There are two types of collectors used in a solar hot water service:
Flat plate solar collectors
Flat plate collectors work on copper pipes running through a glass covered collector, often connected to a water storage tank on the roof. The hot water can then thermo-siphon itself in and out of the tank, thus heating the water.
Evacuated tube solar collectors
Evacuated tubes use a glass tube with a vacuum inside it and copper pipes running through the centre. The copper pipes are all connected to a common manifold which is then connected to a slow flow circulation pump which pumps water to a storage tank below, thus heating the hot water during the day. The hot water can be used at night or the next day due to the insulation of the tank.
The evacuation tube system are superior as they can extract the heat out of the air on a humid day and don't need direct sunlight. Due to the vacuum inside the glass tube, the total efficiency in all areas is higher and there's better performance when the sun is not at an optimum angle - such as when it's early in the morning or in the late afternoon.
The water tank and thermal mixing
As heat rises, the hot water delivered to the tank from the solar collector is drawn from the top for use in the house. As the temperature of the water may exceed 60 degrees Celsius/140 degrees Fahrenheit (a requirement to kill bacteria), in order to ensure a safe temperature at the taps, a tempering valve will reduce the temperature to around 45 degrees Celsius/113 degrees Fahrenheit.
Electricity and gas boosters
While the sun can provide sufficient energy to provide you with plenty of hot water for most of the year, there may be extended periods of cloudy, cold days where your system will need a helping hand. This is provided with an electricity boosted or gas booster system.
Boosting using a tankless gas water heater is the most efficient boosting method as boosting only occurs when hot water is used. With an electric system, the tank is heated as soon as the internal temperature drops.
Retrofitting for solar hot water
If your current hot water system has plenty of serviceable life left or you've recently purchases a gas/electric hot water system, you can still go solar with a retrofit kit!
Hot water and household energy usage
Electric and gas hot water systems accounting for approximately 20% of a household's greenhouse gas emissions. By installing a solar water system you will reduce these emissions and also save up to 75% of your water heating costs!
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