OS2 FAQ

FAQ on OS2

Bold text1. Why are you going with a linear system, the linear Fresnel reflectors?

In short, Ausra is doing it, and they are to date the most successful solar thermal concentrator electric enterprise concept. For the longer answer - simplicity and low-to-the-ground mounting structure combine to the lowest cost possible. Other concentrator systems require large structures for windloading. Note that we are talking about the most effective way to concentrate a lot of sun onto a small target. The key to that is minimizing structure costs. The linear Fresnel system accomplishes this.

2. Why are you going with flat collectors if parabolic collectors are able to focus sun to a finer line? After all, Ausra has curved collectors, and they are the best in the business. Correct on your point. We are optimizing our system for a smaller scale, on the order of KW instead of MW. At this scale, it is more difficult to bend small mirrors of 6 or 12" width. Ausra mirrors are almost 6 feet across. Moreover, because we are not bending our mirrors, we are hoping for lower cost as well. As a third optical detail, you must consider that parabolic mirrors produce defocusing through the day, as the distance of solar rays from the reflectors to the collector tube changes throughout the day. One must draw this out on a piece of paper to see that this is the case for an E-W oriented array.

3. What is the concentration ratio of your system?

We have 16 slats for 16x concentration, with a parabolic shroud on the collector tube for another 3x concentration - for a total of 48x concentration. The collector tube is 2" wide.

4. Can you attain your 650K (377C) temperature with 48x concentration?

Yes. It is a matter of the balance of how much energy enters and leaves the collector tube.

5. How much power can you put into the steam engine at 650K?

We have about 38kW entering the collector tube - see Solar_Collector_Losses_Summary. We have radiation, conduction, and absorptance losses on top of that. This balance allows for 21kW to enter the steam engine, where we assume that all power that does not leave the collector tube is absorbed to heat the water working fluid?

6. Why are you using water as a working fluid? Aren't there more favoarable choices?

Water is the safest, most accessible, and easiest to work with fluid. 70% of power generation in the USA uses water as the working fluid - coal and nuclear power plants. The high heat of vaporization indicates that water is an energy dense working medium. Other fluids may have other advantages.