The idea seems fascinatingly simple, but most people think it belongs to a far-distant future: platforms stationed in space capture the sun’s rays and transmit them by means of laser beams to specially equipped reception devices on Earth. This would provide an urgently needed, long-term solution to the world’s increasing energy needs without increasing the heat and gas rejected into the atmosphere. The technology would provide clean energy from an inexhaustible source.
Energy from geostationary orbit
Space Based Solar Power (SBSP) satellites would be located in geostationary orbit (GEO) to ensure a permanent visibility of ground receivers; it would be accessible to most of the surface of the Earth with reduced power to higher latitudes and would require high pointing accuracy.
With technologies available now or foreseeable in the near-term, a single launched satellite would be capable of providing roughly 10 kW to the ground end-user with a laser power transmission system. This basic building block, with further development, could then be used to construct multi-satellite systems providing power to users with no access to existing electrical power grids.
These ‘off-grid’ power sources would be operational in advance of the development of the very large scale Mega- and Giga-watt orbiting power stations of the future, providing power to the grid as part of a suite of renewable energy sources.
Two technologies of power transmission are in balance, depending on the applications.
The transmission route – laser or high frequency?
The laser system is sensitive to atmospheric conditions, with a drastic attenuation of power level when passing through clouds. It cannot be used as a single source of power for Earth applications, as it cannot guarantee a constant level of power at any single receiver. The safety aspects, in particular human health, lead to selecting a wavelength around 1.5 µ and limiting the power density to 1,000 W/m² (equivalent to solar flux). But this would generate a small spot size, so that the receiver area could remain small (typically a few tens of metres). The high power density and small spot size make this option ideal for mobile and localised user groups in the short and medium term.
The RF system is transparent to the atmosphere, with a frequency within 2 to 10 GHz, but would lead to a large receiver area (typically with a diameter of a few hundred metres). Higher frequencies can reduce both transmit and receive antenna size but it becomes more difficult to generate the very high powers needed. The RF beam power density on the ground would have to be below 10 W/m² to assure the safety of the general public. RF systems might be a preferred solution for long-term very high power applications.
However, there are still some big challenges to be overcome. Today, power is limited by the size of the laser that can be built. The receive side – the conversion of this infrared energy into electricity – is progressing very fast. The principle is to get a very high efficiency of conversion of the infrared laser light into electricity.
The sun – with the right technology, an inexhaustible energy source for the Earth
Astrium could take a world-leading position in the development and exploitation of such an innovation. Development of an environmentally friendly economy is high on Europe’s agenda and this could provide a way of supporting such a strategy. However the obstacles towards the implementation of this technology remain real and significant. The relatively high costs of demonstration and early operational missions must be supported to pave the way to a future clean energy source.
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