Pushing Renewables Higher
The push to decarbonize and electrify our energy systems is currently relying on renewables, especially wind and solar. Geothermal energy and nuclear power might help as well.
Unfortunately, each of these solutions suffers from some limitations:
When it comes to solar power, the intermittency seems an unavoidable feature, with Earth at night half of the time. To compound this issue, cloud coverage can drastically reduce the power output for weeks or even months in some regions of the world, and that is before discussing the problems caused by dust or snow.
What if to avoid nighttime and climatic issues, we were to put our solar power base into space? How would this work? And is there another way to power Earth”s civilizations from space?
Space-Based Solar Power
The first key feature of space-based solar is that as the power satellites orbit Earth, they can be put in an orbit that is never in Earth’s shadow, producing 24/7. Not only does this double production, but it also removes the requirement for batteries of ground-based solar energy plants.
Combined with the absence of reduced production in winter or due to clouds, intermittent solar power turns into almost perfect baseload power.
Another factor is that the atmosphere absorbs much of the Sun’s light even without clouds. The Earth’s inclination and spherical shape also reduce the amount of sun that hits the ground away from the equatorial region.
Orbital solar panels do not suffer from any of these limitations. Thanks to all these factors combined, a solar panel in orbit could produce as much as 40x more than one on the ground.
How Does It Work?
We already know how to produce solar power in space, with high-performance solar panels already powering virtually all satellites and the ISS. In theory, we would just need to send up in the orbit a lot more of such solar panels and send the energy back to Earth.
Source: Solar.com
Surprisingly, the sending back power part is not as difficult as one can imagine. The dominant concept so far is to use microwaves (2.45 GHz), which are not absorbed by clouds. The microwaves are then absorbed and converted back to electricity thanks to a dedicated type of antenna called a rectenna.
Alternatively, power could also be beamed back with lasers.
Source: ESA – European Space Agency
Beaming a massive amount of energy back down to Earth’s surface might sound a little concerning. It tends to create the image of a science fiction supervillain death ray. However, in practice, such a beam would be energy-rich but nowhere as powerful enough to represent a danger to the surface.
It must be noted that one of the advantages of this system is that the DC power created by the solar panels can be directly used for beaming it down, with AC power only created on the ground for injecting the electricity into the grid.
Why Now?
Solar Costs
Producing power from orbital solar plants is an old idea. But it is only now that it is starting to look like it could become viable.
The first reason is the increasing inefficiency and declining costs of solar panels, which are the same factors that made it a viable option on the ground.
Source: News Channel 3
Further progress in technology might see the conversion efficiency increase further. Currently, the commonly used ground solar panels have efficiency in the 20-23% range. The ones used in space are often as high as 30%, as the extra cost is compensated by less weight to carry to orbit, with further gain expected.
“Current panels used in space achieve efficiencies on the order of 30% in converting sunlight to electricity, and in the next 20 years we expect them to reach 40%
Nicola Rossi, Head of Innovation at Enel Group
Launch Costs
The other elephant in the room is the collapsing cost of reaching orbit, almost entirely driven by SpaceX’s achievements in reusable rockets. This cost has already been divided by 10 and is expected to keep getting cheaper with the launch of Starship and the mass production of the largest rocket in history.
Source: Ark Invest
When launch costs were £7,716 per kilogram, it represented approximately £154 per watt of “installation costs”, compared to a mere £2-1.5 on the ground. But if launch costs can drop low enough, this makes space-based solar viable from an economic perspective. And Elon Musk is targeting a mere $100/kg in the long run, thanks to full reusability of the massive Starship payload.
Space-Based Solar Power Limitations
Price And Launch Costs
As explained above, solar-based power is only viable if launch costs decline significantly. While this might be happening, it is unclear how quickly another 10x reduction in orbital launch cost can be achieved.
This could significantly delay the adoption of space-based solar, with most large prototype projects (close to the MW scale) not expected before 2025-2030 at best. A significant impact will not be achieved before building such systems 1,000x larger at the GW level.
Orbital cluttering
Another concern is the real-life durability of the solar panels in orbit. Space is a harsh, high-radiation environment, and the panels will degrade over time. The same is likely to happen to electronic components like the microwave antenna.
In addition, orbital space is getting increasingly cluttered. Space debris is becoming a serious concern, and constellations of Low-Earth Orbit (LEO) satellites are exponentially growing the number of items around our planet.
Space-based solar plants would be several square kilometers in surface, making them likely to be hit regularly by space debris. Even micrometeorites will become an issue if given enough surface and time.
In a worst-case scenario, a major impact would create more debris, which in turn would create more debris, in a catastrophic cascade destroying most of Earth’s satellites. This is a phenomenon known as Kessler syndrome.
