Power can be produced sustainably and reliably by coupling solar power with energy storage, but the combined cost is currently high enough to discourage rapid market-forces-driven adoption. Two megaproject-scale advanced concepts exist that aim to be more economical: Space-Based Solar and Near-Space Solar.
Space-Based Solar (SBS), located in geosynchronous orbit, has the best access to the Sun and needs minimal energy storage. Given the current state-of-the art, SBS is hundreds of times more expensive that Terrestrial Solar because: solar panels are less efficient and degrade faster in space, the power loss in the microwave transmission link is significant, space launch requirements lead to high capital costs and environmental impact, and the approach of beaming power to the Earth has significant environmental and regulatory challenges.
Near-Space Solar outperforms terrestrial solar by placing the solar panels above the weather and in a cool environment. Energy is conducted down to the Earth over vertical power transmission lines. It relies on the creation of a large high-altitude platform called a Tethered Ring. A Tethered Ring is a novel form of an inertially supported active structure that is architected to achieve low operating costs. This platform supports the panels, stores energy kinetically, and transports the energy over great distances with little energy loss. Its underlying technology (a magnetically levitated ring orbiting within a circular evacuated pipeline) is currently at a low technical readiness level.
While the levelized cost of photovoltaic solar power had bolted from last place to first place over the last 14 years (see Figure 1, orange line), solar power is an intermittent technology due to the day-night cycle, the seasons, and the weather. Energy storage is needed to time-shift some of the energy generated when the sun is shining to times when it is not (a process known as “Intermittency Firming”). The energy storage requirement adds considerably to the overall cost. Therefore, it is still more profitable to continue operating an existing fossil-fuel powered plant than it is to shut it down and replace it with a solar energy generation plus storage system.
Figure 1: Average unsubsidized levelized cost of energy (at 12% discount rate at 25 years period): With increasingly widespread implementation of sustainable energy sources, costs for sustainable have declined, most notably for energy generated by solar panels.
There are two megaproject-scale proposals that aim to change the economics so that market forces can accelerate our transition to a sustainable economy. The first is space-based solar power. This concept places the solar panels on a giant satellite in geosynchronous orbit so that they can harvest the sun’s energy almost 24/7. This drastically reduces the amount of energy storage that is needed for firming intermittency. The power harvested in space is then transmitted down to the earth by using a microwave beam and fed into the grid.
The second is near-space solar power. This concept places the solar panels in the stratosphere on an actively supported structure called a Tethered Ring. In the stratosphere the panels have better access to the sun’s energy than they do on the ground. They will last longer and operate with greater efficiency thanks to the cool air in the stratosphere. The energy they generate is stored and transported within the tethered ring’s mass stream (a continuous moving ring), then converted back into electricity and transmitted down to the ground by using vertical transmission lines.
In any advanced concept, the devil is always in the details. To that end, we critically analyze and compare the end-to-end efficiencies of terrestrial solar, space-based solar, and near-space solar. The results of the efficiency analysis are used to determine the levelized cost of 24/7 reliable energy generated with each approach. There are several inputs into the analysis that are listed in the tables below. State-of-the-art values are used by default. Because technology is continually evolving, we’ve made it possible for the reader to edit the values in the “aspirational value” column and observe how changing the assumptions will affect the results of the analysis. Users are also encouraged to comment below. We’d love to hear your thoughts and suggestions on how we can make improvements.
This project is available on Github. You can report a bug, request a feature there. Users with programming experience may wish to branch the project, edit the code, and submit a pull request to incorporate improvements into the main project.
- Large Satellite in GEO Orbit,
- Photovoltaic,
- Microwave Power Transmission (MPT),
- The panels track the sun while the transmitter tracks the Earth,
- Power Link is greater than 5GW,
- The system is engineered to deliver 24/7/365 reliable power,
- Intermittency is firmed,
- Launched by Starship to GEO, with refills in LEO (i.e. fully reusable launch hardware),
- No Concentrators (Mirrors),
- Panels radiate their excess heat into space,
- Other assumptions and formulas can be found in the tables and by examining the code.
- Panels are mounted on actuators and oriented to optimize the trade-off between facing sun and facing the wind stream,
- Panels are air cooled,
- All of the generated energy is stored in the Tethered Ring’s moving rings,
- Power is recovered from the moving rings and transmitted to the surface over transmission lines,
- Other assumptions and formulas can be found in the tables and by examining the code.