Very high altitude offers major solar advantages.  The stratosphere begins at 5 to 30 miles up, depending on where you look and the conditions at the moment.  The stratosphere is has about 3 times the solar radiation intensity than most ground level locations as much of the air absorption is avoided.

That’s a pretty good motivator to examine the possible ways to get up there.  Getting up there is also far cheaper than going into full orbit.  Then the surface area involved is vastly diminished.  Best of all the connection between the collector and the surface can be hard wired.  Makes lots of sense in the broad view.

Brian Wang at NextBigFuture
has been watching a firm called Stratosolar who is plotting to get a solar collector into the air.  With preliminary research and modeling Stratosolar has expanded the list of advantages.

The interesting advantages begin with the extent of the range.  Stratosolar now knows that effective very high altitude collection runs from 60º south to 60º north, covering almost all human habitated areas.  Next is more obvious, weather consideration show that an altitude of 20 kilometers or 12.4 miles (65,500’, 20K meters) would be optimal from 30º north and south of the equator up to the 60th parallels.

The next idea looking practical is scale.  Considering the comparatively calm stratosphere environment really large structures are viable. Perhaps up to 3.6 kilometers across – perhaps more if development continues. This is 1 GWe territory.

StratoSolar Photovoltaic Artists Rendering. Click image for the largest view.

That calm weather situation also offers full harvesting from dawn to dusk with collector steering used for optimal orientation to the sun.

The kick is there is no fuel cost.  Granted there will need to be hydrogen top offs to maintain buoyancy, and other physical requirements.  But the big, by far, cost is the recovery of the investment and what has to be paid to shadow the surface, if anything.

The prime motivation is with a 3-fold gain in incoming energy and full steering gathering nearly 100% of the dawn to dusk resource adding perhaps another 2-fold gain.  The total advantage might be 6 times the effectiveness of applied investment compared to the ground.  If you’ve looked at photovoltaic solar panels – would the price discounted 83% affect your thinking?  There would be little point in paving one’s roof with panels if one could buy a share in a stratospheric solar collector for 17 cents on the dollar.  Or . . . a solar panel budget invested in the stratosphere would buy the electricity and maybe pay for the house as well.

In Wang’s second post on Stratosolar Sander Olson talks with Stratosolar President Edmund Kelly.
The questions point out that the idea is only up to the proposal stage.  The firm may be getting close to looking for development funds.  These would be lab and prototype projects as the basics are on the shelf now.  It’s getting to scale from a few feet on a roof to maybe three miles that’s the research task.  Yet the early calculations show there wouldn’t be “unobtainium” or other extreme materials required.  Its possible, it isn’t easy and the first large scale one is going to cost a fortune.

StratoSolar Concentrated Solar Power Artists Rendering. Click image for the largest view.

Stratosolar is looking at two paths, straight with photovoltaic mounted and buoyed up to altitude and “Concentrated Solar Power” (CSP), a solution path that uses mirroring the light and transporting it down via light pipes to the surface for harvesting energy.  CSP is intriguing as the buoyed weight is reduced.  The projected prices for matured technology of CSP power at the tether anchor could be at or below $0.01 per kWh.

StratoSolar Image Imagines a Collector Viewed From San Francisco. Click image for the largest view.

CSP offers another major plus.  The infrared comes down the light pipe as well.  That makes a CSP a combined thermal and photovoltaic system.  On the other hand the CSP idea is just that – an idea, yet the potential is huge.  Estimates suggest it would only take 30 large-scale collectors to power all of California – and they could be up in a decade.

Just a reminder – the infrared coming down is thermal energy – so far about the cheapest energy to store for brief periods.  Overnight power isn’t going to be such a problem and the cost for thermal compared to battery electron storage is far less expensive.  During the Olson interview a tenth of a cent per kWh was suggested.  This is not a lithium battery pack kind of price.

Assuming that Stratosolar’s basic assumptions are in practical range the prospects could be quite good.  A quick look at the company website – which needs an upgrade – implies they have intellectual resources.  It’s said that some patent applications are in processing suggesting that from a basic standpoint the technology can survive a patent examiners review.

The group of volunteers making Stratosolar go is going to need some high-powered engineering skills, a bunch of money and testing, testing, testing, and more testing.  But there isn’t anything obvious suggesting its impossible.

There are some technologies coming that might help.  We’ll be looking at those soon.  In the meantime this is a concept worthy of close watching.


6 Comments so far

  1. Mitch on July 1, 2011 3:41 AM

    Yes! six times my electric bill would cover the house payment, taxes, insurance with some to spare. Where is the venture capital, NASA and the DOE?

  2. MattMusson on July 1, 2011 7:17 AM

    For years, scientists have been suggesting that orbital solar collectors were the way to go. But, the getting out of the gravity well are prohibitive and will be for the foreseeable future.

    With the correct engineering and materials, this project seems attainable. It’s worth investing in some serious study.

  3. JohnMc on July 1, 2011 8:56 AM

    Novel as it is I do have one question. What the hell happens to the whole damn thing when a tornado or hurricane rolls thru town eh?

  4. Keith Henson on July 7, 2011 11:23 AM

    Matt, as someone who has spent serious effort on StratoSolar as well as space based solar power, it is now foreseeable that are low cost ways to get out of the gravity well.

    See here for a long version of how:

    It is still expensive to set up the transport pipeline to space even if the cost gets down to $100/kg.

    It is a much smaller program to build a few StratoSolar power plants (we think).

    Re John’s question, even if you don’t build them in Tornado Alley, wind is the biggest problem StratoSolar designs face. Low altitude winds, even hurricanes, are not a serious problem for the PV version, but they are for the concentrated thermal design, in the range of 50 million newtons on the light pipe, even with rotating aerodynamic shrouds. If you don’t want it to blow over more than 15 deg, then the excess buoyancy need to be 4 times that much. This takes thousands of tons of hydrogen.

    Even so, the cost of the common materials needed (steel wire, plastic, aluminum, fire brick and hydrogen) comes in well below $1 B/GW even counting the turbines.

    I have not run a full analysis of the payback time, but the hydrogen is a substantial part of it. 5,000 tons of hydrogen at 50 MWh/ton is 250 GWh. I.e., it would take a bit over ten days of operation to pay back the energy in the hydrogen.

    We took this as far as we could with a small team of retired engineers and outlined what it would take. Next step is a few dozen engineers and substantial support staff for a couple of years and then some serious prototypes.

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