Currently, Kessler syndrome would be damaging enough, wrecking telecommunication, space-based imagery, and science, as well as early warning nuclear weapon detection systems.
But if a large part of Earth’s energy is provided by orbital solar plants, such an event would be even more devastating.
Durability And Recycling
Except if located in a very distant orbit, far from LEO, satellite trajectories tend to decline quite quickly. So solar power plants will need to be pushed at higher orbits, toward geostationary orbits (GEO), increasing costs as they require more launch capacity.
This also puts into question their recycling, as these solar panels will consume a lot of precious & non-renewable resources, including silver.
So, in the long run, any large-scale solar power infrastructure will also need to master recycling the panels instead of destroying them by keeping them in orbit or crashing back to Earth.
Lastly, sending material into orbit is very energy-intensive. So, only high-efficiency rockets will make the process viable, allowing for the orbital solar panels to “payback” the energy used not only to manufacture them but also to send them into orbit.
Energy Losses
As we said, solar panels in space receive a lot more energy than on the ground. However, they also must have several more steps than ground-based systems before powering the grid:
- Ground-based: collect sunlight -> convert DC to AC -> send power into the grid.
- Space-based: collect sunlight -> convert microwaves -> convert microwave back to electricity -> convert DC to AC -> send power into the grid.
The multiple extra steps involving beaming down microwave cause massive energy losses, adding to the max 30-40% sunlight -> power conversion efficiency.
“The system we used in our demonstration had end-to-end efficiency of about 5%. That’s not something that would be operationally viable, even though the sunlight is free. For a space-based solar plant to make sense, the efficiency would have to be around at least 20%.”
Jean-Dominique Coste – Senior Manager at Airbus Blue Sky
Stable Orbits And Solar Wind
One last question is how to manage the orbital trajectory of the solar plants.
The solar panel will need to constantly adjust its position to receive the maximum sun exposure. The microwave beams will need to be constantly redirected to hit the right area of the Earth’s surface.
Due to their lightweight and maximized exposure to sunlight, the solar panels will be pushed by sun wings and light. In fact, this pressure from light has been considered to create sun-sails to propel spaceships.
In the context of an orbital solar power plant that needs to stay stable, this might become an issue.
Overall Prospects of Space Photovoltaics
A lot of the future of space-based solar power will depend on the development of the space industry as a whole. A few key factors will need to click together for it to happen:
- Growth of the industry allows for scale and innovation to decrease launch costs to the required levels.
- Development of an orbital and/or cislunar industrial economy, at the very least for maintenance and recycling of the power satellites.
- Proper management of space debris and keeping the orbit a neutral and peaceful zone.
Alternative To Photovoltaic Space Solar
Concentrated Solar And Orbital Mirrors
The light -> power -> microwave -> back to power system is inherently causing massive losses, which counterbalance partially the higher solar output from being in space.
This a core criticism of this concept, even embraced by no one else than Elon Musk as far back as 2012
“Let me tell you of one of my pet pieces: space solar power. OK, the stupidest thing ever.
And if anybody should think, should like space solar power, it should be me. I’ve got a rocket company and a solar company. I should be like – I should really be on it, you know.”
Of course a lot has changed since 2012. Solar panel prices and launch costs have crashed. And the need for renewable baseload power generation is a lot larger.
Still, there might be an alternative: directly reflecting sunlight instead of catching it with photovoltaic panels. This could be achieved by putting a giant mirror into orbit.
One advantage of this method is that we know how to build ultralight and ultra-thin mirrors in space, using aluminum foil. As the material only needs to be reflective with no electronics, it can be a lot cheaper and lighter per square meter than a photovoltaic cell.
The idea is notably championed by Ben Nowack, founder of Reflect Orbital, the University of Glasgow’s SOLSPACE (with a €2.5M grant from the European Research Council), and energy giant Engie’s Laborelec.
The idea is to power ground-based solar farms during the night by beaming sunlight toward them. So, the business model would be to “sell” sunlight to ground solar utilities.
Such a system would not be able to go through cloud cover but could be a great option for solar farms installed in dry or desert areas.
Potentially, the concept could also boost “classic” space-based photovoltaic plants as well, cheaply increasing the total energy they receive before beaming it down to Earth.
In 2018, China announced plans to use such a mirror system to replace nighttime streetlights by 2022. While this was not done, it could be a creative way to use space-based “solar” to reduce our energy consumption at night when renewables under-produce.
Space Factories
As explained above, a major cost in space-based solar power is the issue of having to send hundreds or thousands of tons of material into orbit. A solution to this problem would be to directly produce the solar panels (or mirrors) in space, using resources already on site.
This method would entirely remove from the equation the cost of lifting the solar power plant into orbit. Instead, it would replace it with the cost of sending up only the equipment required for creating a space-based solar panel (or mirror) factory.
