Tech Talk | Space-based solar energy advances
Image: Andrea Viale, NASA
Space-based solar energy is being proposed as the next frontier for supplementing renewable energy supply.
The concept of capturing solar energy in space and beaming it down to the Earth had its origins with the well-known science fiction writer Isaac Asimov in an early short story from his student days during the Second World War.
While it attracted limited attention in the following years, since the turn of the century with the increasing move to renewables, interest has grown and subsequently accelerated, with several initiatives emerging, including in the US, UK, Europe, Japan and China.
The fast-falling costs of satellite launches with their proliferation has given impetus to the proposal. However, while conceptually it is straightforward, technologically it is still very complex – to place solar panels several square kilometres in extent in space and then to deliver the energy via conversion to microwaves and reconversion on the ground with sufficient efficiency.
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Nevertheless, several studies, most recently one from NASA, have indicated that cost parity with ground-based renewables should be possible by 2050, if not before.
With this space-based solar can become a viable addition to the renewables mix, with one of its prime benefits its ability to deliver solar energy on a virtually 24/7 basis – something that earth-based photovoltaics are unable to match, currently at least although not to be ruled out in the future.
For example, the CASSIOPeiA design proposed in the UK with two 1.7km diameter solar collectors is calculated to be able to deliver 2GW to the grid via a 5km diameter rectenna ground station.
Caltech’s space solar power demonstrator
Key to the development of space-based solar is the ability to test the technologies in space where they can be subject to the effects of space weather such as the solar wind.
Last October researchers from the Universities of Surrey and Swansea reported demonstrating the potential of a new solar cell technology based on thin-film cadmium telluride deposited directly onto ultra-thin space qualified cover glass material.
After six years in space, the cells were observed to show no signs of delamination and no deterioration in short circuit current or series resistance but the power output had decreased, which is attributed to an aspect of the cell design and is to be altered for the next generation.
Arguably the most advanced initiative is that at Caltech in the US, which was launched over a decade ago and is seeing investment of over $100 million on a largely philanthropic basis.
One year ago the first space solar power demonstrator was launched into space and while it ceased communication in November, one year on all three of the technologies carried, all fundamental for the delivery of space-based solar, have now been confirmed to have been successful.
These have shown that a flexible mesh material can be carried into space and deployed, that low-cost manufactured solar cells show potential for space use – particularly those with high-performance compound semiconductor materials such as gallium arsenide – and that energy beamed from space can be detected on the Earth.
Reflectors in space
Another option being considered is one that was proposed back in the early 1980s for nighttime illumination of cities – having giant reflectors in space that reflect the sunlight down to Earth, in particular at dawn and dusk when demand is peaking and the output from solar farms is weakening.
In a 5-year project that was started in late 2020 at the University of Glasgow, a reference architecture has been published recently for ‘Solspace’ as a constellation of five hexagonal-shaped reflectors with a combined area of about 1,000m2 – their size dictated by the available other technologies required for example, for attitude control.
With constant solar facing, these are estimated to deliver approximately 280MWh of solar energy daily to large solar farms, around 10km in extent to match the size of the solar beam at the proposed altitude of almost 1,000km, across the Earth.
With an operational lifetime of 20 years, the cost of the electricity is estimated at $70/MWh.
Further results are yet to come from the project, which also was proposed to look at issues such as the use of 3D printing methods for the reflectors, which are proposed to be made from aluminised Kapton and gossamer thin.
These findings and those from the other initiatives are early stage and much work still needs to be done to evolve the technologies and to implement a commercial-scale operation.
But in one form or another, it will happen, and perhaps as early as 2035 if the UK’s Space Solar venture meets its timeline.
