Executive Summary
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 Ring-Mounted 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 over one thousand times as expensive as Terrestrial Solar. Some reasons for this are that solar panels heat up more (making them less efficient) and degrade faster in the space environment, 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. In the words of Dr. Pete Worden, former Director of NASA’s Ames Research Center, “There is not a plausible option in the foreseeable future for a system that uses Space-Based solar [to power Earth’s electricity grids] to make a business case.”
Ring-Mounted Solar outperforms terrestrial solar by placing the solar panels above the weather a high-altitude platform called a Tethered Ring. Energy is conducted down to the Earth over vertical power transmission lines. 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 technology readiness level.
Introduction
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 for 25 years period): With the increasingly widespread implementation of sustainable energy sources, costs for sustainability 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.
With 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.
Terrestrial Solar Cost Analysis
%
B USD
USD/kWh
Space-Based Solar Cost Analysis
%
B USD
USD/kWh
Ring-Based Solar Cost Analysis
%
B USD
USD/kWh
This project is available on our Github. You can report a bug, or 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.
For general discussion, questions, or constructive criticism, we welcome your comments below!
There are many additional sources of information.
Space-Based Solar – This topic was debated at an Aerospace Technical Working Group (ATWG) meeting in December 2008 between Pete Worden and the late Mark Hopkins where Peter Worden argued there was no business case for Space Solar Power. Peter Worden, Director of NASA’s Ames Research Center, shares his point of view here: The Space Show at ~3:30. Mark Hopkins responds with his perspective on the debate here: The Space Show at ~101:00. Robert Zubrin shares his thoughts on the topic here: Robert Zubrin on the Case for Space. Fraser Cain shares his perspective and some recent updates here. Sabine Hossenfelder published an entire episode on her YouTube channel about Space-Based Solar. Joe Scott did a great episode on the topic called “Could Space-Based Solar Save The World“.
Ring-Mounted Solar – Philip Swan discussed this technology at the International Space Development Conference in 2022 and 2023, and at the From Earth to Space Conference in 2022. He also discussed it at the IEEE Aerospace Conference in 2023, and during a talk he gave at an event in Seattle, which you can see on YouTube here.
Most Voted
11 months ago
test
11 months ago
Very Cool!