One way to do so would be to capture asteroids with the right resources, mine them, and directly produce the power plant into orbit.
Conceptually sound, this is however still very speculative, as no asteroid mining of any form has ever been achieved yet.
Moon Base
Even if solar plants are produced in space, the issues of balancing the solar wind impacts from space debris and recycling will remain.
An alternative would be to install the solar stations on the Moon instead. The energy would be collected by massive solar farms built on the Moon and then beamed directly or indirectly to Earth. The microwave beams from the Moon can also be redirected by mirrors, as metals reflect microwaves.
Source: Arizona State University
Compared to LEO and GEO solar satellites, this presents a few advantages:
- Gravity: with 1/6 of Earth’s gravity, the Moon might be a lot more friendly to adapt Earth’s manufacturing process to space than fully weightless environments.
- Perfect for solar: without an atmosphere, the Moon’s surface never suffers from wind, clouds, fog, ice, dust storms, hail, etc. So energy production will be highly reliable and predictable.
- Human maintenance: orbital systems would need to entirely rely on robots for assembly, maintenance, and recycling. Instead, the upcoming plans for Moon bases by the USA as well as China+Russia would provide the local manpower for when robots are not enough.
- Resources: The Moon is a massive celestial body, likely to contain plenty of resources. This makes it a better candidate for a space factory than the unproven idea of asteroid mining.
Silicon, aluminum, and iron can be chemically extracted from lunar soil for the fabrication of solar cells. Trace elements can be brought from Earth for doping solar cells.
It is estimated that a kilogram of materials transported from Earth to the moon would result in the delivery of 200 times as much electric energy to Earth as a kilogram of a solar-powered satellite.
David R. Criswell
However, the idea has some limitations.
Notably, the Moon has a 28-day day/night cycle, forcing such a concept to rely on a succession of power plants spread out on the entire surface of the Moon (or orbital mirrors) to produce a continuous output.
Helium 3, Fusion, and Moon Power Plants
Another discussion about future energy involving the Moon is its deposit of Helium-3. The very rare element on Earth could theoretically power an ultra-efficient form of nuclear fusion.
In theory, this could make space exploration and mining a key feature of our future energy supply. In practice, fusion is still at an experimental stage.
Similar sources of rare isotopes of hydrogen, helium, and other elements, for example, in the gas giant of Jupiter and Saturn, could play a similar role in the long run.
The Moon could also be imagined as a site for a potentially dangerous but highly productive power system (notably nuclear), removing the consequence of a catastrophic failure from Earth. However, the energy loss in beaming back such a source of power, as well as the costs of building in space, might make it unprofitable.
Solar Space Companies
1. Space Solar
Space Solar is a British company looking to develop a 2GW space solar satellite, CASSIOPeiA. This would be by far one of the largest structures ever built by mankind, making some of the tallest skyscrapers tiny in comparison.
Source: Space Solar
CASSIOPeiA would contain 60,000 solar panels, weigh 2,000 tons, and orbit at geosynchronous altitude.
Power transmission would be done using a changing phase array to aim the energy beam. The ground station would need to be 5km in diameter. The power-beaming technology has so far been demonstrated on Earth, with 30kW of power. This was achieved thanks to HARRIER, the first 360° wireless power transmission requiring no moving part, a key factor for high reliability.
The concept of the power satellite would rely on 2 solar reflectors sending back the sunlight into the central collector segment.
Source: Space Solar
The program is expected to cost £17B for the first version, with a cost of £3.6B for subsequent iterations. This would bring it to 1/4 of the cost of an equivalent nuclear power plant of 2GW capacity, a fair comparison, considering the baseload profile of the power plant.
2. Reflect Orbital
As mentioned above, Reflect Orbital is not looking to generate power in orbit. Instead, its business aims to “sell sunlight after dark” to ground-based solar companies.
With peak prices often just after sunset, when people are back home but renewables offline, this can be a good strategy. In addition, the satellite sunbeam can be easily redirected to different locations, allowing for arbitrage between different prices between countries or adverse weather in one area.
This makes it an interesting company to follow in case that, indeed, conversion of sunlight to electricity, then microwave, then back to electricity is a too inefficient process to compete with ground-based solar.
For now, the company is developing its satellites and raising funds. To help explain the concept better, they also did a demo using a hot air balloon 3km high that went viral.
Source: Reflect Orbital
The company is looking to test a prototype by 2025. The satellite would weigh only 35 pounds (16 kilograms) each and would be fitted with mylar mirrors 33 feet by 33 feet (9.9 by 9.9 meters) in size, unfolding once in orbit.
Reflect Orbital plans may be less high-tech than a full orbital or Moon-based solar satellite network. But maybe this could be a strength, as it essentially only uses entirely known technologies in a creative way, already mastered for decades. This could somewhat de-risk the project.