StratoSolar compared with solar power from the desert and space.

Most approaches to improving PV focus on reducing the cost and increasing the efficiency. StratoSolar instead, is based on exploiting a more solar rich environment. A comparison with two other approaches that try to exploit more solar rich environments may better help in understanding StratoSolar. The two other approaches are to exploit the sunshine in deserts and sunshine in outer space. Both have been investigated extensively and are sufficiently plausible to have received significant funding. The most notable desert project is DESERTEC, which aims to exploit sunshine in North Africa and transmit the electricity to Europe. Space based solar power (SBSP) was researched heavily by the DOE in the seventies, and revisited by NASA in the late nineties.  A SBSP start-up company called Solaren obtained a PPA in 2012  from PG&E in California to deliver power in 2016.

In the DESERTEC case, the average PV utilization in North Africa is about 25% versus the average of less than 15% for the whole of Europe. The benefit is less than a factor of two overall. Offset against the benefit is the cost of High Voltage(HV) transmission over an average distance of 2000km. Given that this transmission is tied to the generation, its relatively easy to calculate the transmission cost. At today's PV costs HV transmission about matches the cost of generation. Transmission cost should reduce when HVDC transmission develops, but PV will also reduce in cost, so the ratio may not change much.  DESERTEC wants to exploit Concentrated Solar Power(CSP) but CSP prices are high and not falling, so that may not work out.

For Space based power, the advantage is constant almost 24/7/365 power. Measured using the ground based PV metrics, SBSP has a utilization of 130%, due to the higher intensity sunshine in space. Offset against this is the expected 50% loss in microwave conversion, transmission and receiving which could be regarded as reducing utilization to 65%.  PV efficiency would be higher at a colder operating temperature. PV panel lifetimes in space are short due to damage from cosmic rays. There would be advantages to a CSP solution in space, but the complexity is significantly higher than PV. The big problem with SBSP is the very high cost of launching the material into space, and then the assembly and maintenance costs in space. 

StratoSolar can be viewed as an intermediate point between desert power and space power.  Because of night-time interruption, its average utilization is around 40%, and can exceed 50% with one axis tracking. This is higher than the desert, but lower than space. Its transmission costs are low, 20km straight down versus 2000km from the desert or 35,786km via microwaves from GEO. Its equivalent of launch costs is gas bags full of Hydrogen which are very low cost. In the Stratosphere there is no weather or dust, very nearly like outer space, but there is still enough atmosphere to protect PV from cosmic rays, so without ground based weathering degradation or space based degradation, panels may have very long lives, exceeding thirty years. StratoSolar, unlike the desert, does not need water for washing or cooling, which adds to its major benefit over the desert in that it is situated near the demand for energy with few restrictions on where it can be situated.

So when viewed against deserts and space, both of which have received considerable attention, despite significant problems, perhaps StratoSolar can be seen as a possible contender from science fact, and not something from science fiction.
By Edmund Kelly