Technical Insight
Terrestrial triple-junction array generates kilowatt solar power
A kilowatt-scale terrestrial solar-cell array that employs III-V-based triple-junction technology could spur the improvement of both space-based and terrestrial solar-energy systems.
At the summit of Mount Haleakala, on the island of Maui in Hawaii, engineers have deployed and tested what is believed to be the first ever 1 kW terrestrial triple-junction solar array.
Developed by a team comprising the NASA Glenn Research Center, Boeing and Texas-based Entech, the concentrator array outputs more than 200 Wm-2 at 600 V. This achievement promises to improve solar-power generation using high-voltage arrays in terrestrial and space applications.
"This could enable direct drive of certain types of ion thrusters, and lower conversion losses to high-voltage microwave transmitters," claimed the US team in a paper presented to the Solar Power From Space conference held in Granada, Spain, last month. In the longer term the successful deployment could even represent one of the first steps toward a space-based energy source that is capable of beaming power down to Earth via a laser.
It also demonstrates that future terrestrial concentrator arrays based on triple-junction (GaInP/GaAs/Ge) cells could achieve unprecedented performance at an affordable price.
The solar concentrator array used 240 Spectrolab GaAs P/N solar cells. Two separate modules were employed, each of which had an aperture area of 3 m2.
At an altitude of 3000 m, the Hawaii location was nearest the team could get to having a space-like solar spectrum without executing an actual launch. More short-wavelength radiation can reach cells at the mountain-top site than at sea-level.
According to the team, the peak power output of one of the concentrator modules reached 670 W - almost twice the capability of a standard module based on silicon solar cells. The typical energy output of the array each day was quoted as 16 kWh.
"The results of this experiment lay the foundations for future terrestrial concentrator arrays," claimed the team. "Using color-mixing lenses and triple-junction cells [could] achieve unprecedented performance and eventual cost-effectiveness in mass production."
If the module were deployed in space, the 200 Wm-2 conversion figure would immediately increase by more than 50%. Improvements in array design that have already been identified - such as improved optics - ought to further increase power output. "For future systems with wider cells, edge bus-bars and interconnect tabs, power output will be at least 20% greater, not including anticipated cell-efficiency improvements," said the team.
Entech president Mark O Neill has set out a long-term plan to reduce the power-to-weight ratio of solar systems used in space applications. His target is to reach 1 kW kg-1 specific power in 20 years, which he says will require an advance in multijunction-cell efficiency to 45-50%. A 40% reduction in cell mass would also be needed, something that O Neill suggests could be achieved either by reducing the thickness of the germanium substrates used currently in triple-junction cells, or by employing a silicon substrate.
The work could become the first phase of an end-to-end power-beaming demonstration, which would incorporate either a microwave or a laser beam to direct the generated energy. The plan is to install a NASA-designed power converter at the Hawaiian site as soon as funds become available.
Developed by a team comprising the NASA Glenn Research Center, Boeing and Texas-based Entech, the concentrator array outputs more than 200 Wm-2 at 600 V. This achievement promises to improve solar-power generation using high-voltage arrays in terrestrial and space applications.
"This could enable direct drive of certain types of ion thrusters, and lower conversion losses to high-voltage microwave transmitters," claimed the US team in a paper presented to the Solar Power From Space conference held in Granada, Spain, last month. In the longer term the successful deployment could even represent one of the first steps toward a space-based energy source that is capable of beaming power down to Earth via a laser.
It also demonstrates that future terrestrial concentrator arrays based on triple-junction (GaInP/GaAs/Ge) cells could achieve unprecedented performance at an affordable price.
The solar concentrator array used 240 Spectrolab GaAs P/N solar cells. Two separate modules were employed, each of which had an aperture area of 3 m2.
At an altitude of 3000 m, the Hawaii location was nearest the team could get to having a space-like solar spectrum without executing an actual launch. More short-wavelength radiation can reach cells at the mountain-top site than at sea-level.
According to the team, the peak power output of one of the concentrator modules reached 670 W - almost twice the capability of a standard module based on silicon solar cells. The typical energy output of the array each day was quoted as 16 kWh.
"The results of this experiment lay the foundations for future terrestrial concentrator arrays," claimed the team. "Using color-mixing lenses and triple-junction cells [could] achieve unprecedented performance and eventual cost-effectiveness in mass production."
If the module were deployed in space, the 200 Wm-2 conversion figure would immediately increase by more than 50%. Improvements in array design that have already been identified - such as improved optics - ought to further increase power output. "For future systems with wider cells, edge bus-bars and interconnect tabs, power output will be at least 20% greater, not including anticipated cell-efficiency improvements," said the team.
Entech president Mark O Neill has set out a long-term plan to reduce the power-to-weight ratio of solar systems used in space applications. His target is to reach 1 kW kg-1 specific power in 20 years, which he says will require an advance in multijunction-cell efficiency to 45-50%. A 40% reduction in cell mass would also be needed, something that O Neill suggests could be achieved either by reducing the thickness of the germanium substrates used currently in triple-junction cells, or by employing a silicon substrate.
The work could become the first phase of an end-to-end power-beaming demonstration, which would incorporate either a microwave or a laser beam to direct the generated energy. The plan is to install a NASA-designed power converter at the Hawaiian site as soon as funds become available.
