A solar hot water system is the most efficient way to heat your hot water supply and will generate approximately 80% of your hot water energy requirements from the sun.
At the winter solstice, the sun rises to a height of around 30 degrees from the horizontal plane in Melbourne, so the solar collectors should be positioned facing within 45 degrees of north, and at an incline of between 45 and 60 degrees from the horizontal plane, to best capture the winter solar radiation. It is only in the colder months that a well designed solar hot water system generally requires boosting.
In summer, the solar collectors will generate more heat than required, and will result in releasing water pressure or steam. To minimize the issue of over heating and subsequent water loss, the solar collectors can be shaded with custom built shading systems, and vented water can be directed to rainwater storage tanks.
Solar Evacuated Vacuum Tubes
Solar Evacuated Vacuum Tubes were invented in Australia in the 1980’s and are now the most widely used solar collector in the market. They offer significant advantages over a flat plate collector, however, are generally more expensive to manufacture and install.
The Green Power Company supply both dry and wet (flooded) solar evacuated tubes, coupled with high and low pressure water tanks. These vacuum tubes of borosilicate glass allow greater efficiency than flat panel collectors by reducing conduction and convection heat loss. The circular tubes also minimize the impact of direct hail, snow build up and also allow for greater radiant heat absorbance in the early and latter periods of the day.
Wet solar evacuated tubes are filled with antifreeze treated liquid, which absorbs the radiant heat from the sun, the hot water then rises to the top of the tube via thermosyphon and into the heat transfer tank. Wet evacuated tubes and low pressure heat transfer tanks are a simple and effective way of heating water, which minimizes the threat of legionella, and increases longevity of the system via an open vented low pressure tank.
Dry solar evacuated tubes encapsulate a copper heat absorption tube, in a double layer of toughened borosilicate glass. The tubes focus the suns radiant heat to the inner copper tube, which is filled with heat absorbent antifreeze liquid. The heated liquid within the copper tube rises to the top via thermosyphon, and transfers the heat to the solar collector manifold, which connects each of the copper rods within each of the dry solar evacuated tubes. Dry evacuated tubes are used with high pressure water tanks, which require a pump for circulation and pressure release valve for venting.
Flat Panel Solar Thermal Collectors
Flat panel solar collectors have been used since the 1950’s and are a proven reliable method of capturing the solar radiant heat of the sun and converting it into hot water. There are many types of flat plate collectors including low pressure thermosyphon and pumped systems, serpentine flow systems and flooded absorber copper or aluminum sheet systems. Flat panel systems are susceptible to freezing which can destroy the structural integrity of the collector, therefore antifreeze is a requirement within the circulating liquid.
Flat panel solar thermal collectors comprise of a flat textured layer of toughened glass, encapsulated in a metal box which absorbs radiant heat via a dark flat-plate absorber. As the suns, radiant heat is absorbed by the thermal absorber and conducts the heat via a heat exchange antifreeze fluid, either open or within copper tube manifold system.
Flat Panel collectors can be used with closed couple low and high pressure water tanks, or circulated water via a copper manifold into ground mounted storage tanks.
Low Pressure, Closed Couple, Heat Exchange Solar Hot Water Systems
A low pressure solar hot water system is open vented to atmospheric pressure and does not require a pressure release valve. The steam is vented via an opening in the top of the tank with a solenoid activating the replenishment of water to stabilize levels.
The solar heated water stored within the tank acts as a thermal energy bank conducting heat to an internal copper pipe, where water absorbs heat before use. This heat exchange system acts as a kind of instantaneous hot water system, minimizing legionella risk, and subsequently eliminating the requirement for boosting to 70°C, therefore saving significant energy.
A low pressure, heat exchange, solar hot water system does not require a circulation pump, but taps directly into the pressurized water supply to push water thru the closed copper coil heat exchanger. Water pressure is supplied externally, which minimizes mechanical components and potential for failure.
Closed Couple heat exchange systems are generally mounted on the roof and can be coupled to wetback boosting for off the grid application. Regarded as the simplest type of hot water system, the system is generally mounted on the roof with a maximum capacity of 250L per unit.
High Pressure Solar Hot Water Systems
High Pressure Solar Hot Water Systems circulate water supply through the solar manifold, into the thermal storage tank for use. The potable hot water is stored in the thermal tank and requires boosting to 70°C to kill legionella. As the system is pressurized, a circulation pump is required to circulate the water and a pressure relief valves is needed to vent excess pressure and protect the system.
Pressurized solar hot water systems are generally configured with the solar array/s mounted on the roof, and the thermal storage tank and circulation pump mounted on the ground.