How Do We Harvest Solar Power From Space?
Space-based solar power (SBSP) refers to the concept of collecting solar energy in space and transmitting it wirelessly to Earth. SBSP aims to overcome the problems of intermittent sunlight and atmospheric interference that limit ground-based solar power. The basic premise involves placing large solar arrays into geosynchronous orbit to collect high-intensity, uninterrupted sunlight 24 hours a day. The arrays would convert sunlight into electrical energy and beam it down to Earth using microwave or laser radiation. Receiving stations on the ground would collect the transmission and convert it into usable electricity that feeds into the electrical grid. SBSP has the potential to provide constant, clean energy anywhere in the world. According to studies, space-based arrays could collect over 100 times more solar energy than ground-based ones. SBSP could meet a significant portion of the world’s energy demands and reduce dependence on fossil fuels. The concept offers enormous environmental and economic benefits, but involves complex technological challenges. If these can be overcome, SBSP may become a revolutionary energy source for the future.
Advantages of Space-Based Solar
One of the main advantages of space-based solar power is the potential for unlimited and constant solar energy collection in space. Unlike solar panels on Earth which can only collect sunlight during the day when it is not obscured by clouds or other weather, solar panels in space can collect sunlight 24 hours a day. Satellites in a high orbit around Earth experience nearly constant sunlight with little to no interruptions from the Earth’s shadow. This means space-based solar power could provide a constant source of renewable energy day and night, regardless of weather conditions on Earth 1.
Solar panels in space also benefit from much higher intensities of sunlight compared to panels on Earth’s surface. With no atmospheric absorption or scattering of light, solar intensities in space can be up to 144% stronger than on the ground. And without concerns about nighttime, weather, or seasons, space-based solar power could collect significantly more energy over the course of a year compared to an equivalently sized installation on Earth 2. This unlimited and continuous source of intense solar energy makes space an ideal platform to collect massive amounts of clean, renewable power and transmit it wirelessly to Earth.
History and Development
The concept of harvesting solar power from space dates back to the early 20th century. In 1923, Russian theorist Konstantin Tsiolkovsky first proposed the idea of using orbital mirrors to reflect sunlight to Earth (Wikipedia). Through the mid-1900s, various engineers and scientists further developed the theoretical basis for space-based solar power. For example, in 1941 Isaac Asimov published a science fiction story imagining humankind receiving energy from orbiting solar stations.
In 1968, Peter Glaser introduced the idea of solar power satellites (SPS) that would collect solar energy in space and beam it to Earth using microwaves or lasers. Over the next few decades, NASA and the U.S. Department of Energy conducted studies on the feasibility of space-based solar power. However, high expected costs stalled major developments. In the 1990s, NASA focused on conducting wireless power transmission tests on the ground to advance the underlying technologies needed.
More recently, advances in areas like lightweight materials, robotics, and wireless transmission have renewed interest in space-based solar. Since 2000, NASA, the European Space Agency, and Japan’s space agency JAXA have tested various solar panel and transmission designs both in space and terrestrially (ESA). While still early stage, these demonstrations show the potential for harnessing solar energy in space to meet Earth’s growing power demands.
Satellite and Receiver Designs
There are several different proposed designs for the satellites and receiving stations to collect solar power in space and transmit it to Earth. One of the most developed concepts is called SPS-ALPHA (Solar Power Satellite by means of Arbitrarily Large Phased Array) by the Japan Aerospace Exploration Agency (JAXA). This design consists of a 2 km wide satellite in geostationary orbit that would transmit energy to Earth using microwaves directed at a 1 km diameter rectifying antenna (rectenna) on the ground [1].
JAXA has tested prototype components for SPS-ALPHA, including the transmission of microwave energy over 148 km between two islands in Japan. The microwave transmitter uses a phased array antenna which combines the power of many smaller antennas to precisely direct the beam [1]. Boeing has also patented a design using inflatable structures to reduce launch costs and tested wireless power transmission between aircraft.
An alternative approach is being developed by researchers at the California Institute of Technology called “SANDAR” (Self-Assembling Nanosatellite Solar Array). This design uses modular components that can self-assemble in space into a 1-2 km solar array for cheaper deployment. The modular satellites would beam microwaves between each other before redirecting the combined beam to Earth [2].
The receiving antennas on the ground can also take different forms like standard rectennas or hybriod designs that combine antennas and solar cells for dual functionality. Overall, a range of satellite and receiver options are being explored to optimize space solar power generation and transmission.
[1] https://www.spacesolar.co.uk/our-technology/
[2] https://spinoff.nasa.gov/New-Solar-Array-Design-Saves-Space
Power Transmission Methods
Space-based solar power systems need to transmit the energy they collect wirelessly back to Earth. The two main transmission methods that have been proposed are microwave and laser transmission:
Microwave transmission involves converting the solar energy into radio frequency microwave beams that can penetrate through the atmosphere. Large transmitting antennas or arrays would beam the microwaves towards huge receiving antennas or rectifying antennas (rectennas) on the ground that would convert the microwaves back into electricity.
Some benefits of this approach are that the technology is proven and experiments have demonstrated feasibility. Microwaves also do not get blocked by clouds or weather. However, a large scale system would require incredibly large and complex transmitters and receivers. There are also concerns around the potential biological effects of intense microwave beams passing through the atmosphere.
