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.
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 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.
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.