Next up, we will deal with the details of the solar collector assembly. SAM provides us again with a selection of parabolic trough collectors that we can easily import in our project.

We select the Eurotrough ET150 collector from the list by clicking on the entry. We now find the properties of the Eurotrough collector in the field below. The properties are provided by the SAM library when the option Use library values here is activated. The geometric details of the collector are listed in the first four fields, including the length, aperture, reflective area, and focal length.

Below are the incident angle modifier coefficients. The total optical efficiency of the collector is calculated in SAM by multiplication of several optical efficiency values here.

In addition, a factor for the solar field availability is considered to account for downtimes of the field, for example due to maintenance and repair works. On the next slide, we will take a closer look at the composition and calculation of the optical losses of the parabolic trough collector field.

The Sankey diagram on the left side shows the energy loss mechanisms occurring at the solar collector. First, there are cosine losses due to the fact that the rays of the direct normal solar radiation are not always perpendicular to the reflector surface. To calculate the solar energy after deduction of the cosine losses, the DNI is multiplied by the aperture area

of the collector and the cosine of the angle between the perpendicular of the collector plane and the sunbeam angle. Further optical losses occur in between the reflection of the solar radiation at the reflector and the arrival on the glass envelope of the absorber tube.

The solar radiation is reduced for instance due to the reflectivity factor of the reflector, imperfections of the reflector geometry, and soiling effects on the reflector and glass tube surface. On the way of the solar radiation through the glass tube, a part of the energy is absorbed and lost to the environment by convection losses.

A small portion of the radiation is reflected at the surface. In addition, heat losses occur at the hot absorber tube due to heat radiation. Further energy losses occur at the parabolic trough collector due to the variable incident angle. The incident angle modifier is a function of the incident angle and describes this correlation.

In SAM, the incident angle modifier is calculated with several incident angle coefficients. An example of a variable loss mechanism described by the incident angle modifier are reflective losses occurring at the glass tube that change depending on the variation of the incident angle.

Depending on the azimuth angle of the sun, the solar radiation hits the glass tube at steeper or shallower angles. At shallower angles, more radiation tends to be reflected and as a result higher optical losses occur. The part of the usable energy after deduction of the losses in the collector is described here with QEC, the effective collector power.

The collector efficiency is calculated by dividing the effective collector power with the total incident solar radiation on the aperture area of the collector. On this slide, the formula used by SAM for the calculation of the optical losses of the solar collector assembly is shown.

Two loss mechanisms that we did not discuss on the previous slide are the factor for tracking error and twist and the concentrator factor. The factor for the tracking error and twist considers losses due to inaccurate positioning of the collector towards the sun caused by the tracking system

and also losses due to the different alignment of the sun sensor on one end of the QEC to the other end due to twisting of the collector. The concentrator factor accounts for further not precisely defined energy

losses, for instance due to degradation effects of the parabolic collectors. In SAM, the optical losses of the collector and receiver are defined on separate subpages. A boundary is drawn around the outer shell of the evacuated glass tube. Everything outside the glass tube, including the dirt layer on the glass, is included

in the optical efficiency calculation of the collector, which is covered by the formula here. All loss mechanisms occurring inside the glass tube are included in the efficiency calculation of the receiver, which we will cover on the next subpage in SAM. The formula for the calculation of the incident angle modifier in SAM is shown here.

Three modifier coefficients are used to describe the changing influence on the energy losses depending on the solar incident angle. The total power available to the heat transfer circuit of the solar field is calculated with the next equation where cosine losses, optical losses, the incident angle modifier and the end losses of the collector field are included.

End losses occur at the end of a solar collector assembly due to solar radiation that is reflected by the collector but does not hit the receiver tube as the solar radiation is reflected beyond the end of the receiver tube.

We have already defined the parabolic trough collector EUROTRAF ET150 for our solar field at the beginning. SAM makes it very easy for us here, as all the properties of the collector are automatically taken from the library and we don't need to add or change values manually. In the next step, we will deal with a selection of a suitable receiver tube for our solar field.