A crucial step in the design and development of a cost and energy efficient storage is a comparative cost analysis. Here, the cost and capacity of conventional hot water storage and a PCM-storage have been examined. Below, the details of this study are summarized, and the results are shown and discussed.

1.1. Cost Calculations

For the comparative cost analysis, it is assumed that PCM storage and conventional hot water storage are to serve the same heat load in an identical solar hot water system. It is further assumed that the operating and maintenance cost (O&M) would be the same regardless of the choice of storage technology. Thus, the cost analysis only compares the first capital cost of conventional stratified hot water storage to those of PCM-based hot water storage with variable volume fraction of PCM. The volume fraction is here named the Ice Packing Factor (IPF). Table 1, below, summarizes the first cost categories comprising the heat storage.

The PCM considered here is a commercial PCM with a melting temperature around 58 °C, and with a latent energy storage capacity of around 71 Wh/kg. Its density is 1,46 kg/l giving a latent storage capacity of 103 kWh/m3. In the PCM concept, some additional storage capacity is also given by the sensible heat stored over some temperature range AT. In the analysis, this AT is assumed to be the same regardless of storage technology.

In the calculation, a PCM price of approximately 2.7 Euro/kg was used. This is a bit low as compared to what is possible to obtain today but was discussed with a leading manufacturer as being a reasonable target price for the future assuming a larger scale production and sales.

Finally, the price of the tank is an approximate figure obtained by a Swedish manufacturer of stainless steel tanks suitable for this application.