Harvesting the sun's energy with antennas (infrared)

Idaho National Laboratory ^ | Not indicated | Rachel Courtland

[Outland]

"You apparently haven’t thought very far because if you did you would know that an antenna does nothing but convert electromagnetic energy to electrical. The bigger the antenna, the bigger the voltage to the conductor."

I do know how antennas work.  I think you meant "current" instead of "voltage".

"They use arrays of radio dish antennas to search the galaxy because more antennas means more voltage And when you link MILLIONS of antennas together, you get a much larger voltage."

Again, I think you meant "current", not "voltage" or at least, that's what you should have meant.  In any case, all of those antennas that you refer to are coupled to amplifiers in order to make any meaningful use of the very weak signals.... even with all those antennas.

[Outland]

"I’ve heard tell of people living next to 50,000 watt antennas picking up radio signals on their dental work. Does that count?"

Entertaining perhaps, but it doesn't perform any real productive work.

Depending on how close you are to that 50,000 radio station, odds are that if one's dentures are receiving the signal, they are being radiated with more RF energy than energy from the Sun.

[Outland]

Admittedly, I should have better qualified my statement by relating it to relatively weak sources of energy. Rectennas can output significant amounts of power, but only as long as the source of that power has a high output to begin with (ie: satellite microwave power in the megawatts confined to a narrow radiation pattern or nearby high power microwave sources as in the NASA Microstrip Patch Rectenna article.

By comparison, the Sun's total EM output averages about 1.2kW/m2 at the earth's surface. Compare this with the average 4kW/cm2 of microwave energy used as a source for microwave rectennas with 56% efficiency.. At this rate, all of California would need to be covered in optical rectennas just to power a small part of LA (only 1% efficiency??). Maybe that's not a bad idea on second thought.

[Outland]

"did you even read the article???"

Yes, I did.  Like I said, it was filled with a lot of "maybe's", "might's", and "estimations".  Call me when one of them can do some real work like power your home.

[Outland]

"If every bit of research had to pan out then research would not be done and break throughs would never be made."

True, but one expects that some would have enough intelligence to know when some research projects aren't worth pursuing.

[Outland]

"makes you wonder if direct conversion to electricity is barking up the wrong tree. Leaving it as heat and light may be a better answer."

My thoughts exactly.  Build a solar oven and line it with thermocouples.  Much cheaper too.

The other thought that bothers me is that this idea falls into what I refer to as "California thinking".  Even if those optical rectennas were efficient, they aren't well suited for many areas that aren't graced with long periods of fair weather.  There isn't much useable direct or ambient infrared on a cold and cloudy day in the midwest.

"California thinking"...  like when heat pumps were all the rage until people in states where Winter is a reality discovered that they weren't very practical.  "California thinking"....  like expecting your Toyota Prius to run on battery power when you turn the heat on when it's -10 outside.

[southland]

btt

[junkman72]

obviously that will be too late for you to get in on the rising tide.

[martin_fierro]

Harvesting the sun's energy with antennas

woot.

[monkeyshine]

A rectenna? Hey, I’m all for energy independence but I’ve been told the sun doesn’t shine there... :-)

[Myrddin]

"California thinking"... like when heat pumps were all the rage until people in states where Winter is a reality discovered that they weren't very practical. "California thinking".... like expecting your Toyota Prius to run on battery power when you turn the heat on when it's -10 outside.

My house in Idaho was built with a heat pump (1986). The condenser unit outside is raised off the ground to deal with ice build-up. By the time I purchased the house, the prior owners decided to install a natural gas/forced air heater. The condenser simply serves as part of the air conditioner now. I own a 2nd 1947 vintage house. It was originally a coal burning house. It now has a natural gas furnace that is 92% efficient. The air intakes and exhaust are made of PVC.

I don't have a Prius...I have a Mercury Mariner Hybrid. It gets great mileage during mild Spring and Fall weather. The mileage goes to hell in the summer when you need the air conditioner to fend off +85F to +104F summer temperatures. The mileage goes to hell in winter too. The battery is less efficient in the cold and you have to run the internal combustion engine more to deal with temperatures from +40F down to -15F. My actual MPG varies between 32 MPG (mild) to 22 MPG (hot/cold). That's the real world. The leather seats with seat heat are much appreciated this time of year. Bun warmers.

Electric mode is really neat. It's a stealth golf cart. Totally silent. You can keep it in electric mode up to about 20 MPH when the engine wants to fire up.

I was promised a $3,000 tax credit when I signed the contract. The reality is that I'm only going to get $1202. The socialist $hithead$ that arranged for the tax credits also decided to play the "targeted" game. I make too much to get the whole credit. The red concentric circles are drawn on my back.

[pa_dweller]

I challenge you to describe one item that uses an antenna resonant to any part of the EM spectrum that can gather enough energy to perform actual work without being amplified with another external source of power.

Would passive RFID tags qualify?

[ichabod1]

It depends on what you’re really researching. If the research is “find a way to build a practically free energy source”, then this may not be promising. But if it’s “find original applications for nanoarrays”, then this could be useful in all sorts of ways.

I just find an attitude among some on here that says you’ll never find a cheap energy source, don’t even try. I don’t understand that mindset. One day we’re going to find a cheap/free/safe energy source, and that is going to revolutionize EVERYTHING, much like the discovery of the ability to refine petroleum into fuel did.

[ichabod1]

Yeah, I said to some of my researcher friends, what about the idea that there’s no right or wrong answer in an experiment, only information, and they started laughing. They said, you can’t get a grant saying you’re going to do something and then write a paper saying we thought such and such would happen but it didnt.

[BobS]

"All antennas work by resonance, the same self-reinforcing physical phenomenon that allows a high note to shatter glass."

Wrong. Resonance = standing waves. I scrapped a sum/delta waveguide feed last week because of resonance. It can't be tuned out. You short the feedhorn and look into the output using S11 on the network analyzer. Peaks and valleys = scrap.

[GOPJ]

with higher efficiency than conventional solar cells.

Yes, interesting.

[LongTimeMILurker]

Ray Walston. The first actor to play a space alien as a major character in a TV series.

Very underrated actor. More versatile than William Shatner, but perhaps without the Hollywood looks.

Too bad Mr. Hand couldn’t have put more sense in Sean Penn’s head.

[whd23]

I challenge you to describe one item that uses an antenna resonant to any part of the EM spectrum that can gather enough energy to perform actual work without being amplified with another external source of power.

H₂O molecules in a household microwave oven.

What's my prize?

[Blood of Tyrants]

My mistake. Current is converted to voltage through a resistance. One of the problems I see is handling the voltage and current needed to make it useful.

[Outland]

"Would passive RFID tags qualify?"

Good one. Yes it would, but that energy isn't doing very much productive work. It's akin to an air-powered crystal radio.