Concept: Space-Based Solar Power | RevModo

space-based-power

For many people, solar power seems to be the single most promising technology for escaping the chain of fossil fuels, and why not? There is nothing to mine, no exhaust or fumes, and concerns like changing the surface albedo (reflectivity) and covering the landscape can be dealt with in creative ways to avoid making mankind much more of a nuisance than it already is. Despite all of this, it is not without problems.

For one thing, the places with the best conditions for solar tend to be remote and/or incredibly inhospitable to life. In those places where the sun is plentiful, a great deal of the power generated will wind up going to air conditioning. Your typical American town has its fair share of cloudy days, and if you are anywhere near the northern part of the country, you can count on winters to put a dent in your solar efficiency as well. Then there is the fact that modern solar cells reflect a significant amount of light, and collect dust, which impedes absorption.

Some people have an idea of how to circumvent all of this; shoot solar cells up to where there are no seasons, the sun never sets, and the dust falls into a giant watery vacuum cleaner located a few hundred miles below. Believe it or not, it’s not a new idea; Isaac Asimov wrote a short story in 1941 where solar power was collected in space and beamed down to planets via microwave. Here’ the weird part; his idea is exactly what scientists now think would be the most plausible method. His ideas were later expanded upon by scientist Peter Glaser in 1968, who detailed a basic design for creating a solar satellite, which was essentially an engineer’s vision of Asimov’s idea and form the basis for most modern concepts.

The idea is in concept fairly simple; build a huge solar array, send it up into space and face it toward the sun, then transmit the collected energy via microwave to a collection center on Earth. The microwaves would not be the same intensity that you find in an oven so the threat (or promise, depending on your viewpoint) of grilled game birds falling from the sky is practically non-existent. The collecting device would look similar to a radio telescope, only made out of a mesh, so in all likelihood, it would not have a terrible impact on the natural world around and under it.

The collectors (called “rectennas,” I swear I’m not making that up) would be set well above ground level, reducing the likelihood that any humans would be exposed to the downpour of radiation, although the amount generated is intended to be so diffuse that it would be less radiation than you receive from a cell phone. Aircraft are also not in danger; the beam would simply bounce off like the rest of the stellar radiation that hits them when they are flying high in the air.

Photo Credit: Space Studies Institute

The satellite could sit far away in a geosynchronous orbit, always hovering over the same spot, shooting down converted sunlight to power towns during all hours; if the satellite were far enough away, the amount of intervening night time could be kept down to a couple of hours. Or, as some have suggested, a constellation of satellites could store power when on the day side of the planet and fire off bursts of energy to the station on the night side, keeping a continuous stream of power.

Sounds pretty great so far, right? Well, it turns out that even though it is plausible with modern technology, it may still be a long way off. First off, modern prices for space payloads are… astronomical (ugh… I’m really sorry about that…). Prices range from $1,000 to $3,000 per pound to send something into orbit, and a massive solar array is going to weigh more than a human, which averages $100k per launch.

Then there is this article  where a man much smarter than myself (Tom Murphy, Associate Professor in the physics department at USCD) goes through and does the math for what space based solar power would entail given the laws of physics and modern limitations of technology. It is less than optimistic. One major hurdle is the same major hurdle faced by the current state of solar power; how to store all of that power so it can be used when the external source is unavailable? There is also the issue of sending all of that energy through the atmosphere. The air itself absorbs a decent amount of energy, and reflects still more away, despite it largely being transparent to microwaves.

There is also the (currently) far fetched idea of using a space elevator to transport up the pieces. The major problem with that idea is that the core of the whole concept relies on technology that is not currently possible. In case you are unfamiliar with the concept, the space elevator is a very similar idea to a satellite in geosynchronous orbit, that is to say that we have something up in the sky that hovers more or less over the same spot  all the time. Except the satellite just happens to be orbiting at the right distance and speed to be in the “same place” relative to a point on the Earth at all times.

