Description of the hybrid-MaReCo

The MaReCo

The MaReCo principally consists of an asymmetric reflector trough with a single absorber running along the trough (figure 1). The reflector geometry is specially adapted to the irradiation distribution in Sweden (Karlsson and Wilson, 2000). The reflector consists of two parabolic parts connected by a semi-circular sector. The acceptance angle interval of the collector is between 20° and 65° form the horizon. Since the reflected radiation will reach the absorber on both sides, the absorber should be double sided selective. In the hybrid version, there are solar cells laminated onto the front side of the absorber. The main advantage with the MaReCo-construction is the low material content, which helps to reduce the collector cost.

Figure 1: Principal sketch of a MaReCo, consisting of an asymmetric reflector trough, a

double sided selective absorber, and an AR-treated cover glass.

The first build prototype was made as a sandwich structure with one inner reflector sheet made of aluminum and one outer sheet made of steel. One problem with this construction was, however, that the reflector was deformed at high temperatures. In order to solve this problem, a new construction was developed. In this design, the reflector trough is made of a single steel sheet laminated with an aluminized plastic foil. The aluminized surface gives the reflector a good reflectance, and the steel sheet makes the construction rigid enough to avoid the problem with deformation.

When manufacturing the reflector trough, the reflector plate is first cut to the desired length. It is then bent over a special fixture in order to achieve the correct reflector shape (figure 2).

The gables of the construction consist of a single plate with a groove in which the reflector plate is placed (figure 3).

Figure 3: The reflector trough gable.

The hybrid-absorber

Also different kinds of hybrid-absorbers have been tested in the development project. Problems with stability and high temperatures lead to the development of a specially designed aluminum profile with solar cells laminated onto the front side of the profile (figure 4). The water is fed through copper tubes inserted in the notches on the backside of the profile. In order to increase the solar absorptance, the surface is anodized. The relatively thick aluminum-profile makes the hybrid-absorber stable, and reduces the temperature gradients that arise due to concentration.

Figure 5 shows a close-up of a hybrid-absorber placed in a MaReCo-trough. Here, also the absorber-holder can be seen.

Support and glazing

In figure 6a is shown the mounting support for the reflector trough. Figure 6b shows the collector mounted onto girders that will be used for fastening the collector onto the roof. The larger girders in the photo are exemplifying the girders that are mounted on to the roof.

% a

Figure 6:

The collector trough is covered with an anti-reflection treated glazing that is fastened with silicon. The glazing and the reflector trough together give a rigid construction.

Installation

During spring 2004, 30 m2 (12 units) of the developed MaReCo-hybrid was delivered to Hammarby Sjostad for installation. Figure 7 shows a photo from the roof when the collectors have been lifted up and mounted on the girders on the roof. In the picture, the collectors have not yet been electrically connected or connected to the heating circuit.

Figure 7: Photo from the installation of the MaReCo-hybrid in Hammarby Sjostad.

In order to get a high enough voltage, the modules will be series connected in two parallel units that are connected to the converter.

On the heating side, the collectors will be connected to two accumulators. The generated heat will be used for the production of hot water.

Measurements

In the continuation of the project, measurements will be made on heat and electricity performance. The output will be compared with the available radiation. These measurements have not yet started, since the hybrid-collectors still have not been installed. The measurements will be made during the operation season 2004.

Preliminary measurements on a prototype hybrid-collector placed at Vattenfall Utveckling’s laboratory in Alvkarleby indicate that a yearly heat output of about 145 kWh/m2giass (at an operating temperature of 50°C) and an electricity output of 50 kWh/m2glass are possible to achieve.

Discussion

The construction is considered to be an interesting technique for using solar energy to produce both electricity and heat. The low material costs will help to create a cost effective system. The measurements on the system installed in Hammarby Sjostad will give data on the energy output from the system. This data is then to be used to calculate the energy cost for the produced heat and electricity.

References

Broms G. et al, "Utveckling av solhybridsystem till Hammarby Sjostad’, VUAB report no U 03:34, Vattenfall Utveckling AB, 2004. (Project report concerning the development of the MaReCo-hybrid.)

Helgesson A. et al, “Solvarme, Slutrapport for FUD-program Solvarme 1996 — 99", VUAB report no UD 00:12, 2000. (Final report from the Swedish RD&D-program "Solar heat 1996 — 99".)

Helgesson A. et al, "FUD-program “Solvarme 2001 — 2003”, Slutrapport’, VUAB report no U 03:103, Vattenfall Utveckling AB, 2004. (Final report from the Swedish RD&D-program "Solar heat 2001 — 2003".)

Karlsson B. and Wilson G., “MaReCo-design for horisontal, vertical or tilted installation", Vattenfall Utveckling AB, 2000. (Contribution to EuroSun 2000 in Copenhagen)