Sustainability and Stratosolar

The amount of resources required to build renewable sources of energy is substantial. Comparing ground Solar PV and Stratosolar, there are several areas where Stratosolar requires far fewer resources including glass, steel, mass for storage, and land.

Glass: Conventional PV panels use glass for protection from corrosion, primarily from water. Stratosolar is situated where there is no water in any form, which simplifies the protection problem considerably. Stratosolar panels use no glass and weigh 2kg/m2 or less. Glass for conventional PV panels weighs about 10 kg/m2 and panel total weight approaches 20 kg/m2. 

Today’s PV production is about 200 GW/year and uses about 10 million tons of glass. Scaled up to 2 TW/year to meet a 2050 deadline for net zero CO2 would mean 100 million tons of glass per year. Today's annual glass production is about 200 million tons of which about 100 million tons is for flat glass. Glass production will need to expand rapidly as will the supply of sand and energy to make the glass. To reiterate, Stratosolar needs no glass.

Steel: today's PV uses steel for supporting structures, about the same weight as glass or about 100 million tons of steel per year. Stratosolar needs no steel. 

Energy storage: Ground based energy storage is mostly focused on battery and gravity energy storage technologies. Energy storage comes down to Wh/kg. Batteries range from about 200 Wh/kg for Lithium ion to less than 50 Wh/kg for various long duration storage technologies like flow batteries. Ground based gravity storage is about 0.3 Wh/kg. Stratosolar gravity storage is about 50 Wh/kg. If we estimate mass for storage based on daily storage of 10 hours for an annual addition of 1TW of electricity generation, or 10TWh/year  of storage, this results in the following annual demand.

Ground gravity storage: 40 billion tons of rock, dirt concrete or water.
Stratosolar gravity storage: 200 million tons of water.
Battery storage: 50 million tons to 200 million tons of chemicals.

Because it does not have long duration intermittency to deal with, the stratosolar mass is the complete solution whereas ground PV will need a combination of more storage, excess generation and long distance transmission, all of which add a need for more resources. 

Land: This is perhaps the most constraining resource for ground PV, mostly because of political constraints. Most estimates lowball the need by ignoring the increased demand from an all electric economy and the added demand from economic growth over 30 years. 
Ground PV needs relatively flat land and panels have to be spaced to limit shading. Averaged over all geographies PV generates about 10W of electricity per meter squared (10 W/m2). For 1 TW of new electricity generation this adds up to about 100,000 km2 of land per year, or a total of 3 million km2 over 30 years. The total land mass for the US, Europe and China is about 10 million km2 each. Much of this is mountains and hills or remote deserts. Each of these geographies would need to find flat land near urban areas approaching 1 million square km or build more than 100,000 km of new high voltage transmission lines to remote deserts. 
Stratosolar only directly affects a little land for the tethers and an assembly area. There would be an urban exclusion zone for the area beneath the array, which could be built over mountains or coastal waters. Arrays would be few, perhaps 100 for the US and 1,000 worldwide and would be positioned perhaps 200km from urban areas, minimizing the need for long distance transmission. 

Stratosolar drastically reduces the need for material resources and precious land and is far more sustainable than current intermittent energy sources.

By Edmund Kelly

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