http://selfdestructivebastards.blogspot.com/2009/09/space-based-solar-power.html

I am an electrical engineer and work in microwave communications. One thing I can not understand is how the microwave beam would get through the atmosphere? (what if it is cloudy or there is a lightning storm). I have had huge attenuation on microwave beams that are only 10 to 20 km apart because of weather. I under stand that you would be in a higher freq range to transport power but that would just lead more attenuation and the signal would get so distorted that it would not be useable.
I don’t want to sound argumentative but when ever I hear about space based solar I always think of it as junk science due to the problem of getting through the atmosphere, what am I missing?

You can tell me all about smart people, but 21 dollars per Watt is not competitive even @ 100% capacity factor.

The problem with solar is cost. Approaches that increase the cost and risk are not helping.

I just wish all the smart people would get together on solving energy and climateproblems in my lifetime.

Can you send me that paper you discussed?

Thanks.

Tyler

Thanks for the ausra study link; I’ll give it a look. Personally, I’m primarily a spacecraft engineer, and while I know probably more than most people about how to design solar power satellites, I’m very much still in learning mode when it comes to the details of how the electrical power utility business works. That being said, others who’ve been in this field for many years longer than me have done numerous comparisons of the economics of space-based solar power against those of pretty much every other available large-scale power source, and have certainly taken peak versus baseload power into account; their analyses produce pretty attractive-looking cost estimates (and many of these are *very* impressively smart and accomplished people!).

Too bad you weren’t at the symposium this week. You have a couple of misconceptions about space-based solar power (ones which are are quite common, we’ve found), and you would have found numerous experts there who would have been able to address them. I’ll have ago here:

You wrote, “Space solar won’t be 24/7 power, ie no 100% capacity factor, due to the shadowing effect of the earth problem. 50% would be the theoretical maximum above the equator.” If the Earth’s equatorial plane were in the same plane in which the Earth orbits around the Sun (the ecliptic plane), then what you wrote would be true. However, the Earth’s equator is inclined at 23.5 degrees to the ecliptic plane, and so a satellite in an equatorial orbit stays out of Earth’s shadow for most of the year. It’s true that an equatorial-orbit solar power satellite would (as do all geostationary communications satellites) experience eclipses twice per year, for a few weeks around the spring and fall equinoxes. These eclipses are fairly brief—at worst 72 minutes long, once per day during those periods. Fortunately these are at local midnight, when power demand is near its lowest point of the day.

While it’s a bit hard to visualize at first, geostationary solar power satellites actually *can* provide power 24/7, for most of the year. This greatly offsets the cost differential between space-based solar power and terrestrial solar power, since the latter has such poor availability—about 10% of the availability of power in space.

This also means that space-based solar power does *not* require a long-distance grid to deliver power to its customers; indeed, one of its big advantages is that the receiving antennas can can be built very close to the customers, and power beamed from space almost to their doorstep (i.e., within a few 10′s of kms).

You wrote, “There is also the inherent problem of weapons implications, since the microwave intensity beamed towards earth is big enough to fry your brain in mere minutes. This risk is not to be underestimated or waved at. Frankly, space solar scares the shit out of me for this exact reason.” This one is even harder to develop an understanding of, without first studying electromagnetic theory a bit, so I’m not surprised at how common this misconception is. Fortunately, a microwave power transmission system of the type we’re discussing is *physically incapable* of being made into the sort of “death ray” that you’re scared of.

The physics of the situation is that over long distances (such as the distance from geostationary orbit to the Earth’s surface), the width of a radio beam (or a light beam) expands as it travels from its transmitter. This means that by the time a radio beam reaches the Earth’s surface, it is much less intense than it was up at the transmitter antenna. By “less intense,” I mean that the amount of power flowing through each square meter of cross section of the beam is smaller down at ground level, than it is high up in space. For a given size of transmitter antenna up in space, it is physically impossible to focus a radio beam on the ground to smaller than a certain size. For a typical solar power satellite design, the transmitter antenna would be 1 km ni diameter, and at an altitude of 36,000 km the spot size on the ground would be about 10 km in diameter. For a given amount of power being pumped into the beam up at the satellite, then, you can figure out the absolute maximum power density that the beam will have at ground level. If the satellite collects (say) 1 GW of electrical power, and sends all of that out the transmit antenna as RF power, then the average power density am when it reaches the ground will be 1 GW divided by the beam’s area of pi*10*10/4 = 78.5 square km, which is 12 Watts per square meter—about 2% of the intensity of sunlight on a bright day in the desert, and about equal to Health Canada’s (pretty conservative) limit for microwave exposure from cell-phones and the like. (The intensity will be a *bit* higher than average at the center of the beam, still a perfectly safe level, but to meet Health Canada regulations that’d be fenced off to keep the general public away from that area.) So, unless you’re one of those people who thinks that their cell-phone is emitting death-rays (in which case I can’t help you , you’ll see that the microwave beam from a solar power satellite is at a very safe intensity level.

