Value chain · CLM-1038
In plain terms
In 1980 the Department of Energy calculated that a silicon space solar satellite would take six years to pay back the energy that built it, four times longer than coal or nuclear, and that almost all of that was the energy cost of making the silicon cells; with gallium arsenide cells it was a little over a year.
The claim as recorded
DOE's 1980 comparative net energy analysis of seven electricity systems, at a boundary from primary resource to electricity leaving the plant with electricity inputs counted at four times their energy and no discounting, finds a silicon-cell SPS energy payback of 6.38 years and a lifetime energy ratio of 3.85, against 1.30 years and 17.97 for GaAlAs, 1.1 to 1.5 years for coal, nuclear and solar thermal, and 19.82 years for terrestrial silicon photovoltaics; the silicon-SPS result is set almost entirely by an assumed cell-production energy of 13,900 kWh thermal per kg from a stated range of 1,000 to 26,000, and falls to 1 to 2 years at the low end or with solar electricity used for manufacture.
Evidence behind this: T3-programme comparative assessment (Argonne for DOE), with its own caution that solar data are "limited and, in some cases, highly uncertain".
Scope and limits
THE GaAlAs ENERGY INTENSITY RESTS ON ONE REFERENCE THE REPORT SAYS "SHOULD BE EXAMINED MORE CAREFULLY"; the boundary excludes labour and ends at the plant, so rectenna-to-grid losses and transmission are outside it; and the report's own footnote calls the solar data "limited and, in some cases, highly uncertain". A 1980 silicon energy intensity; modern cell manufacture is not this.
What it assumes
Constant output with cell repair over 30 years; no temporal analysis.
Where it comes from
Table 1.1, PDF p.7, raw: "6.38", "3.85", "1.30", "19.82", and "17.97" at the squashed level, with the two definitions. PDF p.14: the boundary statement, electricity inputs at four times. PDF p.31, normalised: "the energy requirements for silicon solar cell production vary over a wide range (1.0 x 10^3 to 26.0 x 10^3 kWht/kg). The value used in the baseline case, 13.9 x 10^3 kWht/kg, is derived from Ref. 9 and falls in the middle of the range." PDF p.33: reducing the silicon energy requirement by a factor of four. PDF p.38, raw: "(1-2 yr)". PDF p.37: the reconciliation of three earlier SPS studies, removing "the across-the-board multiplication of the output by a factor of 3" that "appears arbitrary".
Basis: years of energy payback; lifetime energy ratio over 30 years, electricity inputs at four times their energy, no discounting
Related records
- Answers question
- QST-008 not published in this release
Cite this
energyaperture.com/c/clm-1038
CLM-1038, Energy Aperture, as of 1980.