Humans are about to start harvesting solar energy from space

Researchers at the California Institute of Technology have made renewable energy history by sending solar panels into space to collect solar energy from orbit, Newsweek reported on its website on 5 January.

On January 3, Caltech researchers successfully launched the Space Solar Power Demonstrator (SSPD). This is a prototype spacecraft that collects solar energy independent of the atmosphere and the diurnal cycle. The spacecraft will use wireless transmission to send solar energy back to Earth.

Solar panels on Earth use the photovoltaic effect to convert sunlight directly into electricity. In this, photons hit a silicon photovoltaic cell, causing electrons to be knocked out of the atoms, thus generating an electric current. Energy can also be harvested from sunlight using concentrated solar thermal (CSP) technology, which uses mirrors or lenses to gather sunlight and allow it to be converted into heat, eventually producing high-temperature steam that is converted into electricity via turbine generators.

In 2021, solar power will account for 4% of the world's electricity production.

However, a major disadvantage of solar energy on Earth is that it can only gather energy during the day and the efficiency of electricity generation is affected by the seasons and cloud cover. These problems can be avoided in space.

The SSPD consists of three components, each of which will be subject to a separate experiment. The first experiment is the Deployable In-Orbit Ultralight Composite Experiment (DOLCE), which will test the deployment of a modular spacecraft, a 6ft (1.83m) square structure that will test the mechanisms required to eventually release a cluster of one-kilometre class spacecraft. The second experiment is ALBA, which will test which of 32 different types of photovoltaic cells are most efficient in space. The final experiment is the Microwave Array for Power Transfer in Low Orbit Experiment (MAPLE), which will test the use of microwaves to transfer energy.

However, there are a number of important milestones to cross to get this emerging technology up and running.

Kevin Trenberth, a climate scientist and distinguished scholar at the National Center for Atmospheric Research, told reporters, "The biggest challenge, in my opinion, is to transmit solar energy back to Earth without huge losses or other problems during that time (such as the solar light column falling outside its intended area)."

This should not be a problem in space, where there is no air," he said. But scattering can happen whenever it is affected by atmospheric atoms (charged atoms in the ionosphere) and molecules."

Trenberth says the most serious problems are likely to be caused by water vapour, which absorbs sunlight and produces some localised heat. This weakens energy transfer and its efficiency.

Some areas of the Earth, such as the subtropics, have less water vapour and could provide some kind of window," he says. But I don't know how to target and make efficient use of these windows on a rotating Earth. Now, this problem can be avoided to some extent by converting solar energy into microwave energy, which can be transmitted through the atmosphere relatively easily unless it is affected by raindrops or particles. On Earth, microwave towers are used to emit energy over a range of about 10 miles (about 16 kilometres), rather than hundreds of miles."

He said, "A big problem is that solar energy spreads out in all directions rather than gathering together. Better aggregation could be achieved using huge antennas, but even that would require huge receivers."

Even if this technology is found to work, some don't think it will be adopted.

Thomas White, a solar cell scientist and associate professor at the University of Sydney in Australia, told reporters, "I find it hard to imagine how this approach could compete with photovoltaic power on the planet, even when the cost of storage is factored in to provide a 24-hour supply."

He said, "While there are some very optimistic scenarios for future technology development, (a recent cost-benefit analysis commissioned by the European Space Agency) suggests that its potential levelised cost of electricity (LCOE) will be between 3.8 and 10.6 euro cents per kWh by 2045. The current LCOE for PV on the planet is already around 3 euro cents per kWh and is decreasing year on year, so it will be well below this price by 2045. The cost of energy storage is also falling rapidly."

If space-based solar cells are successful, White said, they will have to compete with existing technologies, which are already well understood and field-proven as one of the cheapest ways to generate electricity and are on a very predictable path to lower costs.