Value chain · CLM-1120
In plain terms
In 1977 the gallium arsenide option rested on a 20 per cent cell nobody had made, an assumption that it would still be near 20 per cent after thirty years because it heals more easily, and on films a few thousandths of a millimetre thick, because there was not enough gallium for anything thicker.
The claim as recorded
Hughes' 1977 GaAs study for Boeing predicts a beginning-of-life efficiency of 20 per cent at AM0 without concentration "for the 1990 time period", from a 2 x 10^17 cm-3 doped GaAs cell with a 0.2 um (AlGa)As window, against IBM's 18.5 per cent on cells of about 0.1 cm2; it takes proton damage as "predominant" and electron damage negligible in GEO, says radiation damage in GaAs "is not well enough understood to justify quantitatively exact predictions of the end-of-life efficiencies", and nonetheless assumes "an efficiency close to 20% AMO can be expected from GaAs cells for 30 years in synchronous orbit", "especially if temperature annealing can be used"; its thin-film cost-weight estimate is 2 kW/kg of cell at concentration ratio 1 (40 cm2/W, 0.5 g/W) and 10 kW/kg at ratio 5 (8 cm2/W, 0.1 g/W). Boeing adds that the active layer "need by only 3 to 5" um, that present techniques recover 10 per cent of the gallium in bauxite and coal fly ash, and that thin-film technology "is critical" both for gallium supply and for competing with silicon.
Evidence behind this: T3-subcontractor prediction for 1990 cells with the assumptions stated; no SPS cell measured.
Scope and limits
A PREDICTION, NOT A MEASUREMENT, AND THE END-OF-LIFE FIGURE IS AN ASSUMPTION THE REPORT ITSELF SAYS IT CANNOT JUSTIFY QUANTITATIVELY. The kW/kg is cell only, with no cover, substrate, interconnect or blanket. Thin-film GaAs cells of the thickness assumed did not exist ("a technique is not yet available for making high-efficiency solar cells from gallium arsenide layers so thin", normalised, PDF 98).
What it assumes
1353 W/m2; the Intelsat GEO environment model the report cites; the cost figures are 1977 dollars per watt and are not carried.
Where it comes from
PDF 64 / printed 60, raw: "is predicted to be" 20 per cent, the sentence "the beginning-of-life efficiency of a GaAs solar cell under AMO illumination and in the absence of solar concentration is predicted to be, for the 1990 time period:" followed by the boxed result, the Greek eta, "(AMO) = 20%", as a render reading; "IBM has already succeeded in making a limited number of smaller" -area cells of about 0.1 cm2 with an AM0 efficiency as high as 18.5 per cent (normalised fragment, the rest a render reading); PDF 61: the design parameters (N_D = 2 x 10^17 cm-3, window 0.2 um) in the layer. PDF 76 / printed 72, normalised: "proton radiation damage will be predominant, and that electron radiation damage can be neglected". PDF 91 / printed 87, normalised: "The radiation damage in GaAs is not well enough understood to justify quantitatively exact predictions of the end-of-life efficiencies"; "an efficiency close to 20% AMO can be expected from GaAs cells for 30 years in synchronous orbit"; "especially if temperature annealing can be used" (render reading). PDF 96 / printed 92, render read: the table "Cost-Weight Estimate for Thin Film (GaAs) Solar Cells", columns "Concentration Ratio", "Cell Area (cm2/watt)", "Cell Weight (g/watt)", "Power/Weight (kW/kg)(cell)" and "Cost/watt", rows 1: 40, 0.5, 2, 1.00 and 5: 8, 0.1, 10, 0.20. PDF 98 / printed 94, raw: "need by" only "3 to 5" um; "recover 10 pen" cent (raw fragment; the sentence is a render reading). PDF 100 / printed 96, raw: "thin film technology is critical". Recomputed: 1 / 0.5 g/W = 2 kW/kg and 1 / 0.1 = 10 kW/kg; at 20 per cent and 135.3 mW/cm2, 1 W needs 37 cm2 at CR 1, the table's 40; 5 x 8 = 40 cm2 of collecting area at CR 5, consistent.
Basis: per cent at AM0; kW/kg of cell; um of active layer; concentration ratio
Cite this
energyaperture.com/c/clm-1120
CLM-1120, Energy Aperture, as of 1977-04.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-475
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