I will be producing solar heliostat arrays this summer that have a peak solar input of about 18KW.

These are mirror devices that reflect sunlight onto a central receiver. Remember the big government solar projects such as "Solar Two" at Daggett, California, approximately 10 miles east of Barstow, California in the Mojave Desert. This system produces about 10MWatts of electricity. Here's an example:

This is not a price quote. I am only speculating on possible sales prices. My law guy won't let me quote prices yet. I expect to sell our heliostats system at around $10us/ft² of mirror in sizes of around 200ft². Also about $0.20us per installed thermal watt based on 10KW solar thermal output. This then equates to about $2000 per heliostat array. You supply the computer we supply everything else less installation.

For comparison a rule of thumb for PV panels is that they cost about $50us/ft². They then have an installed cost of about $5us per watt not counting the mounts. Of course this is for non tracking panels. Also the wasted energy is not recoverable.

There is plenty enough power to flash water into steam. I'm working on a steam engine to electric power receiver now. I won't be selling this but I do like to find out about the technology. This could be about 20% efficient. If the engine and receiver costs $2000us the total system would now be $4000us. This predicts that electricity would have an installation cost of $2us per watt electric. This system would deliver 1KW of electricity all day and the 9KW thermal waste heat can be stored for domestic heat using hot water.

We can custom make almost any size and any concentration factor you might need. Multiple arrays can work in tandem to multiply the amount of power at a single receiver. Only one computer is needed to run many array units.

The computer is a common IBM PC type. It could even be an old slow 8088. You probably already have one that is not in use. I could supply the computer but that would just increase the cost to you. Besides cheap used computers can be had for around $50. If required I can supply a single board stand alone controller microcomputer these cost about $300 to $400us.

I have been using a Pocket PC from Zeos in the prototype. I also used an 8088 based Compaq laptop. The application simply doesn't require a high powered computer. It does need to have a computer that can use a compiler that uses double precision floating point arithmetic for the solar position calculations. The 8 bit microcontrollers typically don't have enough memory nor have compilers that have double precision floating point math. Even though the calculations are extensive they don't have to be done very often.

I have settled on 200ft² as this size is near my minimum manufacturing cost/ft². If each unit is built larger it needs to be built stronger, read expensive, to resist heavy winds. If built smaller the drive mechanisms become the dominant expense.

The basic engineering design requirements are based on a wind loading of 10lb/ft² from any direction. The minimum safety factor is 8. This makes for a very sturdy and stiff design.

Really low cost manually operated heliostat arrays for the third world are in the works. If the locals build everything and have a village worker do the aiming I think the cost could be as low as $2us/ft² in a 100ft² size. With 9KW peak thermal output it would be easy to do solar cooking and baking. It can also power water desalination and sterilization units.

The mirrors are flat plate glass mirrors. They are each 2.5ft x 8ft in size and 1/8in thick. They are very flexible. To stiffen them I add an aluminum stiffener to the back side. A shaft extends through the ends.

A frame is made to support the mirrors and yet let them rotate about the mirror shaft. In this case I have 10 mirrors in the frame.

                  Up
                   o
          Mirror/ /
               / /
              / /Frame
             / /
            / o
South      / / \   North
          / /   \
         / /     \
          /       \
         o         \
                    \
          Angled Pier\
  ====================\=====
                       \
                  Down

Note! There are a variety of ways this array of heliostats can be used.

1.	The mirrors can be adjusted so they are exactly parallel. This sends all the light in a generally parallel beam. This is used to reflect light to a distant parabolic concentrator dish. The dish secondary concentrator can produce temperatures high enough to melt aluminum and possibly steel. Here are some examples: furnace Sandia's large solar furnace. odeillo Big solar furnace parabolic reflector at Odeillo, France.
2.	The mirrors can be adjusted so they each reflects light on the same distant area. This adjustment doesn't require extra concentration. Since all 10 mirrors reflect on the same area the basic concentration will be 10 to 1.
3.	lighting Each mirror can be adjusted to reflect light to individual distant locations in diverse directions. This is useful for lighting by sending light into north facing windows.

Here is an example from professor Cates:
Hybrid Lighting. By Michael R. Cates.
Lighting and PV electricity.

The whole system uses a computer that controls the movement of the mirrors. Each dimensional parameter is measured carefully and the software moves the mirrors in such a way as to send the light to the receiver. The software operates in "open loop" mode. This means that there is no feedback needed from the receiver. The software calculates to an accuracy of a few arc seconds and the mechanical drivers are good for about 1/10° of arc.

The software first calculates the position of the sun. This program has inputs for longitude, latitude, height above sea level, time, date, barometric pressure, and temperature. This program compensates for all significant errors including the main ones such as atmospheric refraction near the horizon, (called parallax).

I then calculate the half angle between the sun and the receiver. The center mirror is set to a position so that the half angle is perpendicular to the plane of the mirror.

The program also can calculate the position of the moon. When the mirrors are aligned with the moon, at night, the receiver is fairly bright. Its bright enough to do maintenance on the system. Although you have to be careful not to get "moonburn". Its hard to find "MoonTan Lotion" ;^)

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