the TV probably isn't, one would still have to run a cord to the transmitter. And uBeam takes 240 watts of electricity, about a dozen light bulbs' worth, and dumps it into the air for no real reason. That's not good for the environment. Or the power bill. Or the air conditioning - all that heat makes the room hotter.

Re:uBeam's insider story by ex employee? by rev_null on Wednesday May 11, 2016 @12:35PM (#11676807)
What people often forget is that the second law of thermodynamics only applies to a closed system.

So, a startup in a closed system with no product or source of revenue will dissolve into entropy. But a startup with continual funding from VCs can remain as long as the influx of cash continues.

Re:uBeam's insider story by ex employee? by mikeyouse on Wednesday May 11, 2016 @03:27AM (#11673253)
I'm not moved by that post.. Didn't you know Google wasted $100M by investing in D-Wave which has been proven to be no faster than a laptop?

Anyway, there's nothing about thermodynamic limitations in the section about the TV. The author is making several exaggerated statements that are easily refuted to make the TV suddenly possible... Let's focus on the wasted energy (240W or a dozen light bulbs!) to make the point:

* Assume a 48" LED[1] that uses 31W and suddenly you're only wasting 120W.

* His 80% loss figure is a holdover from his calculations about the phone -- cut this in half and you're at 60W of waste heat. (You should be able to achieve a nearly perfect perpendicular 'connection' between transmitter/receiver for a fixed TV).

So far, we're delivering 30W of power and wasting 60W as heat -- not ideal

* If you plan for a worst-case of 8-hrs straight of watching TV and plan on a battery backup, you could get away with delivering 10W to the TV and only wasting 20W as heat which is eminently reasonable.

The "physically impossible" claims are greatly overstated (for non-phone charging use cases).

[1] - https://www.energystar.gov/index.cfm?c=most_efficient.me_tvs...

Re:uBeam's insider story by ex employee? by URSpider94 on Wednesday May 11, 2016 @05:30AM (#11673804)
Your battery solution for the TV doesn't reduce the energy waste, it just spreads it out in time. It's now 20W wasted 24 hours a day instead of 60W for 8 hours a day. Same difference.

Until our houses are powered by 100% renewable energy, any technology that sacrifices more than half the input energy just so someone doesn't have to see an extension cord should be banned by law.

Re:uBeam's insider story by ex employee? by URSpider94 on Wednesday May 11, 2016 @05:52AM (#11673900)
Additionally -- how big is the room in which you want to mount your TV? The loss coefficient for ultrasound in air varies with frequency, temperature and humidity, but it's about 1dB/meter in this range, give or take. If you have a three meter wide room, and you have the transmitter and receiver mounted on opposite walls as you recommend, then you lose 3dB = HALF of the power through the air, and there's nothing you can do about it. To get to your 33% total efficiency number, all of the other losses, including conversion from DC to ultrasound and back and transducer losses at both ends, would have to amount to another 15% at most -- highly unlikely, though maybe not impossible -- though these are all well known numbers that someone skilled in the field could write down for you.

There's a big difference between 30% efficient now and 90% efficient in the future, and "it's never going to get any better than this"