Solar technology is a sustainable, safe, and clean way of harvesting energy—but it's only collected during daylight hours and is often at the mercy of the weather. One solution? Harvest solar energy from space.

The solar energy available in space could make a significant contribution to the world’s electricity requirements.

The demand for electricity is likely to outpace production in the next few decades. It is therefore necessary to look for ways to generate more power, preferably in the form of clean, sustainable energy. Of all the viable energy sources, space solar emerges as an attractive clean energy source.

However, there are many technical, financial, and policy challenges (as well as safety and regulatory concerns) which must be addressed before successfully generating electrical energy and transmitting it from space to the Earth.

Space Solar vs Other Energy Sources

Other energy sources—such as hydro, terrestrial solar, and wind—are dependent on inconsistent and unpredictable environmental factors. Others such as the fossil-fuel generators rely on possibly non-sustainable fuel sources.

Space solar power, on the other hand, is unlimited, available 24 hours a day, and expected to last for another four billion or more years. The potential of generating electrical energy from space is so huge that it can provide continuous base load power (the minimum demand on an electrical over a 24 hour period) and meet future global energy requirements.

Advantages of a Space-Based Solar Power System

Sunshine in space is constant—unaffected by day/night cycles and weather conditions.

It does not emit greenhouse gases like coal, oil, and gas-based sources do, nor does it produce hazardous waste like nuclear plants.

Space solar harvesting doesn’t compete for farmland as does bio-fuels production.

The energy can be beamed to locations where it is required, even to remote places with no grid power. This eliminates the issues associated with long transmission lines.

How a Space Solar Power System Works

A typical setup will involve building a solar-based power station in space and a ground receiver on the Earth’s surface. The solar panels will generate the electrical energy, convert it into microwaves or a laser beam, and wirelessly transmit the energy to a ground receiver. The ground receiver will then convert the received energy into electricity.

Figure 1: Flowchart for space-based solar power transmission. Image courtesy of R. Rajendra.

The system would consist of three main components:

Solar panels

Converter and transmitter

Ground receiver

Solar Power Harvesting in Space

One of the suggested technologies is the use of solar power satellites consisting of solar panels and large mirrors that will direct the sunlight to the panels. This satellite will be placed in geostationary orbit—about 38,500 kilometers above the Earth. The advantages of geostationary orbit are the following:

The solar panels on the satellite will be illuminated throughout the year.

The amount of sunshine is about five times more than what would be available in terrestrial locations.

The satellite will have the same rotational period as the Earth and therefore be fixed over one latitude, enabling the ability to more consistently deliver power to the ground receiving site.

The satellite, equipped with a transmitter, will convert the DC energy into either microwaves or a laser beam and transmit this to the Earth in a safe and controlled manner.

Challenges in Implementing Space-Based Solar Power Systems

The cost of deploying the satellites in space is huge. According to the Space Island Group, it could cost about 200 million dollars to set up a 10-25 MW prototype in low Earth orbit. Assembly, maintenance, and servicing of the solar power systems in space would likely be costly and face many logistical issues.

Currently, there are plans to develop reusable rockets and other technologies that will support mass transportation of equipment to space, thereby lowering the costs to economically viable levels. In addition, robots could be used to assemble and repair the modular structures in space.

That there has also been significant progress in technologies that could potentially enable the harvest and transmission of energy from space. New technologies such as carbon nanotechnology have the potential to reduce the size of equipment and bring down the cost of building and launching solar power satellites. There's also a need to develop large-scale transportation technologies and robotics that can be used to assemble and repair structures in space.

There’s also a concern that the lasers or microwave systems could harm people and property as they transmit energy back to Earth. Keeping the satellites properly aligned with the receiving stations is a complicated task that could result in disaster if calculations are off by the slightest amount. This is a serious danger because the transmission process could result in harm through accidental means or through the systems being repurposed as weapons.

These, among others, are significant challenges that will need to be addressed before space solar can become a reality.

The Future of Solar Power from Space

Researchers from Japan, China, the USA, India, and the UK have made progress on technologies they hope to use to transfer electricity from space to Earth. For example, laser and microwave power transmission technologies have been tested successfully in Japan, the USA, and Europe. In addition, Japan has performed promising experiments involving the transmission of microwaves through the ionosphere

A typical development roadmap towards space solar looks something like the following:

Start with a low-power demonstration unit (less than 100KW) in the lower earth orbit to tests technologies for gravity stabilization, beam control, power transmission, and effect on ionosphere.

Launch a lower orbit 10MW prototype system. Researchers test the robotic assembly, high-power transmission, and control.

Put a pilot system in geostationary orbit where all the required technologies and operations will be tested.

Upscale to a commercial plant in geostationary orbit.

Space research companies such as Japan Aerospace Exploration Agency (JAXA) and Mitsubishi have plans to try out the technologies and if successful launch commercial plants in the next 20 to 30 years.

A rendering of a planned energy-receiving plant. Image courtesy of Japan Space Systems.

JAXA plans to test their technology in the next two years. They will start with a several-kilowatt satellite in low earth orbit by 2018. After that, they hope to put a 100kW satellite, still in the low earth orbit by 2021 and have a 200MW demonstration system in the geostationary orbit by 2028. If all goes well, JAXA will install a 1GW commercial pilot power station by 2031 and start a program of installing one plant per year from the year 2037 onwards.

Mitsubishi Heavy Industries plans to test a 1KW and then a 100KW demonstration unit in the lower earth orbit. Their plans state that this demonstration will be followed by a 10MW pilot plant in the geostationary orbit, ambitiously set to be launched before 2020. If they manage this timeline, they aim to put a 400MW commercial system in the geostationary orbit by 2030.

For more information on space solar power systems, you can refer to this overview from Japan Space Systems.

Transmission of Energy from Space to Earth

In the next article, I will explain the two viable methods proposed for transmitting energy collected from space back to Earth, as well as a third method that combines the two.