R. Haberl1*, E. Frank1, P. Vogelsanger2

1 Institut fuer Solartechnik SPF, HSR University of Applied Sciences of Rapperswil,
Oberseestrasse 10, 8640 Rapperswil, Switzerland

2 Ingenieurburo Peter Vogelsanger, Nidelbadstrasse 94, 8038 Zurich, Switzerland
* Corresponding Author, robert. haberl@solarenergy. ch

Abstract

The effect of various parameters on the cost, the performance and the optimum dimensions of a combined solar heating system (for Domestic Hot Water and space heating) in Central Europe was studied. The parameters varied were: Collector cost and collector performance, storage cost and storage insulation as well as the rise in energy prices. For every set of parameters the optimum size of the collectors and the storage tank was identified with simulations. The cost/benefit ratio was used as the optimisation criterion.

As could be expected, favourable parameters result in economically more viable systems. The simulations showed that good (efficient or inexpensive) collectors also positively affect the system’s size and performance. Surprisingly, reducing the cost of the storage tank does not significantly affect the size and thermal performance of the system with the best cost/benefit ratio. Better insulation of the storage tank even leads to slightly smaller systems. While the price of the backup energy strongly influences the system’s economics, energy prices have hardly any effect on the optimum system size.

All simulations were based on an avant-garde system concept which features an unusual control strategy for space heating and a drain-back collector loop. This lean design could be appropriate to incorporate a non-pressurized tank and could be suitable for substantial cost reduction. However, its thermal performance characteristic is not very different from other, more usual solar combisystem concepts. The cost functions used in the base case simulations were derived from pricing information on products available on the market (i. e. pressurized tanks). The authors therefore suppose that the essential results of this work also apply to other combisystems in a similar climate.

Keywords: Solar heating system, cost/benefit ratio, additional cost, primary energy savings, dimensioning, optimisation.

1. Introduction

With today’s energy prices and without subsidies, the installation of a solar thermal system leads to comparably high payback periods. Thus, the cost effective saving of fossil fuels should take precedence in the comparison of installation costs against any conventional heating system. Better cost effective savings can be achieved with respective improvement of the solar thermal system components as well as paying attention to the combing of them into an ensemble. In this paper, a potential new concept called the MaxLean System is introduced, in the development of which a new dimensioning method has been devised that optimises the cost/benefit ratio instead of the annuity of the system. The principle of the method and the appliance on the MaxLean system

concept is presented. The same approach is then used for investigating the influence of various component parameters and cost function parameters on the dimensioning and the cost/benefit ratio of the system.