Earth friendly: Switching almost all appliances to night-time use using timers reduces the daily peak load on the grid. As hot water during daytime is not replenished, it also encourages water conservation.
Finance friendly: The cost of converting your electricity plan to day/night rates starts at about $130 and should quickly pay for itself with the lower night rate.
Solar hot water or solar thermal (SHW) system. Solar hot water uses a thermal collector to convert sunlight directly into heat for hot water. Evacuated tube collectors have better returns in colder areas.
Earth friendly: Both SHW and photovoltaic contribute towards a 100% renewable energy New Zealand. However, both provide little hot water on short winter days when seasonal peakload is highest.
Cost effective: Cost $5000 to $9000 installed.
Heat pump water heaters (HPWH). These work similarly to space-heating heat pumps, with water heated by extracting heat energy from the ambient air. They are 2.5 to 4.5 times more efficient than standard electric water heaters.
Earth friendly: HPWHs reduce electricity consumption year round, although more so in summer. They can be put on a timer to come on in the middle of the day when it is hottest and to avoid peak load.
Cost effective: Cost about $3000 to $5000 installed. If available, you can buy a reconditioned unit for a lower cost.
Photovoltaics or solar panel systems (PV). These capture sunlight and convert it into electricity, which can be used for the whole house or to power the hot water system.
Earth friendly: As for SHW.
Cost effective: The cost of PV has come down and now compares favourably with SHW or HPWH.
Wetback system. Water is circulated through a water jacket installed in the woodburner’s firebox that heats water before returning it via an insulated pipe to the hot water cylinder.
Earth friendly: Firewood is considered a carbon neutral fuel. In practice it requires some fossil fuel for processing and transportation. As heat is removed from the firebox to heat water, lower temperature combustion may release particulates to the air.
Cost effective: Excellent if you have a free source of timber! Otherwise, heating water this way is expensive. Only suitable for efficient woodburners.
Combinations.
Options include: SHW or PV in summer to complement wetback use in winter. Night-rate ripple control on a standard hot water cylinder heater with PV for daytime electricity generation. PV connected to a HPWH for high efficiencies.
