Lars Broman

TRNSYS The most complete solar energy system modeling and simulation software

The five computer programs TRNSYS, PRESIM, TRNSED, ONLINE and PREBID have been put together into a program package which is the most complete solar energy system modeling and simulation software that is available today.

On the didactics of renewable energy education — drawing on twenty years experience

Didatics includes both sibject knowledge, i.e. what to teach, and methodology, i.e. how to teach. In the paper, renewable energy education is discussed from a didactic point of view. Examples are predominantly drawn from the field of direct utilization of the suns energy.

Fabergé optics and edge filter for a wood powder fuelled thermophotovoltaic system

In order to achieve high efficiency in a TPV generator, it is important that a high fraction of emitted photons with energies below the TPV cell bandgap are reflected back to the emitter. This can be accomplished in several ways. We present the idea of an internally reflecting egg-shaped double cone with the emitter at one end, an edge filter at the wide center, and the TPV array at the other end. This geometry has so far been studied by means of both ray tracing analysis and by means of measurements with a simulated emitter. A sharp switchover from transmission to reflection in a multiple layer dielectric filter can be achieved only if the angles of incident rays are confined to a fairly narrow angular interval. The two methods both show that the studied optics can lower the angular spread of rays incident onto the filter and that some 96% of the emitted rays (in the ideal case) reach their goal without passing the filter or being reflected by the filter more than once. The concept of the whole of the wood powder fuelled TPV system is also given.

An animation tool for demonstrating the importance of edge filters in thermophotovoltaic applications

In order to achieve high efficiency in a thermophotovoltaic (TPV) generator, it is important that a high fraction of emitted photons with energies below the TPV cell bandgap are reflected back to the emitter. This can be accomplished in several ways, and one suggestion is to place an edge filter between the emitter and the TPV cell array in an elliptical optic design. An animation tool, developed in the Excel® program, for determining the efficiency of an optical system is presented. The animation components are a black body emitter, an edge filter, and an array of TPV cells. The tool has been used to demonstrate the importance of an efficient filter and the usefulness of optics that makes the edge of the filter as sharp as possible. It is available at

Parabolic dish concentrators approximated by simple surfaces

Two different concentrating mirrors have been constructed that resemble parabolic dish reflectors. Both mirrors are made of slightly curved strips of flat, bendable material. The strips of the most simplified mirror have only large-radius circles and straight lines as boundaries. The necessary equations for making the mirrors are given. Also a simple way to make a stiff, lightweight frame and support for the mirror strips has been developed. Models of the mirrors have been built and successfully used for cooking and baking.

Animation Tool and Q.E. Measurements for Estimating the Optimum System Efficiency of a TPV Generator

In order to achieve high efficiency in a thermophotovoltaic (TPV) generator, it is important that a high fraction of emitted photons with energies below the TPV cell band gap are reflected back to the emitter. This can be accomplished in several ways, and one possibility is to place an edge filter between the emitter and the TPV cell array in an elliptical optic design. By this arrangement the cooling demand on the TPV cells is reduced and the reflected radiation is reused in the emitter, the fuel demand is decreased. An animation tool, developed in the Excel® program, for determining the optical availability in such a system has been presented previously. The animation components were a blackbody emitter, an adjustable edge filter, and an array of TPV cells. The tool was used to demonstrate the importance of an efficient filter and the usefulness of optics that makes the edge of the filter as sharp as possible.In such a system the TPV cells are the dominant cost. It is possible to tailor the selective fi...

Museum exhibits for the conics

It is rather common nowadays that museums, especially those of the science center type, have showcases where visitors can perform experiments. In the Futures Museum in Borlange we have made an exhibit where interested persons can construct parabolas. In this note we describe this showcase. Analogous exhibits can be made for constructing ellipses and hyperbolas.