Net energy analysis of domestic solar water heating installations in operation

The potential of solar water heating systems to reduce domestic energy use is frequently acknowledged.
However there are two factors that are rarely discussed when studying this technology. Firstly the real
performance of the installed systems in operation, and secondly a life cycle perspective of its energy use.
These two issues are reviewed in this paper, and a field study in Ireland is also presented. In the review,
some studies show that measured real performance of domestic solar water heating systems can be
lower than expectations. Concerning their life cycle energy performance, existing studies show that the
initial energy investment for the systems (their embodied energy) is a small portion of the energy savings
over their lifetime with calculation paybacks generally lower than 2 years. On the field study carried in
Ireland, representative of a maritime north European climate, the ‘energy payback’ based on the expected
energy savings is between 1.2 and 3.5 years, values comparable to previous studies considering the
less favourable climate and installation characteristics. However the measured energy savings generally
worsened the life cycle energy performance of this technology and thus increased the energy payback
period. The study concludes that while there is a real potential for life cycle energy savings through
domestic solar water heating installations, devising mechanisms to ensure proper design, installation
and operation of systems is essential for this technology.