You could take my word for it when I say that it’s not possible to focus the beam more than that, for a given transmitter size and distance. If you’d like to check up on that, I’d be happy to point you towards relevant electrical engineering textbooks and/or technical papers (which is where this sort of specialized knowledge is to be found).

Hope this helps…

- Kieran A. Carroll, Ph.D.
VP Technology
SPACE Canada

http://www.ausra.com/pdfs/ausra_usgridsupply.pdf

Japan doesn’t have such a good solar resource, though it isn’t nearly bad enough to justifiy the abominable economics of space solar. Don’t give me the “it will get cheaper in time” argument, that applies to land based solar and storage as well. Even at today’s CSP, PV and storage cost of thermal storage and underground pumped hydro land based solar is way cheaper than 21 dollars per Watt.

The weapons implications are even more severe than the economics, and is reason enough to abandon the idea of space solar power altogether. I’m not usually immediately opposed to new concepts but space based solar is just not a good idea.

The first problem is raw dollar cost. 21 billon per GWe, that’s 21 dollars per Watt. Lowest cost land based solar farms (big thin film free field powerplants) are around 3 dollars a Watt last I checked and it is declining fairly rapidly. Space solar won’t be 24/7 power, ie no 100% capacity factor, due to the shadowing effect of the earth problem. 50% would be the theoretical maximum above the equator. The system would have to be situated above the poles to get 24/7 power to a fixed location on the earth, which makes transmission to non-polar countries rather difficult. So basically a big HVDC grid has to be built as well. I think the economics of high resource solar with HVDC to low solar resource areas is actually a lot better and less risky in terms of cost.

There is also the inherent problem of weapons implications, since the microwave intensity beamed towards earth is big enough to fry your brain in mere minutes. This risk is not to be underestimated or waved at. Frankly, space solar scares the shit out of me for this exact reason.

Bottom line, IMHO this is 21 billion better spent elsewhere (land based renewables, energy efficiency, and electric transport, to name just a few).

The Symposium is really 2 conferences in one.

Day 1 is an overview of high-level issues related to space based solar power. A main objective of Day 1 is to be a “summit meeting” between leaders of the global climate change community, and of the space based solar power technical community. It will begin with a talk on the global warming issue (by Prof. Richard Peltier of the University of Toronto, a principal author of recent Intergovernmental Panel on Climate Change reports), to remind us of the problem to be solved. Bryan Erb and John Mankins, both of them ex-NASA solar power satellite engineering experts (Bryan’s experience includes being one of the top-level Canadian designers and engineering managers for the Apollo lunar spacecraft in the 1960s), will then provide an overview of what space based solar power system designs look like and how they would work, and critically analyze the pros and cons of this technology versus other large-scale global power supply options. Following this will be a live demo of a microwave power beaming system operating a rover vehicle, then sessions exploring space policy, media, and university/industry collaboration angles.

Days 2 and 3 are a technical conference, where most of the world’s leading space based solar power researchers will gather to present papers on their recent research. (For example, I’ll be giving a paper on the possibility of using microwave power transmission to convey large-scale power from Labrador to Newfoundland.)

From the perspective of issues of interest to the general public, Day 1 is the best day of the Symposium to attend. (Not to detract from the importance of the technical conference! However, the topics discussed there will be more specialized.) Also, I believe that most people attending Days 2 and 3 will also be there on Day 1, whereas some of the Day 1 attendees will likely not stay for the technical conference, so there will be more people to meet and talk to on Day 1.

I’m looking forward to seeing you there! I’ll be there all 3 days, and will be very happy to chat with you.

- Kieran

Tyler