Anna Helgesson, Peter Krohn, and Bjorn Karlsson Vattenfall Utveckling AB, SE-814 26 ALVKARLEBY, Sweden,

Phone no: +46 26 83500, Fax no: +46 26 83670, e-mail: anna. helgesson@vattenfall. com

Introduction: The main disadvantage of using solar electricity is the high cost. By using concentrators to increase the radiation, some of the expensive absorber material can be replaced by cheaper reflecting material. One disadvantage with concentration is, however, that the cell temperature rises, resulting in a reduced electrical efficiency. The performance can be improved by cooling the cells, and this is the background for the development of the so-called MaReCo-hybrid. This is a specially developed concentrating collector giving both heat and electricity. The MaReCo-hybrid has been developed at the Swedish company Vattenfall Utveckling AB, and has now been delivered for installation in a newly build residential area in Stockholm. The paper will present the collector in more detail.

Introduction

Hammarby Sjostad is an old industrial area in Stockholm, Sweden. This area is now changed into a modern ecologically sustainable residential area. The company SBC Bostad has been planning to use solar energy for heating and electricity generation in one of its buildings. The use of solar energy will help to create a green image. The collector to be used is a so-called MaReCo-hybrid, developed at the Swedish company Vattenfall Utveckling AB. This construction gives both heat and electricity, and is therefore an interesting way of making an efficient use of the available roofing area. The utilisation of the heat can also be seen as a way to reduce the costs for the electricity generated.

During spring 2004, 30 m2 of the MaReCo-hybrid was delivered to Hammarby Sjostad. During the rest of the year, measurements will be made on the performance of the hybrid — system.

Background

One barrier for an increased utilisation of the PV technology is the high costs and the low output. By using concentrators to increase the irradiation onto the solar cells, the use of PV can be made more cost competitive. In this way, some of the expensive solar cell area can be replaced by cheaper reflecting material. One disadvantage with concentration of the radiation onto the solar cells is, however, that the cell temperature rises, resulting in a reduced electrical efficiency. By cooling the cells with circulating water, the output from the PV-module can be improved. The heated cooling-water can then also be utilised for heating purposes, and this will result in an increased total energy output and a better performace/cost-ratio. A system giving both heat and electricity is called a hybrid system.

In this case, a special construction named “MaReCo” has been used. The abbreviation MaReCo stands for “Maximum Reflector Collector”, and the name refers to the purpose of the construction, which is to replace some of the expensive absorbing material with cheaper reflector material. The hybrid-MaReCo has been developed at the company Vattenfall Utveckling AB, and it consists of an asymmetric reflector trough and a specially designed hybrid-absorber. A large part of the development work has been made within the frames of two large Swedish RD&D-programmes concerning solar heating that have been
going on since 1996 (Helgesson et al, 2000 and 2004) and within a national R&D — programme concerning solar electricity managed by ELFORSK. The goal of the development of the MaReCo-hybrid has been that the installation cost shall not exceed SEK 2 000 per m2 glazed area, and that the construction shall give a yearly energy output of 50 kWh electricity and 200 kWh heat per m2 glazed area.