Value chain · CLM-1240
Low confidence
The evidence behind this statement is thin, indirect or second-hand. Read it as a lead to check, not as a settled finding.
In plain terms
In 1999 a US national laboratory sent infrared light from a bank of laser diodes across a lab room onto ordinary solar cells and got a few watts out, enough to turn a small motor. The beam was patchy and the run was cut short, so less than one per cent of the electricity put in came out at the far end.
The claim as recorded
A 1999 Lawrence Livermore demonstration beamed light from a non-coherent laser diode array at about 850 nm over a path of about 10 m onto silicon solar cells and drove a small motor. At the test point (42 V, 20 A) the array emitted 28.6 W (3.4 per cent electrical-to-optical). The peak flux at the receiver was 1,850 W/m2, and a 3-cell string gave an estimated 1.8 W, at a cell efficiency of about 32 per cent (or about 14 per cent under a conflicting estimate). The same array emitted 243 W (16 per cent) at 44 V and 35 A, and earlier measured 578 W at 22.4 per cent. The authors project more than 10 per cent DC-to-DC over ranges up to about 100 m with the existing 20 cm aperture. On the drafter's arithmetic, the measured run's DC-to-DC efficiency was about 0.2 per cent for the 3-cell string (1.8 W from 840 W in), or 0.4 to 0.5 per cent for the full receiver's estimated 3.6 to 4.5 W.
Evidence behind this: A laboratory demonstration with measured values (LLNL hardware, NASA Marshall funding), reported as a preprint by its authors, who call their own measurements "low and poorly measured".
Scope and limits
A ROOM-SCALE LABORATORY RUN, NOT ORBIT-TO-GROUND; THE 1.8 W IS INFERRED FROM VOC AND ISC WITH AN ASSUMED 85 PER CENT FILL FACTOR, NOT MEASURED INTO A LOAD. The authors could not reconcile two estimates of beam power (28.6 W against about 65 W). The receiver was damaged by hot spots. The more-than-10-per-cent DC-to-DC figure is a projection. Table 1 (estimated and projected figures) is garbled in the text layer and needs a render.
What it assumes
That "W/n?" is W/m2 and "-14'S" is about 14 per cent (OCR), and that the "10 meter path" matches the drawn layout (1.23 m, 3.78 m and 4.05 m legs).
Where it comes from
PDF p.3 [1], raw: "The diode array compositebeam was refocused by a parabolic mirror over a 10 meter path"; "The maximum cell output obtained was several watts, and the cell output was used to drive a small motor."; "With the existing 20 cm aperture, useful power transmission over ranges to -100 meters should be achievable with a DC to DC efficiency of greater than 10%." PDF p.4, raw: "operate at up to 578 watts at an operating point of 60 A and 43.1 V, for an efficiency (DC to optical power) of 22.4%"; "At these conditions the array optical power output was measured at 243 W, as described below, for an efficiency of 16%. Power transmission tests were run at 42 volts120 A; at these conditions the laser power output was measured at 28.6 W. The associated efficiency is 3.4%."; "The output wavelength was near 850 nm in the near infrared." PDF p.6, raw: "the powcr cxtractahlc by a matched load would have heen I .8 W"; "the estimated power available from the full 9.cell receiver was between 3.6 and 4.5 watts"; "The flux at the receiver, at the pattern peak, was measured with the power meter at 1850 W/n?"; "giving a cell efficiency of 1.8/5.7 = 32%"; "The corresponding PV cell efficiency if this power estimate is correct is -14'S". PDF p.7, raw: "As a result, the overall efficiency and power transmitted were both low and poorly measured." Arithmetic: 42 V x 20 A = 840 W; 28.6 / 840 = 3.4 per cent; 44 x 35 = 1,540 W, and 243 / 1,540 = 15.8 per cent; 1.8 / 840 = 0.21 per cent; 3.6 to 4.5 / 840 = 0.43 to 0.54 per cent.
Basis: W of optical and electrical power; per cent efficiency; wavelength in nm; path length in m; receiver flux in W/m2
Related records
- Answers question
- QST-026 not published in this releaseQST-036 not published in this release
Cite this
energyaperture.com/c/clm-1240
CLM-1240, Energy Aperture, as of 1999-02.