Heliobeaming is the technique of using mirrors to direct and concentrate sunlight onto a moving device to provide that device power. It differs from heliostats based power plants in that it is assumed that the receiving target is mobile, and this mobility impacts the position, shape and movement of the mirrors and other optical systems.

Heliobeaming is the technique of using mirrors to direct and concentrate sunlight onto a moving device to provide that device power. It differs from heliostats based power plants in that it is assumed that the receiving target is mobile, and this mobility impacts the position, shape and movement of the mirrors and other optical systems.

Range

The range of a heliobeaming system is mostly determined by the diameter of it's primary mirrors. As a rule of thumb it is 100:1. That means that mirrors of 4 ft diameter will have a range of about 400 ft. The range is a function of the apparent size of the sun. On Earth the apparent size is 32 arc seconds or about 1/2 degree. The spread of a 1/2 degree beam can be calculated with trig by treating the beam as a triangle. However the rule of thumb of 100:1 is normally accurate enough. When a point target is less than this 100:1 range the image of the sun reflected in the mirrors is complete. While the image is complete the power level is the same as if the target was closer than 100:1. This means that there is little power loss through the effective range. Once the target moves past the 100:1 range the power level drops following the square law. That means that at a distance of 200:1 the power level is 1/4 of the 100:1 level. Focusing the mirrors vs leaving them flat can increase the power level within the 100:1 range and can also mitigate the fact that any receiver will not be a point target. Beyond the 100:1 range a focused mirror lessens the power level. It is also worth noting that the receiver will make best use of the availible power by roughly matching the mirror size. That means that a 4 ft solar panel will match well with a 4oo ft range.

Interestingly the range of a heliobeaming system on Mars is 150:1 because of the smaller apparent size of the sun there.

Power level

The power level is basically the number of mirrors times the mirror efficiency times cosign losses. This assumes that we are using flat mirrors and operating within the 100:1 range. On Earth the atmosphere scatters a noticeable portion of the sunlight and this scattered light is lost in the reflection from mirrors but is available to a solar panel pointed directly at the sun. This portion varies from around 10% to 20% in round numbers. The mirror itself will typically be over 90% efficient. It is the sum of these two factors that make up the mirror efficiency. Generally this falls around 80%. Mirror efficiency is also lowered by manufacturing quality.

Peak power.

More mirrors lead to a virtually unlimited amount of available power. However it is generally best to avoid the need for supplemental cooling. Supplemental cooling raises the cost, weight and complexity of the system. On a mobile platform these issues are more important than on a fixed platform. If you avoid supplementary cooling then the limit becomes the maximum operating temp of your receiver combined with the natural radiative and conductive cooling. For triple junction solar cells my tests and conversations with manufacturers have led me to believe that in the most general terms that 8 to 10 suns is the rule of thumb limit for the Earth and an equvlilent power level for the Moon.

These factors lead to a typical system consisting of 13 to 20  mirrors. More mirrors can be used instead of larger mirrors by calculating an equivalent diameter. Cosign losses can be ignored if the angles are good. Otherwise more mirrors can be added to compensate.

Archimedes Death Ray

A heliobeaming system and an Archimedes Death Ray are very similar. The Death Ray is designed to raise the temp of the target above the auto ignition temperature. A heliobeaming system is only trying to get to the optimum power level. A Death ray will typically have to reach 50+ suns to reach auto-ignition on even favorable targets. A heliobeaming system will typically be set for around 10 suns concentration.

Solar Power Plants

The solar power plant(s) Solar One and Solar two produced a lot of literature on the subject of heliostat power plants and much of that applies to heliobeaming. There is now a power plant in Spain based on those concepts. Solar One and Two were a research power plant in the desert southwest of the United States. If I understand it correctly the summary of these multiyear experiments was that it is cheaper to burn coal. I suspect that carbon trading could change that equation. Spain has carbon trading and does not have all the cheap coal available in the US. I also have developed ideas to help lower the cost of such an installation.

I hope to refine this document after the competition. Check it for errors, and put in the accurate formulas. But this should give an idea of how the concept plays out.

Brian Turner

Captain