The experimental work undertaken as part of this comparison project included design and development of the 2 solar water heaters as well as their operation and data collation over a period of 2 months. The results of the experimental work have been rigorously analysed to present detailed ecological and financial accounts of the two heaters. The results indicate that the aluminium heater performs better than the stainless steel heater in every respect.
The average annual daily energy output from stainless steel and aluminium heaters is calculated to be 2.3 kWh and 2.9 kWh giving respective efficiencies of 47% and 61%. It has been shown that over the life cycle of 20 years, the stainless steel and the aluminium solar water heaters are capable of respectively producing 16.5 MWh and 21.3 MWh of energy.
For industrial applications, the monetary payback period for the stainless steel and aluminium heaters has been found to be equivalent to 3.9 years and 1.4 years, respectively. It has also been shown that over the life time the stainless steel and aluminium solar water heaters are capable of respectively saving as much as 1.9 and 2.5 tonnes of Carbon per m2 aperture area.
HEAT TRANSFER
In most designs of solar water heating system, heat is stored remotely from the solar panel/collector. Mass flow of water is generally used to transfer heat from the solar panel/collector to the store.
While it is possible to use convection
Example of convection
During convection, heated portions of fluid rise from the source of heat, while colder portions sink.
To move water between the solar panel/collector and the heat store, this requires wide bore pipe raising the thermal capacity of the primary circuit which reduces the speed of its response to sunlight. It also imposes the requirement that the heat store be higher than the solar panel/collector, and is relatively inefficient because the flow of convecting water is not adequate to transfer heat from the solar panel at full efficiency.
SOLAR HEAT STORES
Solar water heaters/storage tanks require a well insulated heat store. This is integrated with the solar panel/collector by means of copper pipes which are controlled by valves and a control sensor. These copper pipes feed into coils located inside the storage tank. Solar Free Power use a system called; INDIRECT FEED. Our preferred heat store has two coils contained inside the storage tank and the fluid inside these coils never come into contact with the domestic hot water used when the hot water tap is turned on.
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.
