Consumer impacts on dividends from solar water heating

Common domestic solar water heating system usage patterns were investigated by a survey of 55 installations. These usage patterns were modelled by simulation based on the actual occupants' use of boiler or other auxiliary heating control strategies. These strategies were not optimal, as often assumed. The effectiveness of the technology was found to be highly sensitive to the time settings used for auxiliary water heating, and the 65% of solar householders using their boilers in the mornings were found to be forgoing 75% of their potential savings. Additionally, 92% of consumers were found to be small households, whose potential savings were only 23% of those of larger households, which use more hot water. Overall the majority (at least 60%) of the systems surveyed were found to be achieving no more than 6% of their potential savings. Incorporating consideration of Legionella issues, results indicate that if solar thermal technology is to deliver its potential to CO2 reduction targets: solar householders must avoid any use of their auxiliary water heating systems before the end of the main warmth of the day, grants for solar technology should be focused on households with higher hot water demands, and particularly on those that are dependent on electricity for water heating, health and safety requirements for hot water storage must be reviewed and, if possible, required temperatures should be set at a lower level, so that carbon savings from solar water heating may be optimized.