[tt4442 (OP)]

Just to note - I'm not knowledgeable in physics, so do excuse me.

I'd like to know if the following is possible.

Let's say I have an 'emitter' (could be a laser/radio/visible light, whatever is established), ideally something relatively safe, as to be used in public spaces.

I then have a 'receiver', this could be between 10x10xm to 1x1 meter in diameter, and this is approximately 5 meters away from the emitter.

1. What technologies/electromagnetic spectrum/other form of energy could be used to do this with the maximum of both:
- public safety
- maximum wattage
- lowest wasted energy

2. And with that, what would the wattage be?

*This is not for data transfer, it is for power transfer*

Thanks.

[RD]

Let's say I have an 'emitter' (could be a .../.../visible light, whatever is established), ideally something relatively safe, as to be used in public spaces.

If you're trying to transfer data, (rather than power), see LiFi ... https://en.wikipedia.org/wiki/Li-Fi

[evan_au]

The simplest solution is to use WiFi.
- It can manage a range of 5m, if the transmitter and receiver have a direct line of sight, and preferably elevated above people's heads.
- There are a huge range of devices available, fairly cheaply, with standardised computer interfaces.
- It is quite safe.

[tt4442 (OP)]

Thanks for the replies.

Just to clarify - this is specifically for power, not data transmission.

[RD]

The existing indoor lighting is going to be the about the maximum acceptable level ,
 a few tens of Watts per square meter , only enough to power a calculator or clock.

The amount of light/radio power to, say, boil a kettle, would blind/cook people who got between the "emitter" & "receiver".

https://en.wikipedia.org/wiki/Wireless_power_transfer

[tt4442 (OP)]

The existing indoor lighting is going to be the about the maximum acceptable level ,
 a few tens of Watts per square meter , only enough to power a calculator or clock.

The amount of light/radio power to, say, boil a kettle, would blind/cook people who got between the "emitter" & "receiver".

I'm not interested in power that would boil a kettle - more rather 50 watts is good.

Is there technology for this not in the human visible spectrum? Not critical, just asking.

Thanks.

[chris]

I was chatting to someone earlier this week about the idea of collecting solar energy in space, where incident radiation - unattenuated by the atmosphere - is much stronger, and then "beaming" the energy down to Earth in some format for harvest and re-deployment.

I am sure that someone proposed a microwave system for doing this. Was such an approach ever tested, or is this a totally unfeasible idea?

[RD]

... the idea of collecting solar energy in space ... and then "beaming" the energy down to Earth ...  microwave system for doing this.
Was such an approach ever tested, or is this a totally unfeasible idea?

Still speculative ... https://en.wikipedia.org/wiki/Space-based_solar_power#In_the_21st_century

If for safety's sake, the microwave energy-levels used were limited so they were comparable with existing background levels, why bother the enormous-expense of launching satellites, just harvest the solar microwave energy, (assuming that was cost-effective).

Visible solar is far more plentiful than radio from the sun ...


https://www.windows2universe.org/sun/spectrum/multispectral_sun_overview.html

[evan_au]

A number of space elevator competitions have been run over multiple years.
I understand they have worked with microwaves and lasers as the power source for the climbers.

Start at 30 seconds:

See: https://en.wikipedia.org/wiki/Space_elevator_competitions

[syhprum]

Electromagnetic radiation from the Sun in the 0.5 micron range is widely used and forms as much as 20% of the electricity in some countries this is the frequency range that is most abundant beneath the atmosphere and there is little point trying to utilise other frequencies

[chiralSPO]

A few points and questions:

Why transmit electromagnetic energy energy over a distance of 5 m? Wires are an excellent way to transmit very high powers (wattages) efficiently and safely over distances large(ish) and small.

People will absorb a significant percentage of the energy for EM radiation through the UV, visible, and much of the IR range. Some microwave frequencies will also be absorbed strongly, while I understand that most radio waves will not interact with us at all. Higher frequencies can be focused onto smaller areas more easily than lower frequencies, so could potentially be safer in that the beam would take up less space, but would also be more problematic if encountered...

Efficiency will depend on all sorts of factors, but is going to be (much) less than 100%. The atmosphere itself absorbs EM, especially in the UV, and IR (it's no coincidence that the visible part of the spectrum is what the atmosphere is transparent to http://gsp.humboldt.edu/OLM/Courses/GSP_216_Online/lesson2-1/atmosphere.html ) Then there is the issue of how easily the energy can be emitted, and how easily it can be converted back into usable energy.