The main parameters which influence the optical performance and solarfield investment are the hight H of the receiver, the gap D between primary mirrors and their number N. The influence of variation of each parameter on the LEC is shown in figure 7a-c. The calculation was made for three different optical errors. It is obvious that higher optical errors decrease the performance of the collector and increase the LEC. For small optical errors the optimal receiver height is displaced to higher values. The optimum gap between primary mirrors, which is assumed to be constant, is less dependent on the optical errors. The ground coverage is about 80%. Additional primary mirrors reduce the specific collector-cost but also decrease the specific performance.

As mentioned above the primary-mirrors are curved elastically, hence they have a distinct focal length f. The relative focal length f is defined as the ratio of the focal length and the distance from the mirror to the absorber. The influence of the relative focal length f on the LEC is shown in figure 7d[11]. The optimum of f is a bit higher than one, with less dependence to higher than to minor values.

(c) variation of primary mirrors (d) variation of the focal length

An optimization of the three parameters corresponding to different optical errors leads to lower LEC shown in table 2. By reaching a high optical accuracy, a higher placed receiver enables more primary mirrors and hence the cost reduction potential is very high.

Table 2: LEC of the configuration opti — [mrad] 2.32 4.65 6.98

mized on the optical errors LEC 11.3 12.1 13.2

It is also possible that the gaps between primary mirrors are increased linearly rather than constantly. A linear increasing gap effectuates an optimum for lower receiver heights, because the blocking at high zenith angles is reduced. The difference at the boundary conditions presented here is very low. The LEC of a collector with constant gaps is about 3-8 0/00 higher. The decision whether to use linear or constant gaps depends on the specific cost of the receiver hight Ch and the expense of the linear increasing gap. With respect of simplicity a constant gap might be more favorable.

Conclusion

The linear Fresnel-concept has the potential of low electricity cost prices. Considering

the numerous possibilities of variation in geometry an optimization for a distinct purpose

in respect of reachable accuracy and specific cost factors is important. With the method

presented it is possible to evaluate intended improvements regarding the LEC.