Among the satellites on the Transporter 6 mission yesterday, an interesting payload stood out to me. CalTech launched a satellite to test out some ideas related to placing solar panels in space and beaming the energy back down to the power grid.
I'm not sure when I first ran across this idea, but I'll SWAG in the late 1990s. My reference point is that I was at a conference around '05 or '06 for Radio Frequency and Microwave design engineers that had a presentation on it and it was well known by then. We referred to it as “The Microwave Engineer's Full-Employment Act.” The questions swirl around how to implement such an idea. All that said, this article points out there are known possible ways to attempt it but no hard data on the best ways to proceed. Caltech is doing the experiments to try out different things.
Maybe we should start with why and a rough overview of these systems. Everyone that has used or experimented with solar panels knows their dirty little secret; as in they get dirty and their energy conversion drops. Not just dirt and dust, but bird droppings, insect droppings, insect nests or anything else that can coat them (around here: salt mist from the Atlantic). Clouds are no secret, I'd imagine everyone knows that on cloudy, rainy (or snowy) days, efficiency just goes into the toilet. Space has two significant advantages as a place to put panels: first off, there's loss of some power in the atmosphere; so the same size panel could harvest more energy in space than in a desert somewhere. Second, there's no dirt in space to degrade the panels. There's space junk that could damage panels, but that hasn't been a big problem with satellites so probably won't be with solar panels.
All the energy panels could capture in space won't do the power grid any good without being transmitted down to earth. Much thought has been given to this and it seems the likely method would be beaming it down by radio. Most likely would be by microwaves; the antennas will need to be specialized to have narrow beamwidth with (ideally) no power outside the antenna arrays themselves will receive the power, so that's considerably easier with microwaves than VHF or lower frequencies. The problem will be all about getting every last bit of efficiency out of the transmitter and microwaves up to around 30 GHz are pretty mature in terms of this sort of tech.
All of that out of the way, Caltech's approach is based on the simple economics that, at least for now (Starship has the potential to change this), the cost per pound to put stuff in orbit will be the hardest constraint.
The design limits weight partly by minimizing the support structure for the functional hardware, including the wiring. It does so by making its "panels" self-contained, having their own structural support and power transmitter. These individual panels will be assembled like tiles to form a larger surface but will operate independently.
That design dictates what the Caltech team needs to test: a lightweight power transmitter, a thin membrane that can be deployed in space, and different photovoltaic materials that can be placed on the flexible membrane. And that's exactly what's now in space on their test hardware.
The hardware includes a unit called MAPLE (Microwave Array for Power-transfer Low-orbit Experiment), a set of lightweight, flexible microwave transmitters that are capable of the precise phasing relationships needed to form the transmit antenna beam. In addition, MAPLE has two different test receivers on board so that the ability to beam the transmission in specific direction can be tested.
The photovoltaic array being carried will be four square meters, and something that big has to be folded up to fit in pretty much any launch vehicle. Their penchant for cute names for things for this mission calls this DOLCE.
DOLCE is the Deployable on-Orbit ultraLight Composite Experiment, and it will extend once in orbit to cover a surface area of roughly four square meters. It's meant to test the framework used to extend and support the solar array in space.
The DOLCE hardware in its compact, flight-ready form. Caltech/Momentus photo.
There's yet another module on the mission called ALBA, but Caltech didn't say what that stands for. It's important, though. It will be a collection of 22 different photovoltaic materials and will be used to determine which of these holds up well to being in space.
commonly quoted value
of solar power at the top of the atmosphere is 1367 W/m2 (watts per
square meter) and I believe this will be the case at whatever altitude the
satellite is flying, so if that's really a four square meter solar array,
it'll be getting 5468 Watts. Of those 22 different photovoltaic materials they're
testing we have to assume that the efficiency will vary.
Tests of DOLCE, which largely consist of determining whether it successfully unfolds, should happen relatively quickly, with the results captured by onboard video cameras and streamed back to Earth. By contrast, they expect that tests of the photovoltaic materials will require about six months in orbit to produce clear results.
