To assess climatic performance of energy producing systems, the indicator IPCC, 100a is maybe the most commonly employed in life cycle analysis, LCA. The result is expressed as the amount of green house gases that is emitted to the atmosphere during production of one energy unit as e.g. kg CO₂ equivalents per 1 MJ of energy produced or transferred by the system considered. To translate this indicator into cost the rate for green house emission trading in EU would at least in principle be applicable but has not been used for that purpose in connection with product design yet as far as we know.

The analysis of the LCA data on the two solar heating systems found in the Ecoinvent data base shows that the total cost methodology proposed by Carlsson would be a suitable tool to compare performance of different solar heating systems not only in terms of direct costs but also in terms of the indirect costs that can be attributed to the environmental negative impact the life cycles of the solar systems are causing.

The analysis has also shown that to make an adequate comparison between two solar systems with respect to environmental performance or environmental cost, the two systems have to be analysed when operating under the same external conditions with respect to outdoor climate and heat demand. The solar fraction utilized by the systems must be the same which means that only the design and the size of the two systems are different.