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"
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...