Solar Highbeams Target Design compared with Crescent Dunes

The Solar Highbeams Target Design compared with the Crescent Dunes Solar Energy Project. Underlying image quoted from Google Maps.

Table comparing the Solar Highbeams Target Design with the Crescent Dunes Solar Energy Project.

The ratings assume that the annual average power per mirror area of Crescent Dunes (51 W/m2) can also be achieved in the target design. Maximum boiler temperature at Crescent Dunes is 565 °C (1050 °F).

Advanced steam turbine technology: plant efficiency vs. steam temperature. Image quoted from EPRI, "Materials Technology to Enable High-Efficiency Advanced Ultrasupercritical (A-USC) Steam Power Plants"

The plot of plant efficiency vs. steam temperature above suggests that increasing steam temperature from Crescent Dunes' 565 °C (1050 °F) to an A-USC (advanced ultra supercritical) turbine's 760 °C (1400 °F), would increase plant output by about a factor of 46.5/42.3 = 1.10. That gives some leeway in rating the Solar Highbeams Target Design at 1 GW though its atmospheric turbidity losses will be greater than Crescent Dunes', and possibly its rather different shading and blocking losses will be greater as well. Eventually, thermophotovoltaic (TPV) conversion may offer even higher efficiencies.

Comparison of conventional and telescopic heliostat fields at the same tower height

For the same height at the central receiver or beam-down optics, a telescopic heliostat field will have about twelve times the power rating of a conventional heliostat field. About a factor of three comes from increased field radius, and a about factor of four from improved land utilization.

For the same height at the central receiver or beam-down optics, a field of telescopic heliostats has about twelve times the power rating of a field of conventional heliostats. Of this factor of twelve, about a factor of three comes from increased field radius (the field radius is 14 times the tower height as opposed to 9 times) and about a factor of four comes from covering the land more densely with heliostat mirrors (81% mirror fill as opposed to 17%.)

Take for example the 160 m tower height of the solar plant now under construction in Crescent Dunes, Nevada. A telescopic heliostat field with beam-down optics topping out at a height of 160 m would have a heliostat field radius of 2225 m, and 81% mirror fill, giving an approximately 1.3 GW solar plant instead of the 110 MW the plant being built at Crescent Dunes. Significantly, with telescopic heliostats, this full-sized power plant would be ground-mounted rather than on a tower.

The radius/tower ratio of 14 for a field of telescopic heliostsats was calculated in a previous post.

The mirror fill of 81% for a field of telescopic heliostats was estimated as follows.

The packing efficiency of circles in a hexagonal arrangement on the plane is 0.907. Taking the mirror fill in the solid phase of the heliostat field to be 90%, the previous calculations assumed the mirror fill in the outermost ring of heliostats would be 0.6 of this value or 54%, so, on average, the mirror fill in the gas phase of the heliostat field will be roughly the mean of 54% and 90%, or 72%. Since the gas and solid phases of the heliostat field have equal areas, overall the mirror fill is the mean of 90% and 72%, or 81%.

Mirror/land ratios in solar power tower generating stations

Based on Google imagery, the heliostat field of Ivanpah 1 is very nearly a square, 1995 m on a side, with three corner truncations, giving a heliostat field land area of about 3,800,000 square meters. This unit has 53,527 heliostats each with a mirror area of 15 square meters, giving a total mirror area of 803,000 square meters. The mirror/land ratio is 0.21.

Based on Google imagery, the heliostat field of the Crescent Dunes Solar Energy Project is very nearly circular, with a diameter of about 2804 m, giving a heliostat field land area of about 6,200,000 square meters. This unit will have 17,170 heliostats, each carrying 62.4 square meters of mirror, giving a total mirror area of 1,070,000 square meters. The mirror/land ratio is 0.17.

The mean radius of the heliostat field (the radius of a circle having the same area as the field) is 1100 m for Ivanpah 1; 1402 m for Crescent Dunes. The tower heights are 140 m and 160 m respectively, giving mean field radius to tower height ratios of 7.9 and 8.8.