What kind of testing does the Solar Generator Laboratory carry out
To be certain the performance of solar cells and photovoltaic technology can be reliably predicted in space, the Laboratory operates them in simulated conditions.
Samples are exposed to specially-filtered light whose spectrum is as close as possible to sunlight at the top of the atmosphere – known as 'air mass zero' – and their power output recorded. Solar cell efficiency declines over time, and additional measurements are made once the samples have undergone representative degradation effects. Ultraviolet irradiation can be achieved within the Laboratory's solar simulator while exposure to charged particles, ultraviolet radiation or electrostatic discharge can be carried out in other ESA laboratories.
To gain further 'end-of-life' operating data, solar cell strings are artificially aged when subjected to rapid temperature shifts resembling those that will be experienced in orbit as spacecraft move from sunlight into shadow. For instance a satellite in low Earth orbit will undergo about 5500 thermal cycles between --110°C and +110°C in a year, a length of time which can be simulated in about three weeks. Thermal cycling occurring much further from Earth can also be simulated, from the scorching surroundings of the Sun to Jupiter's icy orbit.
The performance of larger photovoltaic arrays, including those already integrated onto satellites, can be rapidly verified by firing rapid pulses of light along a sequence of wavelengths. This 'snapshot' approach measures the photovoltaic system's response in terms of its 'current-voltage curve'.
The single most efficient variety of photovoltaic devices are triple-junction solar cells, which have multiple semiconductors placed on top of each other, each tuned to different segments of the total light spectrum. Spectrum response testing is an important diagnostic tool for multi-junction cells of this kind. Their light absorption performance is assessed in ten nanometre increments as a way of fine-tuning designs.
Laboratory testing of this kind takes place to qualify designs for flight and assess the potential of new technology. Experiments can also be run on a rapid 'firefighting' basis to investigate hardware anomalies or failures and evolve solutions, coordinating with external solar generator laboratories if needed.
Last update: 29 September 2009