For the microwave bands that they expect to use, the current regulatory limits
for exposure to radio radiation in the microwave bands we're talking about is 10 milliwatts per square cm; there are 10,000 sq.cm in one sq. meter, so 10 mW/cm2 times 10,000 converts
to 100 W/m2. A common design factor when putting up
solar power is that 30% of that incoming 1367 W/m2 is lost in the
atmosphere, leaving 957 W/m2 at the surface. I feel pretty certain that any designer putting together a system downloading millions or billions of watts to the surface will constrain their power density (W/m2) to meet whatever limit is allowed. It strikes me as noteworthy that the radio power density at the surface will be close to 1/10 of the power of sunlight. I'd be willing to bet you know more people afraid of being exposed to radio signals than sunlight.
" I'd be willing to bet you know more people afraid of being exposed to radio signals than sunlight."ReplyDelete
And yet, and yet... people have no problem standing next to an operating microwave oven. Which leaks.
We will see if this works!
They don't leak that much, and if it worries you, step back a few feet. Power drops off as the square of the distance, so the leakage drops pretty quickly.Delete
One of the principles of electromagnetics and physics is that energy in an EM wave is inversely proportional to wavelength. Called the De Broglie wavelength, it's why ultraviolet is more damaging to our skin than visible light, for example. Microwaves are millions of times longer wavelength than light. The conclusion is that sunlight would be more damaging than a microwave beam even if they were the same power density.Delete
Then there's the matter of leakage vs antenna patterns. Microwave ovens operate at 2450 MHz; the wavelength is around 4-1/2 inches (the longest visible light waves are around 25 millionths of an inch). What are the gaps in a closed door, 15 thousandths? 2450 isn't getting through that gap. Some diffraction? Sure.
Comparing the leakage around a microwave oven's door to the environment inside the oven is like comparing a little mist coming out of around the sides of a hose nozzle to the main stream coming out of it.
I remember reading about this in the early 1960's in Popular Science. Thought it was hare-brained at the time, and still do.....ReplyDelete
Using the microwave power downlink beam to warm people exposed to cold way up North
I seem to recall a number of stories of military personnel being injured after the original DEWS Line was constructed. I think it was MP/Guard folks. Seems someone noticed that if you stand in front of the antennas you felt warmer...Delete
Legends of how the heating effects of RF were discovered are interesting. There's a story that might be legend and might be true that an early radar researcher discovered the heating effects when a chocolate bar in his shirt pocket started melting. That would have been in the '50s, I think. Wikipedia says the first DEW line stations were in '57.Delete
I have a feeling heating was one of those things that had been observed before then but maybe not widely known.
In the late 1970s NASA and JPL presented papers on this. In 1977 I sat in a lecture by JPL on this very topic.ReplyDelete
Cue idiots like that horse-faced Scandinavian climate-twit teenager showing clips of the Death Star in 3, 2, ...ReplyDelete
Well a "Death Star" would be a useful tool for some parts of this world!Delete
Problem with a "Death Star" solution is it's binary nature. "Destroy planet? (Y/N/Q)" what we need is a more selective tool. Maybe a "Severe Respiratory Ailment Star"?Delete
How about if we had one we could aim at the World Economic Forum?Delete
We have other weapons that would do just nicely for that problem.Delete
The losses due to converting to microwave, focusing at longer wavelenths, collecting and reconverting to power must be considerable. Why not just giant magnifying mirrors beaming down shafts of light directly to solar arrays? Enough energy density and they will evaporate clouds in their way! Call it the "full employment for optical engineers act."ReplyDelete
L-5 Society, 1974,ReplyDelete
When I was a young engineer I worked for a creative engineer named Erv Nalos. One of his past projects was a Solar Power Satellite design.ReplyDelete
The first microwave ovens were the RADARranges- the warming effect was noticed, and commercialized.ReplyDelete