Laser transmission focuses sunlight into laser beams which are transmitted to photovoltaic receivers on the ground. This method could provide very precise targeting and high efficiency. However, lasers may be impacted by atmospheric interference like clouds and dust. Maintaining precise pointing over vast distances is also a challenge. Laser transmission also raises potential safety concerns related to the intensity of laser beams if off-target.
Overall, microwave transmission is the more developed and practical option currently. But laser transmission offers theoretical advantages if technical challenges can be overcome. More research and development is needed to determine the optimal power transmission method for large-scale space-based solar installations.
Launching and Deployment
Getting a solar power satellite into geosynchronous orbit requires a powerful launch vehicle. Some proposed designs call for modular satellites launched in pieces and assembled in space, which requires launches of many components. The most likely launch vehicles are heavy-lift rockets like NASA’s Space Launch System or SpaceX’s Starship, which are capable of carrying over 50,000 kg into orbit (Caltech, 2023).
Once in orbit, the solar panels and antennas would deploy and the satellite would be positioned in geosynchronous orbit about 36,000 km above the equator. This high orbit allows the panels and antennas to be aligned properly for continuous coverage of the same area on Earth. Deploying and testing the systems can take weeks or months before the satellite becomes operational (ESA, 2022).
Maintaining the satellite’s orbit and orientation is crucial so the microwave beam remains accurately targeted at the ground receiver. Thrusters and reaction wheels are used to make minor orbital adjustments and counteract disturbances. The satellite must be designed with redundancy to operate reliably for decades in the harsh space environment.
Efficiency and Cost Analysis
The overall end-to-end efficiency of space-based solar power systems is currently quite low, in the range of 5-30% according to some estimates[1]. This includes efficiency losses from conversion of sunlight to electricity at the satellite, wireless power transmission, and then conversion back to usable electricity on Earth. However, there is room for improvement as technology advances. Some satellite solar panels can already achieve over 30% efficiency[2], and microwave transmission efficiency can theoretically reach well over 50%.
Cost is another major factor holding back adoption of space-based solar. Current estimates put launch costs at $200-$500 per watt of capacity[3], much higher than terrestrial solar panels which can cost around $1 per watt. However, if launch and deployment costs can be reduced through reusable rockets and other innovations, space solar may become economically viable. Some analysts project costs declining to around $100 per watt in the next 10-20 years if sufficient scale is achieved.
Challenges and Concerns
While space-based solar power could provide unlimited clean energy, there are significant challenges that need to be addressed before it becomes commercially viable. Some of the key challenges relate to technical feasibility and reliability.
The conversion of sunlight into microwaves or lasers and transmitting the energy wirelessly involves complex technology that needs to be proven and reliable. According to a study by the European Space Agency, developing wireless power transmission systems operating at high power levels over large distances is a major technical challenge (source). The wireless transmission needs to be efficient and safe for humans, animals, and the environment.
The space infrastructure also needs to operate reliably over decades in the harsh space environment. Engineers need to develop lightweight solar arrays, structures, and components that can withstand radiation, temperature extremes, and micrometeorite impacts. Operating and maintaining this infrastructure remotely over large distances poses additional challenges.
There are also policy, legal, and regulatory issues that need resolution. A space-based solar power system would likely involve multiple countries and require international agreements on issues like orbit allocation and wireless transmission regulations. Policies need to be developed regarding ownership, operations, liability, and access rights to the space infrastructure (source). Regulatory approval processes in individual countries may also pose challenges.
Overcoming the technical hurdles and achieving global policy alignment will likely take decades of concerted effort and substantial investment from both private and government entities.
Current Projects and Next Steps
There are several key public and private initiatives underway today focused on developing space-based solar power technology and infrastructure:
NASA is funding research on wireless power transmission and autonomous assembly robots as part of its Space Solar Power Project. In 2021, they awarded Caltech a $100 million grant over five years for a Space Solar Power Project to demonstrate wireless power beaming from space to Earth.
Private companies like Solaren and Space Energy are also pursuing early stage development of space solar farms. Solaren has a contract with PG&E to deliver power from space by 2026, while Space Energy is working on modular hardware and plans to launch test satellites this decade.
In China, a national lab recently announced a roadmap to establish a first space-based solar station in 2028, then scale up to gigawatt levels of power delivery by 2050. The China Academy of Space Technology sees space solar providing a significant portion of the country’s electricity needs in the long run.
Looking ahead, continued progress will depend on driving down launch and infrastructure costs through reusability and automation. Key milestones will be launching test satellites, demonstrating wireless power transmission over longer distances, and conducting in-space assembly and maintenance with robots. If these technical hurdles can be overcome in the coming decades, space-based solar may become a viable clean energy source capable of large-scale, global impact.
Conclusion
In summary, space-based solar power has immense potential as a clean, renewable energy source. By harnessing solar energy in space and beaming it down to Earth, we could meet rising global energy demands with reduced environmental impact. Research indicates that space-based solar could provide terawatts of energy globally, far exceeding other renewable sources. While still early in development, pilot projects like those underway in China, the US and Japan, are advancing space solar technologies such as efficient photovoltaic arrays, wireless power transmission and cost-effective launches.
To make space-based solar a viable part of our energy future, continued innovation and investment will be key. More research is needed to improve solar cell performance for the space environment. Wireless power transmission methods need refinement to send energy over vast distances efficiently. With focused efforts to mature technologies and reduce costs through dedicated projects and public-private partnerships, space-based solar may yet emerge as a critical solution for clean, limitless energy.