The space elevator would actually be attached to the Earth, using the station at the end as a pendulum and the shaft would be a tether, and the whole building acts much like holding the string of a yoyo and spinning quickly. This way, you could not only just lift the supplies into space without having to place them on a controlled bomb, you could theoretically place the collector on the pendulum and send the energy down through the shaft. Of course, all of this hinges on being able to produce commercially viable carbon nanotubes that can be build hundreds of miles long. Not this week.

But it’s not all gloom and doom for the solar satellite of the future; NASA has been taking the idea seriously, and is working on starting up a project to test it out right now. Likewise, In February, at the ARPA-E Energy Innovation Summit, space based solar was suggested as a technology with real potential in the coming decades. It is gaining popularity because while the start up costs are high, the payback is potentially much greater. When you think about it, how much money was originally being generated by GPS? It was used mostly by the military, and a great deal of the equipment using it was flying through windows and levelling buildings. Now it is big business, with cars and mobile devices including it standard now. Solar power is immediately useful in a commercial form.

The satellites themselves are a bit of a paradox; they will need to have huge surface areas to collect as much light as possible, but at the same time the materials necessary to make them are readily available. With modern photovoltaics, they use silicon, which is one of the most abundant elements in the Earth’s crust (second only to oxygen). The solar cells themselves don’t even have to be very large; A single panel could be used with an array of mirrors to focus the sunlight on it like Earth-based focus arrays.

In fact, the mirrored array is what NASA is banking on working the best. They have concept designs of a flower-shaped reflector that would concentrate sunlight on a solar collector that would be built into the microwave transmitter. Since they would not be using a single massive mirror, but an interferometer of sorts, it could be built piecemeal by piggybacking on other space missions and would be far easier to repair, It doesn’t matter if one of the mirrors is hit by space debris because it has an army of other mirrors behind it to take up the slack until it can be replaced.

This is not to say that other methods have not been suggested. There have been ideas of sending up a single massive mirror, likely made of mylar, that would act as the focuser/collector, or full arrays of solar cells, and not being a scientist I can only guess at what might be the most efficient. However, I also think NASA probably knows better than I do, so I will assume that the mirror array is the best bet so far.

NASA isn’t the only group setting hopes on solving our energy needs through space based solar; there are a number of startups that have an eye on orbital solar collectors, Of which Solaren, Space Energy and PowerSat are currently the most prominent. Solaren has already signed a contract with PG&E to provide space based solar power by 2016 to California. They anticipate it being slightly more expensive, in the beginning anyway, than California’s current power cost, until the technology is more refined. They plan on using their concept satellite to provide a continuous stream of 200 megawatts for at least 15 years; with this strategy, they have positioned themselves to be the first company to produce space based solar power.

Space Energy was founded by a group of business people, and as a result seem to have a more cooperative idea behind their startup; they have an $80 million grant from China and have given presentations to Japan. They appear to be interested in creating a more international company, which has some obvious advantages. (Not the least of which is the huge pile of money they acquired)

PowerSat is different from the other two in that it has a large number of scientists working for them, and they have not been trying to launch any satellites or sign contracts yet. Instead, they have focused on designing and patenting concepts that would outline an overall architecture of how the system would work, as well as some surprisingly innovative ideas, like a constellation of smaller collectors working together and an ion-thrust system to maneuver the satellites using nothing but the solar power collected to achieve the feat.

Photo Credit: UCAR

They are also dreaming up ways to make the receiving system more efficient than other designs, all in hopes that once they enter the race, they will quickly dominate it through more advanced, efficient technologies.

Solaren is, to date, the most ambitious with their due date set only four years from now. The others are looking for about a decade before things are mature enough to move forward. If they are able to achieve what they are setting out to accomplish, we could be a decade away from a revolution in powering everything from our homes to our vehicles, with inexpensive energy shot down from space, twenty four hours a day, regardless of weather. Not bad for an eighty one year old idea.

Source:  http://revmodo.com/2012/08/24/space-based-solar-power-could-it-work-and-would-it-be-worth-it/

 

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